Division of Research
& Innovation
Report CA07- 0103
December 2008
Vegetation Conversion to Desirable
Species Along Caltrans Rights- of- Ways
Final Report
Vegetation Conversion to Desirable Species
Along Caltrans Rights- of- Ways
Final Report
Report No. CA07- 0103
December 2008
Prepared By:
Division of Agriculture & Natural Resources
University of California, Davis
Davis, CA
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.
i
STATE OF CALIFORNIA DEPARTMENT OF TRANSPORTATION
TECHNICAL REPORT DOCUMENTATION PAGE
1. REPORT NUMBER
CA07- 0103
2. GOVERNMENT ASSOCIATION NUMBER
3. RECIPIENT’S CATALOG NUMBER
5. REPORT DATE
August 31, 2007
4. TITLE AND SUBTITLE
Vegetation Conversion to Desirable Species along Caltrans
Rights- of- Ways 6. PERFORMING ORGANIZATION CODE
59 - 319
7. AUTHOR( S)
Young, S. L. and Claassen, V. P.
8. PERFORMING ORGANIZATION REPORT NO.
10. WORK UNIT NUMBER
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Division of Agriculture & Natural Resources
University of California, Davis
Davis, CA 11. CONTRACT OR GRANT NUMBER
65A0137
13. TYPE OF REPORT AND PERIOD COVERED
Final Report,
12. SPONSORING AGENCY AND ADDRESS
California Department of Transportation
Division of Research and Innovation, MS- 83
1227 O Street
Sacramento CA 95814
14. SPONSORING AGENCY CODE
15. SUPPLEMENTAL NOTES
in cooperation with the U. S. Department of Transportation, Federal Highway Administration
16. ABSTRACT
This study evaluates several establishment sequences to determine effective ways to convert existing
annual non- native vegetation to native perennial species. Sustained weed control for several years is
shown to be required for vegetation conversion. No single treatment was sufficient, but each provided
different weed control characteristics. Burning provides control of non- native seeds and plants and
stimulates native perennial plant growth. Tillage prepares the seed bed, stimulates germination of
weed seed and provides soil volumes for root penetration. Ecotypic plant species are thought to be
adapted to different topographic zones away from the road edge. Herbicide use was important to
selectively reduce non- native annual plant species. Chemical treatments to control weeds included 1)
postemergence, non- selective ( glyphosate), 2) postemergence, broadleaf selective ( clopyralid) and 3)
preemergence, non- selective ( chlorsulfuron). After vegetation conversion, herbicide use is shown to
be reduced or eliminated except for occasional weed control. After three years of cultural and
chemical management, we found native perennial grasses most abundant in sites that had been burned
once and sprayed at least twice. In established roadside stands of native perennial grasses, a
combination of spraying, mowing and/ or burning for two consecutive years is required to reduce or
eliminate non- native, invasive species, such as yellow starthistle. Once established, native perennial
grass stands can persist for more than a decade and remain relatively weed resistant.
17. KEY WORDS
revegetation, native plants, weed control,
herbicides, soil treatments, vegetation type
conversion, road edges
18. DISTRIBUTION STATEMENT
No restrictions. This document is available to the
public through the National Technical
Information Service, Springfield, VA 22161
19. SECURITY CLASSIFICATION ( of this report)
Unclassified
20. NUMBER OF PAGES
128
21. PRICE
Evaluating Alternative Methods for Vegetation Control
and Maintenance Along Roadsides, Study II
FINAL REPORT
August 31, 2007
Research Technical Agreement # 65A0137
Expense Authorization 680527
California Department of Transportation
Steve Young
Vic Claassen
University of California, Davis
ii
EXECUTIVE SUMMARY:
Annual vegetation cover on roadside rights- of- way is associated with several
undesirable characteristics, including fire hazard, and mowing and herbicide
requirements and exclusion of native plants. Conversion to native perennial species can
produce a stable plant community with potential to reduce annual grass and broadleaf
cover and improve habitat, but establishment is difficult due to extensive pressure from
invasive non- native annuals. This study evaluated several establishment sequences to
determine effective ways to convert existing annual non- native vegetation to native
perennial species.
Persistent weed control is shown to be required for vegetation conversion from
annual to perennial grasses, and during the early years of establishment. No single
treatment was sufficient, but each provided different weed control characteristics.
Burning provides control of non- native seeds and plants and stimulates native perennial
plant growth. Tillage prepares the seed bed, stimulates germination of weed seed and
provides soil volumes for root penetration. Ecotypic plant species are thought to be
adapted to different topographic zones away from the road edge. Herbicide use was
important to selectively reduce non- native annual plant species. Chemical treatments to
control weeds included 1) postemergence, non- selective ( glyphosate), 2) postemergence,
broadleaf selective ( clopyralid) and 3) preemergence, non- selective ( chlorsulfuron). After
vegetation conversion from annual weeds to native perennial grass dominated systems,
herbicide use is shown to be reduced or eliminated except for occasional weed control.
The frequency and intensity of additional herbicide use is anticipated to depend
on several factors. If the native grass stand is dense, then starthistle, as an example weed,
iii
is effectively excluded and will require no continuing treatment. Disturbance that opens
up the canopy ( low mowing, car tracks through wet soil, fires that remove thatch) can
allow starthistle to establish, therefore requiring targeted herbicide application. Perennial
weeds such as johnsongrass or perennial pepperweed, if they invaded, would require
treatment even in an established stand. Thinner stands ( with more open area between
native grass plants) may require weed control during wet years but not during normal or
dry years. Herbicide treatments would not need to be regularly scheduled, but would be
triggered was weather patterns and new weeds trigger a response. Timing of existing
“ maintenance” activities like mowing can also be optimized to favor desirable plants, and
thus reduce the need for secondary responses such as herbicide application. Reducing
mowing from every year to every 2 or three years in some strips away from the road edge
could be used to favor desirable perennial grass vegetation and reduce weed management
effort by maintaining a denser canopy.
After three years of cultural and chemical management on annual grass sites, we
found native perennial grasses most abundant in sites that had been burned once and
sprayed at least twice. During the period of this study, the initial seed mix had little
impact on the density and diversity of native perennial grass establishment. We also
found that deep cultivation was not needed to establish native perennial grasses at two
sites where soils prior to road construction were possibly used for farm production or
pasture. In established roadside stands of native perennial grasses, a combination of
spraying, mowing and/ or burning for two consecutive years is required to reduce or
eliminate non- native, invasive species, such as yellow starthistle. Once established, native
perennial grass stands can persist for more than a decade and remain relatively weed
resistant.
iv
Disclaimer Clause
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
manufacturers’ names appear in this report only because they are considered essential to
the object of the document.
v
TABLE OF CONTENTS
EXECUTIVE SUMMARY: ................................................................................................ i
Problem Statement ____________________________________________________________ 1
Introduction _________________________________________________________________ 1
Phase I: Literature and Site Review.................................................................................. 3
Literature review: ( bulleted summary) ___________________________________________ 4
Native species have been established along roadsides with appropriate management. .......................... 4
Ecological factors must be considered for establishing native perennial grasses. .................................. 4
Literature review: summary ____________________________________________________ 5
Literature review: revegetation studies ___________________________________________ 8
Roadsides evolve with roads .................................................................................................................. 8
Roadside revegetation today................................................................................................................. 10
Difficulties of revegetation along roadsides ......................................................................................... 11
Roadside revegetation by Caltrans ....................................................................................................... 13
Other attempts at roadside revegetation ............................................................................................... 17
Revegetation of roadside- like sites....................................................................................................... 19
Other revegetation studies .................................................................................................................... 22
Native plant community competition ............................................................................................... 23
Plant competition.................................................................................................................... ..... 23
Out- competing the exotics............................................................................................................ 27
Water: a resource that can dictate plant community development ............................................... 29
Native plant community resistance to invasion ................................................................................ 32
Site review: ( Yolo County, California) ( bulleted summary)__________________________ 37
Establishment of native plant communities varied under three broad levels of management. ............. 37
Phase II: Roadside native plant establishment............................................................... 39
Phase II, Part A: Desirable plant materials _______________________________________ 40
Introduction ............................................................................................................................... .......... 40
Methods for installation of plant species .............................................................................................. 41
Results of native perennial grass species selection............................................................................... 63
Conclusions ............................................................................................................................... .......... 69
Phases II, Part B: Site preparations ( I- 5 median trials) _____________________________ 70
Summary ............................................................................................................................... .............. 70
Introduction ............................................................................................................................... .......... 71
Methods for planting and establishing native perennial grasses........................................................... 76
Results ............................................................................................................................... .................. 84
Discussion ............................................................................................................................... ............ 88
Conclusions ............................................................................................................................... .......... 93
Phase III: Maintenance procedures for improving native grass performance ............. 94
Summary ............................................................................................................................... .............. 94
Introduction ............................................................................................................................... .......... 96
Methods of integrated vegetation management .................................................................................. 104
Results ............................................................................................................................... ................ 111
Discussion ............................................................................................................................... .......... 116
Conclusions ............................................................................................................................... ........ 117
Overall Project Summary............................................................................................... 119
Literature cited ............................................................................................................... 121
1
Problem Statement
Rapid and dense growth of invasive annual plants in roadside rights- of- way and
their associated problems of fire and invasive spread have led to a cycle of spraying,
mowing and fire control. These invasive annual stands keep native perennial plants from
colonizing and establishing in natural communities, which provide benefits to the
roadway environment.
Introduction
The California Department of Transportation ( Caltrans) manages approximately
15,000 miles of highway and more than 230,000 acres of right- of- way throughout the
state. A major portion of Caltrans’ management and maintenance effort is associated with
vegetation control. This need is driven by safety concerns, such as ensuring visibility of
traffic and highway structures and minimizing fire potential by reducing vegetative
biomass. Additionally, vegetation control provides benefits by reducing the presence of
noxious weeds and other pests. Vegetative cover is a major component of erosion and
sedimentation control. Proper vegetative cover within Caltrans rights- of- way has the
potential to improve motorist safety and erosion control, while reducing the need for
mowing and/ or herbicide use.
With the completion of an Environmental Impact Report ( EIR) in late 1992, a
shift in focus from relying solely on chemical vegetation control to establishing native
grasses and low- growing non- native fescues has begun to take shape. As part of an
integrated roadside vegetation management ( IRVM) program, Caltrans has completed
2
revegetation seeding projects on numerous construction sites. The results from these
projects have not been monitored extensively to determine whether they were either
successes or failures. In addition, the revegetation practices that can result in successful
establishment have not been determined for the range of growing conditions within Lake,
Colusa and Yolo counties.
The establishment of native species has many potential benefits that include: 1)
prevention of new weed species from becoming established; 2) reduced weed corridors
into native areas; 3) reduced long- term maintenance compared to current practices; 4)
reduced use of herbicides; 5) reduced flash point for fires by the presence of green plant
material, a less dense canopy and/ or low- growing stature; 6) reduction in current weed
populations; 7) increased plant species diversity; 8) increased control of sediment
transport ( erosion control); 9) increased duration of green plant tissue during summer and
fall and 10) improved or changed aesthetic value that more closely matches pre-civilization
landscapes in California.
The goal of this project is to select desirable plant materials and to improve the
methodology for successfully establishing native or desirable, low- maintenance
vegetation on sites/ soils following road construction or where elimination of undesirable
vegetation has occurred. The project was split into three phases facilitate the achievement
of this goal:
The first phase ( Phase I) of the project involves literature review and summary of
information from personal contacts in Caltrans, University of California, Davis ( UCD)
and other knowledgeable sources ( i. e. California Native Grasslands Association ( CNGA),
California Native Plant Society ( CNPS), Society for Range Management ( SRM)). Phase I
3
will be ongoing throughout the first part of the project, and will summarize current
revegetation procedures used by Caltrans. The information from Phase I provides both
the evidence for needed changes in specifications for Caltrans revegetation projects and
the justification for the chosen methods and materials in the second phase ( Phase II). A
common garden field experiment was conducted in Phase II, Part A to evaluate various
plant materials at two locations ( SR 29 in Lake County and I- 505 in Yolo County), using
the latest procedures and techniques from CNGA members or UCD researchers for
establishing native perennial roadside grasses. A demonstration site using two large plots
( greater than 1 mile) in the median of I- 5 in Colusa County was established in Phase II,
Part B to out- plant the most successful native perennial grasses identified in Part A while
testing different cultural and chemical management operations for establishment. Phase
III incorporated the successful procedures identified from Phases I and II into field sites
where an existing stand of native perennial grasses has been overrun by non- native,
annual species ( i. e. yellow starthistle). Each successive phase utilizes information from
other phases as available at the time.
Phase I: Literature and Site Review
Previous vegetation conversion projects as reported in Young, SL and Claassen, VP.
2004. Phase I: Roadside revegetation: Success and failure. Part 1: Literature review; Part
2: Site review. California Department of Transportation. Sacramento, CA.
4
Literature review: ( bulleted summary)
Native species have been established along roadsides with appropriate management.
1) Several typical Sacramento Valley roadsides, consisting of several topographic
zones ( i. e. road edge, swale, back slope), have been converted to native species that
persist for decades.
2) Native species can co- exist in a way that does not encroach or invade like
many non- native, exotic species.
3) Initial cost to establish natives may be higher, but savings are expected to be
realized over time as maintenance and replanting costs decline.
4) Site preparation, plant species selection and weed management are all
important for improving the success of roadside revegetation projects with native
perennial grasses.
Ecological factors must be considered for establishing native perennial grasses.
1) Non- native annual grasses gain a competitive advantage over native perennial
grasses by establishing roots in the upper soil profile and depleting available water.
2) Intensive management is necessary during establishment of native grasses.
3) Artemisia californica germination, first season growth and survival were all
reduced by neighboring annual grasses.
4) Inoculation with mycorrhizal fungi alone is insufficient for establishing
Nassella pulchra; weed control practices still need to be employed.
5) Competition from exotic annual grasses has been shown to stress or kill oak
seedlings.
5
Literature review: summary
Roadside revegetation research has a long history in departments of transportation
( DOT) nationwide as well as in private restoration companies and academic institutions.
Within this body of research, there have been a limited number of scientific studies on the
subject of long- term establishment of native plants along roadsides. Therefore, it was
determined that research literature on roadside revegetation be summarized. In addition,
the most current and representative roadside revegetation projects within northern
California would be surveyed to identify existing roadside locations that contain
examples of native plant establishment and persistence. Phase I of this project was broken
into two parts: 1) a comprehensive literature review of roadside revegetation studies and
2) a survey of vegetation cover and native plant establishment at roadside revegetation
field sites that were related to Phase II and III of this project.
The literature cited examples at which short- term establishment of native plants
along roadsides was accomplished with appropriate management techniques and with
consideration for local ecological patterns. The main management components needed
for success of native roadside vegetation conversion projects were site preparation, plant
species selection and weed management. Initial costs to establish natives were high, but
long- term savings were realized with declining maintenance and replanting costs. Several
ecological factors must also be considered for establishing native plants. The topographic
zones ( i. e. road edge, swale, back slope) of a roadside range broadly in soil composition,
vegetation diversity and available resources. Intense competition with non- native annual
plants for root and shoot space, soil moisture and nutrients occurred during and following
the establishment of native plants, so soil resources and competition were important
6
factors to control.
A preliminary site review of roadside revegetation projects within Yolo County,
California showed that establishment of native plant communities varied under three
broad levels of management. Observations suggested that a low level of management, in
which natives were planted and left to survive without any further assistance, lead to poor
establishment and in some cases a reversion back to weeds. The effects of medium and
high levels of management for establishing roadside native plants were difficult to
determine with only observational ratings. Some level of management, whether mowing,
spraying or burning, seemed to promote a good stand of native plants. At this point,
native species establishment and cost for maintenance cannot be quantified without stand
counts and management regimes. This data will be collected in the spring when plants are
actively growing and landowners overseeing site maintenance can be identified.
The literature review and site surveys show quite clearly that a level of long- term
management is needed following the initial, short- term establishment of native plants.
Therefore, it has been concluded that the ecological considerations of the site, the proper
native plant selection and at least a medium level of management are needed for the long-term
establishment of native plants. The conclusions drawn from Phase I will be tested
scientifically in Phase II, roadside native plant selection and Phase III, management of
established roadside native plant stands.
7
Introduction
Roadside revegetation after construction disturbance is important for reducing
erosion and weed invasion, and to improve aesthetic appearance. The greatest concern for
roadsides projects is usually to reduce soil erosion by having some type of temporary
erosion control vegetation. Fast growing plants are often selected without considering the
growth habit, invasiveness, indigenous qualities or overall long- term sustainability. The
initial flush of growth of fast growing plants in the first fall or spring after seeding
eventually gives way to the persistent, weedy vegetation that is often similar to that
which dominated the site prior to road construction.
Several state DOTs have incorporated native plants in roadside planting projects,
including Iowa, Texas, and Minnesota. Research has been conducted on roadside
revegetation, covering a wide range of topics, including plant competition and soil water
relations. Several field studies have been conducted on roadside revegetation in
California. Many of these studies were observational, without numerical analysis and
publication. Evaluation of existing sites where native plants were used and treatment
histories were recorded would be a valuable source of information for improving current
methods of establishment. Therefore, the goal of this report is to summarize research on
roadside revegetation and to identify existing roadside locations containing examples of
native plant establishment and persistence.
This Vegetation Conversion project is divided into three phases. A literature
review is presented as a Phase I report. Phase II involves regeneration or establishment of
native vegetation on barren sites without existing native plant cover. Phase III involves
evaluation of management effects used to increase desirable or native vegetation or to
8
reduce weed invasion of sites without removing existing vegetation. Phase I objectives
included in this report are twofold: Part 1 will be to summarize roadside revegetation
research that is in print through a literature review and Part 2 will survey existing
roadsides within northern California where varying success rates have occurred with
native plants. Results from Phase I will be used to support treatments that are evaluated in
Phase II, roadside native plant selection and establishment, and in Phase III, management
of existing roadside native plant stands.
Literature review: revegetation studies
Roadsides evolve with roads
Roadside revegetation practices have changed with the modernization of roads, as
roadway excavation has become more intensive and disruptive. In the earliest days when
travel was by horse or wagon, roads were built cheaply and by following the easiest
available route ( Bowers 1950) with minimal grading. The permanent, hard- surfaced roads
with their improved ( more direct) alignment created larger erosion problems due to the
greater number and depth of cuts and fills in mountainous, rolling or, in some cases, flat
terrain ( Bowers 1950).
From the Sierra- Nevada to the Pacific Ocean, the climatic variations in California
have led to a wide range of erosion control problems along roadsides. Observations in
1950 by Bowers revealed that an undisturbed, natural slope was different from a
9
disturbed slope. The prime factors for the difference related to vegetative cover, litter
layer and topsoil presence and condition. The conclusion in 1950 ( just like today) was,
“… to endeavor to duplicate on the artificial slope the conditions which prevent damage
on the natural slope.” Even though it may have been difficult to do, the establishment of
vegetation along roadsides was ( and still is today) seen as the ultimate cure for erosion in
order to stabilize the soil and/ or slope to protect the road surface from collecting debris or
being washed out. The long- term establishment of desirable vegetation along a roadside
depends on plant species selection and equally, if not more importantly, the condition of
the soil. A poor soil lacks the depth, nutrient and microbial content and water holding
capacity that is needed for long- term support of native or desirable plant species.
Contrary to reports by Clements ( 1934), Beetle ( 1947), Burcham ( 1957) and
Heady ( 1988), Bowers ( 1950) reported from notes taken by early- day explorers and
missionaries that wildflowers, not grasses, were growing all across the state. If
observations were made in passing, this could be a reflection of the time of year when
wildflowers are abundant in many locations. He makes a comment that the common and
widespread invasive annual and perennial plants that are now naturalized and today are
erroneously referred to as “ natives”, were yet to be introduced to the state of California at
the time of these early pioneers. Bowers does seem to be in agreement with the
previously mentioned authors in terms of how non- native plants were first introduced to
California: seeds from new plants were brought in by accident or on purpose, became
naturalized and literally crowded out the true natives. It is interesting to note that today
some of these same plants have become highly invasive and are costing state DOTs at
least $ 1 million per year to control ( Westbrooks 1998).
10
The search by California DOT for suitable vegetation for soil stabilization along
roadsides began with trial plantings of grasses and forage plants over 50 years ago
( Bowers 1950). Perennial plants were found to be too difficult to establish and provided
no advantage that would prove them superior to annuals for their [ Caltrans’] purpose. It
was concluded that any annual plant with seed that was cheap, easy to obtain and
germinated quickly with the first fall rains would be a good nurse crop to provide
adequate and immediate protection for the natives. The annual natives were assumed to
appear in the first or second year from topsoil or windblown seed that had been caught
and held by stalks and stubble of the nurse crop.
Barley has been the most frequently used plant for soil stabilization along
roadsides ( Bowers 1950). Other plants commonly used in roadside plantings include rye
grain, oats and vetch. Ice plant ( Mesembryanthemum crystallinum L.) has been used in
localized areas where extensive erosion has taken place and wildflower seeds have been
tested with success limited to areas where sprinkling systems provide adequate irrigation.
Some of the same plants and revegetation strategies discussed by Bowers ( 1950) are
currently being used by Caltrans. Although some of the information is still applicable,
there is a need for new research to find new, preferably native, plant species that will
provide long- term cover and require less maintenance.
Roadside revegetation today
As of August 2002, there were only a handful of studies from Caltrans Office of
State Landscape Architecture that were being conducted to address roadside vegetation
issues. Statewide, Caltrans has eight projects under way ( including this one) that focus on
11
some aspect of the roadside environment. Only two of those are directly related to the
establishment of native grasses. The other study areas include biological control of
yellow starthistle, Russian thistle, German cape ivy, French broom and gorse, alternatives
to synthetic chemicals for vegetation control, inoculation with mycorrhizal fungi for
establishment of vegetation ( native species) for erosion control and amendment of
adverse soils to establish native plant species.
The first native grass study is entitled “ Developing a native grass evaluation pilot
program” ( Contract No. 53A0032). This project is designed to install and monitor five 1-
mile long native grass plantings using various planting methods. The roadside plantings
are located in the first ten feet immediately adjacent to the road edge and include many
plant material and seeding trials. Because replicated plots and unamended control plots
were not constructed, and because the sites cover long sections of roadway, close
comparison of plant growth on the different plots is difficult. The general trends that are
observed on the sites can be evaluated with subsequent, more controlled experiments.
Difficulties of revegetation along roadsides
Roadsides can be difficult locations for establishing native plants. Site conditions
that can limit the success of any revegetation effort include topography, soil, climate and
existing vegetation. Brooks ( 1995) found that plant cover on fill slopes was significantly
higher than on cut slopes along highways in the Tonto National Forest in central Arizona.
The revegetation treatments used for visual impact mitigation, as judged by the public,
were unsatisfactory on 72% of the cut slopes evaluated. Poor establishment of vegetation
on disturbed sites following an operation like hydroseeding is often the result of improper
12
species selection, seeding at an inappropriate time, and/ or improper seed mixes, fiber and
tackifier ( Hallock et al. 2002). The end result can sometimes be a reversion to weeds in
the years following a planting if a one- step hydroseeding process is used ( Ivanovitch
1975). Harper- Lore ( 1998) conducted an informal search of natural communities for
plants that tolerate the same problems in nature that are found on harsh roadside
environments. Her most significant finding was a 50- year project at the University of
Wisconsin, Madison to restore a native grassland on a highly disturbed agricultural site. It
was shown that plant diversity is dependent on what is sown ( not necessarily what exists
naturally) and that the weeds that exist before the planting will continue to plague the
project long after establishment. Similar studies have shown that relying solely on the
seed bank for restoration of native vegetation is nearly impossible ( Kalamees and Zobel
1998; Smith et al. 2002; Laughlin 2003), except in rare cases ( Dreman and Shaw 2002).
In order to overcome these problems, the solution was to prepare the site before planting
and select a diverse range of plant species when seeding. Harper- Lore ( 1998) found that
the specific cultural practices were site specific and included fertilization, maintenance,
seeding rate ( 7 and 20 lbs./ acre), site preparation and method of planting. These two
reviews and others ( Robbins 1999; CNGA 2001; Woodward 2002) emphasize the
importance of site preparation, plant species selection and weed management for
improving the initial success of roadside revegetation projects. Soil amendment was not
considered by Robbins ( 1999) and CNGA ( 2001) because locations were predominantly
in alluvial valley landforms. For long- term maintenance for establishment of native
species, future work activities must be planned for and may include reseeding,
13
refertilization, remulching and/ or erosion protection for areas, which responded poorly to
the initial attempt at seeding. ( Ivanovitch 1975; Hansen et al. 1991).
Roadside revegetation by Caltrans
Only a few studies have been conducted exclusively by Caltrans that pertain
specifically to revegetation of roadsides ( Harris 1970; Edmundson 1976; Clary 1983).
Many conclusions in these earlier studies are also observational in nature and were not
numerically documented. One study, “ Planting techniques and materials for revegetation
of California roadsides ( Clary, 1983) address both the problems and geographic areas
along California highways. He discusses 1) the establishment of herbaceous and shrub
species in several areas around California and the revegetation of problem soils; 2) the
determination of the rate of invasion of woody plants onto disturbed sites; and 3) the
reevaluation of plantings made during the Caltrans- SCS cooperative study between 1970
and 1975. Only observational information was collected from the studies with no
attempts to perform statistical analyses on the data. He collects information on 1)
herbaceous and woody plant material [ non- native] in plots on both Mojave Desert and
problem soils ( serpentine, high boron, high/ low pH soils) establishment ( survival),
erosion control and aesthetics; 2) plant invasion and rate of natural revegetation by
woody plants on cut and fill slopes and slopes of different ages along roadsides and 3)
changes in plant performance that could influence current seeding and planting
recommendations, which were noted in the 1970- 1975 cooperative plots. First, he
concluded that no perennial grass [ non- native or native species were not distinguished]
performed well enough for use in a seeding mixture for the Mojave Desert. Annual
14
grasses [ non- native] and legume species were the best herbaceous plants to seed. He
found that woody plants were the most successful seeded species, using direct drill
seeding with straw mulch whenever possible. Second, he determined that woody plant
invasion onto highway cut and fill slopes was a slow process influenced by herbaceous
competition, availability of seed and slope conditions. Third, he found that “ problem
soils” ( defined as substrates that are difficult to vegetate due to their structure or toxicity)
could be attributed to four different types of plant growth limiting problems:
droughtiness, low fertility, high magnesium- to- calcium ratios or toxic levels of trace
elements. Finally, he noticed in seeded plots that annual species were non- existent and
only four perennials and one legume were growing from original plantings in sites in the
North- Central Coastal and Sierra Nevada Foothills. Eight woody species were doing well
in the same region. In the Tahoe Basin, seven perennial grasses ( pubescent wheat grass,
intermediate wheat grass, fairway crested wheat grass, big bluegrass, smooth brome,
orchardgrass) and one perennial legume ( cicer milkvetch) appeared to do better over a
nine year period. Several shrub species grown from containers also appeared to be
outstanding. Because of the observational format of the study, there are no numbers to
support the observations, and no comparisons to untreated controls. The perennial grasses
and legume “ appeared” to do better. The shrubs from containers “ looked” to be
outstanding. Woody species were “ doing well”. This information is, however, useful for
the time and the location in which it was observed.
Edmundson ( 1976) conducted a plant materials study in northern California with
study sites from the North Central Coastal Foothills to the Lake Tahoe Basin. His
objectives were to 1) evaluate and select or develop self- perpetuating, drought- tolerant
15
annual and perennial grasses, legumes and other ground cover plants for erosion control;
2) evaluate and select native shrubs and trees suitable for revegetation; 3) evaluate shrubs
for general landscape use; and 4) conduct special studies. He established several grasses,
legumes and California poppy along highways in northeastern California and evaluated
them for erosion control, fire control and aesthetic purposes. “ Shrubby” species were also
evaluated for revegetation and general landscaping. There were special and
supplementary studies conducted that were relevant to plant propagation and
establishment. The plants in each study were evaluated on representative highway sites
using “ common methods applied by contractors”. The establishment and evaluation
methods used in this study were only generally described, leaving out details necessary
for repeating his studies or making close evaluation of the results. From observational
studies, he was able to make the following broad conclusions. 1) Once a grass- legume
( non- native) cover was established and initial erosion control was provided, there seemed
to have been little need for maintenance. 2) Successful establishment was observed where
soils were not too droughty, competition from herbaceous species was low and some type
of control was used on the mice, grasshoppers and other predators present. 3) Forty
pounds of seed per acre “ seemed” to be satisfactory for seeding of grasses and legumes
where erosion was not critical. 4) No winter active herbaceous species “ seemed” to be
immune to herbicide sprays applied by Caltrans. 5) California poppy “ seemed” to be
persistent only in rocky, gravelly or sandy soils where herbaceous species offer little
competition. From these studies, a general guide to herbaceous seeding and a list of
native shrubs and trees classified by major land resource areas were produced for
California. Edmundson had additional observational studies on cereal grains, erosion
16
control materials, fertilizers, irrigation, and seed inoculant, but they are not relevant to
this report.
Techniques for revegetation of problem soils are another area of Caltrans
research. Parks and Nguyen ( 1984) observed that topsoil, lime and revegetation
treatments were used to neutralize the acidic leachate at two out of three highway cut
slopes sites. The third site contained serpentine soil and could not be evaluated. They
describe the mitigation measures for these types of problem soils and evaluate their
effectiveness. Again, many sites were evaluated but data were not collected.
Out of all the documented roadside revegetation studies conducted exclusively
within Caltrans, only one was found to have used a scientific approach. Harris ( 1970)
experimented with woody and herbaceous plant establishment in a range of
environmental conditions without irrigation. He used three methods of seeding ( spot and
range drill seeding and hydromulch seeding) at five [ geographic] locations ( Point Reyes,
Yosemite, Davis, Bakersfield, Los Banos). He found that direct seeding resulted in the
establishment of 23 of 54 species seeded, although the definition of “ establishment”
changed with time at the field sites. The response of species grown at various sites
indicated differences in environmental conditions between locations and within location,
making a good argument for site- specific revegetation, as opposed to a region- wide
approach. Seedlings in either dry compared to moist or wet areas ( Bakersfield or
Yosemite and Point Reyes, respectively) were established. In some areas direct seeding
failed due to extreme environmental conditions and the lack of knowledge in the
limitations of species adaptation and seeding technique. He found that spot and range
drill seeding were more satisfactory than hydromulch seeding. He concluded that the
17
varying environmental conditions required both the selection of species with a wide range
of adaptability and the seeding of several potentially suitable species to assure greater
establishment success. Other aspects that were found for successful seeding included time
of seeding, seed quality, seeds per hole, seed dormancy, seeding depth, fertilization, weed
and pest control, soil preparation, mulching and irrigation. Unfortunately, the data was
not available for tabular listing at this time.
The results from numerically documented studies such as Harris ( 1970) are what
Caltrans needs to support its decision- making regarding use of various techniques and
materials for roadside revegetation. The conclusions are based on sound, scientific data
that has been tested with replications and control plots. The results have been subjected to
statistical analyses and the methods can be repeated for verification and/ or demonstration
of the results, if needed.
Other attempts at roadside revegetation
Other roadside studies have taken into consideration plant mixture for establishing
natives along roadsides ( Bugg et al. 1997; Anderson and Long 1999; Bugg and Brown
2000; M. C. Wolfe and Associates 1988). Both polycultures and monocultures were used
by Bugg et al. ( 1997) to evaluate the establishment of non- native ( desirable) and native
perennial grasses. They were trying to determine if several native grass species of a local
strain could be established and managed on disturbed sites. They seeded either a mix of
native grasses ( polyculture) or single species ( monoculture) into a rural roadside near the
town of Winters, California, consisting of several topographic zones ( i. e. road edge,
swale, back slope).
18
There was no significant difference in the amount of canopy cover for the
polycultures on different topographic zones, but the biomass of the natives was less than
for the non- natives. In the monocultures, California brome ( Bromus carinatus), blue
wildrye ( Elymus glaucus), slender wheatgrass ( E. trachycaulus), meadow barley
( Hordeum brachyantherum ssp. brachyantherum, California barley ( H. brachyantherum
ssp. californicum), purple needlegrass ( Nassella pulchra) and nodding needlegrass
( Nassella cernua) had good canopy cover. Sheep fescue ( Festuca ovina), squirreltail ( E.
multisetus), Idaho fescue ( Festuca idahoensis), creeping red fescue ( F. rubra) and pine
bluegrass ( Poa secunda ssp. secunda) had poor canopy cover. Polycultures performed
well in all topographical zones. Monocultures with persistent stands were established for
several species. Competition from resident vegetation ( weeds) was found to influence
establishment in both the polycultures and monocultures. They concluded from their
study that, despite difficulties due to herbicides, persistent stands of local native species
could be used along roadsides and other rights- of- way in the Sacramento Valley. They
deem accessions retaining 25% or greater canopy cover in monocultures to be suitable for
use in roadsides in the Sacramento Valley.
The Bugg et al. ( 1997) study would have been stronger had they evaluated the
sites for longer than three years. The importance of weed control cannot be overlooked
for establishing native grasses along roadsides and to state that a 25% minimum canopy
cover for natives would have been greater had the herbicides been more effective is a
large assumption. There was mention of a range in soil moisture conditions in all blocks
for the polycultures, but no data were presented that supported this statement. Soil depth
19
and water holding capacity could play a significant role in establishment of native plants
along roadsides.
In another roadside study by Bugg and Brown ( 2000), existing stands of native
grasses were used in combination with native forbs to control non- native ( undesirable)
species. The idea was to determine the establishment efficiency of local forbs and
perhaps use the most robust and vigorous species as an alternative to conventional
management ( herbicides, mowing or blading) for controlling undesirable species. The
methods employed included either seeding a mixture of forbs into both established native
perennial bunchgrasses and tilled, bare ground or transplanting two perennial forbs into
both established native perennial bunchgrass stands and tilled, bare ground. They found
that Arroyo lupine ( Lupinus succulentus), California poppy ( Eschscholzia californica),
chick lupin ( Lupinus microcarpus) and Spanish clover ( Lotus tanacetifolia) established
well when seeded into tilled, bare ground, while annual tansy ( Phacelia tanacetifolia) and
the perennials, narrow- leaf milkweed ( Asclepias fascicularis) and blue- eyed grass
( Sisyrinchium bellum), were poorly established. None of the forbs tested established well
by direct seeding into pre- existing stands of native perennial bunchgrasses. When
transplants were inserted within plots of established native perennial bunchgrasses, their
vigor was not significantly reduced compared to those placed in tilled plots.
Revegetation of roadside- like sites
Revegetation projects are not restricted to roadsides. Other locations with similar
conditions to roadsides include irrigation canals, farm hedgerows and nature reserves
( M. H. Wolfe 1999; Anderson and Long 1999; Harper- Lore; 2000). Similar to the Bugg
20
and Brown ( 2000) search for alternatives to conventional weed control, Wolfe ( 1999)
conducted a study to evaluate the use of revegetation as a tool to minimize chemical
weed and pest control along irrigation canals in central California. They also investigated
the possibilities for reduced erosion and maintenance costs with revegetation. They
conducted a series of revegetation trials to test the establishment of numerous native
perennial and two naturalized ( desirable) annual species of grasses, forbs and shrubs.
They made both qualitative and quantitative analyses on germination and establishment
of individual species and on planted seed mixes for cover, shrub densities and ground
squirrel burrows, respectively. From their qualitative data, needle- and- thread grass
( Hesperostipa comata ( Trin. & Rupr.) Barkworth) was the most successful individual
species evaluated. They also found that creeping wild rye ( Leymus triticoides ( Buckley)
Pilger), Indian ricegrass ( Achnatherum hymenoides ( Roemer & Schultes) Barkworth),
Arizona brome ( Bromus arizonicus ( Shear) Stebb.) and meadow barley ( Hordeum
brachyantherum Nevski) had strong results, although the precise definition for “ strong
results” was unclear. Of the shrubs tested, they found that California buckwheat
( Eriogonum fasciculatum Benth.), bladderpod ( Isomeris arborea Nutt.) and desert
saltbush ( Atriplex hymenelytra ( Torr.) S. Wats.) were all successful, while goldenbush
and winterfat ( Krascheninnikovia lanata ( Pursh) A. D. J. Meeuse & Smit) failed to
produce viable stands. Mainly through observations, it was found that successful
establishment of plant populations and beneficial insects resulted in substantially lower
pressure of invasive weeds and injurious insects on seeded plots and less need for
herbicide and soil sterilizers. Costs associated with erosion and wild land pest controls
21
were also lowered considerably with an increase in the aesthetic and ensuing real estate
values, enhanced by the increase in plant and wildlife biodiversity.
In a more scientifically based study by Anderson and Long ( 1999), costs of
establishing hedgerows were measured on field crop farms in Yolo county, California. In
addition to determining costs of establishment, they wanted to develop management
practices for “ insectary” hedgerows on field crop farms. They selected sites based on
diversity of soil type, site location and farmer practices. They also took into account the
adjacent canals, fences and roads that would impact the hedge plants. Hedge plants in
plots 15’ by 1,500’ were perennial California species ( highly adaptable, require little to
no irrigation after two years). Most were chosen with a range of flowering periods that
would be available for beneficial insects. Native perennial grasses were planted after the
hedge plants and a mix was selected based on environmental tolerances and soil type.
They found that the costs for establishing a hedgerow fell into five categories: 1) site
preparation $ 350, 2) hedge plants $ 685, 3) perennial grasses $ 385, 4) weed control
$ 1,045, 5) irrigation $ 760, for an estimated total cost of $ 3,235 for a 1,500’ hedgerow.
Hedgerows take time and money to establish, but a couple of the benefits from
hedgerows, once they are self- sustaining, include acting as a filter strip, wind break
and/ or dust barrier and stabilizing the soil which provides natural weed control and
habitat for beneficial insects and wildlife. In this case, it is apparent that native species
( hedgerows or grasses) co- exist in an environmentally friendly way that does not
encroach or invade like many of the non- native exotic species. The initial cost to
establish natives is high, but savings can be realized over time with a decline in
maintenance and replanting costs.
22
National parks and recreation areas are not exempt from roads and the need for
establishment of native or desirable species ( Legg et al. 1980; Moritsch and Muir 1993;
Zabinski et al. 2002). Harper- Lore ( 2000) took a 1,553 mile long road trip with highway
department and roadway engineers from Victoria, New South Wales and Queensland.
The author found that roadways in Australia are critical for preservation of native flora.
She found that roadside rights- of- way are termed “ road reserves” because they contain
25% of all endangered species and 45% of remaining native grasslands. Named World
Heritage Areas by the United Nations, these particular roadsides have raised awareness
and validity to conservation practices. The Roadside Conservation Advisory Committee
defines management objectives, strategies, actions plans, assessments and support for
roadside conservation. A coalition of public and private agencies has been formed that
works together with same goals: 1) to work with the community and 2) to achieve
sustainable land and water resources through improving vegetation management
practices. Although this probably is not carried out nationwide, it provides a good
example and motivation for other areas where establishment of native or desirable
roadside vegetation is a major concern.
Other revegetation studies
Native plant establishment along roadsides is an area of research that often
receives little attention. Through this project, factors for the successful long- term
establishment of a native plant community are being reviewed in the literature and in
current field sites, researched in the field and documented for practical field
application( s).
23
In addition to the broad field of roadside native plants, two other topics related to
restoration are of particular interest to the author. These topics, important to restoration of
both roadsides and landscapes in general, include native plant community competition
( rivalry between siblings and relatives) and purity ( keeping invaders out of the family).
The questions being asked are: 1) what is the pattern of water use by both native and
weedy species and can this resource be manipulated to favor the native plants? 2) Does
interplanting with native forbs successfully keep exotic annuals from invading an
established native grass community? 3) How is the competition for soil moisture in a
native plant monoculture ( single species) different from a polyculture ( multiple species)?
The major emphasis for the following section of the report will be on studies
dealing with inter- and intraspecific competition, plant water use and invasiveness.
Studies from non- roadside landscapes are cited because they are much more numerous
than roadway- related research.
Native plant community competition
Plant competition
Numerous experiments have been conducted on the inter- and intraspecific
competition of native species ( Hamilton et al. 1999; Dyer and Rice 1997; Carlsen et al.
2000; Brown and Rice 2000; Schultz 1996; Eliason and Allen 1997; Nelson and Allen
1993). Hamilton et al. ( 1999) wanted to determine 1) if interference among native
perennial and non- native annual grasses was important across all life- stages of the
perennial, Nassella pulchra, 2) if N. pulchra competes with non- native annual grasses
24
and 3) if competition for water is an important component of these interspecific
interactions in a water- limited system. They conducted a series of field and greenhouse
experiments using removals of neighboring plants and additions of water. They found
that the natural recruitment of N. pulchra seedlings from grassland soil was extremely
low, but the addition of water to field plots increased density and total aboveground
biomass of established N. pulchra plants. A simulated drought early in the growing
season had a greater negative effect on the biomass of the annual seedlings than on the
seedlings of N. pulchra. This may have been due to the deeper or more established
rooting system of the native grass. The presence of annuals reduced growth and seed
production of all sizes of N. pulchra, and these effects did not decrease as N. pulchra
individuals increased in size. The addition of water caused the same increases in
aboveground biomass and seed production of N. pulchra as removing all annual
neighbors. Persistence of native bunchgrass species like N. pulchra maybe enhanced by
greater mortality of annual than perennial seedlings during drought and possibly by
reduced competition for water in wet years because of increased resource availability.
Several conclusions can be inferred from the work conducted by Hamilton et al.
( 1999). 1) In locations that have a low level of a naturally occurring seed bank of a
particular native grass species ( in this case N. pulchra), it may be important to add more
seeds. 2) Additional water increases the size of the first year seedlings, which could
provide an advantage in later years when competing with non- native annuals. 3) The
removal of weeds results in higher production of native seeds and biomass while
decreasing the stress on the plants. 4) Annual grass seedlings are not influenced by the
removal of native perennial grasses. 5) Native grasses tolerate drought better than non-
25
native annual grasses. 6) Native grass seedling establishment is primarily limited by
water availability due to depletion by annual plant neighbors. 7) If water is limited, then
non- native annual plants influence native grass growth but if water is unlimited, then
non- native annuals have no effect on native grass growth. 8) The two ways to minimize
negative effects from weed on native grass establishment are to kill them or to provide
abundant water to cancel the effects of the non- native annuals, even though their size
may become excessive.
The result of the presence of the annual fescue, Vulpia myuros ( Zorro fescue), on
native perennial grass aboveground biomass, density and seedling size was studied by
Brown and Rice ( 2000). They evaluated the growth and performance of a mixture of
California native perennial grasses and resident weeds when grown with varying
densities of V. myuros. They found that the perennial grass seedling survival and
aboveground biomass decreased with increasing seeding densities of V. myuros. They
also found that V. myuros suppressed other weeds and had a more negative effect on
weed densities than on native perennial grass densities. Nevertheless, the suppression of
weeds by V. myuros is far from what could be considered a selective tool for weed
control. To date, no studies have shown that V. myuros or any other grass, for that matter,
can distinguish whether a neighboring plant is a weed or native perennial but may
functionally do so by competing for a specific resource such as water.
Selection of plant material for roadside revegetation is critical when considering
the long- term plant establishment. Brown and Rice ( 2000) state that the two most
common purposes for reseeding ( i. e. post- construction) are for establishment of native
plants and for erosion control. Through their research, they found that neither of these
26
goals were met when V. myuros was used in seeding mixtures. Furthermore, the idea of
annual grasses acting as nurse plants to native perennial grasses was not supported by
their results. Annual plants, such as V. myuros, are poor choices for weed suppression,
prior to the planting of native perennial grasses. A more aggressive approach ( i. e.
mechanical, chemical) is better suited to controlling weeds in preparation for planting
native grasses.
When considering fast germinating annuals for erosion control, the rainfall pattern
is very important. A young stand of annuals is likely to be too small to provide erosion
control from an early- season downpour. A more effective approach would be to apply
mulch or to control drainage of early season water movements. Overall, Brown and Rice
( 2000) found that the inclusion of the exotic annual V. myuros in native seed mixtures is
counterproductive to restoration efforts because of the suppressive effects on native
grasses and the fact that erosion control with annuals is highly susceptible to fluctuating
weather patterns.
In addition to native grasses, the establishment of native shrubs can also be
heavily impacted by exotic annual species ( Schultz 1996; Eliason and Allen 1997).
Schultz ( 1996) and Eliason and Allen ( 1997) both studied the seedling establishment of
native shrubs in a Mediterranean annual grassland. Schultz ( 1996) examined how exotic
invasions could affect a coastal sage scrub and how they produce a type conversion from
shrubland to grassland. Similarly, Eliason and Allen ( 1997) looked at the mechanisms by
which grasses might exclude native shrubs and persist after release from disturbance.
Artemisia californica, a dominant native shrub on the coast of California, was planted
into different densities of grasses. A. californica germination, first season growth and
27
survival were all negatively related to the density of neighboring annual grasses and most
likely due to the depletion of soil water by the grasses. In the second season, the effects
of the grasses were no longer significant on A. californica. They concluded that while
succession alone may not return annual grasslands to their former shrubland composition,
restoration might be possible with container plantings or removal of the grasses prior to
seeding.
Out- competing the exotics
From these studies and many others like them, it is clear that native species,
including grasses, are under intense pressure from non- native or exotic annual species
during and following establishment. Therefore, it is important to find ways to reduce
competition through cultural practices such as weed control and species selection.
In studies conduct- ed by Dyer and Rice ( 1997), the objective was to assess the
general effectiveness of burning and grazing as grassland management strategies for
increasing N. pulchra abundance and reducing competition from annual species. These
two management techniques are probably not applicable to roadsides unless used in
altered forms such as controlled burn or flaming and mowing. They measured the
influence of competition on growth and survival of N. pulchra. They used summer fire
and spring sheep grazing to reduce weed competition in non- weeded plots. They also
established plots to determine the effect of rooting volume on the competitive
interactions. Their results indicated that diffuse competition ( a competitive neighborhood
composed of high densities of many species) had the biggest negative influence on N.
pulchra growth in all treatments. Burning had longer- lived effects in weeded plots and N.
pulchra mortality was significantly increased by diffuse competition. Finally, survival
28
was greatest in plots that were weeded, grazed and had soil deeper than 50 cm; all
management techniques that could be implemented for roadsides following road
construction. Intensive management is often necessary for the early establishment of
native grasses. The conclusion by Dyer and Rice ( 1997) was that the recruitment of N.
pulchra within inland California grasslands is reduced by the adverse environment
created by high densities of alien annual species.
Carlsen et al. ( 2000) studied native grasses as a management tool for weed control
for a rare California native forb, which was a different approach for the use of native
species than just simply trying to establish them. Their objectives were to determine 1) if
the forb, Amsinckia grandiflora would perform better in a matrix of native perennial
bunchgrasses compared to a matrix of annual exotic grasses and 2) if competition for
water played a significant role in the performance of the forb. They transplanted A.
grandiflora seedlings into experimental plots of either exotic annual grassland or restored
perennial grassland of Poa secunda in a field competition experiment. They found that P.
secunda and exotic annual grasses reduced soil water potential from - 1 to - 3 MPa and
also reduced production of A. grandiflora inflorescences. The exotic annual grasses at
low or intermediate densities reduced A. grandiflora to a greater extent than did P.
secunda. They concluded that restored perennial grasslands at intermediate densities have
a high habitat value for the potential establishment of the native annual A. grandiflora.
This could be extrapolated to heterogeneous native grass communities ( both early ( Poa)
and later ( Nassella) phenology) to allow a mix of native forbs.
Nelson and Allen ( 1993) studied the affect of vesicular- arbuscular mycorrhizae on
the growth and competition between the native perennial Stipa pulchra and the
29
introduced annual, Avena barbata. They found that mycorrhizae did not alleviate the
negative effects of competition of A. barbata on S. pulchra, similar to demonstrations
between other weedy and non- weedy species. They also found that once annual grassland
has been revegetated with the native S. pulchra, the original fungal species composition
may return relatively quickly. Their conclusions were that inoculation with mycorrhizal
fungi alone will not suffice for establishing S. pulchra and the usual practices for control
of weed competition need to be employed.
Water: a resource that can dictate plant community development
The use of water by native species is critical to their establishment and ultimate
survival. Several studies have been conducted that address the use of water by native
species and the role that undesirable species play in limiting the amount available
( Hamilton et al. 1999; Gordon et al. 1989; Gordon and Rice 1992; Holmes and Rice
1996; Momen et al 1994; Gordon and Rice 1993). Many non- native annual grasses gain a
competitive advantage over native perennial grasses by quickly establishing roots in the
upper soil profile and depleting available water before the slower- developing natives can
get to it. Persistence of native grasses could be enhanced either if non- native annual
populations are decreased or if resource availability is increased ( Hamilton et al. 1999).
Gordon and Rice ( 1992) compared soil water depletion for an annual forb and
grass common in California. Holmes and Rice ( 1996) conducted studies on the alteration
of soil water availability by exotic cool season annuals and the resulting effect on native
perennial bunchgrasses. In both studies, the annuals produced extensive roots in the upper
soil surface resulting in quick depletion of the available water. The native perennial
bunchgrass, Nassella pulchra, produced more uniform distribution of roots to depths
30
exceeding 0.5 m. It has been hypothesized that even though native grasses continue soil-water
utilization well into the dry season, their growth habit is an energy- consuming
behavior that can be detrimental in either drought years or under severe competition with
a large population of exotic annuals.
Holmes and Rice ( 1996) measured rooting patterns of native perennial
bunchgrasses and exotic cool season annuals and point out the lack of research on the
impacts of exotic annuals and native perennial grasses on the soil- water regimes in
California. They address the importance of understanding how invasive annuals have
altered soil- water status and the resulting displacement of native species, hypothesizing
that differing patterns of soil- water utilization could be based on the life histories of these
two types of grasses. Annuals avoid drought by completing their life cycle while soils are
moist, allocating a high proportion of their biomass to photosynthetic activity ( rapid
growth). On the other hand, native perennials develop an extensive, deep system of dense
roots to get to water beyond the reach of annual plants and dry- season soil evaporation.
Despite this apparent partitioning of soil water utilization with depth when they
are mature, annual plants compete directly with perennial seedlings during fall and winter
establishment when both plant types are small and have shallow root systemsIn addition,
data from the second and third year of the Holmes and Rice ( 1996) study show that the
exotic annuals depleted the surface water that would have recharged the deeper root zone.
Additionally, root biomass of native perennial plants will continue to grow year after
year, while exotic annuals will produce just enough roots to complete their life cycle.
Astrategy for native plant establishment is to exploit the growth habit of the
exotic annuals in a way that benefits the natives. The first germinating rain of the autumn
31
season will result in a flush of weeds that can be killed with either cultivation or
herbicide. This same technique can be used following planting by killing the emerging
weeds with herbicide prior to native grass emergence, which is often slower by a week or
more.
Reduced water uptake by native perennial bunchgrass roots may explain their
poor survivability in dense stands of exotic grasses. Holmes and Rice ( 1996) suggest
monitoring transpiration and soil evaporation throughout the growing season in
conjunction with recording measurements of soil water potential to provide a picture of
water balance at the stand level for a particular native grass. Additionally, they encourage
further investigations into the effects on soil- water status by other exotic cool season
annuals and native perennial bunchgrasses, especially given the diversity of the two grass
types in California. There has yet to be any reported work on soil plant water relations in
the areas mentioned by Holmes and Rice ( 1996).
In other soil- water relations studies, Momen et al. ( 1994) and Gordon et al. ( 1989)
studied the effects of available seedling water on blue oak establishment within a
California woodland. Results indicated that the exotic annual grasses were the cause of
either stressed or dead oak seedlings. Similar to what Holmes and Rice ( 1996) found in
native grass species, competition for soil water also effects blue oak seedling
establishment. Oak seedling emergence and growth responses were significantly affected
by annual plant density ( Gordon et al. 1989). Only 20% of the acorns planted in high
density Bromus diandrus neighborhoods showed aboveground shoot growth; 56% of
those planted in low density B. diandrus or Erodium botrys emerged. Furthermore,
32
relative growth rates of oak seedling root and shoots were directly dependent on soil
water potentials.
Competition for water is the key factor for survival for all plants and its
availability could be directly related to the water holding capacity of a soil. Dahlgren et
al. ( 2003) found that blue oak trees [ and possibly native herbaceous plants also] created
islands of enhanced soil organic matter, water holding content and fertility across a
variety of soil parent materials. The combination of soil water availability and soil quality
appear to be related and may be the reason why In degraded soils with lower water
availability, seedlings of blue oak and native perennial grasses are poor competitors with
exotic annual grasses, which complete their lifecycles during the winter season when
there are frequent rainfall events to recharge the soil.
Native plant community resistance to invasion
Native plant communities are susceptible to invasion from exotic alien species.
Successful invasion of a natural community requires dispersal, establishment and
survival, with the number of species in an area being determined by a balance between
immigration and extinction ( Lonsdale 1999). If most invading species fail to establish, as
suggested by Williamson ( 1996), then the likelihood of successful invasion is usually
low. The abundance of invasive problems in California may also be attributed to faulty
management practices. The potential of open niches or ecosystems in California to be
invaded by non- native or exotic species is also a problem that relates to proper
management, not just to efficient invaders.
Riparian zones, coastal meadows and grasslands are a few of the ecosystems
where exotic species have been introduced ( accidentally or purposefully) and established
33
to varying degrees ( Robinson et al. 1995; Stohlgren et al. 1995; Planty- Tabacchi et al.
1996; Kotanen 1997; Rice et al. 1997; Tilman 1997; Thompson et al. 2001; Zalba and
Villamil 2002). The inconsistency in experimental results and controversy in the
invasibility theory ( Lonsdale 1999) have led to differing views in the field of ecology
pertaining to the influence that species richness has on determining invasibility. One
theory suggests that areas that are more species rich are assumed to have a more complex
or efficient use of limiting resources, and thus be less invasible ( Robinson et al. 1995).
Elton ( 1958) first hypothesized this scenario thinking that exotic species might more
easily invade areas of low species diversity than areas of high species diversity. In
contrast, May ( 1973) argues that a highly diverse community is intrinsically unstable,
with some species dropping in and out routinely. In a global review, Rejmanek ( 1996)
found little evidence to support the idea that native species richness between 50 º N and
50 º S latitude was directly responsible for greater resistance to invasion, although Elton’s
hypothesis was generally supported at continental scales.
Invasion rates depend on the plant community being invaded and the plant species
that are invading. Many factors determine the invasibility of plant communities. Tilman
( 1997) studied experimental plots for a year before seed addition to quantify initial plant
species composition and abundance, species richness, the amount of bare mineral soil, the
extent of recent soil disturbance by gophers and extractable levels of soil nitrate and
ammonium. His objective was to determine if local interactions were the overriding
factor determining local diversity or if “ open sites” allowing for greater recruitment in
plant communities were the mechanism that allowed numerous species to coexist when
competing for a single resource. He found that both local biotic interactions and
34
recruitment dynamics determined diversity, species composition and species abundances
in native grassland communities. Bergelson et al. ( 1993) also studied the significance of
“ open spaces” in terms of invasion by weeds outside an established plant community.
Specifically, the objective was to determine how the spatial distribution of bare ground
influences the rate at which offspring of an introduced invader spread through a perennial
ryegrass community. They found that gap size and distribution within a plant community
significantly affected the rate of spread of Senecio vulgaris and that plants moved a
greater distance when the gaps were large and underdispersed.
Thompson et al. ( 2001) tested the roles of productivity and disturbance as major
factors controlling invasibility of plant communities. They found that invasibility in an
unproductive limestone grassland was correlated with the availability of unused
resources. Furthermore, both disturbance and fertilizer addition increased the availability
of resources and invasibility was clearly greater where both were combined. Kotanen
( 1997) also studied the effect of soil disturbance in field experiments conducted with
natives and aliens in California grassland vegetation. He disturbed the soil using either
excavation, burial or simulated gopher mounds and then measured revegetation and
compared it between disturbed and undisturbed control plots for three years. He found
that native bulbs and perennial graminoids were slow to recover, while exotic annual
grasses became increasingly dominate.
In another grassland study, Rice et al. ( 1997) reported that the conversion of
valley grasslands of California from a perennial bunchgrass prairie to an annual grassland
was nearly complete. They found that Mediterranean exotic annual grasses produced
dense canopies that reduced light to bunchgrass seedlings at the time as the plants needed
35
photosynthate for root development into deeper soil layers. The conversion of California
grasslands from a deep- rooted perennial bunchgrass system to a shallow- rooted annual
grassland is thought to have significantly increased moisture at soil depths below 75 cm,
allowing the invasion of other exotic species ( i. e. Centaurea solstitialis).
In addition to plant community characteristics, such as spatial scale, biome and
vegetation type, availability of resources and species- specific responses to disturbances
( Stohlgren et al. 1999) that might lead to favorable conditions for invasion, the
characteristics of the invader must also be considered. In a 5- year study by Thompson et
al. ( 2001), seeds from 54 native species were sown into a grassland at the Buxton Climate
Change Impacts Laboratory in the UK. They found that early stages of invasion ( first two
years) favored invaders with regenerative traits ( seed mass and germination
characteristics), but after 5 years, these traits were unrelated to success of the invaders.
Additionally, they found that no single trait was a good predictor of invasiveness and the
most successful invaders were perennial grasses. This is consistent with the hypothesis
that the identity of successful invaders depends strongly on the invaded environment,
excluding Tilman’s ( 1997) findings because of the strongly nitrogen- limited system he
was working in at Cedar Creek.
Gerlach and Rice ( 2003) examined thistles from the Centaurea family in order to
determine whether each one’s invasiveness was related to differences in life history traits.
They compared each thistle congener ( different thistles related by family) using qualities
of 1) seed germination and seedling establishment, 2) vegetative growth under
competition, 3) vegetative growth and flowering, 4) breeding systems. They found that C.
solstitialis ( yellow starthistle) was strongly positive in its response to combinations of
36
clipping and canopy gaps ( annual grass competitors) and its ability to extend its growing
season into the dry summer months when competition from annuals is minimal. They
found that the less invasive Centaurea species were more self- compatible than C.
solstitialis. They concluded that C. solstitialis is such an effective invader due to its
persistence in competition with annual grasses and its plastic growth and reproductive
responses to open, disturbed habitat patches.
These and other studies on plant invasions are beginning to provide information
for understanding of the role of plants both as established natural communities and as
invaders. Even so, Stohlengren et al. ( 1999) notes that community ecologists do not yet
understand the causes and patterns of native species richness. Therefore, it is the hope
that fieldwork related to Phase I will provide additional, California- specific information
on the interaction between exotic alien species and native plant communities. Mack
( 1996) states that the need for prediction [ of plant invasions] is the same as in
epidemiology: early detection of an invader combined with knowledge of its attributes
and limitations allows maximization of a control effort. Here, the control effort will be
through modification of water resources ( improving soil depth and water holding
capacity) and planting the appropriate species ( late season native forbs that compete
directly with exotic annuals).
37
Site review: ( Yolo County, California)
( bulleted summary)
Establishment of native plant communities varied under three broad levels of
management.
1) Observations suggested that a low level of management, in which natives were
planted and left to survive without any further assistance, leads to poor establishment and
in some cases a reversion back to weeds ( Table 1).
2) The effects of medium and high levels of management for establishing roadside
native plants were difficult to determine with only observational ratings. Some level of
management, whether mowing, spraying or burning, seemed to promote a good stand of
native plants.
Table 1. Preliminary visual observations of vegetation communities for roadside
revegetation sites established by the Yolo County Resource Conservation District.
Site Location Est. Grasses Forbs Rating* Comments**
Native Exotic Native Exotic
1 Rd 27, N side,
½ mile E of Rd
88
1993 √ √ √ √ 3.5 Exotics: PL, WO, others
Natives: GC, ES, milkweed,
MR, NP, EG, shrubs
Management: regular
2 Rd 27, S side,
½ mile E of Rd
88
1993 √ √ √ √ 3.5 Exotics: PL, WO, others
Natives: GC, NP, EG
Management: burned/ mowed
5 Rd 88, W side
from Rd 26 to
27
1983 √ √ √ 4.5 Exotics: PL, WO single plants
Natives: Dense EG, MR, NP
Management: regular
8 Rd 89, W side,
from ½ mile S
of Hwy 16 to
Rd 23A
1995 √ √ √ 3.5 Exotics: PL and others
Natives: grasses and shrubs
Management: some, but could
be better
9 Rd 23, N side,
from Rd 89 to
Rd 31
2001 √ √ √ 1.0 Exotics: mowed
Natives: mowed
Trees planted along back ditch
Management: not for natives
38
10 Rd 102, E side,
from Rd 16 to
Rd 15
1998 √ √ 0.0 Management: weed cover
managed between road and
field edges.
12 Rd 89, W side,
from ¾ mile N
of Rd 31 to ¼
mile N of 31
1999 √ √ √ 4.0 Exotics: PL, YST, Alfalfa?
Natives: NP, EG, HBB
Management: road edge
mowed and spot handweeding
on 9/ 8/ 03.
15 Rd 95, E side,
from Rd 19 to
Rd 18A
1990 √ √ √ 3.5 Exotics: PL, BW, YST some
Natives: NP, EG, LT, MR
Management: mow edge &
between poles
17 Rd 20, S side,
from ¼ mile W
of Rd 97 to 97
1996 √ √ √ 2.0 YST dominates; PL, BW, WO
NP dominates; LT?
Management: mowed once
( not recently)
19 I- 505, E side
( adjacent to NB
lane), from Rd
14 along Rd
12A
2001 √ √ √ 4.0 Exotics: YST
Natives: EG, NP
Management: sprayed with
transline; mowed once or
twice?
21
A
Russell Blvd, N
side, from Rd
97 to Glide
Ranch E
2001 √ √ √ 3.5 Exotics: BW, YST, PL
Natives: EG, LT, MR, ES
Management: little/ none?
21
B
Russell Blvd, S
side, from 1
mile W of Glide
Ranch to Glide
Ranch
2001 √ √ √ 3.5 Exotics: Mustard spp, BW,
PL, Ryegrass
Natives: EG, NP, HBB?, ES
Management: little/ none?
26 Rd 95, W side,
from Rd 96 to
Rd 97
2000 √ √ √ 1.0 Exotics: PL, YST dominate
Natives: where?
Management: none?
27 Rd 31, S side,
from Rd 98 to
Lake Blvd
1997 √ √ √ √ 2.5 Exotics: johnsongrass,
mustard spp, YST, others
Natives: shrub row and MR
Management: little
* 0 = reject ( no natives, all exotics); 1 = poor ( a few natives, mainly exotics); 2 = fair ( some natives, many
exotics); 3 = average ( natives and exotics equal); 4 = good ( mostly natives, a few exotics); 5 = excellent ( all
natives, no exotics).
** Exotics: PL ( prickly lettuce), YST ( yellow starthistle), WO ( wild oat), BW ( field bindweed). Natives:
NP ( Nassella pulchra), EG ( Elymus glaucus), ES ( Eremocarpus setigerus), LT ( Leymus triticoides), HBB
( Hordeum brachyantherum ssp brachyantherum), HBC ( Hordeum brachyantherum ssp californicum), MR
( Mulenbergia ripens), GC ( Grindelia camporum)
39
Phase II: Roadside native plant establishment
Native grasses are under intense pressure from non- native or exotic annual species during
and following establishment. Therefore, it is important to find ways to reduce
competition through cultural practices such as species selection, site development and
weed control. In order to allow for the sustainable growth of native perennial grasses
along roadsides, we designed our project to determine:
1) Desirable plant materials ( Phase II, Part A)
2) Site preparations ( Phase II, Part B)
3) Maintenance procedures ( Phase III).
40
Phase II, Part A: Desirable plant materials
Introduction
Field studies were initiated along two interstate highways in north central
California. Twelve native grass species that typify the valleys and foothills of northern
California were selected from a local seed source for planting along State Route 29
( SR29) in Lake County and Interstate 505 ( I505) in Yolo County ( Table 2).
Table 2. Native perennial grass species out planted along highway rights- of- way in
Northern California.
Common name Species name lbs/ A
Blue wild rye Elymus glaucus 4
California barley Hordeum brachyantherum californicum 3
California brome Bromus carinatus 3
California onion grass Melica californica 4
Creeping wildrye Leymus triticoides 6
Foothill needlegrass Nassella lepida 2
June grass Koeleria macrantha 1
Meadow barley Hordeum brachyantherum brachyantherum 4
Nodding needlegrass Nassella cernua 6
One sided bluegrass Poa secunda secunda 2
Purple needlegrass Nassella pulchra 10
Squirrel tail Elymus multisetus 3
41
Single species were drill seeded from the edge of the highway in a perpendicular
direction to the road. Site preparation and maintenance included typical cultural practices
( i. e. soil analysis, soil seedbed preparation and weed control) that have been
demonstrated to be most effect for establishing a native plant community ( Anderson and
Long 1999; Brown and Rice 2001; CNGA and CCIA 2001; Anderson 1999; Wolfe et. al.
1999). Observational studies were used to monitor plant growth. In spring and summer,
establishment of native perennial grasses was determined by measuring the density of
plants in drill rows that had been staked shortly after planting in the fall.
The goal was to determine which native perennial grasses ( Table 1) would
establish at what location ( edge, swale, back slope) away from the highway edge.
Methods for installation of plant species
2002- 2003 Season
In October, two experimental research sites were established along Caltrans
rights- of- way in Lake County ( State Route 29, mile 3.1, along southbound lane) and in
Yolo County ( Interstate 505, mile 14.9, between northbound on- ramp and highway).
Each site had particular features that warrant experiments on establishing native or
desirable species. The first site in Lake County ( hereafter referred to as SR29A) was flat
with a uniform stand of annual non- native plants growing abundantly. This site
represented a typical condition for native perennial grass establishment in an oak savanna
type landscape. The Yolo County site ( hereafter referred to as I505), represented a valley
soil on which native perennial grasses would be established, similar to SR29A.
Fall was selected for planting because best germination occurs when soil
42
temperatures are about 70° F and rain is imminent to re- fill the soil profile ( McGourty
1994). Because frequent irrigation applications are not practical for roadside
maintenance, native species establishment must be initiated in the fall for adequate plant
development before daytime temperatures begin to rise in late spring.
Following the general guidelines described by Wrysinski ( 1999) and Anderson
( 1999), I505 and SR29A were burned on November 22 and 19, respectively to remove
existing vegetation. The controlled burn at both sites was incomplete due to green
vegetation that had begun to emerge with the onset of fall rains. The I505 site had been
mowed a month before the burn by Caltrans, which further reduced the amount of thatch
needed to carry a hot fire.
Plant species to be included in the out- plant test included perennial grasses native
to California that would be most suitable for roadside establishment from pavement edge
out to 15 m ( Table 1). Growth characteristics were similar to native plants used by Bugg
( 1997) with plant height as an important characteristic because of the affect on
maintenance to sight clearance, fuel loads for fires and wildlife cover. The grasses most
adjacent to the road ( unimproved/ recovery area) consisted of the shortest species and
included Bromus carinatus ( California brome) and Poa secunda ssp secunda ( One- sided
bluegrass). Grasses selected for the side slope area included medium height species such
as Festuca idahoensis ( Idaho fescue), Hordeum brachyantherum ssp brachyantherum
( Meadow barley), Melica imperfecta ( Coast range melic) and Nassella cernua ( Nodding
stipa). For the area beyond the side slope ( could include open- cut ditch) the tallest grasses
selected were Elymus glaucus ( Blue wildrye) and Muhlenbergia rigens ( Deergrass).
In addition to height, other important considerations ( Anderson 1999; Bugg, et. al.
43
1997; CNGA and CCIA 2001; McGourty 1994; Wrysinski 2000) for species selection
were season of growth ( cool or warm), soil or habitat ( soil moisture content, air
temperatures, soil characteristics), life form ( perennial or annual), level of tolerance to
fire ( remaining green during the summer season) and/ or mowing and others ( i. e.
competitiveness, root structure and depth).
The I505 site was drill seeded on December 3 using a Truax ™ no- till planter
pulled by a farm tractor. The planter was calibrated to deliver 25- 35 lbs of native grass
seed per acre. Treatment plantings were laid out according to Figure 1.
------------------------------------------ Freeway --------------------------------------------
----------------------------------------------------------------------------------------------- 1 m from road edge -----------------------------------------------------------------------------------------------
a a b c d a a b c d a a a a a a b c d a b c d a a b c d b c d a
----------------------------------------------------------------------------------- 10 m from road edge ----------------------------------------------------------------------------------------------
a a b c d a a b c d a a a a a a b c d a b c d a a b c d b c d a
----------------------------------------------------------------------------------- 15 m from road edge ----------------------------------------------------------------------------------------------
a a b c d a a b c d a a a a a a b c d a b c d a a b c d b c d a
Plot position ( north end = 1, south end = 31)
0
0
0
1
0
2
0
3
0
4
0
5
0
6
0
7
0
8
0
9
1
0
1
1
1
2
1
3
1
4
1
5
1
6
1
7
1
8
1
9
2
0
2
1
2
2
2
3
2
4
2
5
2
6
2
7
2
8
2
9
3
0
3
1
Block
A A A A P B B B B P P C C C C P D D D D E E E E F F F F
a = best guess mix: north 6 rows = mix 1; south 6 rows = mix 2 ( 12 rows = 1 drill pass or 10 feet)
b = single species 1: 3 rows each of NP, HBC, MC, NL ( 12 rows = 1 drill pass or 10 feet)
c = single species 2: 3 rows each of PSS, NC, KM, EM
d = single species 3: 3 rows each HBB, EG, BC, LT
Figure 1. The experimental layout for drill seeding with native perennial grasses. Native
grass species code: NP ( Nassella pulchra), HBC ( Hordeum brachyantherum
californicum), MC ( Melica californica), NL ( Nassella lepida), PSS ( Poa secunda
secunda), NC ( Nassella cernua), KM ( Koeleria macrantha), EM ( Elymus multisetus),
HBB ( Hordeum brachyantherum brachyantherum), EG ( Elymus glaucus), BC ( Bromus
carinatus) and LT ( Leymus triticoides).
44
The same planting procedure and experimental layout was used at SR29A on
December 12 ( Figure 2). Glyphosate ( Roundup Ultra ® at 1 qt./ A) was applied less than
nine days after planting at I505 and SR29A for annual weed control prior to emergence
of native perennial grasses ( Anderson and Long 1999). Native grass seed germination
usually occurs in about 2- 4 weeks when planted in the fall ( Anderson 1999). Once native
grasses had emerged and begun to establish ( early to mid- spring), selective herbicides
were applied to control broadleaf weeds.
Figure 2. Experimental layout at SR29A following the drill seeding of native
perennial grasses on December 12, 2003.
Native grasses emerged at I505 and SR29A by January 6 and 14, respectively.
The stand at I505 was poor ( Figure 3) and was thought to be due to the cold weather. By
January 29, weed control was not adequate from the glyphosate so Buctril ® was applied
45
at 0.5 pt./ A on February 14.
Figure 3. Native perennial grass emergence is sparse in the experimental plots at
I- 505 on February 11, 2003
Poor germination of native grasses continued at I505 because of possible
‘ damping off’ disease, which attacks grass seed, damage from spraying glyphosate to
close to native grass emergence or seed loss from predation by birds and varmints
( Figure 4).
46
Drill seeding
No cultivation ( seed
left exposed on surface)
Cultivation
Figure 4. Potential problem for planting with no- till drill seeder.
A field visit to I505 with a local native grass grower on March 4 confirmed a poor
native grass stand because of disease or predation. Even though greater numbers of native
grasses had emerged in spots where the controlled burn was hottest, overall emergence
was below normal. The Buctril ® could have damaged the young plants, especially if no
adjuvant was used or the spray tank had not been thoroughly rinsed from a previous use.
By March, a good stand of native grasses had emerged at SR29A ( Figure 5). In
the previous month, Caltrans sent notification that the highway was due for widening and
installation of a lighted intersection, which would severely impact a major part of the site
and fatally harm the native grasses. Construction was to begin in July, so the site was
monitored and data collected up until ground breaking. An application of triclopyr
( Garlon ™ 4 at 1.2 pt/ A with non- ionic surfactant) was made at SR29A on March 26. At
I505, clopyralid ( Transline ™ at 6 oz./ A) was sprayed on March 29 to control broadleaf
weeds, especially yellow starthistle.
47
Figure 5. Native perennial grass stands at SR29A on May 2, 2003. Native grasses
include Hordeum brachyantherum californicum, Bromus carinatus and Elymus
glaucus.
Figure 6. Poor stand of native perennial grasses at I505 on May 13, 2003. ( A
year of weed control, but native perennial grasses were not persistent enough to
establish. A new planting was designed for the same site to begin fall 2003.)
48
Figure 7. Young stands of native perennial grasses at SR29A on June 18, 2003. At
the road edge is Nassella pulchra ( A), Elymus multisetus ( B) and Leymus
triticoides ( C). ( Unforeseen road construction at Lake 29 that began in July 2003
caused SR29A to be lost. Once a new location was identified, ( SR29) the
organization process of preparing and planting the site in fall 2003 was started
immediately.)
The SR29 site was cultivated on April 5, to preserve soil moisture and eliminate
late emerging weeds in preparation for planting native grasses in the fall. Nassella
pulchra emergence was lagging behind the other native grasses on May 2 at SR29A.
Koeleria macrantha and Poa secunda were emerging slowly, while all remaining native
grasses had emerged from drill seeded rows ( Figure 5).
The final stand counts at 20 meters from the road edge were made at I505 on May
14. Sparse populations of native grasses would be problematic for trying to establish a
competitive stand to resist annual weeds ( Figure 6). I505 was sprayed with glyphosate
( Roundup Ultramax ® at 2.5 pt./ A) on May 15 in preparation for another native grass
planting in fall 2003. Before spraying I505, stand counts were taken along the back slope
( Graph 1). Stand counts of native grasses at SR29A were taken on May 28 at 1 m, 4 m
and 10 m from the road edge ( Graph 2). Glyphosate ( Roundup Ultramax ® at 2.5 pt./ A)
was sprayed at SR29 on May 29 to control summer annual weeds in preparation for
planting in fall 2003. Final observations of native perennial grass establishment were
made at SR29A prior to road construction ( Figure 7).
A B C
49
On July 24, I505 was burned to remove dead vegetation and reduce annual weed
seed load ( Figure 8).
Figure 8. Burning at I- 505 ( July 24, 2003)
2003- 2004 Season
After poor establishment ( I505) and road construction leading to loss of research
plots ( SR29A) in 2002- 2003 season, planning and site preparations were started anew for
the 2003- 2004 season. A year’s worth of weed control was obtained at I505 along with
more knowledge on seedbed preparation ( i. e. spray timing and avoidance of cold weather
conditions) and the problems of native grass pests ( i. e. disease and predators). The
planting success at SR29A prior to construction would hopefully be transferred to the
50
new site, SR29, at mile 10 between the northbound on- ramp and highway at Hill Road
overcrossing in Lake County. The site was fallowed, beginning in early spring 2003.
Soil samples were taken at I505 and SR29 on September 19 and 23, respectively,
and analyzed at the A& L Lab in Davis ( Tables 2 and 3).
Table 2a. Soil characteristics near and back from road edge at I505, Yolo County, CA.
Location OM HCO3_ P pH K Mg Ca Na CEC % K % Mg % Ca % Na
20 m
from
road
1.7 21 8.0 282 1881 3505 22 34 2 46 52 0
1 m
from
road
1.9 14 7.8 269 1335 4001 61 32 2 35 63 1
Table 2b. Soil characteristics near and back from road edge at I505, Yolo County, CA.
Location NO3_ N S Zn Mn Fe Cu B S__ SALTS % SAND % SILT % CLAY
20 m
from
road
7.7 10.4 0.1 7.1 9.1 1.1 0.5 0.3 20 34 45
1 m
from
road
7.0 8.0 0.2 39.6 33.9 1.2 0.5 0.3 25 34 41
Table 3a. Soil characteristics near and back from road edge at SR29, Lake County, CA.
51
Location OM HCO3_ P pH K Mg Ca Na CEC % K % Mg % Ca % Na
10 m
from
road
1.6 11 6.9 138 2069 2245 63 30 1 57 38 1
1 m
from
road
1.5 11 6.8 173 1947 2143 57 30 2 54 35 1
Table 3b. Soil characteristics near and back from road edge at SR29, Lake County, CA.
Location NO3_ N S Zn Mn Fe Cu B S__ SALTS SAND SILT CLAY
10 m
from
road
10.0 1.6 0.2 70.2 45.4 1.3 0.1 0.3 49 20 31
1 m
from
road
9.2 2.2 0.1 49.0 35.5 0.9 0.1 0.3 27 34 39
In addition to lab analysis, soil pits were dug to determine soil morphological
characteristics and identify factors ( i. e. hard pan layers, poor soil structure) that could be
contributing poor native grass establishment. On October 31, deep soil ripping ( 60 cm on
½ m centers) treatments were conducted at I505 ( Figure 9). Ripping and discing
operations were conducted after the burn to provide soil seedbed preparation and control
weed seedlings. The seedbed was made firm and smooth so seed could be seeded with a
Truax machine drill. Additionally, a light cultivation to approximately 3 cm was done on
November 4.
52
Figure 9. Ripping and cultivation at I505, Yolo County, CA ( October 2003).
Similar ripping and cultivation treatments as at I505 were conducted at SR29 on
November 3 ( Figure 10).
53
Deep soil ripping trts and drill seeding
Each plot =
12.5 m long x
5 m wide
( Photo not to
scale. Road
edge plots not
as wide.)
Drill
seeding
rows.
Figure 10. Soil ripping plots constructed prior to drill seeding at SR29 in Lake
County, CA ( November 3, 2003).
At both sites, non- ripped control plots were included for comparison following
native grass planting and establishment. Soil structure at SR29 appear to be more
developed than at I505. Near the road edge, soils were subangular blocky or platey from
0- 20 cm deep, while away from the edge structure was subangular blocky down to 30 cm.
At both sites, soil structure below 30 cm was massive with little structural development.
On November 13 and 18, native grasses were drill seeded at I505 and SR29,
respectively. The planting format was similar to fall of 2002 ( see Figure 1) with the
addition of deep soil ripping and cultivation treatments at both sites ( Figure 11).
54
------------------------------------------ Freeway --------------------------------------------
----------------------------------------------------------------------------------------------- 1 m from road edge -----------------------------------------------------------------------------------------------
n n n n r r r r n n n n r r r r n n n n r r r r
----------------------------------------------------------------------------------- 10 m from road edge ------------------------------------------------------------------------------------------
n n n n r r r r n n n n r r r r n n n n r r r r
----------------------------------------------------------------------------------- 15 m from road edge ------------------------------------------------------------------------------------------
r r r r n n n n r r r r n n n n r r r r n n n n
Plot position ( north end = 1, south end = 31)
0
0
0
1
0
2
0
3
0
4
0
5
0
6
0
7
0
8
0
9
1
0
1
1
1
2
1
3
1
4
1
5
1
6
1
7
1
8
1
9
2
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2
1
2
2
2
3
2
4
2
5
2
6
2
7
2
8
2
9
3
0
3
1
Block
A A A A B B B B C C C C D D D D E E E E F F F F
r = deep soil rip + cultivation; n = no deep soil rip + cultivation
Figure 11. Experimental layout with soil ripping ( r) and no soil ripping ( n) treatments
applied prior to drill seeding of the native grasses. Treatments r and n tested at the road
edge ( 1 m) and away from the road edge ( 10- 20 m).
At both sites, seeding was done perpendicular to the highway and crossed the
ripped and non- ripped treatments. The slope back from the road edge at I505 was steeper
and wider (> 20 m) than at SR29 ( Figure 12).
55
Ripping treatments
Back slope
Road edge
Swail
Ripping treatments
Figure 12. Drill seeding a second time at I505 after poor native grass emergence
and persistence the previous year ( November 13, 2003).
Following drill seeding, soil in each row was raked lightly over the seed trench to
insure against native grass seed loss from predation by birds and varmints as in 2002-
2003. The open seed trench condition seemed to be more common in 2003- 2004 because
of drill seeding into damp soil, which was less friable than earlier in the fall.
On November 24 and 25, glyphosate ( Roundup Ultra ® at 2 pts/ A) was applied to
kill annual weed seedlings prior to native grass emergence at I505 and SR29,
respectively. Following herbicide application, native grass straw ( Melica californica) was
applied at 2 tons/ A or approximately 3/ 4” deep ( 2002 Caltrans/ CNGA workshop) to
control soil loss and disturbance of native grass seed ( Figures 13 and 14).
56
Figure 13. I505 ( Fall 2003). A close- up view of the deep ripper used at I505 and
SR29 prior to planting in fall 2003 ( A). The planted seedbed was raked by hand to
insure good soil to seed contact and prevent seed loss by wild life ( B). A post-planting
herbicide application was made to control weeds before emergence of
native perennial grass seedlings ( C). Straw was applied prior to the rainy season
to control excessive soil loss ( D).
A B C
D D
57
Figure 14. SR29 was drill seeded with native perennial grasses ( A), sprayed with
glyphosate to control weeds before native grasses emerged ( B) and covered with
straw to control excessive soil loss across the site and along the road edge ( C)
( November 2003).
On December 16, native grasses had begun to emerge mainly along the road edge
at I505 where the straw mulch was thinner. Early after planting, low emergence is not
uncommon, especially during excessively cool and wet periods, but in spots with
excessive straw mulch (> 3/ 4”), native grasses were less likely to be found. The
emergence of native grasses at SR29 had yet to occur and ponding water was observed in
several locations.
Native grasses began to emerge in both heavily mulched (> 3/ 4”) and lightly
mulched (< 3/ 4”) areas of I505 by January 23 ( Figure 15).
A B
C
C C
58
Figure 15. Native grass emergence at I- 505 on January 23, 2004.
The straw mulch was either non- selective in slowing the emergence of weeds and
native grasses or the herbicide application was very effective or the straw mulch was
having no effect as weather conditions were adversely inhibiting weed and native grass
emergence. Whichever the case, weed control was near 100% at I505 and SR29 in late
January.
On February 4, native grasses continued to come up through the mulch and weed
growth was beginning at I505. The straw mulch, in addition to controlling soil loss, may
have inhibited some growth of the native grasses by retaining water in an already
excessively wet condition, maintaining low temperatures, blocking light and physically
impairing vegetative growth. Native grass seedlings were in the 2- 3 leaf stage at I505 on
February 9 and still emerging from under the straw mulch.
59
Native grasses were slow to emerge at SR29. The site was still very wet on
February 20 with ponding water visible in a few spots. The growth of weeds was minimal
to nil with only a few small patches of grasses and some sedges here and there.
On March 3, clopyralid ( Transline ® at 6 oz/ A) was sprayed at I505 to control
vetch and other annual broadleaf weeds. The application may have injured the young
native grasses seedlings ( 3- 5 leaves and 6- 10”), but the weeds were becoming a problem
and could have inhibited native grass growth, especially with warm, dry weather
conditions. The application was effective for control of the vetch and yellow starthistle,
but ineffective on fiddleneck and certain species of mustard. On March 15, exotic annual
and native perennial grasses were growing well in patches and appeared to have either
not been injured or recovered from injury by the clopyralid application.
An attempt was made at uprooting weeds at I505 on March 22, but removal of
broadleaves and vetch ( tares) also caused damage to the desired plants, so they were left
in the field to be controlled by burning ( Matthew, 1952) other chemical, mechanical or
cultural means, such as tillage or native perennial grass competition. At this time, annual
grasses ( i. e. ripgut brome, Italian ryegrass) were still vegetative and above the native
perennial grasses.
On March 23, native grasses had clearly emerged in many of the drill rows from
the fall planting at SR29. An application of clopyralid ( Transline ™ at 6 oz/ A) was made
to control broadleaf weed growth, which was beginning to impeded native grass
establishment.
A selective mowing was conducted at I505 on March 30. The site was mowed at
approximately 10- 12”, which was just above the tallest native grasses, yet low enough to
60
remove the inflorescences of many of the annual grasses. McGourty ( 1994) recommends
mowing native grasses in early spring to a height of four inches to suppress winter weeds
and promote tillering of the developing grasses, but we elected not to mow due to
adequate control from glyphosate applied in the fall. When mowing was done, the mower
height was kept at a height that would kill weeds (~ 10”), but that prevented permanent
damage to the native grasses. Anderson and Long ( 1999) mowed hedgerow plots with
native grasses once or twice in the spring to control annual grasses before they set seed.
Timed mowings are also recommended by Wrysinski ( 1999) as a weed control tool that
can reduce annual weed canopy and allow sunlight to reach shorter, less vigorous natives.
Mowing of native grasses in this study was employed in a similar fashion for weed
control, albeit later in the growing season than recommended.
Preliminary observations were made on number of native perennial grasses and
weed growth in ripped and non- ripped treatments at I505 on March 30. Of the 12 native
perennial grass species planted, Bromus carinatus, Melica californica, Elymus glaucus,
E. multisetus, and Hordeum brachyantherum ssp brachyantherum were present in 4 to 6
out of 6 replications at row lengths of 1 m or greater. Nassella lepida, Nassella pulchra
and Koeleria macrantha were present in 2 out of 6 replications and Nassella cernua, Poa
secunda ssp secunda, Hordeum brachyantherum californicum and Leymus triticoides
were not present during the spring stand count. Weed growth appeared to be reduced in
non- ripped treatments compared to ripped treatments, irregardless of nearness to road
edge. The observation of greater weed growth in ripped treatments is not uncommon as
previous research has documented the stimulatory effect that soil disturbance has on
weed seed germination.
61
On May 29, native grasses were establishing at SR29 in drill rows from the fall.
The most prevalent native grasses were B. carinatus, E. glaucus, E. multisetus, H.
brachyantherum ssp brachyantherum, P. secunda ssp secunda, K. macrantha and H.
brachyantherum californicum ( Figures 16 and 17). Although native grasses seldom filled
out an entire drill row from road edge to back slope, plants that were present were robust,
green and appeared to be growing with vigor. Native grass species that had been planted
yet were not seen were N. lepida, N. pulchra, N. cernua, and L. triticoides.
Figure 16. Native perennial grass establishment at Lake 29 on June 18, 2004.
Elymus glaucus ( A) and Hordeum brachyantherum californicum ( B) growing in
drill rows planted in November 2003.
A B
62
Figure 17. Native grass emergence at Lake 29 on June 18, 2004. A robust stand
of Elymus multisetus ( A) and Leymus triticoides ( B).
Stand counts were recorded for native grasses at I505 and SR29 on June 19
( Graphs 4- 7). The number of native grasses was greater at SR29 than I505. Native grass
establishment had occurred at SR29, even though many weeds were still present ( Figures
16 and 17). This is not an uncommon phenomenon, as most native grass restoration
projects require 3 to 5 years of maintenance following the initial planting to become the
dominant plant type that out compete weeds. At I505, native grasses were present, but
weeds were overwhelming most of the native grass plants. A more vigilant approach to
weed control appears to be necessary ( i. e. preemergent herbicide in fall, selective wiping
of taller annual grasses in spring, mowing techniques that avoid knocking annual weeds
down without actually cutting them).
A B
63
Results of native perennial grass species selection
2002- 2003 Season
Single species of N. pulchra ( NPU), E. multisetus ( EMU) and E. glaucus ( EGL)
emerged at a rate of greater than 10 plants/ m along the road edge at I505 in spring 2003
( Graph 1). Populations of H. brachyantherum ssp californicum ( HCA), M. californica
( MCA), H. brachyantherum ssp brachyantherum ( HBR), E. glaucus ( EGL) and B.
carinatus ( BCA) had at least 3 plants/ m stand counts at 10 m from the road edge, while
E. multisetus ( EMU), E. glaucus ( EGL) and B. carinatus ( BCA) had greater than 3
plants/ m stand counts at 1 m from the road edge at SR29A spring 2003 ( Graph 2).
Emergence of native grasses planted out from Interstate 505 roadedge in Yolo
County, California May 14, 2003
0
5
10
15
20
25
NPU HCA MCA NLE PSE NCE KMA EMU HBR EGL BCA LTR
plants / m
Graph 1. Native grass emergence at Interstate 505 in Yolo County, CA ( May 14, 2003).
64
Emergence of native grasses planted out from the edge of State Route 29 in
Lake County, California May 28, 2003
0
1
2
3
4
5
NPU HCA MCA NLE POS NEC KAM EMU FID HBR EGL BCA LTR
native grass species
plants / meter 1 meter
4 meter
10 meter
Graph 2. Native grass emergence at State Route 29A in Lake County, CA ( May 28,
2003).
2003- 2004 Season
Single species stands of Elymus glaucus ( Blue Wildrye), Bromus carinatus
( California Brome), Elymus multisetus ( Squirrel Tail), Melica californica ( California
Onion Grass) and Hordeum brachyantherum californicum ( California Barley) had an
establishment rate of greater than 2 plants per m2 at SR29 and I505 in year one after
seeding. In the ripped plots at the road edge of I505, Blue wildrye, B. carinatus and E.
multisetus establishment was 4, 3 and 4 plants per m2, respectively. Except for M.
californica and Hordeum brachyantherum ( Meadow Barley), plant establishment in the
back slope of I505 was not different for ripped and non- ripped areas. At SR29,
establishment in the back slope was 4, 6, 3, 5 and 4 plants per m2 in the ripped treatments
for H. brachyantherum californicum, E. multisetus, H. brachyantherum, Blue wildrye and
65
Leymus triticoides ( Creeping Wildrye), respectively. Except for H. brachyantherum
californicum, E. multisetus and H. brachyantherum, plant establishment was similar in
ripped and non- ripped plots at the road edge of SR29. At SR29 and I505, establishment
for Nassella pulchra ( Purple Needlegrass), Nassella lepida ( Foothill Needlegrass), Poa
secunda secunda ( One- sided Bluegrass), Nassella cernua ( Nodding Needlegrass) and
Koeleria macrantha ( June Grass) did not exceed 1 plant per m2.
Establishment varied at each site with respect to location ( road edge or back
slope) and cultural amendment ( soil ripping or non- ripping). Native grass establishment
was greater along the back slope at SR29 ( Fig. 4), but soil ripping was not beneficial in
both locations ( Figs. 5 and 6). Conversely, I505 had the best native perennial grass
establishment at the road edge ( Fig. 7) and ripping tended to improve establishment at
both road edge and back slope locations ( Figs. 8 and 9). We found that first year
establishment of native perennial grasses were affected by micro- site differences ( e. g.
climate, soil), which resulted in variation in plant numbers, but only eliminated between 1
to 4 out of the 12 plant species that were tested. The effect from ripping was not
determined in subsequent years.
66
0
5
10
15
20
np hbc mc nl ps nc km em hbb eg bc lt mix
native grass species
# plants/ 2m back slope
road edge
Native grass establishment at SR29
Figure 4. Establishment of native perennial grasses along the road edge and back slope of
a Caltrans’ highway right- of- way in Lake County, CA ( June 19, 2004).
Native grass establishment along road edge at SR29
0
5
10
15
20
np hbc mc nl ps nc km em hbb eg bc lt mix
native grass species
# plants/ 2m
Non- ripped
Ripped
Figure 5. Establishment of native perennial grasses along the road edge of a Caltrans’
highway right- of- way in Lake County, CA using cultural treatments ( June 19, 2004).
67
Native grass establishment along back slope at SR29
0
5
10
15
20
np hbc mc nl ps nc km em hbb eg bc lt mix
native grass species
# plants/ 2m Non- ripped
Ripped
Figure 6. Establishment of native perennial grasses along the back slope of a Caltrans’
highway right- of- way in Lake County, CA using cultural treatments ( June 19, 2004).
0
5
10
15
20
np hbc mc nl ps nc km em hbb eg bc lt mix
Native grass species
# plants/ 2m back slope
road edge
Native grass establishment at I- 505
Figure 7. Establishment of native perennial grasses along the road edge and back slope of
a Caltrans’ highway right- of- way in Yolo County, CA ( June 19, 2004).
68
Native grass establishment along road edge at I505
0
5
10
15
20
np hbc mc nl ps nc km em hbb eg bc lt mix
native grass species
# plants/ 2m Non- ripped
Ripped
Figure 8. Establishment of native perennial grasses along the road edge of a Caltrans’
highway right- of- way in Yolo County, CA using cultural treatments ( June 19, 2004).
Native grass establishment along back slope at I505
0
5
10
15
20
np hbc mc nl ps nc km em hbb eg bc lt mix
Native grass species
# plants/ 2m Non- ripped
Ripped
Figure 9. Establishment of native perennial grasses along the back slope of a Caltrans’
highway right- of- way in Yolo County, CA using cultural treatments ( June 19, 2004)
69
Conclusions
The study in 2002- 2003 and 2003- 2004 seasons gave a comparison of plant
growth in bands of different species from the road edge, through the shoulder, swale and
backslope areas. Due to road construction disturbance and seeding failure ( fungal
damping off during an early wet period) in 2002- 2003, experiments were repeated at or
near the original locations in 2003- 2004. In 2003- 2004, additional seedbed preparation
operations were employed in the form of cultivation and deep soil ripping. Native grass
combinations and individual species were planted similar in both years.
Establishment of native perennial grasses along the road edge and back slope was
dominated by: Hordeum brachyantherum californicum ( hbc), Elymus multisetus ( em),
Elymus glaucus ( eg), Bromus carinatus ( bc) and Hordeum brachyantherum californicum
( hbc), Elymus multisetus ( em), Elymus glaucus ( eg), Bromus carinatus ( bc), Leymus
triticoides ( lt), respectively. Other native perennial grass species with potential included
Nassella pulchra, Melica californica, H. brachyantherum and Disticulus spicata, but
these were not planted because seed was not available at time of planting.
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Phases II, Part B: Site preparations ( I- 5 median trials)
Summary
The establishment of native perennial grasses within sections of California
highway rights- of- way has the potential to maintain motorist safety and improve erosion
control, while reducing the need for mowing and/ or herbicide use. Prior to native
perennial grass planting and establishment, specific cultural and chemical management
treatments are needed to control non- native vegetation. Field studies were initiated at two
sites ( I- 5 North and I- 5 South) along Interstate 5 near Williams, California to determine
the effect of burning, spraying, cultivating and species selection on the establishment of
native perennial grasses and persistence of non- native annual vegetation. Two perennial
grass mixes of species native to northern California were selected using local seed
accessions. These include Hordeum brachyantherum, Nassella pulchra, Elymus
multisetus, Elymus glaucus and Poa secunda in a “ dry site” mix. A “ wet site” mix
included H. brachyantherum, Leymus triticoides, E. multisetus and E. trachycalus .
Burning and spraying had the most significant effect on native grass establishment and
non- native vegetation persistence at both sites. Burning increased H. brachyantherum and
decreased L. triticoides establishment at both sites, but significantly lowered the
persistence of non- native annual grasses and increased the persistence of non- native forbs
at I- 5 North. Non- native annual forb cover was significantly less in the clopyralid or
chlorsulfuron herbicide regimes at I- 5 South, while non- native annual grasses were
reduced in the chlorsulfuron herbicide regime at I- 5 North. Cultivation and species
selection had no significant effect on native perennial grass establishment or non- native
71
annual vegetation persistence. A major limiting factor in the establishment of native
perennial grasses is non- native vegetation, which can be easy to eradicate but often hard
to manage, once highway rights- of- way have been planted with native perennial grasses.
Cultural and chemical management techniques are necessary to improve the
establishment success of native perennial grasses in the first two to five years after
planting along highway rights- of- way in California.
A properly timed prescribed burn and two or more herbicide applications can
provide good control of non- native annual vegetation in the year prior to and the first two
years after drill seeding native perennial grasses. Following establishment, a less costly
non- native control plan can be used to manage a highway right- of- way stand of native
perennial grasses in northern California
Introduction
Native species are known to have slow germination, low seedling vigor and slow
growth rates ( Wrysinski 1999). Intensive management is required in the first few years to
reduce competition from more vigorous, non- native annual species. Roadside projects
that are funded for only a year of vegetation control often result in a return to the typical
weedy vegetation. Anderson and Long ( 1999) found that weed control was 34% of the
total cost for establishing four hedgerows that included native grasses in Yolo County.
The other remaining costs were for site preparation, plants, grasses, pest control and
water that were 8%, 20%, 18%, 4% and 16%, respectively, of the total revegetation cost.
While management is important for establishing native grasses along roadsides,
persistence of native plants after establishment occurs at some sites with even minimal
72
management ( O’Dell et al. 2007). In most instances, it is desirable to control weeds for an
entire year or more prior to planting native species in order to reduce the weed seed bank
( Kimball and Lamb 1999). Although time and resources may restrict this practice, it
could mean the difference between success and failure for establishing a native plant
community.
Roadsides can be difficult locations for establishing native plants. Site conditions
that can limit the success of any revegetation effort include topography ( steepness), soil
( shallow, rocky, compacted, chemically imbalanced), climate ( region, slope, aspect,
seasonal variation) and existing vegetation ( competition, invasion).
Figure 1. Restoration of severe slopes along highways in Northern California. Photos
courtesy of S. L. Young.
Brooks ( 1995) found that plant cover on fill slopes was significantly higher than
73
on cut slopes along highways in the Tonto National Forest in central Arizona. The
revegetation treatments used for visual impact mitigation, as judged by the public, were
unsatisfactory on 72% of the cut slopes evaluated. Poor establishment of vegetation on
disturbed sites following surface applications like hydroseeding are often the result of
improper species selection, seeding at an inappropriate time, and/ or improper seed mixes,
fiber and tackifier ( Hallock et al. 2002) or soil preparation. The end result can sometimes
be a reversion to weeds in the years following a planting if a one- step hydroseeding
process is used ( Ivanovitch 1975).
Studies have shown that relying solely on the seed bank for restoration of native
vegetation is nearly impossible ( Kalamees and Zobel 1998; Smith et al. 2002; Laughlin
2003), except in rare cases ( Dreman and Shaw 2002). In order to overcome these
problems, the solution was to prepare the site before planting and select a diverse range
of plant species when seeding. Harper- Lore ( 1998) found that the specific cultural
practices were site specific and included fertilization, maintenance, seeding rate ( 7 and 20
lbs./ acre), site preparation and method of planting.
Other roadside studies have taken into consideration the effects of plant mixtures
for establishing natives along roadsides ( Anderson and Long 1999; Bugg and Brown
2000; M. C. Wolfe and Associates 1988). Both polycultures and monocultures were used
by Bugg et al. ( 1997) to evaluate the establishment of non- native ( desirable) and native
perennial grasses. A mix of native grasses ( polyculture) or single species ( monoculture)
was seeded into a rural roadside consisting of several topographic zones ( i. e. road edge,
swale, back slope) near the town of Winters, California. There was no significant
difference in the amount of canopy cover for the polycultures on different topographic
74
zones, but the biomass of the natives was less than for the non- natives. In the
monocultures, California brome ( Bromus carinatus), blue wildrye ( Elymus glaucus),
slender wheatgrass ( E. trachycaulus), meadow barley ( Hordeum brachyantherum ssp.
brachyantherum), California barley ( H. brachyantherum ssp. californicum), purple
needlegrass ( Nassella pulchra) and nodding needlegrass ( Nassella cernua) had good
canopy cover. Sheep fescue ( Festuca ovina), squirreltail ( E. multisetus), Idaho fescue
( Festuca idahoensis), creeping red fescue ( F. rubra) and pine bluegrass ( Poa secunda
ssp. secunda) had poor canopy cover. Polycultures performed well in all topographical
zones, developing different community compositions. Monocultures with persistent
stands were established for several species of the abovementioned species. Competition
from resident vegetation ( weeds) was found to influence establishment in both the
polycultures and monocultures. They concluded from their study that, despite difficulties
due to herbicides, persistent stands of local native species could be used along roadsides
and other rights- of- way in the Sacramento Valley. They deem accessions retaining 25%
or greater canopy cover in monocultures to be suitable for use in roadsides in the
Sacramento Valley.
In another roadside study by Bugg and Brown ( 2000), existing stands of native
grasses were used in combination with native forbs to control non- native ( undesirable)
species. The idea was to determine the establishment efficiency of local forbs and
perhaps use the most robust and vigorous species as an alternative to conventional
management ( herbicides, mowing or blading) for controlling undesirable species.