Minimizing Risk
of Cheatgrass Invasion and Dominance at the Idaho National
Laboratory
Investigators
and Affiliations
Lora Perkins, Ph.
D. student, Department of Natural Resources and Environmental
Science, University of Nevada Reno, Reno NV
Robert S. Nowak, Professor, Department of Natural Resources and
Environmental Science, University of Nevada Reno, Reno NV
Kimberly G. Allcock, Postdoctoral Associate, Department of
Natural Resources and Environmental Science, University of
Nevada Reno, Reno NV
Funding Sources
U.S. Department
of Energy Idaho Operations Office
Nevada Arid Rangeland Initiative and the Nevada Agricultural
Experiment Station
Background
Predicting plant
community susceptibility to invasion by introduced species and
determining mechanisms of resistance are fundamental concerns of
ecology and ecosystem management. In the Great Basin, the
invasive introduced annual cheatgrass (Bromus tectorum)
currently dominates 3 million acres, with another 14 million
acres heavily infested and 60 million acres considered at risk
for potential domination (Pellant and Hall 1994). However, the
eastern portion of the Snake River Plain, including the INL, has
largely escaped the cheatgrass dominance found in the western
portions of the Snake River Plain and in northern Nevada.
Anderson and
Inouye (2001) concluded that maintenance of cover of native
species may make the vegetation of the INL resistant to
invasion. However, the eastern Snake River Plain also differs
climatically from most cheatgrass-invaded areas: winter
temperatures are colder and there is more late spring
precipitation. The relatively minor extent of cheatgrass
invasion at the INL in comparison with surrounding areas
provides a unique opportunity to identify environmental
conditions, community characteristics, or management practices
conferring ecosystem resistance to invasion.
Objectives
The goal of this
project is to use a combination of field surveys and mechanistic
hypothesis-driven greenhouse experiments to determine the
influences of environment, plant community, and land management
on invasion success.
Comparative
surveys - We will conduct comparative surveys along a
latitudinal climatic gradient from north central Nevada, where
cheatgrass dominates much of the landscape, to the INL. We will
establish sampling plots at several hundred locations in four
areas along this ‘mega-transect’ taking care to adequately
sample sites with different types of disturbance and management
histories as well as different vegetation composition and
temperature and precipitation regimes. We will sample
intensively at the INL; at sites near INL (and therefore
climatically similar) but with different land use and ownership;
at sites in far southern Idaho and northern Nevada (Owyhee
Plateau) with a range of disturbance and community composition;
and in north central Nevada near a set of permanent experimental
plots that were established to assess restoration success of
cheatgrass-dominated rangeland (Allcock et al. 2006). We will
use information ranging in scale from microscopic (nutrients and
microbes) to landscape (climate and land use patterns) to
parameterize a structural equation model (SEM; Grace 2006) and
specifically test hypotheses about how site characteristics
affect invasion success of cheatgrass.
SEM is a powerful
statistical way to infer causality: specifically we will use it
to determine why cheatgrass is more abundant in certain
locations and less abundant in others. An additional benefit of
SEM is that we can include variables based on ‘expert opinion’
rather than relying on strictly empirical data. This means we
can include a wealth of invaluable information that would not be
otherwise useable in a quantitative model. We will be collecting
observational data from the field and combining it with site
specific variables.
Controlled
greenhouse studies – We will use controlled-environment
experiments that involve individual species and constructed
communities to establish a mechanistic understanding of
competition between cheatgrass and native species. We will
investigate competitive relationships, effects of diversity,
density, and disturbance, and response to variation in water
regime (timing and pulse size). Preliminary single-species
trials indicate that cheatgrass and perennial species differ in
their abilities to respond to water pulses depending on size and
frequency of watering events, and that moisture at the right
time in the life cycle of cheatgrass could promote high
competitive ability and possibly invasion (K. Allcock,
unpublished data). A mesocosm experiment is currently underway
to test the interactions of precipitation timing and community
composition in determining invasion success.
Accomplishments
through 2006
Comparative
surveys: In September 2006, we visited the INL and traveled the
length of our proposed ‘mega-transect’ to identify potential
sampling locations. We have obtained and are processing fire
history, soil maps, vegetation classification data and digital
elevation models for the sampling areas we identified. We will
convert the information to digital GIS layers and use the GIS to
help with the selection of exact data collection points. The GIS
will also provide information that will be used in the final SEM
model.
Controlled
greenhouse studies: In September and October of 2006 we began
establishing an experiment to test the effects of community
composition, precipitation amount, and precipitation timing on
establishment and success of cheatgrass. We collected
individuals of six perennial grass species from a field location
near Reno, NV. We used these to create a series of two-species
‘communities’ in 50-gallon barrels in a greenhouse on the
University of Nevada campus. These communities are composed of
species that are active earlier in the growing season (Poa
secunda, Acnatherum hymenoides, and Elymus
elemoides), later in the growing season (Hesperostipa
comata, A. thurberiana, and Pseudoroegneria
spicata), or a combination (one early species and one late
species). One quarter of the barrels contain no perennial
plants. Between April 2007 and June 2007 these communities will
receive either a total amount of water based on the long-term
average precipitation for the Reno area, or an elevated amount
of precipitation (in line with climate change predictions; 50
percent more than the long term average). This total amount of
water will be administered either primarily in the ‘early
season’ (April-May) or in the ‘late season’ (May-June). All
communities have been seeded with cheatgrass at a rate of 2000
seeds per m2. In summary, there are four community types (early,
late, mixed, no perennials); two total water levels (ambient,
elevated); and two precipitation timings (early, late). We have
six replicates for each treatment combination, giving a total of
96 barrels. We will monitor soil moisture; cheatgrass density,
biomass, seed production and photosynthetic rates; and the
growth, reproduction, and photosynthetic rates of the perennial
plants.
Results
This project was
still in its developmental stage in 2006, and we have not
collected any field or experimental data. We have begun to
compile site-related information including fire history, climate
variables, soil survey data, and topographic variables into a
GIS database. We will begin collecting data on our greenhouse
studies in May 2007.
Plans for
Continuation
This project will
continue through 2009. We will begin collecting field data from
the comparative field plots at INL and other areas starting in
late-May and June 2007. In subsequent seasons, we will continue
to collect vegetation, soil and climate data from additional
survey plots in order to obtain as much data as possible for
parameterization of the SEM. SEMs may require a minimum of 100
data points in order for the algorithms used to identify
reliable parameter values (Tanaka 1987), and we aim to sample
approximately 400 individual plots among the four locations
through the course of the study.
As outlined in
the previous section, our mechanistic greenhouse study is just
getting underway and this experiment will continue through the
end of June 2007. We will use the results from this first
experimental iteration to refine our understanding of how
precipitation timing, precipitation amount and community
composition affects cheatgrass performance. We will perform
additional greenhouse studies over the next several years to
test and refine further our understanding of the mechanisms of
plant interaction and cheatgrass establishment in perennial
grass ecosystems.
Publications,
reports, theses, etc.
We anticipate
several peer reviewed publications (e.g. the results of the SEMs
and the results of the greenhouse experiments) and conference
proceedings in addition to the Ph.D. dissertation to be
completed by Lora Perkins in 2009.
References
Allcock, K, R. Nowak, R. Blank, T. Jones, T. Monaco, J. Chambers,
R. Tausch, P. Doescher, J. Tanaka, D. Ogle, L. St. John, M.
Pellant, D. Pyke, E. Schupp and C. Call (2006) Integrating weed
management and restoration on western rangelands. Ecological
Restoration 24:199-200.
Anderson, J., and R. Inouye. 2001. Landscape scale changes in
species abundance and biodiversity of a sagebrush steppe over 45
years. Ecological Monographs 71:531-556.
Pellant, M. and C. Hall. 1994. Distribution of two exotic grasses
on intermountain rangelands: status in 1992. p. 109-112 In: S.B.
Monsen and S. G. Kitchen (compilers). Proceedings—ecology and
management of annual rangelands. General Technical Report
INT-GTR-313, Ogden, UT, USDA Forest Service, Intermountain
Research Station.
Tanaka, J.S. 1987. How big is big enough? Sample size and
goodness-of-fit in structural equation models with latent
variables. Child Development 58: 134-146.
