Predictive Modeling of Cheatgrass Invasion Risk for the Lake Tahoe Basin
II. Proposal Narrative
a. Justification Statement
Montane meadows in the Lake Tahoe Basin (LTB) face substantial impacts from
invasion by both native and exotic plants. Here, we aim to understand the response of the
noxious exotic annual plant cheatgrass (Bromus tectorum) to climate change and disturbance.
Consistent with “Theme 4: Climate Change; Subtheme: Climate Change and Application of
Predictive Models,” our study will develop and apply a spatially explicit model of cheatgrass
invasion risk in montane meadows of the LTB, generating practical information for early
detection of cheatgrass invasion and appropriate management responses.
b. Background/Problem Statement
In the Sierra Nevada of California, meadows play important roles in hydrology, erosion
control, nutrient cycling, provision of animal food and shelter, and human recreation
(Kattelmann and Embury 1996). They provide habitat for several important bird species,
including at least one species of major conservation concern, the Willow fly catcher (Empidonax
trailli) (Flett and Sanders 1987, Harris et al. 1987, Ohmart 1994, Graber 1996), as well as a
number of sensitive plant species, including grape ferns (Botrychium spp.) and moss species
(e.g., Sphagnum and Meesia spp.) (USFS 2004). In addition to providing critical habitat for
terrestrial plants and wildlife, the condition of meadow vegetation is closely related to the biotic
condition of adjacent streams (Menke et al. 1996). Meadows are also important in hydrological
processes downstream, reducing peak stream flows, channel erosion, and nutrient loads (Carter
1986, Johnston 1991, Johnston 1993).
Montane meadows are found from the subalpine zone down to 1200 m (4000 ft). They
are typified by high water tables and dominance by native perennial sedges and grasses,
interspersed with a high diversity of native perennial forbs (Allen 1987, Kattelmann and Embury
1996). This vegetation is extremely responsive to water availability, and meadow community
composition shows striking variation along local and regional topographic and hydrologic
gradients (Allen 1987, Manley et al. 2000, Millar et al. 2006).
Meadow drying is one of the most significant forms of change that has occurred in the
LTB and many other places in the Sierra Nevada, primarily as a result of past overgrazing and
resulting changes in the water table (Wagoner 1886, Hughes 1934, Ratliff 1985, Menke et al.
1996). Montane meadows have been identified among the most vulnerable and damaged habitat
types of the Sierra Nevada (Krzysik 1990, Kattelmann and Embury 1996, USFS 2004), and the
Tahoe Regional Planning Agency (TRPA 2002) has identified meadow ecosystems as an
important focus area for restoration efforts in the LTB.
Global warming is a new threat to the condition of Sierran meadows, and is likely to
exacerbate the problem of meadow drying. Globally, the 1990s were the warmest of the last
millennium (Mann et al. 1999), and 2006 was the warmest year on record (NOAA 2007). In
mountain areas, earlier snowmelt is shrinking snowpacks, decreasing stream flows and ground
water supply, and increasing drought stress on plants (Fig. 1; Grabherr et al. 1994, McCarty
2001, Walther et al. 2002, Hamlet et al. 2005). Because of their high sensitivity to drying,
montane meadows have been suggested as early indicators of environmental changes associated
with warming (Debinski et al. 2004).
New invasions by non-native species are one potential consequence of anthropogenic
change to Sierran meadows (Menke 1996, Schwartz et al. 1996, D’Antonio et al. 2004). While
Predictive Modeling of Cheatgrass Invasion Risk for the Lake Tahoe Basin
these meadows have historically been highly resistant to the establishment and spread of nonnatives, exotic plants are increasingly recorded both in and around montane meadows (Manley et
al. 2000). Meadow drying has been observed to cause the replacement of native perennials with
non-native annuals (Burcham 1970, Hagberg 1995). An increase in invasive species prevalence
may inhibit the ability of native species to adapt or migrate in response to further drying
(D’Antonio et al. 2004).
Cheatgrass (Bromus tectorum) is an exotic species of major concern that is increasingly
detected in Sierran meadows. This notorious annual grass has been a major driver of ecosystem
change in the intermountain west (Schwartz et al. 1996, Manley et al. 2000), due to its tendency
to dramatically increase the frequency of early season fires via the highly flammable nature of its
early-drying herbage (Brooks et al. 2004). While cheatgrass is present in some meadows in the
LTB, especially in drier, disturbed sites in the Carson Range, it is at a relatively early stage of
invasion. Continued cheatgrass invasion and subsequent changes in fire regimes could result in a
loss of meadow biodiversity and hydrologic function and a lowering of habitat quality (Harris
1967, MacDonald et al. 1988, Hunter 1991, D’Antonio & Vitousek 1992, MacDonald et al.
1999). Perhaps most ominously, fire and fuels treatment restoration efforts for removal of
lodgepole pine (Pinus contorta) in the LTB (TRPA 2002) may act as a disturbance that may
benefit cheatgrass invasion into meadows and subsequently into adjacent conifer stands, with
serious consequences for forest and fire management (Keeley 2006).
Examining the distribution of cheatgrass along environmental gradients, such as the eastwest rainfall gradient and local wet-to-dry gradients within and among meadows, will allow us to
develop a spatially explicit predictive risk model of cheatgrass invasion and to apply it under
both the current climate and future climate scenarios. In addition, incorporating a parameter for
disturbance level will improve model accuracy and predictive value. The resulting information
will be useful for creating management scenarios to resist species invasion, restore natural
communities, and sustain biodiversity and ecosystem function in meadows in the face of
changing climate.
c. Goals, Objective(s), and statement of hypotheses to be tested
Our examination of the relationship between climate change and species invasion in
meadows of the LTB will consist of spatially explicit predictive risk modeling. We focus on a
key species of invasion concern in meadows: cheatgrass (Bromus tectorum). Our analysis uses
two major environmental moisture gradients: the east-to-west “regional” gradient of increasing
precipitation, and the dry-to-wet “local” gradient, both within and among meadows, caused by
their variable topography and hydrology. Our goals are to understand how these gradients and
other factors affect plant invasion in meadows, to predict future impacts, and to suggest
management solutions.
Objective: Develop and apply a spatially explicit predictive risk model of cheatgrass invasion in
the LTB.
While cheatgrass is present in the LTB, it has not yet become abundant in meadow
ecosystems. In an effort to forecast if climate change and disturbance will trigger further
cheatgrass establishment and spread, we will model the environmental factors related to current
cheatgrass distribution and abundance in LTB and adjacent areas. Such a model will then be used
for predicting future spread of cheatgrass in the LTB under climate change and disturbance
scenarios. We will assess three hypotheses:
Predictive Modeling of Cheatgrass Invasion Risk for the Lake Tahoe Basin
H1: Cheatgrass distribution is strongly related to the regional and local moisture gradients,
and cheatgrass is more prevalent and abundant at the drier ends of these gradients,
especially those highly disturbed (e.g., fire, grazing).
H2: Conditions suitable for cheatgrass establishment and spread are already widespread in the
LTB, but the species has not yet reached most of these suitable locales.
H3: The future climate that is forecasted for the Sierra Nevada will expand the suitable
habitat for cheatgrass establishment and spread in the LTB, which will be exacerbated by
increased disturbance.
d. Approach, Methodology, and Geographic Location of Research
Statistical modeling is a powerful technique to synthesize information on the controls of
the distribution and performance of natural organisms. Such models have been successfully
developed for invasive species of many taxa, including plants, pathogens, and animals (e.g.,
Zalba et al. 2000, Peterson and Vieglais 2001, Kolar and Lodge 2002, Meentemeyer et al. 2004).
The Pacific NorthWest Regional Collaboratory created a model for cheatgrass invasion risk in
southeast Idaho (Fig. 2). We will develop an analogous model of the current distribution of
cheatgrass in montane zones of California. We will create a GIS layer containing the point
locations of ~200 occurrences of cheat grass, from the USFS meadow monitoring plots (which
include abundance info as well), and remotely sensed environmental variables, including
latitude, longitude, topographic moisture index, elevation, slope, solar illumination index,
potential and actual evapotranspiration, precipitation and temperature, and disturbance history.
Using both ordination and CART (classification and regression tree) approaches, we will
determine which environmental variables are significant in predicting both the presence and the
abundance of cheatgrass. From the ordination, we will select 40 sites in the Sierra Nevada that
represent the range of environmental conditions found in the LTB. The sites will be visited for a
detailed field survey of environmental characteristics and vegetation. Using random quadrat
sampling, vegetation composition and soil moisture, depth, and texture will be determined using
standard methods. Soil samples will be collected for lab analysis of soil chemistry at UC Davis,
including total N content and organic matter. Meadows will also be assessed for disturbance
history, including time since fire, bank incisement, and grazing. For final model construction, we
will use generalized additive models (GAM; Hastie and Tibshirani 1986) to analyze the
relationships of cheatgrass to explanatory variables across the 40 sites.
The resulting predictive model of cheatgrass occurence will then be used to predict the
hypothetical current distribution of cheatgrass in the LTB. The USFS meadow monitoring plots
will be used to source the vegetation data. If the model predicts more cheatgrass abundance than
is actually observed, then cheatgrass distribution in the LTB is likely primarily dispersal-limited
and meadows may be at high risk for invasion once cheatgrass is introduced. However, if the
climatic or soil conditions of LTB meadows do not predict cheatgrass above the current
abundance, then its distribution in the LTB is primarily niche-limited and the LTB is currently
resistant to cheatgrass invasion (i.e. under current climate and other conditions).
To analyze how the meadow conditions may change to either facilitate or resist
cheatgrass invasion given climate change and disturbance, the resulting model will be run for
each meadow at 5 year increments for 500 years under five general climate scenarios, with and
without disturbance: (1) increased temperature, decreased moisture availability, (2) increased
temperature, decreased moisture, (3) no change in temperature, increased moisture, (4) no
Predictive Modeling of Cheatgrass Invasion Risk for the Lake Tahoe Basin
change in temperature, decreased moisture, (5) increased temperature, no change in moisture.
Exact amounts of increases and decreases are yet to be determined, but will follow general
procedures used in previous California climate change/ecosystem dynamics modeling (e.g.,
EPRI 2003, Lenihan et al. 2003).
Significance
Early detection is the most effective way to reduce the impact of invasive species.
Cheatgrass is one of the most notorious invasive species in North America, causing dramatic and
apparently irreversible degradation of natural communities. Our proposed research will be one of
the first studies to analyze a potentially disastrous invasion before it gets out of control, creating
an opportunity to adjust management practices accordingly. Creating a spatially explicit model
of invasion risk for the LTB will allow managers to predict where invasion will be most likely
given forecasted climate warming, drying, and disturbance. Given the ecological, hydrological,
and social value of the meadows in the LTB, as well as the sensitive species they provide habitat
for, preventing the dramatic impacts of cheatgrass invasion is of utmost importance.
References
Allen, B.H. 1987. Forest and meadow ecosystems in California. Rangelands 9: 125-28.
Brooks, M.L., C.M. D’Antonio, D.M. Richardson, J.M. DiTomaso, J.B. Grace, R.J. Hobbs, J.E.
Keeley, M. Pellant, and D. Pyke. 2004. Effects of invasive alien plants on fire regimes.
Bioscience 54:677-688.
Burcham, L.T. 1970. Ecological significance of alien plants in California grasslands.
Proceedings of the Association of California Geographers 11: 36-39.
Carter, V. 1986. An overview of the hydrologic concerns related to wetlands in the United
States. Canadian Journal of Botany 64: 364-374.
D’Antonio, C.M. and P.M. Vitousek. 1992. Biological invasion by exotic grasses, the grass/fire
cycle, and global change. Annual Review of Ecology and Systematics 23: 63-87.
D’Antonio, C.M., E.L. Berlow, and K.L Haubensak. 2004. Invasive exotic plant species in Sierra
Nevada ecosystems. USDA Forest Service General Technical Report. PSW-GTR-193.
Debinski, D.M., M.E. Jakubauskas, and K. Kindscher. 2000. Montane meadows as indicators of
environmental change. Environmental Monitoring and Assessment 64: 213-225.
EPRI (Electric Power Research Institute). 2003. Global climate change and California: potential
implications for ecosystems, health, and the economy. Report commissioned by the
California Energy Commission. Palo Alto, California, USA.
Flett, M.A. and S.D. Sanders. 1987. Ecology of a Sierra Nevada population of Willow
Flycatchers. Western Birds 18: 37-42.
Graber, D. 1996. Status of terrestrial vertebrates. In Sierra Nevada ecosystem project: final
report to congress, Volume 2, Assessments and scientific basis for management options,
Centers for Water and Wildland Resources, University of California, Davis,
California.Grabherr, G., M. Gottfried, and H. Pauli. 1994. Climate effects on mountain
plants. Nature 369: 448.
Hagberg, T. 1995. Relationships between hydrology, vegetation and gullies in montane meadows
of the Sierra Nevada. Master’s thesis. Humboldt State University, Arcata.
Hamlet A.F., P.W. Mote , M.P. Clark, and D.P. Lettnmaier. 2005. Effects of temperature and
precipitation variability on snowpack trends in the western U.S. Journal of Climate 18:
4545–4561.
Predictive Modeling of Cheatgrass Invasion Risk for the Lake Tahoe Basin
Harris, G.A. 1967. Some competitive relationships between Agropyron spicatum and Bromus
tectorum. Ecological Monographs 37: 89–111.
Harris, J.H., S.D. Sanders, and M.A. Flett. 1987. Willow Flycatcher surveys in the Sierra
Nevada. Western Birds 18: 27-36.
Hastie, T. and R. Tibshirani. 1986. Generalized additive models. Statistical Science 1: 297-310.
Hughes, J.E. 1934. Erosion control progress report. Milford, CA: U.S. Forest Service, Plumas
National Forest, Milford Ranger District.
Hunter, R. 1991. Bromus invasion on the Nevada test site: Present status of B. rubens and B.
tectorum with notes on their relationship to disturbance and altitude. Great Basin
Naturalist 51: 176–82.
Johnston, C.A. 1991. Sediment and nutrient retention by freshwater wetlands. Critical Reviews
of Environmental Control 21: 491-565.
Johnston, C.A. 1993. Material fluxes across wetland ecotones in northern landscapes. Ecological
Applications 3: 424-40.
Kattelmann, R., and Embury, M. 1996. Riparian areas and wetlands. In Sierra Nevada ecosystem
project: final report to congress, Volume 3, Assessments, commissioned reports, and
background information, Centers for Water and Wildland Resources, University of
California, Davis, California.
Keeley, J.E. 2006. Fire management impacts on invasive plant species in the western United
States. Conservation Biology 20: 375-384.
Kolar, C.S. and D.M. Lodge. 2002. Ecological predictions and risk assessment for alien fishes in
North America. Science 298: 1233 - 1236.
Krzysik, A.J. 1990. Biodiversity in riparian communities and watershed management. In
Watershed planning and analysis in action, edited by R.E. Riggins, E.B. Jones, R. Singh
and P.A. Rechard, 533-48. American Society of Civil Engineers, New York.
Lenihan, J.M., R. Drapek, D. Bachelet and R.P. Neilson. 2003. Climate change effects on
vegetation distribution, carbon, and fire in California. Ecological Applications 13: 16671681.
MacDonald, I.A.W., D.M. Graber, S. DeBenedetti, R.H. Groves, and R.R. Fuentes. 1988.
Introduced species in nature reserves in Mediterranean-type climatic regions of the world.
Biological Conservation 44:37–66.
MacDonald, I.A.W., L.L. Loope, M.B. Usher, and O. Hamann. 1989. Wildlife conservation and
the invasion of nature by introduced species: A global perspective. In Biological
invasions: A global perspective, edited by J.A. Drake, H.A. Mooney, F. DiCastri, R.H.
Groves, F.J. Kruger, M. Rejmanek, and M. Williams, 215–56. John Wiley, New York.
Manley, P.N., W.J. Zielinski, C.M. Stuart, J.J. Keane, A.J. Lind, C. Brown, B.L. Plymale, and
C.O. Napper. 2000. Monitoring ecosystems in the Sierra Nevada: the conceptual model
foundation. Journal of Environmental Monitoring and Assessment 64: 139–152.
Mann, M.E., R.S. Bradley, and M.K. Hughes. 1999. Northern hemisphere temperatures during
the past millennium: Inferences, uncertainties, and limitations. Geophysical Research
Letters 26: 759–762.
Mas, J.F. 1999. Monitoring land-cover changes: a comparison of change detection techniques.
International Journal of Remote Sensing 20: 139-152.
McCarty, J.P. 2001. Ecological consequences of recent climate change. Conservation Biology
15: 320–331.
Predictive Modeling of Cheatgrass Invasion Risk for the Lake Tahoe Basin
Meentemeyer R.K., D. Rizzo, W. Mark, and E. Lotz. 2004. Mapping the risk of establishment
and spread of sudden oak death in California. Forest Ecology and Management 200: 195214.
Menke, J.W., C. Davis, and P. Beesley. 1996. Public rangeland / livestock grazing assessment. In
Sierra Nevada ecosystem project: final report to congress, Volume 3, Assessments,
commissioned reports, and background information, Centers for Water and Wildland
Resources, University of California, Davis, California.
Millar, C.I., H.F. Diaz, D.R. Cayan, M.D. Dettinger, D.B. Fagre, L.J. Graumlich, G. Greenwood,
M.K. Hughes, D.L. Peterson, F.L. Powell, K.T. Redmond, N.L. Stephenson, T.W.
Swetnam, and C.Woodhouse. 2006. Mapping New Terrain: Climate change and
America's West. USDA Miscellaneous Publication. Misc-PSW-77.
National Oceanic and Atmospheric Administration (NOAA). 2007. NOAA reports 2006 warmest
year on record for U.S. General Warming Trend, El Niño Contribute to Milder Winter
Temps. NOAA news release: http://www.publicaffairs.noaa.gov/releases2007
Ohmart, R.D. 1994. The effects of human-induced changes on the avifauna of western riparian
habitats. A century of avifaunal change in western North America, edited by J. R. Jehl, Jr.
and N.K. Johnson, 273-85. Studies in Avian Biology No. 15.
Peterson, A.T., D.A. Vieglais. 2001. Predicting species invasions using ecological niche
modeling: new approaches from bioinformatics. BioScience 51: 363–371.
Ratliff, R.D. 1985. Meadows in the Sierra Nevada of California: state of knowledge. General
Technical Report PSW-84. Berkeley: U.S. Forest Service, Pacific Southwest Forest and
Range Experiment Station.
Schwartz, M.W., D.J. Porter, J.M. Randall, and K.E. Lyons. 1996. Impact of non-indigenous
plants. In Sierra Nevada ecosystem project: final report to congress, Volume 2,
Assessments and scientific basis for management options, Centers for Water and
Wildland Resources, University of California, Davis, California.
Turner, M.G., S.M. Pearson, P. Bolstad, and D.N. Wear. 2003. Effects of land-cover change on
spatial pattern of forest communities the Southern Appalachian Mountains (USA).
Landscape Ecology 18: 449–464.
TRPA. 2002. Final draft Threshold Evaluation Report. Tahoe Regional Planning Agency,
Zephyr Cove, NV.
USFS. 2004. Sierra Nevada Forest Plan Amendment. Final supplemental Environmental Impact
Decision. Record of Decision. Publication R5-MB-046. USDA-Forest Service, Pacific
Southwest Region, Vallejo, CA.
Wagoner, L. 1886. Report on forests of the counties of Amador, Calaveras, Tuolumne, and
Mariposa. In First biennial report of the California State Board of Forestry for the years
1885-1886, 39-44. Sacramento: State Board of Forestry.
Walther, G.-R., E. Post, P. Convey, A. Menze, C. Parmesan, T.J.C. Beebee, J. Fromentin, O.
Hoegh-Guldberg, and F. Bairlein. 2002. Ecological responses to recent climate change.
Nature 416: 389-395.
Wood, S.H. 1975. Holocene stratigraphy and chronology of mountain meadows, Sierra Nevada,
California. Ph.D. Dissertation, California Institute of Technology, Pasadena, California.
Zalba, S.M., M.I. Sonaglioni, C.A. Compagnoni, and C.J. Belenguer. 2000. Using a habitat
model to assess the risk of invasion by an exotic plant. Biological Conservation 93: 203208.
Predictive Modeling of Cheatgrass Invasion Risk for the Lake Tahoe Basin
e. Strategy for Engaging with Managers
We will collaborate and maintain communications with the US Forest Service throughout
the study period. One of the proposal Co-PIs is the Forest Service Region 5 Regional Ecologist
(Safford), and is also the current acting IBET Province Ecologist, i.e., this proposal originates
from the management side of the Forest Service (National Forest System). Safford lives at Lake
Tahoe during the field season and works out of the LTBMU supervisor’s office. Opportunities
for engagement with LTBMU staff are many. Various LTBMU fire, vegetation management,
and resource staff have seen our study sites and are familiar with our proposed project, and there
is strong support for this work within the LTBMU. We intend to continue this intimate working
relationship with the LTBMU. The products of our work will be of direct management interest.
Management input will be vital to both parameterizing the predictive model during model
development and interpreting model predictive output. Through the workshop, managers will be
directly engaged in using the model as a tool to plan future activities. We will also generate a
technical report summarizing lessons learned and providing management recommendations.
f. Deliverables/Products
Spatially and temporally explicit invasion risk model for cheatgrass, including GIS layers and
maps of cheatgrass invasion.
Technical report on management guidelines for controlling cheatgrass.
Development of manuscript for submission to peer-reviewed journal
Workshop with LTB land managers (USFS, TRPA, Washoe Tribe)
g. Schedule of Events/Reporting and Deliverables
Invoicing is handled through financial department of UC Davis.
June 2008-Aug 2008
Create GIS model, run ordination analysis, and select 40 cheatgrass sites for visiting in summer.
August-October 2008
Survey 40 cheatgrass sites in Sierra Nevada, collect field environmental data and soil samples.
September 1, 2008: Quarterly report
October 2008
Analyze soils data.
October 2008 – April 2009
Develop predictive model of cheatgrass risk for the LTB.
December 1, 2008: Quarterly report.
Predictive Modeling of Cheatgrass Invasion Risk for the Lake Tahoe Basin
March 1, 2009: Quarterly report.
May 2009
Write USFS technical report.
June 1, 2009: Quarterly report.
October 2009
Submission of manuscript to scienctific journal
November 2009
Hold workshop.
December 1, 2009: Quarterly report.
III. Figures
-4.5
4.5
Figure 1: Number of days change in timing of peak snowpeak since 1951. (from Hamlet et al. 2005)
Figure 2: Predictive model of cheatgrass risk in southeast Idaho.
Collaboratory, www.pnwrc.org)
(from Pacific NorthWest Regional