Division of Research
& Innovation
Report CA08- 0623
December 2008
Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control
Final Report
Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control
Final Report
Report No. CA08- 0623
December 2008
Prepared By:
Western Transportation Institute
Montana State University – Bozeman
Bozeman, Montana
Prepared For:
California Department of Transportation Division of Research and Innovation, MS- 83 1227 O Street Sacramento, CA 95814 DISCLAIMER STATEMENT
This document is disseminated in the interest of information exchange. The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the State of California or the Federal Highway Administration. This publication does not constitute a standard, specification or regulation. This report does not constitute an endorsement by the Department of any product described herein.
Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Technical Report Documentation Page
STATE OF CALIFORNIA DEPARTMENT OF TRANSPORTATION TECHNICAL REPORT DOCUMENTATION PAGE 1. REPORT NUMBER 2. GOVERNMENT ASSOCIATION NUMBER 3. RECIPIENT’S CATALOG NUMBER CA08- 0623 5. REPORT DATE December 31, 2008 4. TITLE AND SUBTITLE Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control 6. PERFORMING ORGANIZATION CODE 59 - 319 7. AUTHOR( S) 8. PERFORMING ORGANIZATION REPORT NO. Dollhopf, D., Pokorny, M., Dougher, T. A. O., Stott, L., Rew, L. J., Stark, J., Peterson, M., Fay, L., Shi, X. 10. WORK UNIT NUMBER 9. PERFORMING ORGANIZATION NAME AND ADDRESS California Department of Transportation Division of Research and Innovation, MS- 83 1227 O Street, P. O. Box 942873 Sacramento CA 94273- 0001 11. CONTRACT OR GRANT NUMBER 65A0181 13. TYPE OF REPORT AND PERIOD COVERED Final Report 12. SPONSORING AGENCY AND ADDRESS California Department of Transportation Sacramento, CA 95819 14. SPONSORING AGENCY CODE 15. SUPPLEMENTAL NOTES in cooperation with the U. S. Department of Transportation, Federal Highway Administration 16. ABSTRACT The objective of this research was to develop and demonstrate native grass sod for sediment control from disturbed lands associated with California highways. The research evaluated native grass species for inclusion in sod and evaluated the sod at a California highway field site. Seed mixes, including rhizomatous and bunchgrass species, were evaluated in a greenhouse setting for six California ecoregions. Growth and sod development potential of each seed mix for each ecoregion were evaluated. Seed mixes for three California ecoregions were further evaluated with a reinforcement material, and for establishment and weed suppression. Establishment and weed suppression of select ecoregion seed mixes and reinforcement materials were evaluated. Results indicated that multispecies sod has potential for use in revegetation of disturbed lands associated with highways. Native grass seed mix designs developed for the California Grassland ecoregion were field tested on a highway steep slope and swale area near Sacramento. Following an eight month propagation period, a sod composed of four native grass species was transplanted using conventional harvest and transport procedures. The sod resisted weed invasion from the underlying soil seed bank, no bare ground was present, and sediment loss was exceptionally low ( 0.1- 0.6 tons/ hectare/ year). Native grass sod was more expensive to implement compared with conventional hydroseeding, but their long- term maintenance and environmental costs associated with weed control, mowing, soil erosion, and fire control are expected to be much lower. 18. DISTRIBUTION STATEMENT 17. KEY WORDS No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161 erosion control, sediment control, native grass sod, weed control, herbicides, roadsides, highway runoff 19. SECURITY CLASSIFICATION ( of this report) 20. NUMBER OF PAGES 21. PRICE Unclassified 126
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USING REINFORCED NATIVE GRASS SOD FOR BIOSTRIPS, BIOSWALES, AND SEDIMENT CONTROL by D. Dollhopf, Ph. D. and M. Pokorny T. A. O. Dougher, Ph. D. and L. Stott KC Harvey, Inc. Plant Sciences & Plant Pathology Dept. 376 Gallatin Park Drive College of Agriculture Bozeman, Montana 59715 Montana State University – Bozeman and L. J. Rew, Ph. D. and J. Stark M. Peterson, L. Fay, and X. Shi, Ph. D., P. E. Land Resources & Environmental Service Dept. Western Transportation Institute College of Agriculture College of Engineering Montana State University – Bozeman Montana State University – Bozeman Prepared For The California Department of Transportation Division of Research and Innovation, MS- 83 1227 “ O” Street, P. O. Box 942873 Sacramento, CA 94273- 0001 December 31, 2008 Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Disclaimer
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DISCLAIMER The contents of this report reflect the views of the author( s) who is ( are) responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the State of California or the Federal Highway Administration. This report does not constitute a standard, specification or regulation. The United States Government does not endorse products or manufacturers. Trade and manufacturer names appear in this report only because they are considered essential to the object of the document. Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Acknowledgements
ACKNOWLEDGEMENTS This project was funded by the California Department of Transportation. The Research and Innovative Technology Administration of the U. S. Department of Transportation also provided funding for two graduate fellowship students for this study. Dr. Xianming Shi, P. E. of the Western Transportation Institute ( xianming_ s@ coe. montana. edu) served as the principal investigator for this multi- disciplinary research project. The authors thank Sue Jerrett of Montana State University, Jennifer Vermillion and Melissa Mitchem of KC Harvey, Inc., all located in Bozeman, Montana, for conducting research and providing support during report preparation. We thank Dr. Joel Cahoon of the Civil Engineering Department and Dr. Jerry Stephens of the Western Transportation Institute, both at Montana State University, for providing insightful review of this final report. We thank the Plant Growth Center staff at Montana State University for the use of their facilities. We also thank Mike Tutus of Restoration Resources, Sacramento, California, for soil preparation and weed control services at the highway test plot location. John Anderson, Hedgerow Farms in Winters, California, provided sod propagation service and expertise in native grass ecology. Ed Zuckerman, Delta Bluegrass Company, Stockton, California, provided superb sod propagation service and expertise in transplanting procedures. California Department of Transportation project officers based in Sacramento— Jack Broadbent, Martin Horvilleur and Douglas Brown— all provided excellent guidance and demonstrated admirable patience during the term of this investigation. Western Transportation Institute Page iii
Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Table of Contents
TABLE OF CONTENTS
1. .............................................................................................................................. 1 Introduction
1.1. ............................................................................................................ 1 Research Objective
1.2. ....................................................................................................................... 1 Introduction
1.3. ............................................................................................................................... . 2 Scope
1.4. .......................................................................................... 2 How This Report is Organized
2. ................................ 4 Background: Use of Sod and Native Species in Roadside Revegetation
2.1. ....................................................................................................................... 4 Introduction
2.2. ................................................................................. 5 Use of Sod in Revegetation Projects
2.3. ................................................................................................................. 7 Literature Cited
3. .................................. 11 Evaluation of California Native Grass Species for Sod Development
3.1. ..................................................................................................................... 11 Introduction
3.2. ...................................................... 11 Evaluation of Multispecies Sod for Each Ecoregion
3.2.1. ............................................................................................ 11 Materials and Methods
3.2.2. ..................................................................................................................... 15 Results
3.2.3. ............................................................................................................... 21 Discussion
3.2.4. ............................................................................................................. 23 Conclusions
3.3. ............................................... 24 Native Grass Species Mix and Plant Density Evaluation
3.3.1. ............................................................................................ 24 Materials and Methods
3.3.2. ..................................................................................................................... 25 Results
3.3.3. .............................................................................................................. 25 Conclusion
3.4. ............................................. 26 Native Grass Species Mix and Reinforcement Evaluation
3.4.1. ............................................................................................ 26 Materials and Methods
3.4.2. ..................................................................................................................... 28 Results
3.4.3. .............................................................................................................. 33 Conclusion
3.5. ............................................................................................................... 33 Literature Cited
4. ..................... 35 Establishment Success and Weed Suppression Potential of Multispecies Sod
4.1. ..................................................................................................................... 35 Introduction
4.2. .................... 36 Annual Weed Suppression Potential of Multispecies Sod – the " A" Trials
4.2.1. ............................................................................................ 37 Materials and Methods
4.2.2. ..................................................................................................................... 38 Results
4.2.3. ............................................................................................................. 42 Conclusions
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Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Table of Contents
4.3. ........................................ 43 Establishment Success of Multispecies Sod – The " A" Trials
4.3.1. ............................................................................................ 43 Materials and Methods
4.3.2. ..................................................................................................................... 43 Results
4.3.3. ............................................................................................................. 44 Conclusions
4.4. 44 Weed Suppression under Different Reinforcement Materials and Sod – The " B" Trials
4.4.1. ............................................................................................ 44 Materials and Methods
4.4.2. ..................................................................................................................... 45 Results
4.4.3. ............................................................................................................. 49 Conclusions
4.5. ........................................................................................................ 50 Overall Conclusions
5. ............................................................................................................................... .. 51 Highway Reclamation Using Native Grass Sod for Sediment Control and Aesthetic Enhancement
5.1. ..................................................................................................................... 51 Introduction
5.2. ..................... 51 Propagation of Native Grass Sod for the California Grassland Ecoregion
5.2.1. ..................................................... 51 Propagation of MSU Native Grass Sod – Sierra
5.2.2. .............................................. 52 Propagation of MSU Native Grass Sod – Hedgerow
5.2.3. ...................................................... 66 Propagation of MSU Native Grass Sod – Delta
5.3. ...................................................... 69 California Grassland Highway Demonstration Area
5.3.1. ............................................. 69 Native Grass Sod Highway Demonstration Location
5.3.2. ............................................. 70 Precipitation Record during the Investigation Period
5.3.3. ................................................ 70 Experimental Design – Treatment Implementation
5.4. .................................................... 78 Native Grass Establishment with Sod and Hydroseed
5.4.1. ............................................................................................ 78 Monitoring Procedures
5.4.2. .... 79 Sod and Hydroseed Traits Immediately Following Treatment Implementation
5.4.3. .......................................................... 81 Origin of Weedy Plant Species in Test Plots
5.4.4. ...... 81 Sod and Hydroseed Plant Traits Six Months after Treatment Implementation
5.4.5. ........................ 87 Sod and Hydroseed Plant Traits 18 Months After Implementation
5.4.6. .. 92 MSU Native Grass Sod – Delta Plant Traits Three Months After Transplanting
5.5. ............................................................................................................................. 95 Loss of Sediment from Highway Disturbances Using Native Grass Sod and Hydroseeding
5.5.1. ............................... 95 Environmental Factors Used to Estimate Sediment Loss Rate
5.5.2. ................................................................................................. 98 Sediment Loss Rate
5.6. ................................................................................. 100 Cost- Benefit of Native Grass Sod
5.6.1. ........................................................ 100 Estimated Cost of Native Grass Sod in 2008
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5.6.2. ............................................................... 100 Native Grass Sod Versus Hydroseeding
5.7. .......................................................................................... 101 Summary and Key Findings
5.7.1. .......................................................... 101 Native Grass Sod Propagation and Harvest
5.7.2. .............................................................................. 101 Highway Demonstration Area
5.7.3. .......................... 102 Vegetation Growth Traits at the Highway Demonstration Area
5.7.4. ................................................ 102 Sediment Loss from Sod and Hydroseeded Areas
5.7.5. ................................................................................................................ 103 Sod Cost
5.8. ............................................................................................................. 103 Literature Cited
6. .......................................................................................................................... 104 Deployment
7. ................................................................................................... 106 Summary of Key Findings
7.1. .......................... 106 Evaluation of California Native Grass Species for Sod Development
7.2. ............. 107 Establishment Success and Weed Suppression Potential of Multispecies Sod
7.3. ............................................................................................................................ 107 Highway Reclamation using Native Grass Sod for Sediment Control and Aesthetic Enhancement
7.3.1. .......................................................... 108 Native Grass Sod Propagation and Harvest
7.3.2. .............................................................................. 108 Highway Demonstration Area
7.3.3. .......................... 108 Vegetation Growth Traits at the Highway Demonstration Area
7.3.4. ................................................ 109 Sediment Loss from Sod and Hydroseeded Areas
7.3.5. ................................................................................................................ 110 Sod Cost
8. .............................................................................................................................. 111 Appendix
Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control List of Tables
LIST OF TABLES
Table 3.1 Selected species for all ecoregions and their role in the chosen mixtures. For each ecoregion, RX, RY indicate species used for their rhizomatous growth habit. 3B indicates the three bunch- type species used in all mixtures. 5B indicates the two additional bunch- type species used when five bunch- type species were included......... 12
Table 3.2 Day and night temperature settings and achieved mean day and night temperatures (° C) and standard deviations by month for each ecoregion............................................ 16
Table 3.3 Mean daily accumulated photosynthetically active radiation ( PAR) ( mol• m• day), monthly accumulated growing degree days ( GDD) ( computed using baselines of 5° C for cool season and 10° C for warm season species), and average day and night relative humidity ( RH) by month for each ecoregion. - 2- 1.................................................... 17
Table 3.4 Summary of regression of individual species percent cover and accumulated growing degree days....................................................................................................... 20
Table 3.5 Species mixes used for each ecoregion in establishment success and weed suppression experiments................................................................................................. 25
Table 5.1 Grass species included in the MSU Native Grass Sod – Sierra..................................... 52
Table 5.2 Grass species included in the MSU Native Grass Sod – Hedgerow.............................. 53
Table 5.3 Soil physical traits and plant nutrient availability for two soil samples from Hedgerow Farms, Winters, California............................................................................ 53
Table 5.4 Mean vegetative density for MSU Native Grass Sod– Hedgerow, native grass monocultures, and monocultures/ cover crops at Hedgerow Farms in January 2006..... 54
Table 5.5 Mean canopy cover for MSU Native Grass Sod– Hedgerow, native grass monocultures, and monocultures/ cover crops at Hedgerow Farms in January 2006..... 55
Table 5.6 Percent soil cover for MSU Native Grass Sod– Hedgerow, native grass monocultures, and monocultures/ cover crops, and at Hedgerow Farms in January 2006........................................................................................................................... ..... 56
Table 5.7 MSU Native Grass Sod– Hedgerow species mix and seeding rate................................ 61
Table 5.8 Grass species seeded in September 2007 and seeding rate for the MSU Native Grass Sod – Delta............................................................................................................ 66
Table 5.9 Soil physical traits and plant available nutrients at the Delta Bluegrass Company farm........................................................................................................................... ..... 67
Table 5.10 Physical and chemical traits of the “ Topsoil Blend” provided by Redi- Gro Corporation, Sacramento, California, that was applied between sod and underlying natural soil....................................................................................................................... 75
Table 5.11 Analysis of water used to irrigate test plots at the Mack Road site............................. 77
Table 5.12 Mean plant density at the highway steep slope and drainage swale area as a function of grass establishment treatments in November 2006...................................... 79
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Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control List of Tables
Table 5.13 Mean percent canopy cover at the highway steep slope and drainage swale area as a function of grass establishment treatments in November 2006................................... 80
Table 5.14 Mean percent soil cover at the highway steep slope and drainage swale area as a function of grass establishment treatments in November 2006...................................... 80
Table 5.15 Undesired grass and forb species present in the preexisting soil seed bank and the MSU Native Grass Sod– Hedgerow at the Mack road test area...................................... 82
Table 5.16 Mean percent canopy cover at the Mack Road slope and swale test areas and at the Delta Bluegrass Company sod farm in May 2007.................................................... 83
Table 5.17 Mean plant density at the highway fill- steep slope and the drainage swale locations as a function of native grass establishment procedures in May 2007............. 84
Table 5.18 Above- ground biomass ( live vegetation) at the highway fill- steep slope and the drainage swale locations as a function of native grass establishment procedures in May 2007........................................................................................................................ 84
Table 5.19 Plant species richness at the highway fill- steep slope and the drainage swale locations in May 2007 as a function of native grass establishment procedures............. 86
Table 5.20 Percent soil cover for the highway fill- steep slope and the drainage swale in May 2007 as a function of native grass establishment procedures......................................... 86
Table 5.21 Canopy cover at the Mack Road steep slope and drainage swale area and at the Delta Bluegrass Company sod farm in May 2008.......................................................... 88
Table 5.22 Mean plant density at the Mack Road steep slope and drainage swale area and at the Delta Bluegrass Company sod farm in May 2008.................................................... 89
Table 5.23 Mean above ground plant biomass at the Mack Road steep slope and drainage swale area and at the Delta Bluegrass Company sod farm in May 2008........................ 89
Table 5.24 Species richness at the Mack Road steep slope and drainage swale area and at the Delta Bluegrass Company sod farm in May 2008.......................................................... 91
Table 5.25 Soil cover at the Mack Road steep slope and drainage swale area and at the Delta Bluegrass Company sod farm in May 2008.................................................................... 92
Table 5.26 Mean canopy cover in August 2008 for the MSU Native Grass Sod– Delta located on the highway steep slope and drainage swale test area............................................... 93
Table 5.27 Mean plant density in August 2008 for the MSU Native Grass Sod– Delta located on the highway steep slope and drainage swale test area............................................... 94
Table 5.28 Mean above ground plant biomass in August 2008 for the MSU Native Grass Sod– Delta located on the highway steep slope and drainage swale test area................. 94
Table 5.29 Percent soil cover in August 2008 for the MSU Native Grass Sod– Delta located on the highway steep slope and drainage swale test area............................................... 94
Table 5.30 Key environmental factors used in the RUSLE2 model to estimate sediment loss from highway landscape features.................................................................................... 95
Table 5.31 Soil physical and nutrient availability traits at the Mack Road test plot area in November 2006.1.............................................................................................................. 96
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Table 5.32 Mean below ground dry root biomass in steep slope and drainage swale test plots in May 2007.................................................................................................................... 97
Table 5.33 Mean below ground dry root biomass at the Mack Road steep slope and drainage swale test areas and at the Delta Bluegrass Company sod farm in May 2008................ 97
Table 5.34 Mean surface roughness in each treatment for the steep slope and drainage swale area in May 2007............................................................................................................ 98
Table 5.35 Sediment loss rate on a highway fill- steep slope and a drainage swale area that received sod and hydroseed treatments near Sacramento, California............................. 99
Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control List of Figures
LIST OF FIGURES
Figure 3.1 Effect of sod composition and days after planting on clipped dry weight for the Intermountain Sagebrush ecoregion mixtures. Points represent means and error bars represent standard errors from the SAS MIXED model......................................... 18
Figure 3.2 Effect of sod composition and days after planting on clipped dry weight for the Sierran Forest ecoregion mixtures. Points represent means and error bars represent standard errors from the SAS MIXED model................................................. 19
Figure 3.3 Effect of sod composition and days after planting on total ground cover for the a) Chaparral, b) Great American Desert, c) Intermountain Sagebrush, and d) Sierran Forest ecoregions. Points represent means and error bars represent standard errors from the SAS MIXED model................................................................. 22
Figure 3.4 Early growth of 1.2 m x 1.5 m plot of the high density Chaparral mix ( left) and early growth of 1.2 m x 1.5 m plot of the low density Sierran Forest mix ( right).......... 25
Figure 3.5 Effect of planting density on the sod strength of native grass mixes for the Sierran Forest, Chaparral, and Pacific Forest ecoregions............................................... 26
Figure 3.6 Three deep soil boxes each with 12 transported sod pieces ( both high and low initial planting density) on reinforcement mats or bare ground. Dried weeds can be seen breaking through the sod.................................................................................... 27
Figure 3.7 The transported sod and invasive weed biomass of the Pacific Forest ecoregion at termination of the experiment..................................................................................... 27
Figure 3.8 Effect of initial planting density on the composition of the sod for red fescue ( Festuca rubra) and California brome ( Bromus carinatus) ( A), on the weed number and weed cover ( B), and weed and grass biomass ( C) in the Chaparral mix............................................................................................................................ ..... 29
Figure 3.9. Effect of initial planting density and reinforcement mat on percent red fescue in the plots of the Sierran Forest mix.................................................................................. 30
Figure 3.10 Effect of initial planting density and reinforcement mat on the percent bare ground in the Sierran Forest mix.................................................................................... 30
Figure 3.11 Effect of initial planting density on the weed number and weed cover ( A) and weed and grass biomass ( B) in the in the Sierran Forest mix......................................... 31
Figure 3.12 Effect of initial planting density and reinforcement material on the weed number ( A), weed cover ( B), on weed and grass biomass ( C) in the Pacific Forest mix............................................................................................................................ ..... 32
Figure 4.1 The multispecies sod before it was laid in 2006........................................................... 35
Figure 4.2 The line- source used to establish the four levels of irrigation regime plus a no irrigation control ( Experiment A). 1................................................................................ 36
Figure 4.3 Canola sown as seed bank beneath the multispecies sod in the first year Experiment A ( 2007). 2.................................................................................................... 36
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Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control List of Figures
Figure 4.4 Inside the frame are two of the six 0.21 m subplots of multispecies sod shown during the first year of A ( 2007). Flipping the frame down the plot reveals the other four subplots. 22......................................................................................................... 37
Figure 4.5 Canola seedlings in Eexperiment A before harvest in August 2007, with the closest plot receiving only natural precipitation and those further away receiving supplemental water. 2........................................................................................................ 38
Figure 4.6 Seed bank and seed rain proportional emergence of sown canola during the first year the sod was laid: A) Experiment A in 2006, B) Experiment A in 2007. Density and water effects are removed from experiment Ato visually demonstrate results. Each box captures 50% of the data. The dark line represents the median with whiskers extending to the minimum and maximum values within 95% of the data. Circles represent outliers. 122 .................................................................... 39
Figure 4.7 Canola proportional emergence of seed rain sown canola in Experiment Ain 2006, the first year the sod was laid, and in 2007 when the sod was more established. 1 ...................................................................................................................... 39
Figure 4.8 Seed rain canola emergence the second year of Experiment A( 2007) when the sod was more established. 2 ............................................................................................... 40
Figure 4.9 Proportional survival of emerged seed bank and seed rain canola seedlings the first year the sod was laid ( 2006) in Experiment A( r = 0.0076, p < 0.05). 1 2................. 40
Figure 4.10 Canola proportional survival of emerged canola seedlings sown as seed rain in Experiment Ain 2006, the first year the sod was laid, and in 2007 when the sod was more established. 1 ..................................................................................................... 41
Figure 4.11 The one canola plant that survived of all the emerged seedlings. The plant was in a 1000 seeds/ 0.21 m subplot in the high water treatment in the second year of Experiment A ( 2007). 21.................................................................................................... 41
Figure 4.12 Vegetative biomass of the canola plants that survived the first year from both Experiments A and A: A) seed bank ( r= 0.5060, p < 0.001), B) seed rain ( r= 0.4178, p < 0.001). 122 2 .......................................................................................................... 42
Figure 4.13 Seed weight of the canola plants that survived the first year from both Experiments A and A. No significant difference was observed between seed bank and seed rain so the results are combined. 12............................................................. 42
Figure 4.14 Relative abundance of photosynthesizing ( non- dormant) and non- photosynthesizing ( dormant) plants in Experiment A: A) September 2006, B) September 2007. X- axis indicates cumulative water treatment categories: “ Low” is lowest water level with no supplemental irrigation, “ MedL”, “ Med”, “ MedH” are the three intermediate water levels respectively: medium low, medium, medium high. “ High” is the highest water level. 1............................................................ 43
Figure 4.15 Lowest water level sod plots in Experiment A: A) September 2006, B) September 2007.1............................................................................................................. 44
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Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control List of Figures
Figure 4.16 Installation of the four reinforcement materials: coconut- straw, jute, excelsior, and nylon netting ( control) placed beneath the multispecies sod in Experiment B( 2007). 2 ............................................................................................................................. 45
Figure 4.17 Proportional emergence of canola from the seed bank under different reinforcement materials and multispecies sod in Experiment B( 2007), the first year the sod was laid. 2 ...................................................................................................... 46
Figure 4.18 Proportional emergence of canola from the seed bank under different water levels. Experiment B( 2007), the first year the sod and reinforcement materials were laid ( r= 0.0723, p < 0.05). 2 2 .................................................................................... 46
Figure 4.19 Canola proportional survival of emerged seedlings by reinforcement material for Experiments Band Bthe first year the sod was laid. 1 2 ............................................. 47
Figure 4.20 Canola proportional emergence by year for Experiment B. 1..................................... 47
Figure 4.21 Canola proportional emergence from seed rain the second year of Experiment B( r= 0.3029, p < 0.01). 1 2 ............................................................................................... 48
Figure 4.22 Canola proportional emergence and survival by year for Experiment B A) first year ( 2006) the year the sod was laid ( p < 0.001), B) second year ( 2007) when the sod was more established,( p < 0.001). 1: ............................................................ 48
Figure 4.23 Canola productivity in the first year of Experiment BA) vegetative biomass, ( r = 0.3257, p < 0.001), B) seed weight ( r = 0.3452, p < 0.001). Note different y- axis scale. 1: 22........................................................................................................................ 49
Figure 4.24 Canola productivity in the first year of Experiment B: A) vegetative biomass ( r = 0.3137, p < 0.001), B) seed weight ( r = 0.3128, p < 0.001). Note different y- axis scale. 2 22........................................................................................................................ 49
Figure 5.1 Test cut of creeping wildrye sod at Hedgerow Farm in January 2006......................... 57
Figure 5.2 A test cut of purple needlegrass sod indicated it rolled but the root system was not able to hold the sod together for the transplant and unrolling at Hedgerow Farm in January 2006...................................................................................................... 58
Figure 5.3 Cut sod of Sandberg’s bluegrass showing root– soil matrix ( left photo) and sod roll ( right photo) at Hedgerow Farm in January 2006.................................................... 59
Figure 5.4 California meadow barley formed sod and cut well, but because the plant formed soil- root clumps, the sod fell apart into plate size pieces at Hedgerow Farms in January 2006.................................................................................................... 60
Figure 5.5 MSU Native Grass Sod– Hedgerow propagation area at Hedgerow Farms in January 2006................................................................................................................... 61
Figure 5.6 Sandberg’s bluegrass sod transplant plot at Hedgerow Farm in May 2006. The right side of the photo shows the bluegrass- hairgrass sod, and the left side is bluegrass- Quickguard sod transplant. ® ........................................................................... 62
Figure 5.7 California meadow barley sod transplant plot at Hedgerow Farms in May 2006........ 63
Figure 5.8 Example of poor native grass survival when the tall cover crop Quickguard was present in transplanted sod at Hedgerow Farms in May 2006. ® ....................................... 64
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Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control List of Figures
Figure 5.9 MSU Native Grass Sod– Hedgerow propagation area before herbicide treatment and mowing at Hedgerow Farms in May 2006............................................................... 64
Figure 5.10 MSU Native Grass Sod- Hedgerow propagation area illustrating live canopy cover ( left photo) and soil cover ( right photo) at Hedgerow Farms in April 2007......... 65
Figure 5.11 Grass seeder ( left photo) and Brillion seeder used to pack and cover the seed ( right photo) at the Delta Bluegrass Company farm in September 2007........................ 67
Figure 5.12 MSU Native Grass Sod– Delta in the propagation area at the Delta Bluegrass Company farm in January 2008...................................................................................... 68
Figure 5.13 Test harvest of the MSU Native Grass Sod– Delta in the propagation area at the Delta Bluegrass Company farm in February 2008......................................................... 68
Figure 5.14 Location of native grass sod demonstration areas at the intersection of Mack Road and Highway 99 south of Sacramento, California ( Section 4, Township 7N, Range 5E) ( 3828.43’ N by 12125.49’ W). oo..................................................................... 69
Figure 5.15 Highway fill- steep slope ( left photo) and drainage swale ( right photo) located at the Mack Road and Highway 99 intersection............................................................. 69
Figure 5.16 Actual precipitation received during the period of this native grass sod investigation compared to historical average precipitation............................................ 70
Figure 5.17 Experimental design for the highway fill- steep slope and the drainage swale area located at the Highway 99 and Mack Road intersection south of Sacramento, California..................................................................................................................... .. 71
Figure 5.18 View of the Caltrans Hydroseed treatment on the highway fill- steep slope in November 2006............................................................................................................... 72
Figure 5.19 Cutting MSU Native Grass Sod– Hedgerow at Hedgerow Farms in November 2006 and placement of sod slabs on transport boards..................................................... 73
Figure 5.20 Lifting the cut sod onto boards using a shovel ( left photo) and stacking the boards for transport on a trailer bed ( right photo)........................................................... 73
Figure 5.21 Placing MSU Native Grass Sod– Hedgerow on the highway fill- steep slope area in November 2006........................................................................................................... 74
Figure 5.22 Harvested rolls of MSU Native Grass Sod– Delta prepared for transport to the highway test area in May 2008....................................................................................... 76
Figure 5.23 Installation of MSU Native Grass Sod– Delta on the highway fill- steep slope test area in May 2008...................................................................................................... 76
Figure 5.24 Installation of MSU Native Grass Sod– Delta on the highway drainage swale test area in May 2008...................................................................................................... 76
Figure 5.25 Installed sod was rolled to enhance contact with underlying soil ( left photo), then staples were inserted by hand to hold sod in place ( middle and right photos)....... 76
Figure 5.26 Irrigation line installation following transplanting the MSU Native Grass Sod– Delta on the drainage swale ( left phote) and steep slope ( right photo) areas on May 7, 2008.................................................................................................................... 77
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Figure 5.27 Photos of grass and forb establishment in the drainage swale ( A, B) and steep slope ( B, C) test plot area in May 2007........................................................................... 85
Figure 5.28 Photo of MSU Native Grass Sod– Delta at the Delta Bluegrass Company farm in May 2008 shortly before being transplanted to the Mack Road test plot area........... 87
Figure 5.29 Biomass and canopy cover data collection in the Delta Fescue Sod treatment located on the drainage swale test plot in May 2008...................................................... 88
Figure 5.30 Photos of MSU Native Grass Sod- Hedgerow on the drainage swale ( A, B, C) and on the steep slope plot area in May 2008................................................................. 90
Figure 5.31 MSU Native Grass Sod– Delta on the drainage swale test plot on July 21, 2008....... 93
Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Executive Summary
EXECUTIVE SUMMARY The objective of this research was to develop and demonstrate native grass sod for use in sediment control and permanent stabilization of disturbed lands associated with California highways. The research was divided into two components— evaluation of native grass species for inclusion in sod and an evaluation of the sod at a California field site. Various mixtures of native grass seeds, including rhizomatous and bunchgrass species, were evaluated in a greenhouse setting for six California ecoregions. Growth and sod development potential of each seed mix for each ecoregion were evaluated. Fewer grass species in a mix resulted in strong sod with reduced diversity. Increasing the diversity of rhizomatous species increased sod strength. The initial greenhouse research identified multispecies mixes for four California ecoregions– Pacific Forest, Sierran Forest, Chaparral, and California Grasslands— that grew native grass sod with adequate sod strength for harvesting and transportation. Seed mixes for three California ecoregions were further evaluated for establishment and weed suppression, with and without a reinforcement material. A small- scale field experiment performed over two years indicated that multispecies sod established and survived without supplemental water. Multispecies sod reduced weed emergence sown as a seedbank and as seed rain, and survival of weeds was significantly reduced as the sod became more established. The reinforced multispecies native grass sod increased potential for desired species establishment and increased weed suppression, even under low precipitation conditions. These results indicated that multispecies sod has potential for use in revegetation of disturbed lands associated with highways. Native grass seed mix designs for the California Grassland ecoregion for the field evaluation were selected based on plant growth characteristics, growth habits, and results from the research in the greenhouse component of this study. The seed mixes that were developed were composed of either four or five native grass species; ultimately, two different sods were transplanted to a field site located just south of Sacramento, California. In the field, plant growth parameters, weedy species invasion, and soil erosion parameters were monitored. The results of the field demonstration support the greenhouse and field data, indicating that a native grass sod species mix must be one that develops a strong- contiguous root mass, enables harvest of large sod rolls, and provides a dense sod that precludes weedy species propagation from the soil seed bank. The MSU Native Grass Sod– Delta ( composed of red fescue, purple needlegrass, California meadow barley, and California brome), produced in California, had a near zero sediment loss rate ( steep slope 0.6 and drainage swale 0.1 tons/ hectare/ year) beginning the day of sod installation, and three months after installation the site was almost entirely composed of desired native grass species. The cost to propagate, harvest and install native grass sod was estimated to be approximately five times greater than the cost of the hydroseed- mulch procedure; nonetheless, long- term maintenance and environmental costs associated with weed control, mowing and fire control are expected to be greater for hydroseeding when compared to native grass sod. Western Transportation Institute Page xvi
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1. INTRODUCTION 1.1. Research Objective The objective of this research was to develop and demonstrate native grass sod for control of sediment loss from land disturbances associated with the California highway system. Efforts to establish native grass from seed require long establishment periods before a degree of stabilization is attained on slopes and water conveyance features. Native grass sod has the potential to provide immediate and permanent stabilization of highway land disturbances. Use of native grass sod raises concern pertaining to propagation and transplant methods, effectiveness in controlling sediment loss, weed control, and cost, which are addressed in this investigation. 1.2. Introduction Disturbed lands associated with recently completed highway construction can be extremely erosive sources of sediment in water resources. To prevent sediment displacement during runoff events that can impair streams, wetlands, and water quality, surface stabilization is essential on land adjacent to highways, particularly land associated with steep slopes and water conveyance features. Biological methods of erosion control that establish a protective vegetation cover not only reduce sediment yield and runoff but also enhance the aesthetic values of an area. Numerous methods have been tested for native grass species establishment on highway project sites including broadcast seeding, drill seeding, combinations of broadcast and drill seeding, hydroseeding with mulch, and erosion control blankets impregnated with seed. Common to these methods is that plant establishment and root development that helps to hold the soil together and prevent erosion is slow. Thus soil erosion control may not be effective for many years or never if early erosion reverses the control itself. During the initial stages of native plant establishment from seed, there is an abundance of bare soil. The bare soil provides potential sites for not only the sown native species but also the non- native weedy species. Many weed species are annuals with high growth rates and seed production, thus are able to exploit the environment more rapidly than the generally slower growing perennials. If weed species become established they may further jeopardize establishment and growth of native grass species due to their above ground dominance and reduction in the number of safe sites for germination. The presence of weeds means that considerable resources have to be spent to control them. In many counties, herbicides are the primary management control option, and large quantities of money are spent on an annual basis. Many Californians are concerned about the increasing use of herbicides to reduce noxious and other non- native plant species on highway sites. While selective herbicides can be used to target specific weeds, they often have an injury impact on some of the native species which reduces their productivity. The use of native grass sod can reduce the risk of non- native weeds because it is placed on top of the soil or geological material and because weed seeds in the seed bank will be buried five centimeters or more. In addition, the native species are well established in the sod, therefore, have a competitive advantage over any weed seeds that do germinate and establish through the reinforced sod layer. Reinforced sod should consolidate the soil more immediately than
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broadcast seed application approaches, thus reducing soil erosion, and improving water quality. Furthermore, because the native species are adapted to the local environment, once established they should require minimal maintenance and should continue to grow and spread into adjacent areas which were not laid with sod. The growth habit and maximum height of most of the native species means that they should not obstruct the view of highway drivers and that neither mowing nor supplemental water would be required. With the methods that are currently in place, large amounts of money are being spent trying to resolve the problems associated with highway construction. Using native grass sod is more expensive in the short term, but can reduce maintenance, herbicide and water treatment costs, thus may be more cost- effective in the long term. If sod composed of grass species native to the area of interest can be commercially produced and harvested, native multispecies sod could become another tool for rehabilitation efforts. Such sod could be particularly useful for sensitive areas found along roadsides, including those areas near streams, areas prone to high erosion rates ( such as steep slopes), and areas where the rapid establishment of non- native species reduces the establishment success of native species planted by other methods. 1.3. Scope This study began with an evaluation of several native grass species from six different ecoregions in California to determine their suitability to be used in multispecies sod for roadside rehabilitation. Seed mixtures developed specifically for the conditions in each ecoregion were sown in greenhouse growth chambers at Montana State University, and sod development was monitored relative to species biomass, relative ground cover, and total ground cover. Based on these results, the best species mixes for three ecoregions were further studied with respect to sod production. Greenhouse plots were used to investigate the effect of seeding density and reinforcement material on sod strength. Field experiments were subsequently conducted at a research farm at Montana State University to further investigate weed suppression potential of multispecies sod. These experiments were conducted without and with various reinforcement materials, and under different water regimes. Over a two year period ( and possibly continuing into the future), weed emergence, biomass, and survival were evaluated relative to the above variables in conditions. Additionally, limited work was done on the effect of watering treatment on basic establishment success of unreinforced sod. Based on the knowledge gained from the research described above, a field experiment was conducted on a disturbed area along a highway south of Sacramento, California. Work began with an evaluation of the propagation of three native grass sods by three different commercial sod producers in California based on species presence, canopy cover and weed emergence. Two native grass sods were subsequently transplanted at the field test site, and part of the site was restored using Caltrans standard hydroseeding practice. Native grass establishment was then monitored for a 20 month period. Observations were made of plant density, canopy cover, weed development, root biomass, and sediment loss. 1.4. How This Report is Organized Following this introduction, Chapter 2 of this report presents a review of salient literature on the use of native grass sod for re- vegetating disturbed soils. Chapters 3 and 4 discuss the greenhouse and field research experiments conducted at Montana State University ( MSU) to investigate
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native grass sods for applications along California roadways. Chapter 5 presents the field research conducted at the field site just south of Sacramento, California. In general, each chapter is dedicated to individual sets of experiments. Each chapter includes a brief introduction, experimental methodology, results of experiments, and conclusions. Chapter 6 reports on how the results can be used, and some insights of future directions of this research. Finally, Chapter 7 summarizes the key findings across all the research that was conducted. Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Chapter 2
2. BACKGROUND: USE OF SOD AND NATIVE SPECIES IN ROADSIDE REVEGETATION 2.1. Introduction Roadside corridors are particularly susceptible to invasion by non- native species ( Spellerberg 1998; Tyser et al. 1998). Non- native species are typically well- suited to such highly disturbed sites and can establish rapidly there ( Greenberg et al. 1997). In fact, because they are inexpensive and easy to establish, non- native species such as smooth brome ( Bromus inermis) have been intentionally sown on disturbed roadside soil ( Rentch et al. 2005). Non- native species are used because they are able to quickly stabilize disturbed soil ( Wilson 1989), reducing erosion and sedimentation. The documented difficulty of obtaining quality native seed in large quantities may be another reason for the frequent sowing of non- native species ( Lippett et al. 1994; Stevenson et al. 1995). Aside from the fact that sowing non- native species alters the vegetation of a community, roadside areas can also be regarded as separate ecosystems due to the major changes in soil structure, fertility and hydrology incurred during construction ( Forman & Alexander 1998). These changes result in soil instability and can increase erosion ( Forman & Alexander 1998) which warrants the rapid reestablishment of vegetative cover. However, revegetating disturbed sites with non- native species has shown the potential to compromise adjacent ecosystems ( Pysek et al. 1995). Non- native species can alter water and fire regimes, damage natural resources, increase soil nitrogen levels, release toxic chemicals, harbor diseases, and displace native species that are vital for herbivore consumption ( Pysek et al. 1995; National Park Service 1996). In addition, non- native species may be more susceptible to stress and may interfere with the recruitment and establishment of native species ( Wilson 1989; Jefferson et al. 1991; Tyser et al. 1998). Consequently, the use of native species for rehabilitation is preferable to that of non- native species for both ecological and aesthetic reasons ( Tyser et al. 1998) because a mixture of native species more closely resembles the natural plant communities present before disturbance than does a mixture or monostand of non- native species. Some of the non- native species that invade roadsides are listed as noxious weeds and, by law, must be controlled. The Federal Noxious Weed Act, enacted in 1975, mandates that both private landowners and government agencies apply control measures for species designated as “ noxious.” Applying chemical control is one potential method of controlling noxious weeds. However, herbicides are expensive and may not be labeled for use in sensitive areas ( such as those near water). Therefore, pre- empting the establishment of noxious weeds as well as other unwanted non- natives has great potential economic and ecological benefits. Revegetating roadside corridors after extensive disturbance with native species is a potential method of preventing the establishment of non- native species and noxious weeds. In fact, Rentch et al. ( 2005) found that the composition of species after rehabilitation was most likely to be influenced by the species initially planted during rehabilitation. Therefore, the rapid establishment of native species could preclude the establishment of non- native ones ( Bugg et al. 1997; Rentch et al. 2005). Indeed, Booth et al. ( 2003) demonstrated that, once established, native perennial grasses have shown the ability to suppress non- native annual species. Accordingly, the rapid establishment of non- native species ( particularly noxious weeds) has been cited as grounds for prompt rehabilitation efforts with native species ( Tyser et al. 1998) because Western Transportation Institute Page 4
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correctly chosen native species ( i. e., those from the same ecoregion) do not pose a threat to the biodiversity of adjacent plant communities ( Berger 1993; Wilson and Gerry 1995; Grant et al. 2003). Additionally, native species are more suited to local environments and require less maintenance ( Humphrey & Schupp 2002). Accordingly, the within species genetic variance of native grass species and the importance of using a locally appropriate seed source has been well documented ( Quinn & Ward 1969; Akeroyd 1994; Lippett et al. 1994; Millar & Libby 1994; Knapp & Rice 1996; Bugg et al. 1997; Montalvo et al. 2002; Landis et al. 2005). It is difficult to rapidly mimic all of the environmental and biological conditions that have created a diverse stable community during the course of a rehabilitation project. Accordingly, post- rehabilitation communities often differ from their pre- disturbance conditions ( Ehrenfeld 2000; Maina & Howe 2000). To minimize this post- restoration difference, optimal methods to plant and establish native species must be delineated to ensure establishment success. There are many potential methods of establishment. Broadcast seeding is inexpensive, but establishment is very slow and weeds tend to be prevalent ( Beard & Green 1994). Imprinting and drill seeding are successful methods, but the required use of large machinery precludes the use of these methods in small areas or on steep slopes ( Caltrans 2004). Hydroseeding may be a successful method of native species establishment depending on site- specific characteristics. Hydroseeding is more expensive than broadcast seeding, drill seeding or imprinting, but can be used on very steep slopes ( Caltrans 2004). All of these methods result in increased erosion and weed proliferation before the seeded species become established ( Caltrans 2004). The same is true for plugging, but it is very labor- intensive and even more expensive ( Caltrans 2004). Each of these methods has advantages and disadvantages; however, a common disadvantage persists for all of these methods. Broadcast seeding, imprinting, hydroseeding, drill seeding and plugging all result in delayed vegetation establishment and, consequently, the potential for weed proliferation ( Caltrans 2004). 2.2. Use of Sod in Revegetation Projects One potential method for rapidly revegetating roadsides with native species is the use of sod. Sod installation has long been used to rapidly establish turfgrass in home and commercial landscape settings ( Beard & Rieke 1969; Beard & Green 1994). Despite the fact that sod has been used to quickly establish grass cover in lawns and commercial landscapes, only limited research has been done on its use as a rehabilitation tool. Montana State University began research with native grass sod for highway stabilization in the 1970s. Jensen and Sindelar ( 1979) used a “ dryland- sodding machine” to extricate rangeland sod four to eight centimeters thick composed of western wheatgrass ( Elymus smithii), Kentucky bluegrass ( Poa pratensis), or inland saltgrass ( Distichlis spicata). These sods were applied to highway construction disturbances that required rapid stabilization due to high erosion potential. The Kentucky bluegrass sod was the most effective for site stabilization due to a thick fibrous root mat. The western wheatgrass sod provided an effective erosion control mat, but lack of a thick fibrous root mat necessitated careful handling so that it would not break apart during transplant efforts. The inland saltgrass sod was not effective primarily due to poor survival. These results prompted the U. S. Forest Service to engineer the Sod Mover Bucket at the Missoula Equipment Development Center in 1980. The bucket fit on a front- end loader and was used to extricate two meter by four meter slabs ( 10- 20 cm thick) of native grass sod and shrubs. These slabs were then placed in strategic patterns on an adjacent highway construction project. Results pertaining to establishment and
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aesthetics were encouraging, but cost was notable and transplant- slabs raised concern that the borrowed areas served to increase the land disturbance. A major step forward occurred in 2001 when Montana State University ( MSU), in association with Bitterroot Turf Farms, Corvallis, Montana, propagated ten hectares of two native grass sod types for use in land reclamation projects. One sod was composed of a mix of western wheatgrass, thickspike wheatgrass ( Elymus lanceolatus), Idaho fescue ( Festuca idahoenis) and Canada bluegrass ( Poa compressa). The other sod was developed for wetland landscapes and was composed of beaked sedge ( Carex rostrata). In Spring 2003, MSU ( Dollhopf, Dougher and Stone 2003) established test plots in a 33 centimeter precipitation zone on a south- facing highway construction fill with a 40% slope gradient. At the same site, the native grass sod mix was compared to broadcast seeding, using the Montana Department of Transportation native grass seed mix for that region, covered with a hydromulch, and broadcast seeding covered with an erosion control blanket. The highway fill site had no topsoil applied and was composed of unconsolidated geologic sediments. The native grass sod was irrigated on the day of plot construction, but no supplemental water was added after that date. At peak plant growth during Summer 2003 perennial grass production on native grass sod plots was 15- 135 times greater than broadcast seeding methods. Weed invasion on native grass sod plots was zero, while both perennial and annual forb weed species established in broadcast seeded plots covered with either the erosion control blanket or hydromulch. Both perennial plant basal and canopy cover was 95.8% on the native grass sod plots compared to 2- 8% for broadcast seeded plots. The California Department of Transportation ( Caltrans) ( 2004) conducted limited experimentation with monostands of native grass sod. This sod showed promise for reducing erosion and potentially reducing weed seed recruitment. Stone ( 2004) showed that native sod installed on steep slopes was capable of reducing soil runoff and erosion in comparison to broadcast seeding with either a hydromulch or straw blanket cover. The installation of native sod showed promise as a future rehabilitation tool, particularly for areas with steep slopes and those with a large non- native species seed bank, where rapid rehabilitation is essential. Though sod installation is labor intensive and initially more expensive ( Hottenstein 1969), sod has been shown to cover the ground more rapidly than broadcast seeding ( Beard & Rieke 1969; Beard & Green 1994). Additionally, by covering the existing seed bank, weed germination and establishment are reduced compared to broadcast seeding ( Beard & Green 1994; Caltrans 2004), which could potentially reduce the amount of chemical controls necessary to combat weed establishment. Research has shown that sod used for erosion control applications can remove up to 99% of the total suspended solids in runoff ( USEPA 2002). In Maryland, Krenitsky et al. ( 1988) compared runoff and sediment loss on turf ( bluegrass) grass slopes ( 8- 21% gradient) to slopes treated with wood excelsior, jute fabric, coconut fiber blanket, coconut strand mat and straw. Using simulated rainfall, sod reduced runoff rates 54- 59% more than all other treatments. McGinnies and Wilson ( 1982) evaluated blue gramma ( Bouteloua gracillis) sod for rangeland revegetation in Colorado. Different sites were covered with sod from May through August and each was irrigated. They concluded that sod should be wetted prior to cutting, and sod placement should be done early in the growing season then irrigated as soon as possible following placement. In Australia, Jimbomba Turf Group ( 2004) developed Stayturf ® which is a turfgrass designed to line channels where concentrated water flow is expected. This product consists of turfgrass growing in an organic geotextile mat supported with a polymer netting. It is
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intended to line water conveyance channels and replace some types of rock and concrete water drop structures on highway projects. The advent of new technologies that allow sod to be harvested and installed mechanically may render the commercial production of native sod more feasible. Advances in technology that allow sod to be harvested with reinforcement materials in “ big rolls” ( Bucyrus Equipment Company) and installed mechanically with equipment such as the Brouwer turf installer ( Brouwer Turf Equipment) could make the use of sod more affordable and practical as a rehabilitation management tool. Prior research suggests that a mixture of species more closely resembles native vegetation ( Bugg et al. 1997) and is more appropriate than a monoculture for ecological and aesthetic reasons ( Tyser et al. 1998). In addition, niche theory suggests that community assembly is based on competition and that multiple species are present to the extent that they occupy different niches ( Tilman 1997). Brown et al. ( 1998) also suggested that a variety of species with varied rooting depths and growth characteristics would be more likely to compete with existing weed species because of pre- emptive niche occupation. Therefore, including a greater number of species in rehabilitation sod may lead to more rapid and complete ground cover and to greater potential weed suppression capabilities as different species occupy different niches. 2.3. Literature Cited Akeroyd, J. R. 1994. Some problems with introduced plants in the wild. Pages 31- 40 in A. Perry and R. G. Ellis, editors. The common ground of wild and cultivated plants: introductions, invasions, control and conservation. National Museum of Wales, Cardiff. Beard, J. B. and R. L. Green. 1994. The role of turfgrasses in environmental protection and their benefits to humans. Journal of Environmental Quality, 23: 452- 460. Beard, J. B. and P. E. Rieke. 1969. Producing Quality Sod. In A. A. Hanson and F. V. Juska, editors. Turfgrass Science. American Society of Agronomy, Inc. Madison, Wisconsin. Berger, J. J. 1993. Ecological restoration and nonindigenous plant species: a review. Restoration Ecology, 1: 74- 82. Booth, M. S., M. M. Caldwell and J. M. Stark. 2003. Overlapping resource use in three Great Basin species: implications for community invasibility and vegetation dynamics. Journal of Ecology, 91: 36- 48. Brown, C. S., K. J. Rice and V. Claassen. 1998. Competitive growth characteristics of native and exotic grasses. Final Report. California Department of Transportation New Technology and Research Program, University of California, Davis. Bugg, R. L., C. S. Brown and J. H. Anderson. 1997. Restoring native perennial grasses to rural roadsides in the Sacramento Valley of California: establishment and evaluation. Society for Ecological Restoration, 5: 214- 228. Caltrans ( California Department of Transportation). 2004. Caltrans Native Grass Evaluation Pilot Program ( Comprehensive Report). California Department of Transportation, Landscape Architecture Program. Presented by P& D Environmental. Orange, CA.
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Dollhopf, D. J., T. A. O. Dougher and K. Stone. 2003. Using native grass sod for stabilization of slopes on Montana highway construction projects. Progress statement to the Montana Department of Transportation, Helena, Montana. Reclamation Research Unit, Montana State University, Bozeman. Ehrenfeld, J. G. 2000. Defining the limits of restoration: the need for realistic goals. Restoration Ecology, 8: 2- 9. Forman, R. T. T. and L. E. Alexander. 1998. Roads and their major ecological effects. Annual Review of Ecology and Systematices, 29: 207- 231. Grant, D. W., D. P. C. Peters, G. K. Beck and H. D. Fraleigh. 2003. Influence of an exotic species, Acroptilon repens ( L.) DC, on seedling emergence and growth of native grasses. Plant Ecology, 166: 157- 166. Greenberg, C. H., S. H. Crownover and D. R. Gordon. 1997. Roadside soils: a corridor for invasion of xeric scrub by nonindigenous plants. Natural Areas Journal, 17: 99- 109. Hottenstein, W. L. 1969. Highway Roadsides. In A. A. Hanson and F. V. Juska, editors. Turfgrass Science. American Society of Agronomy, Inc. Madison, Wisconson. Humphrey, L. D. and E. W. Schupp. 2002. Seedling survival from locally and commercially obtained seeds on two semiarid sites. Society for Ecological Restoration, Jefferson, E. J., M. S. Lodder, A. J. Willis, and R. H. Groves. 1991. Establishement of natural grassland species on roadsides of southeastern Australia. Pages 333- 339 in D. A. Saunders and R. J. Hobbs, editors. Nature Conservation 2: The Role of Corridors. Surrey Beatty and Sons, Chipping, New South Wales, Australia. Jensen, I. B. and B. W. Sindelar. 1979. Permanent stabilization of semiarid roadsides with grass, legume and shrub seed mixes and native grass dryland sodding. Research Report 141, Reclamation Research Unit, Montana Agricultural Experiment Station, Montana State University, Bozeman. Jimbomba Turf Group. 2004. http:// www. jimboombaturf. com. au/ index. htm. Knapp, E. E. and K. J. Rice. 1996. Genetic structure and gene flow in Elymus glaucus ( blue wildrye): implications for native grassland restoration. Restoration Ecology, 4: 1- 10. Krenitsky, E. C., M. J. Carroll, and R. L. Krouse. 1998. Runoff and sediment loss from natural and man- made erosion control materials. Crop Science 38: 1042- 1046. Landis, T. D., K. M. Wilkinson, D. E. Steinfield, S. A. Riley and G. N. Fekaris. 2005. Native Plants, Fall 2005: 297- 305. Lippitt, L., M. W. Fidelibus and D. A. Bainbridge. 1994. Native seed collection, processing, and storage for revegetation projects in the western United States. Society for Ecological Restoration, 2: 120- 131. Maina, G. G. and H. F. Howe. 2000. Inherent rarity in community restoration. Conservation Biology, 14: 1335- 1340.
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McGinnies, W. J. and A. M. Wilson. 1982. Using blue gramma sod for range revegetation. J. Range Management 35: 259- 264. Millar, C. I. and W. J. Libby. 1994. Disneyland or native ecosystem: genetics and the restorationist. Restoration & Management Notes, 7: 18- 24. Montalvo, A. M., P. A. McMillan and E. B. Allen. 2002. The relative importance of seeding method, soil ripping, and soil variables on seeding success. Society for Ecological Restoration, 10: 52- 67. National Park Service. 1996. Preserving our Natural Heritage— A Strategic Plan for Managing Invasive Non- Indigenous Plants on National Park System Lands. www. nature. nps. gov/ biology/ invasivespecies/ stratppl. htm. Pysek, P. K., K. Prach and P. Smilauer. 1995. Relating invasion success to plant traits: an analysis of the Czech alien flora. Pages 39- 60 in P. Pysek, K. Prach, M. Rejmanek and M. Wade, editors. Plant Invasions: General Aspects and Special Problems, SPB Academic Publishing, Amsterdam, The Netherlands. Quinn, J. A. and R. T. Ward. 1969. Ecological differentiation in Sand Dropseed ( Sporobolus cryptandrus). Ecological Monographs, 39: 61- 78. Rentch, J. S., F. H. Fortney, S. L. Stephenson, H. S. Adams, W. N. Grafton and J. T. Anderson. 2005. Vegetation- site relationships of roadside plant communities in West Virginia, USA. Journal of Applied Ecology, 42: 129- 138. Spellerberg, I. F. 1998. Ecological effects of roads and traffic: a literature review. Global Ecology and Biogeography Letters, 7: 317- 333. Stevenson, M. J., J. M. Bullock and L. K. Ward. 1995. Re- creating semi- natural communities: effect of sowing rate on establishment of calcareous grassland. Restoration Ecology, 3: 279- 289. Stone, K. M. 2004. Evaluation of native grass sod for stabilization of steep slopes. M. S. Thesis, Land Resources and Environmental Science Department, Montana State University, Bozeman. 292 p. Tilman, D. 1997. Community invasibility, recruitment limitation, and grassland biodiversity. Ecology, 78: 81- 92. Tyser, R. W., J. M. Asebrook, R. W. Porter and L. L. Kurth. 1998. Roadside revegetation in Glacier National Park, U. S. A.: effects of herbicide and seeding treatments. Restoration Ecology, 6: 197- 206. Wilson, S. D. 1989. The suppression of native prairie by alien species introduced for revegetation. Landscape and Urban Planning, 17: 113- 119. Wilson, S. D. and A. K. Gerry. 1995. Strategies for mixed- grass prairie restoration: herbicide, tilling, and nitrogen manipulation. Restoration Ecology, 3: 290- 298. U. S. Environmental Protection Agency. 2002. National pollutant discharge elimination system ( NPDES). Construction site storm water runoff control. http:// cfpub. epa. gov/ npdes/ stormwater/ menuofbmps/ site_ 31. cfm.
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U. S. Forest Service ( 1980). Sod mover bucket. U. S. Dept. of Agriculture, Equipment Development Center, Missoula, Montana. Publication ED& T 8046. 12 p. Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Chapter 3
3. EVALUATION OF CALIFORNIA NATIVE GRASS SPECIES FOR SOD DEVELOPMENT 3.1. Introduction The objective of this part of this study was to evaluate a number of native grass species and reinforcement materials for their suitability for contributing to a harvestable multispecies sod for roadside rehabilitation. The initial evaluation for determining native grass species was performed using species from six different ecoregions of California. The second evaluation, for determining suitable reinforcement materials, was conducted on native grass species for three of those ecoregions. Evaluations were performed using sample plantings in a greenhouse setting. Basic species evaluation was done using biomass, species abundance, and total ground cover. Reinforcement materials were evaluated with respect to effect on sod strength for different seeding densities. 3.2. Evaluation of Multispecies Sod for Each Ecoregion 3.2.1. Materials and Methods 3.2.1.1. Species Selection Native grass species selections were performed for each of six selected Californian ecoregions: Pacific Forest, Chaparral, California Grasslands, Intermountain Sagebrush, Sierran Forest, and Great American Desert, as defined by Jepson ( Hickman 1993). Selection of the most appropriate species for inclusion in our study included evaluations of habitat requirements, geographic distribution, and typical elevational range, which was achieved primarily by using the information in Hickman ( 1993), the Native Grass Database ( Caltrans 2001) and United States Department of Agriculture, Natural Resource and Conservation Service ( USDA, NRCS ( 2007)). The frequency of each species within each of the selected ecoregions was evaluated by determining the number of counties in which the species was present out of the total number of counties in the ecoregion. By combining frequency data with growth characteristics ( rhizomatous, stoloniferous or bunchgrass), warm or cool season grass, and habitat preferences, the species most frequently found across counties and recorded in the widest range of habitats were selected. Some selected species could not be used because a commercial seed source could not be procured, which further reduced the number of species to those shown in Table 3.1. All seed accessions were acquired from commercial enterprises that provided information on the locality of their seed collection. The seed source had to be within the intended ecoregion to meet our requirements. Two seed accessions used in the Great American Desert ecoregion— Indian ricegrass ( Achnatherum hymenoides) and prairie junegrass ( Koeleria macrantha)— were the exceptions and were from the Chaparral region because no seed could be commercially sourced from the Great American Desert. Nomenclature used in this document comes from the Native Grass Database ( Caltrans 2001). Western Transportation Institute Page 11
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Table 3.1 Selected species for all ecoregions and their role in the chosen mixtures. For each ecoregion, RX, RY indicate species used for their rhizomatous growth habit. 3B indicates the three bunch- type species used in all mixtures. 5B indicates the two additional bunch- type species used when five bunch- type species were included. California GrasslandsChaparralGreat American DesertIntermountain SagebrushPacific ForestSierran ForestAchantherum hymenoides3BAchnatherum occidentale5BAristida purpurea5BBromus carinatus3B3B3B5BElymus elymoides3B3B3BElymus glaucus3B5B3B5BElymus multisetus5BElymus trachycaulusRXRYRYRYFestuca idahoensis3BFestuca rubraRYRYRXRXHordeum brachyantherum3BKoeleria macrantha3B3B3B5BLeymus cinereus3BLeymus condensatusRXLeymus triticoidesRXRXMelica californica5B5BMuhlenbergia rigens3BNassella cernua3B5BNassella lepida3BNassella pulchra5B5BPleuraphis rigidaRY 3.2.1.2. Experimental Design Six seed mixtures were chosen for each ecoregion, with the exception of the Great American Desert ecoregion, which had two mixtures. The six different mixtures for each ecoregion were as follows: rhizomatous species X ( RX) and the three most frequent bunchgrass species ( 3B) ( i. e., RX3B); rhizomatous species Y ( RY) with the same three bunchgrass species ( i. e., RY3B); rhizomatous species X ( RX) with the same three bunchgrass species, plus a the next two most frequent bunchgrass species ( 5B) ( i. e. RX5B); rhizomatous species Y ( RY) with the same five
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bunchgrass species ( i. e., RY5B); rhizomatous species X and Y ( RXY) with the first three bunchgrass species ( i. e., RXY3B); and, lastly, rhizomatous species X and Y ( RXY) with all five bunchgrass species ( i. e., RXY5B). The experiment was set up as a complete randomized block with three replications. Only two mixtures, RX3B and RX5B, were planted for the Great American Desert ecoregion with nine replications in a completely randomized design. This reduction of mixtures evaluated was due to the fact that the RY species, big galleta ( Pleuraphis rigida), was eliminated from the study after preliminary tests revealed poor germination. 3.2.1.3. Growth Chambers Six polycarbonate growth chambers with wood framing and 1.5 m x 1.8 m x 0.9 m were constructed to mimic the climate of each of the six selected California ecoregions for the seven- month growing period when sod is most likely to be grown. These growth chambers were then placed in a greenhouse. Horizontal air flow ( HAF) fans were placed in each chamber to provide continuous air movement. Each chamber was also fitted with a heater bar ( Ceramic Channel Strip Heater, 350 W, Tempco Electric Heater Corporation, Wood Dale, Illinois) which was placed in front of the HAF fan to permit the spread of heated air throughout the chamber. Two cooling fans were placed in diagonally opposite corners of each chamber to pull air from the greenhouse into the chambers in order to cool them when necessary due to a “ double greenhouse effect” caused by the growth chambers being inside a greenhouse. All fans used were axial fans ( 4WT46, Dayton Electronic Manufacturing Company, Niles, Illinois) rated at 115 CFM. Each chamber ( except the Great American Desert ecoregion chamber) was equipped with a fogger system designed to increase relative humidity. Two ultrasonic foggers ( The Mist Maker Model M0001, Mainland Mart Corporation, El Monte, California) were placed in five- gallon buckets filled with water. The foggers were placed in baskets buoyed up by Styrofoam ® rings, which kept the foggers at the appropriate water depth continuously, despite evaporation. The water buckets were refilled with tap water as needed. Algae removal was also performed when necessary. Each chamber was equipped with a line quantum sensor ( Model LQS506, Apogee Instruments, Inc., Logan, Utah) to measure photosynthetically active radiation ( PAR) and a relative humidity and temperature probe ( HMP- 45C, Campbell Scientific, Inc., Logan, Utah). These sensors provided input for the two dataloggers ( CR- 10X, Campbell Scientific, Inc., Logan, Utah) that were used to control the heating, cooling, and humidification of the chambers. 3.2.1.4. Climate Control Monthly settings for each growth chamber were determined by calculating the mean minimum and maximum temperature and mean relative humidity data from historical data obtained from the Western Regional Climate Center for weather stations within each respective ecoregion. These metrics were calculated for each month from September through March for the California Grasslands, Chaparral, Great American Desert and Pacific Forest ecoregions, and from March through September for the Intermountain Sagebrush and Sierran Forest ecoregions. Growing degree days ( GDD) for cool season species were calculated based on baseline temperatures for wheat ( 5° C), while GDDs for warm season species were calculated based on baseline temperatures for corn ( 10 ° C). Day and night relative humidity and PAR ( mol• m- 2• day- 1) were also recorded for each ecoregion.
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3.2.1.5. Sowing and Establishment Eighteen round black plastic pots ( 30.5 cm diameter and 35.5 cm deep) were arranged in a completely randomized design for each chamber. These pots were filled with a soil mixture of 1: 1: 1 ratio by volume containing Canadian sphagnum peat moss, washed concrete sand, and loam soil. AquaGro 2000 G wetting agent was blended in at a rate of 0.59 kg per cubic meter of soil. Media was pasteurized with aerated steam at 80° C for 45 minutes. The soil level was 5 cm below the container rim in each pot. Germination tests were performed on all seed lots prior to sowing to determine accurate seeding rates. Pots were seeded at a rate of 5,382 pure live seed per meter squared ( PLS/ m2) based on research by Burton et al. ( 2006), which suggests that higher sowing densities result in more rapid ground cover. Each species was equally represented by dividing the seeding rate by the number of species to determine the rate for each species. The seeds of all species were mixed together and then sprinkled on the soil surface and covered with a 0.5 cm layer of soil. The soil was kept evenly moist until the seeds germinated. Volunteer dicot species ( mostly clover ( Melilotus ssp.)) and grass species ( mostly downy brome ( Bromus tectorum)) were removed by hand. Pots were checked daily and hand- watered as needed. Pots in each ecoregion were re- randomized at each mowing. Each mixture received two applications of granular fertilizer ( Wil- Gro 16- 16- 16 7S, Wilbur- Ellis, San Francisco, California) at a rate of 4.9 g of elemental N/ m2, one at 60 days after planting ( DAP) and the second at 120 DAP. Supplemental lighting ( GE Multi- Vapor MVR1000/ C/ U, GE Lighting, General Electric Company, Cleveland, Ohio) was provided for eight hours per day from November 30, 2005, through April 10, 2006. The supplemental lighting was adjusted periodically to coincide with sunrise times such that it did not extend day length but rather supplemented natural light. 3.2.1.6. Measures of Growth Each mixture was grown for a period of seven months and was clipped to 8 cm above the soil surface at two- week intervals. Clippings were bagged, dried for 48 hours at 50 º C then weighed to determine clipped dry biomass. Once the clippings were removed, the percent cover of each species and total ground cover within each pot were visually estimated for each mixture of species and harvest date. These assessments were not conducted at the first two harvests of the Pacific Forest and Chaparral ecoregions, nor at the first harvest of the California Grasslands ecoregion. Red fescue ( Festuca rubra) and Idaho fescue ( Festuca idahoensis) were extremely difficult to differentiate in the greenhouse and thus were pooled together for the purpose of percent species composition for the Pacific Forest ecoregion— the only region in which they were planted together. In the California Grasslands ecoregion, purple needlegrass ( Nassella pulchra) and nodding needlegrass ( Nassella cernua) were also pooled because of difficulty distinguishing between the two species in the greenhouse. 3.2.1.7. Data Analysis Clipped dry biomass, species abundance ( percent cover), and total ground cover ( percent) were the response variables used for analysis. For species occurring in more than one ecoregion, analysis of variance ( ANOVA) with repeated measures statements was used to compare differences in abundance between ecoregions. Where significant differences existed, data from the differing ecoregion( s) were separated. Data from all other ecoregions were combined. Western Transportation Institute Page 14
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Linear regression was performed using accumulated growing degree days as a predictor of percent species abundance. All statistical analyses were performed using SAS ( SAS Institute, Cary, North Carolina). In order to account for temporal autocorrelation, ANOVAs were conducted using repeated measures statements with the PROC MIXED procedure using an autoregressive correlation structure as described by Littell ( 1998). 3.2.2. Results 3.2.2.1. Climate Control The growth chambers representing each ecoregion were all located in the same greenhouse; desired temperature settings could not be consistently achieved for every ecoregion simultaneously due to the vast range in temperatures between ecoregions. For this reason daytime temperatures were generally higher or lower than the intended set point. In addition, night temperatures were warmer than the temperature settings because temperatures could not fall below the minimum greenhouse setting due to greenhouse climate control system limitations. Monthly temperature settings and mean day and night temperatures for each ecoregion are reported in Table 3.2. Mean accumulated daily PAR ( mol• m- 2• day- 1), monthly accumulated GDD, and day and night relative humidity are reported in Table 3.3 for each month and each ecoregion. Despite some differences between desired temperature settings and achieved temperatures, the chambers accomplished their purpose of creating different environments for each ecoregion in terms of relative humidity and temperature as evidenced by significant differences between chambers in both relative humidity and temperature ( p < 0.0001 for both— data not shown).
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Table 3.2 Day and night temperature settings and achieved mean day and night temperatures (° C) and standard deviations by month for each ecoregion. SetSetSetSetMonth 13224.5± 2.191416.3± 3.04Month 12723.3± 3.071212.8± 1.12Month 22624.7± 2.401018.2± 4.15Month 22522.0± 2.18912.9± 1.50Month 31821.4± 3.43612.3± 2.86Month 31924.2± 3.62619.0± 3.76Month 41321.4± 3.59311.1± 0.79Month 41622.9± 4.07310.9± 0.80Month 51321.4± 3.52311.4± 0.64Month 51623.3± 4.37411.0± 0.85Month 61623.7± 3.91511.6± 0.59Month 61724.2± 4.84511.1± 0.64Month 71924.2± 2.98616.4± 3.38Month 71928.0± 4.99613.3± 3.76SetSetSetSetMonth 13127.4± 3.041517.1± 3.22Month 11423.4± 2.01- 413.9± 2.53Month 22524.6± 1.34911.6± 0.72Month 21823.4± 2.54- 118.5± 4.76Month 31820.8± 2.99411.6± 0.70Month 32319.1± 2.90311.8± 0.73Month 41422.5± 3.35011.5± 0.59Month 42820.2± 3.56612.2± 0.68Month 51424.0± 2.77115.9± 3.94Month 53220.2± 3.24911.9± 0.51Month 61625.4± 3.57213.7± 1.91Month 63122.5± 3.09815.3± 3.89Month 71826.9± 2.69415.3± 1.26Month 72723.4± 2.90413.4± 1.74SetSetSetSetMonth 12221.0± 2.781012.5± 1.13Month 11123.9± 1.88- 117.6± 2.79Month 21919.8± 1.70814.4± 3.07Month 21523.1± 3.08118.2± 4.55Month 31522.5± 3.79618.5± 3.72Month 32019.2± 3.10411.4± 0.73Month 41320.9± 4.05410.3± 0.81Month 42520.5± 3.78811.8± 0.62Month 51320.8± 4.42410.4± 0.91Month 52920.3± 3.411011.7± 0.56Month 61421.2± 3.85510.5± 0.75Month 62922.5± 3.111015.0± 3.93Month 71523.6± 3.72611.9± 3.63Month 72523.3± 2.87713.7± 1.89Actual ± SDDay Temp. (° C) Night Temp. (° C) Day Temp. (° C) Night Temp. (° C) Day Temp. (° C) Night Temp. (° C) Day Temp. (° C) Night Temp. (° C) Day Temp. (° C) Actual ± SDActual ± SDActual ± SDActual ± SDNight Temp. (° C) Pacific ForestSierran ForestActual ± SDActual ± SDActual ± SDIntermountain SagebrushGreat American DesertChaparralCalifornia GrasslandsDay Temp. (° C) Night Temp. (° C) Actual ± SDActual ± SDActual ± SDActual ± SD Western Transportation Institute Page 16
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Table 3.3 Mean daily accumulated photosynthetically active radiation ( PAR) ( mol• m- 2• day- 1), monthly accumulated growing degree days ( GDD) ( computed using baselines of 5° C for cool season and 10° C for warm season species), and average day and night relative humidity ( RH) by month for each ecoregion. California Grasslands Chaparral GDD RH (%) GDD RH (%) PAR 5° C 10° C Day Night PAR 5° C 10° C Day Night Month 1 4.5 442 - 26 39 3.9 365 - 36 48 Month 2 4.4 476 - 29 44 5.5 367 - 27 34 Month 3 5.4 347 - 30 40 5.7 476 - 29 46 Month 4 7.3 290 - 29 42 7.8 349 - 24 38 Month 5 8.9 339 - 36 49 9.8 317 - 26 41 Month 6 13.5 340 - 37 46 9.3 352 - 33 49 Month 7 12.6 401 - 57 70 15.6 477 - 37 50 Total 2636 2703 Great American Desert Intermountain Sagebrush GDD RH (%) GDD RH (%) PAR 5° C 10° C Day Night PAR 5° C 10° C Day Night Month 1 6.1 518 358 22 36 6.1 411 - 23 34 Month 2 8.9 344 209 24 36 6.2 459 - 27 42 Month 3 9.1 339 184 32 43 6.6 327 - 27 34 Month 4 12.1 346 191 34 45 8.8 296 - 30 37 Month 5 13.9 397 257 50 59 8.0 323 - 37 45 Month 6 15.8 432 272 60 77 8.8 405 - 46 50 Month 7 12.2 418 278 57 72 10.1 390 - 59 72 Total 2793 1748 2610 Pacific Forest Sierran Forest GDD RH (%) GDD RH (%) PAR 5° C 10° C Day Night PAR 5° C 10° C Day Night Month 1 4.2 321 - 39 50 5.7 457 307 24 38 Month 2 5.6 344 - 30 39 4.0 447 297 30 45 Month 3 6.7 443 - 34 49 5.0 317 157 30 39 Month 4 8.7 309 - 29 43 6.7 289 149 33 43 Month 5 10.6 274 - 32 47 7.0 318 163 41 50 Month 6 10.5 311 - 38 53 8.6 399 244 48 54 Month 7 13.3 376 - 43 55 10.1 414 249 61 72 Total 2378 2642 1567 Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Chapter 3
3.2.2.2. Clipped Dry Biomass Differences in the clipped dry biomass between mixtures over time ( DAP) within an ecoregion could indicate that some mixtures established more rapidly than others. There were no significant sod composition ( mixture) main effects for the California Grasslands, Chaparral, Great American Desert and Pacific Forest ecoregions, which indicated that there were no differences in clipped dry biomass between mixtures for these ecoregions. A significant DAP main effect merely indicated that biomass changed over the course of production, which was the case for all ecoregions. For the Intermountain Sagebrush ecoregion, there was a significant sod composition by DAP interaction ( p = 0.0308), which indicated that there were significant differences in dry biomass between mixtures at some harvests, but not at others. RX5B mixtures had significantly lower clipped dry biomass than all other mixtures from 100 through 128 DAP, but, from 156 DAP through the final harvest, there were no significant differences between mixtures ( Fig. 3.1). Days After Planting0255075100125150175200225Dry Weight ( g) 02468RX3B RY3B RX5B RY5B RXY3B RXY5B Figure 3.1 Effect of sod composition and days after planting on clipped dry weight for the Intermountain Sagebrush ecoregion mixtures. Points represent means and error bars represent standard errors from the SAS MIXED model. There was also a significant sod composition by DAP interaction for the Sierran Forest ecoregion ( p = 0.0199). RX3B mixtures were significantly lower from the first harvest through 74 DAP than all other mixtures. However, beyond 172 DAP, there were no significant differences between mixtures ( Figure 3.2). Western Transportation Institute Page 18
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Days After Planting0255075100125150175200225Dry Weight ( g) 02468RX3B RY3B RX5B RY5B RXY3B RXY5B Figure 3.2 Effect of sod composition and days after planting on clipped dry weight for the Sierran Forest ecoregion mixtures. Points represent means and error bars represent standard errors from the SAS MIXED model. 3.2.2.3. Species Abundance The contribution of individual species to a mixture’s composition was evaluated by estimating the percent cover of each species within it. Species composition varied widely within and between mixtures as well as across ecoregions. Such variation was expected. Data for all ecoregions were initially analyzed together and where significant differences occurred, as determined by ANOVA, an ecoregion’s data were regressed separately. Squirrel tail ( Elymus elymoides), blue wildrye ( Elymus glaucus), slender wheatgrass ( Elymus trachycaulus), prairie junegrass ( Koeleria macrantha) and California melic grass ( Melica californica) were separated by ecoregion for this analysis and the response of these species for the different ecoregions is provided in Table 3.4. Cover of most species ( 16 of 20) increased significantly as growing degree days accumulated ( Table 3.4, as indicated by an r2 > 0.20 and p < 0.0001). Red fescue, prairie junegrass, California melic grass ( California Grasslands ecoregion), deergrass ( Muhlenbergia rigens), and nodding needlegrass ( Great American Desert ecoregion) all had especially strong positive correlations ( r2 > 0.50). Cover for a few species, including blue wildrye ( Chaparral ecoregion) did not change significantly as GDDs accumulated ( r2 ≤ 0.20 and p ≥ 0.05), while other species ( particularly slender wheatgrass) changed significantly over GDDs, but very little of this variation was explained by a linear regression ( r2 ≤ 0.20 and p < 0.05) ( Table 3.4). 3.2.2.4. Total Ground Cover Total ground cover changed significantly over the course of the experiment ( DAP). A significant sod composition main effect indicated that some mixtures covered the ground more completely than others. For example, in the Great American Desert ecoregion, the sod
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composition main effect was significant ( p = 0.0102), with RX5B mixtures having significantly greater total ground cover than RX3B mixtures ( Figure 3.3b). Neither the sod composition main effect nor the sod composition by DAP interaction were significant for the California Grasslands or Pacific Forest ecoregions. In terms of differences in total ground cover, there were no differences in sod establishment for these two ecoregions. At the final harvest, total ground cover averaged 72% for the California Grasslands ecoregion and 82% for the Pacific Forest. Table 3.4 Summary of regression of individual species percent cover and accumulated growing degree days. SpeciesEcoregion( s) r2f Valuep > fAchnatherum hymenoidesGreat American Desert0.33123.47< 0.0001Achnatherum occidentaleIntermountain Sagebrush0.012.550.1132Aristida purpureaGreat American Desert0.3671.14< 0.0001Bromus carinatusCalifornia Grasslands, Chaparral, Pacific Forest, Sierran Forest0.34415.72< 0.0001Elymus elymoidesIntermountain Sagebrush, Sierran Forest0.002.260.1337Elymus elymoidesGreat American Desert0.0617.29< 0.0001Elymus glaucusCalifornia Grasslands0.013.730.0547Elymus glaucusChaparral0.0911.450.0010Elymus glaucusPacific Forest, Sierran Forest0.026.180.0134Elymus multisetusIntermountain Sagebrush0.4082.93< 0.0001Elymus trachycaulusPacific Forest, Chaparral0.0723.50< 0.0001Elymus trachycaulusIntermountain Sagebrush, Sierran Forest0.014.810.0291Festuca rubraCalifornia Grasslands, Chaparral, Sierran Forest0.55566.22< 0.0001Festuca rubra/ idahoensisPacific Forest0.38418.87< 0.0001Hordeum brachyantherumSierran Forest0.36143.72< 0.0001Koeleria macranthaChaparral, Pacific Forest0.60480.37< 0.0001Koeleria macranthaGreat American Desert, Intermountain Sagebrush0.66978.83< 0.0001Leymus cinereusIntermountain Sagebrush0.44195.90< 0.0001Leymus condensatusGreat American Desert0.48230.07< 0.0001Leymus triticoidesCalifornia Grasslands, Intermountain Sagebrush0.27122.45< 0.0001Melica californicaPacific Forest- 0.010.010.9233Melica californicaCalifornia Grasslands0.74329.47< 0.0001Muhlenbergia rigensSierran Forest0.66490.94< 0.0001Nassella cernuaGreat American Desert0.62206.89< 0.0001Nassella lepidaChaparral0.36123.40< 0.0001Nassella pulchraChaparral0.2230.82< 0.0001Nassella pulchra/ cernuaCalifornia Grasslands0.2163.14< 0.0001 Significant sod composition by DAP interactions occurred for the three remaining ecoregions ( Chaparral, Intermountain Sagebrush and Sierran Forest), indicating either changes in rank order or differences between mixtures in total ground cover at some clipping dates, but not others. There was a significant sod composition by DAP interaction for the Chaparral ecoregion ( p = 0.0035). RX3B mixtures had significantly greater total ground cover than all other mixtures at Western Transportation Institute Page 20
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159 DAP, while RX5B mixtures had significantly less total ground cover than all other mixtures at 117 and 159 DAP. Beyond 159 DAP, there were no significant differences in total ground cover between mixtures ( Figure 3.3a). There was a significant sod composition by DAP interaction for the Intermountain Sagebrush ecoregion ( p < 0.0001). Minor variations in total ground cover occurred early on, but major differences were present beginning at 100 DAP ( Figure 3.3c). RX3B mixtures had the statistically greatest ground cover for most of the remaining experiment, followed by the two RXY mixtures. The RX5B mixtures and the two RY mixtures consistently had the lowest ground cover after 100 DAP. There was also a significant sod composition by DAP interaction for the Sierran Forest ecoregion ( p < 0.0001). Ground cover of all mixtures linearly increased until 100 DAP when ground cover percentages plateaued ( Figure 3.3d). Ground cover for five bunchgrass mixtures was significantly greater than mixtures with only three bunchgrasses. Beyond 100 DAP, RXY5B and RY5B mixtures had the greatest total ground cover for most of the remaining growth period, followed closely by RX5B mixtures. RY3B mixtures consistently had significantly less total ground cover than all other mixtures after 100 DAP. Mixtures with five bunchgrasses were similar in ground cover throughout the experiment, while the ground cover rank of mixtures with three bunchgrasses fluctuated throughout the growing period. 3.2.3. Discussion Natural plant communities are commonly species- diverse, and this diversity is regarded as essential to the stability of these communities ( Tilman 1996) and often to their ability to resist disturbance and invasion ( Elton 1958; Tilman 1997; Brown et al. 1998; Levine and D’Antonio 1999; but see Stohlgren et al. 1999; Stohlgren et al. 2003). When a major disturbance does occur, it opens a pathway to a drastic shift in community assemblage ( Mouquet et al. 2003; but see Connell 1978; Huston 1979). Over time, the progression of re- colonization generally moves from annuals and biennials to perennial species ( Grime 1979). During this period, plant communities are more susceptible to change and invasion ( Hobbs & Huenneke 1992). This time period offers an opportunity for a diverse native community to be replaced by non- native species. Thus, in accordance to native community ecology, native rehabilitation sod should be composed of as many species as possible to increase its versatility and adaptability to varied installation sites and to mimic the diversity found in many natural communities. However, limitations imposed by a species habit, seed availability, soil moisture and texture, etc. may greatly limit the number of species that may be included in a rehabilitation sod. This supports Ehrenfeld’s ( 2000) stand that restoration goals must be realistic because it is impossible to mimic all of the events that have contributed to the pre- disturbance state of a plant community during the course of a restoration project.
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Total Ground Cover (%) 020406080RX3B RY3B RX5B RY5B RXY3B RXY5B Days After Planting0255075100125150175200225Total Ground Cover (%) 020406080Days After Planting0255075100125150175200225Total Ground Cover (%) 020406080Total Ground Cover (%) 020406080a) b) c) d) Figure 3.3 Effect of sod composition and days after planting on total ground cover for the a) Chaparral, b) Great American Desert, c) Intermountain Sagebrush, and d) Sierran Forest ecoregions. Points represent means and error bars represent standard errors from the SAS MIXED model. The majority of species we studied increased significantly in abundance over time, as evidenced by the significant positive correlation between accumulated GDDs and percent abundance. A few species, such as blue wildrye, squirrel tail and slender wheatgrass, persisted at moderate percentages ( 5 to 10%) over the course of the experiment. However, we would not recommend that such species be excluded from native sod mixtures as we would envisage that the composition of a sod would change over time, depending on where it was laid. In addition, with regard to the vacant niche hypothesis having a diverse number of species in the sod would increase the number and type of niches and resources being exploited which could reduce the establishment of undesired species from seed. Germination requirements of seeds is another consideration; for our experimental purposes we did stratify species that required it prior to sowing but this would be more difficult in commercial situations. For example, even though there was a significant positive correlation between accumulated GDDs and Indian ricegrass cover, the species made up less than 3% of the total
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ground cover at the final harvest of Great American Desert samples. This is likely because Indian ricegrass requires a 60- day cold stratification for germination. This stratification was performed prior to sowing but still resulted in minimal germination. In a commercial production setting it may be necessary to sow Indian ricegrass in the fall prior to spring sowing of the remaining species. The capacity to achieve this is unknown but should be investigated for this and other species requiring cold stratification for germination. Some warm season species may also require special consideration. Deergrasss is a warm season species and did not begin to establish until nearly 1,000 GDDs had accumulated. However, purple three- awn grass ( Aristida purpurea), another warm season species began to establish immediately. Either deergrass required more GDDs to establish ( such information was not located) or this seed lot performed poorly in general. Different performance of the same individual species sown in different mixtures and ecoregions was observed. California melic grass cover did not increase significantly over GDD in the Pacific Forest ecoregion, and cover at cover increased significantly as GDDs accumulated and final percentages ranged from the final harvest ranged from 2- 5%. However, in the California Grasslands ecoregion, California melic grass 16- 36%. In constrast, there was no significant difference in blue wildrye cover between the Pacific Forest and Sierran Forest ecoregions. In both cases, seed from the relevant ecoregion was used but our experimental design did not allow us to evaluate the relative role of seed source versus interspecific competition. There was no obvious direct relationship between total ground cover and species diversity. The performance of individual species more readily explained differences between mixtures in total ground cover than did species diversity. For example, the decline of particular species in the Intermountain Sagebrush ( western needlegrass ( Achnatherum occidentale), slender wheatgrass, and squirrel tail), and Sierran Forest ecoregions ( slender wheatgrass, squirrel tail, and blue wildrye) reduced total ground cover for the mixtures in which they were included as compared to mixtures in which they were not. When two or more of these species were present in the same mixture, the effect was compounded. For the Great American Desert ecoregion, differences in total ground cover between mixtures seemed to be an artifact of the “ sampling effect” ( i. e., the occurrence of a particularly productive species that dominated the overall pattern) as originally suggested by Aarssen ( 1997) and Huston ( 1997) ( see Wardle 2002). In the Great American Desert ecoregion, nodding needlegrass was very productive and made up a large percentage of total ground cover. This species was only included in the RX5B mixtures, which likely explains the significantly greater total ground cover of these mixtures. However, this same effect was not observed in the California Grasslands ecoregion, but this could be explained by differences in interspecific competition and/ or seed source for the two ecoregions. 3.2.4. Conclusions Although species do not perform equally in terms of percent cover and biomass production, seeding as many species as possible should aid in the diversity of sod. When grown for seven months ( essentially the establishment phase for sod production in California), there appeared to be no difference in establishment success of mixtures that contained four to seven species as indicated by total ground cover. Accordingly, as long as a species does not fail to establish or disappear over the course of sod production, they should be included in the initial mix to ensure
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ecological versatility and overall diversity in the native rehabilitation sod. This study has demonstrated the capacity for producing native multispecies sod and its potential for use as a rehabilitation tool in these six ecoregions. The methods and results of this study could also be expanded in order to produce native multispecies sod for use in other geographical areas. These results have several important implications for practice including: • Native grass sod mixtures can mimic the diversity of native ecosystems while providing a method for rapid rehabilitation and restoration. • Mixtures of native grass species can be grown together and harvested as sod. • Native grass sod provides immediate soil surface stabilization and plant cover and can be used in areas where rapid rehabilitation is required. • Theoretically, native grass sod for restoration should be composed of many species. However, native grass seed availability is limited. As demand for native grass seed increases, more consistent sources of quality native seed will be required. 3.3. Native Grass Species Mix and Plant Density Evaluation In light of the results of the previous experiments evaluating multispecies sod, the research team selected the best species mixes for three ecoregions for further evaluation. At the same time these recommendations were sent to nursery collaborators so these sod mixes could be grown in sufficient quantity to establish test plots. 3.3.1. Materials and Methods The three selected ecoregions were Sierran Forest, Pacific Forest, and Chaparral. The selection criteria used to determine these ecoregions focused on areas within California that showed the greatest need for native sod to treat storm water run- off. Caltrans officials and the MSU native grass sod project team collaborated on this determination. The best sod mixes from each region ( Table 3.5) were grown on 1.2 m x 1.5 m ( 4 ft x 5 ft) plots under California environmental conditions and sod production standards. Each ecoregion mix was grown at two densities, 500 PLS/ ft22 ( same as the multispecies evaluation conducted previously) and 1,000 PLS/ ft. A reinforcement material, biodegradable coconut blanket comprised of 100% coir fiber coconut with biodegradable double jute netting ( 1.5 inch thread spacing), was added at harvest in accordance with sod harvesting general practices. At eight months, the sod was harvested and tested for sod strength ( Figure 3.4).
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Table 3.5 Species mixes used for each ecoregion in establishment success and weed suppression experiments. Native Grass Species Selected for Three Ecoregions Pacific Forest Sierran Forest Chaparral Festuca rubra Festuca rubra Festuca rubra Elymus trachycaulus Muhlenbergia riggen Elymus trachycaulus Bromus carinatus Elymus elymoides Bromus carinatus Festuca idahoensis Horeum brachyantherum Nassella lepida Elymus glaucus Koeleria macrantha Figure 3.4 Early growth of 1.2 m x 1.5 m plot of the high density Chaparral mix ( left) and early growth of 1.2 m x 1.5 m plot of the low density Sierran Forest mix ( right). 3.3.2. Results Similar to the results from the multispecies experiment, sod from the Pacific Forest ecoregion produced the highest sod strength. In all three ecoregions, the higher seeding density increased sod strength ( Figure 3.5). Native grass sod most likely benefited from a higher seeding rate when compared to traditional non- native sod because native grass growth habits are less aggressive rhizomatous and bunch types. These growth habits will not become denser with time as will traditional non- native species. Therefore, the initial seeding rate of native grass sod will need to be higher to construct a sod as strong and dense as non- native species. Reinforcement materials for sod were further tested for sod establishment and weed suppression. 3.3.3. Conclusion Native grass seed at this juncture can be prohibitively expensive. In the initial experiment, multispecies sod growth efforts produced some sods with adequate sod strength. For the Pacific Forest region, the standard 500 PLS/ ft2 should be adequate. For all other ecoregions, a higher seeding rate should be considered.
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Sierran ForestSod Strength ( kg/ cm of width) 012345ChapparelSod Strength ( kg/ cm of width) 012345Pacific ForestPlanting Density ( pure live seed per square foot) 5001000Sod Strength ( kg/ cm of width) 012345 Figure 3.5 Effect of planting density on the sod strength of native grass mixes for the Sierran Forest, Chaparral, and Pacific Forest ecoregions. 3.4. Native Grass Species Mix and Reinforcement Evaluation Additional experiments were conducted on the native grass sods grown in the experiment described above to further study their performance when transplanted onto deep soil beds ( similar to the situation encountered in actual field deployment). These experiments were done both with and without reinforcement material. 3.4.1. Materials and Methods Sod of the Chaparral, Sierran Forest, and Pacific Forest ecoregions were cut into six 0.37 m x 0.38m pieces ( 14.5” x 15” pieces). The sod was grown in the experiment discussed in Section 3.3 of this report at a high ( 1000 PLS/ ft22) and low ( 500 PLS/ ft) initial seeding density. The sod pieces were transported onto deep soil beds mimicking the soil of a roadside. Three pieces of each ecoregion sod were placed over a reinforcement mat ( Excelsior ® recycled wood product with a biodegradable string added at harvest in accordance with the general practice of sod Western Transportation Institute Page 26
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harvesting) or over bare ground. One hundred weed seeds ( canola) were planted beneath each of the sod pieces with and without reinforcement material. Sod was watered in at the beginning. The sod was then only watered intermittently to coincide with natural rainfall for the ecoregion. The sod was grown for 6 months. Each month, information was collected on species diversity, percent green coverage, percent ground coverage, number of weeds, and percent cover of weeds. Six months after transport, weeds, weed pods, and above ground biomass were harvested, dried, and weighed. Figure 3.6 Three deep soil boxes each with 12 transported sod pieces ( both high and low initial planting density) on reinforcement mats or bare ground. Dried weeds can be seen breaking through the sod. Figure 3.7 The transported sod and invasive weed biomass of the Pacific Forest ecoregion at termination of the experiment. Western Transportation Institute Page 27
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3.4.2. Results 3.4.2.1. Chaparral The initial planting density greatly affected the sod composition. The majority species in the high density sod was red fescue ( Festuca rubra) while the majority in the low density sod was California brome ( Bromus carinatus) ( Figure 3.8A). The reinforcement mat did not affect weed suppression, but rather a higher initial planting density reduced the number of weeds and the percent weed coverage ( Figure 3.8B). Weed biomass production was higher under low density sod, but the overall grass biomass was not significantly different ( Figure 3.8C). The presence or absence of reinforcement mat did not affect weed or grass biomass production. 3.4.2.2. Sierran Forest The initial planting density affected many parameters of the Sierran Forest sod, while the reinforcement mat affected only red fescue percent sod composition and percent bare ground. There was a higher percentage of red fescue at low density and treatments without mats ( Figure 3.9), while bare ground made up for the difference rather than filling in with other species ( Figure 3.10). Contrary to our hypothesis, the low planting density suppressed more weeds and weed cover ( Figure 3.11A). This was also reflected in the final harvest weed biomass ( Figure 3.11B). It was evident that the higher percent bare ground at the high initial planting density allowed weed germination and growth. 3.4.2.3. Pacific Forest From the previous experiments, it was evident that sod from the Pacific Forest ecoregion was the easiest to establish and was the strongest sod. Weed suppression characteristics were clearly significant while all other parameters were not. Both high initial planting density and the presence of reinforcement material aided in the suppression of weeds ( Figure 3.12A, 3.12B). The final harvest biomass revealed that initial planting density affected weed biomass, but grass biomass was unaffected ( Figure 3.12C). Western Transportation Institute Page 28
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FestucaInitial Planting Density ( PLS/ ft2) 5001000Sod Composition (%) 020406080100BromusInitial Planting Density ( PLS/ ft2) 5001000Sod Composition (%) 020406080100Initial Planting Density ( PLS/ ft2) 5001000Weeds ( number per plot) 0246810121416Initial Planting Density ( PLS/ ft2) 5001000Weed Cover (%) 02468101214WeedsInitial Planting Density ( PLS/ ft2) 5001000Biomass ( g) 020406080100GrassInitial Planting Density ( PLS/ ft2) 5001000Biomass ( g) 020406080100
A
B
C Figure 3.8 Effect of initial planting density on the composition of the sod for red fescue ( Festuca rubra) and California brome ( Bromus carinatus) ( A), on the weed number and weed cover ( B), and weed and grass biomass ( C) in the Chaparral mix. Western Transportation Institute Page 29
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Initial Planting Density ( PLS/ ft2) 5001000Sod Composition (% Festuca) 020406080100Reinforcement Materialmatno matSod Composition (% Festuca) 020406080100 Figure 3.9. Effect of initial planting density and reinforcement mat on percent red fescue in the plots of the Sierran Forest mix. Initial Planting Density ( PLS/ ft2) 5001000Bare Ground (%) 020406080100Reinforcement Materialmatno matBare Ground (%) 020406080100 Figure 3.10 Effect of initial planting density and reinforcement mat on the percent bare ground in the Sierran Forest mix. Western Transportation Institute Page 30
Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Chapter 3
A
% festuca Initial Planting Density ( PLS/ ft2) 5001000Weeds ( number per plot) 02468101214161820Initial Planting Density ( PLS/ ft2) 5001000Weed Cover (%) 0246810121416WeedsInitial Planting Density ( PLS/ ft2) 5001000Biomass ( g) 020406080100GrassInitial Planting Density ( PLS/ ft2) 5001000Biomass ( g) 020406080100
B Figure 3.11 Effect of initial planting density on the weed number and weed cover ( A) and weed and grass biomass ( B) in the in the Sierran Forest mix. Western Transportation Institute Page 31
Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Chapter 3
Initial Planting Density ( PLS/ ft2) 5001000Weeds ( number per plot) 02468101214Reinforcement Materialmatno matWeeds ( number per plot) 02468101214WeedsInitial Planting Density ( PLS/ ft2) 5001000Biomass ( g) 020406080100GrassInitial Planting Density ( PLS/ ft2) 5001000Biomass ( g) 020406080100Initial Planting Density ( PLS/ ft2) 5001000Weed Cover (%) 020406080100Reinforcement Materialmatno matWeed Cover (%) 020406080100
A
B
C Figure 3.12 Effect of initial planting density and reinforcement material on the weed number ( A), weed cover ( B), on weed and grass biomass ( C) in the Pacific Forest mix.
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3.4.3. Conclusion Overall, all transported sod, regardless of ecoregion, initial planting density, and reinforcement material successfully reestablished on the deep soil plots. Red fescue and/ or California brome species dominated the resulting sod in all three ecoregions. Although planted at equal seed numbers, the other species in each mix comprised less than 5% of the ground cover by the end of the transport experiment. These species were present throughout the duration of the experiment and could fulfill a niche not addressed in these experiments, but that are likely to occur in sensitive and roadside conditions. A general conclusion regarding initial planting density and the use of reinforcement mats cannot be drawn across ecoregions. It is believed that the sod composition at the time of transport determines the sensitivity to the reinforcement mat. 3.5. Literature Cited Aarsen, L. 1997. High productivity in grassland ecosystems: effected by species diversity or productive species? Oikos, 80: 183- 184. Brown, C. S., K. J. Rice and V. Claassen. 1998. Competitive Growth Characteristics of Native and Exotic Grasses ( Final Report). California Department of Transportation New Technology and Research Program, University of California, Davis. Burton, C. M., P. J. Burton, R. Hebda and N. J. Turner. 2006. Determining the optimal sowing density for a mixture of native plants used to revegetate degraded ecosystems. Restoration Ecology, 14( 3): 379- 390. Caltrans ( California Department of Transportation). 2001. Native Grass Database URL http:// www. dot. ca. gov/ hq/ LandArch/ nativedb/ [ Downloaded on 16 May 2005] Connell, J. H. 1978. Diversity in Tropical Rain Forests and Coral Reefs - High Diversity of Trees and Corals Is Maintained Only in a Non- Equilibrium State. Science 199: 1302- 1310. Ehrenfeld, J. G. 2000. Defining the limits of restoration: the need for realistic goals. Restoration Ecology, 8: 2- 9. Elton, C. S. 1958. The Ecology of Invasions by Animals and Plants, The University of Chicago Press. Grime, J. P. 1979. Plant Strategies and Vegetation Processes. 2nd edition. 2001. John Wiley and Sons, Sussex, England. Hickman, J. C. ed. ( 1993). The Jepson Manual: Higher Plants of California. University of California Press, Berkeley. Hobbs, R. J. and L. F. Huenneke. 1992. Disturbance, Diversity, and Invasion: Implications for Conservation. Conservation Biology 6: 324- 337. Huston, M. A. 1979. General Hypothesis of Species- Diversity. American Naturalist 113: 81- 101. Huston, M. A. 1997. Hidden treatments in ecological experiments: re- evaluating the ecosystem function of biodiversity. Oecologia 110: 449- 460. Levine, J. M. and C. M. D'Antonio. 1999. Elton Revisited: A Review of Evidence Linking Diversity and Invasibility. Oikos, 87: 15- 26.
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Littell, R. C., P. R. Henry and C. B. Ammerman. 1998. Statistical analysis of repeated measures data using SAS procedures. Journal of Animal Science, 76: 1216- 1231. Mouquet, N., P. Manguia, J. M. Kneitel and T. E. Miller. 2003. Community assembly time and the relationship between local and regional species richness. Oikos, 103: 618- 626. Stohlgren, T. J., D. Binkley, G. W. Chong, M. A. Kalkhan, L. D. Schell, Lisa D., K. A. Bull, Y. Otsuki, G. Newman, M. Bashkin and Y. Son. 1999. Exotic Plant Species Invade Hot Spots of Native Plant Diversity. Ecological Monographs 69: 25- 46. Stohlgren, T. J., D. T. Barnett and J. Kartesz. 2003. The Rich Get Richer: Patterns of Plant Invasions in the United States. Frontiers in Ecology and the Environment 1: 11- 14. Tilman, D. 1996. Biodiversity: population versus ecosystem stability. Ecology, 77: 350- 363. Tilman, D. 1997. Community invasibility, recruitment limitation, and grassland biodiversity. Ecology, 78: 81- 92. USDA, NRCS ( United States Department of Agriculture, Natural Resource and Conservation Service). 2007. The PLANTS Database. URL http:// plants. usda. gov [ accessed on 3 May 2007). Wardle, D. A. 2002. The regulation and function of biological diversity. In S. A. Levin and H. S. Horn, editors. Communities and ecosystems: linking the aboveground and belowground components. Princeton University Press, New Jersey. Western Regional Climate Center. URL http:// www. wrcc. dri. edu/ Climsum. html [ accessed on 3 May 2007]. Using Reinforced Native Grass Sod for Biostrips, Bioswales, and Sediment Control Chapter 4
4. ESTABLISHMENT SUCCESS AND WEED SUPPRESSION POTENTIAL OF MULTISPECIES SOD 4.1. Introduction Field experiments were conducted to assess the potential of multispecies sod to suppress weeds of different density and with different reinforcement materials over a two year period. Two distinct series of trials were performed. Plots sodded without reinforcement materials were used to assess suppression of weeds sown at six densities ( the " A" trials). Reinforcement materials are often required to transport harvested sod. The effect of this material on weed suppression was assessed ( the " B" trials). Both experiments were conducted from 2006 to 2008 at Montana State University ( MSU). In both experiments the surrogate weed, canola ( Brassica napus), was