Global Change

Project Title: Interactions of Climate Change and Other Environmental Factors With Invasive Plant Infestation in the Arid West

Principal Investigator: Jonathan M. Friedman, Fort Collins Science Center

Co-Investigators: Jayne Belnap, Southwest Biological Science Center; Kathryn Thomas, Southwest Biological Science Center

Introduction

Invasive, non-native plants dominate terrestrial and riparian landscapes in the arid western United States and are an increasingly important challenge for land and water managers. Abundance of invasive species and their native competitors is influenced both by coarse-scale factors like climate and fine-scale factors like soil chemistry, grazing, and flood timing. Understanding the interplay of these factors is essential for predicting the effects of land use and global change on invasive plant distributions. We are addressing three groups of invasive species: annual grasses, forbs, and riparian trees. We are using recently collected databases documenting the distribution of these species to develop models predicting the likelihood of invasion at any site as a function of both climatic and non-climatic factors. In addition, we are carrying out physiological experiments to identify critical biological mechanisms controlling susceptibility to invasion. Our results will provide land and water managers with general and site-specific information on site susceptibility to invasion and factors controlling abundance of invasive species. This information is essential for developing and prioritizing realistic cost-effective strategies for dealing with invasive species in a changing climate.

Annual grasses now cover much of the West, with cheat grass (Bromus tectorum) alone dominating at least 40 million hectares. In deserts, non-native annual grasses are among the most threatening biological invaders primarily because they increase fire frequencies, thus altering nutrient dynamics and native communities. In addition, they have direct negative affects on native ecosystems that have resulted in the impoverishment of US rangelands. Annual grasses have high nutrient requirements, and in the low fertility soils of deserts, are likely restricted to a subset of soils with high nutrient availability. Soil temperature and moisture can influence nutrient availability, especially nutrients bound by calcium carbonates, as carbonates can dissolve in winter. Thus, the distribution of annual grasses is likely to change as temperature and precipitation regimes change. In addition, the deposition of anthropogenic nitrogen is increasing in deserts and will also likely alter the distribution of annual grasses as well.

The invasive forb component of this project is developing spatial models of the predicted distribution for 20 invasive forbs in the southwest. Predictive model development explores the premise that invasive forbs can act as generalists constrained only by climate or as specialists limited not only by climate but also by other factors including native species composition, soil type, and disturbance. The second premise of the study is that landscapes that have been predicted to be vulnerable to native vegetation change as a result of global climate change will also be susceptible to colonization by invasive species. MODIS satellite imagery is being explored as a means to identify vulnerable landscapes that may already be experiencing change and infestation by invasive species.

In western North America, riparian cottonwood and other native species are being replaced by invasive non-native trees. For example, the invasive tamarisk (Tamarix ramosissima and T. chinensis), is now the dominant riparian woody species in the Southwestern United States. These invasions have been associated with loss of plant diversity, degradation of habitat for vertebrate animals, decreased channel conveyance, and increased water loss from evapotranspiration. We are relating abundance of 46 widespread native and non-native riparian woody plants to a suite of environmental factors at 476 sites in 17 western states. We are also comparing cold hardiness in the native plains cottonwood (Populus deltoides subsp. monilifera) and the introduced tamarisk in a common garden of trees collected across the Great Plains. Finally, we are performing DNA micro-satellite analysis of cottonwood and tamarisk to determine whether regional variation in cold hardiness is related to genetic isolation.

Contact Information

Jonathan M. Friedman
Fort Collins Science Center
3215 Marine Street, Suite E-127
Boulder, CO 80303-1066
Phone: 303-541-3017
Fax: 303-447-2505
E-mail: jonathan_friedman@usgs.gov