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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.

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