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Title: The influence of historical climate on the population dynamics of three dominant sagebrush steppe plants.

item DALGLEISH, HARMONY - Utah State University
item Moffet, Corey
item KOONS, DAVID - Utah State University
item HOOTEN, MEVIN - Utah State University
item ALDER, PETER - Utah State University

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2010
Publication Date: 1/10/2011
Citation: Dalgleish, H.J., Moffet, C.A., Koons, D.N., Hooten, M.B., Alder, P.B. 2011. Climate influences the demography of three dominant sagebrush steppe plants. Ecology. 92(1):75-85.

Interpretive Summary: Climate change has the potential to either increase or decrease the size of populations of dominant plants of the sagebrush steppe. Such changes could have dramatic effects on species’ interactions and forage availability for both wild and domestic animals. We combined novel methods with historic datasets from the U.S. Sheep Experiment Station to mathematically model the population growth of three key species (bluebunch wheatgrass, needle-and-thread grass, and three- tipped sagebrush) to determine whether survival of existing plants, growth of existing plants, or recruitment of new individuals had the greatest potential to drive population growth. Using climate data collected over the same period, we also determined the impact of climate on plant survival, growth and recruitment for each species. Our analysis showed that survival and growth were most important for driving population growth in all species and that the timing and type of precipitation (i.e., rain or snow) have a large impact on survival and growth. Our historical analysis illustrates that future work should focus on understanding the interactions among grazing management, plant population dynamics, and winter snowfall and precipitation regimes in order to accurately forecast the effects of future climate change on the sagebrush steppe ecosystem. Other scientists can use these analytical methods and results to inform their work on the effects of climate change on plant species in other environments. Land managers within the sagebrush steppe can use the results of this study to guide management decisions aimed at mitigating the likely effects of climate change.

Technical Abstract: Climate change could alter the population growth of dominant species, leading to profound effects on community structure and ecosystem dynamics. Understanding the links between historical variation in climate and population vital rates (survival, growth, recruitment) is one way to predict the impact of future climate change. Using a unique, long-term dataset from northeast Idaho, we parameterized Integral Projection Models for Pseudoroegnaria spicata, Hesperostipa comata, and Artemisia tripartita to identify the demographic rates and climate variables most important for population growth. We described survival, growth and recruitment as a function of genet size using mixed effect regression models and then regressed climate variables against the random year parameters from the vital rate functions. Within a species, the importance of growth, retrogression, survival and recruitment was dependent upon genet size. Populations increase when the smaller genets grow beyond a size threshold where survival is near 100%, and decrease when genets shrink back to sizes vulnerable to mortality. For the shrub, lower previous year’s precipitation increased survival and population growth. For the bunchgrasses, increased February and March snowfall and winter precipitation increased survival, though February and March snowfall increased population growth more than winter precipitation alone. Future shifts from a snow- to rain-dominated winter precipitation regime could decrease the abundance of perennial grasses relative to shrubs, resulting in decreased forage availability for domestic and wild ungulates. Evaluating the influence of climate variability on the population dynamics of these species requires several years of observations due to the lagged effects of snow and precipitation on survival and growth. Our historical analysis suggests that future work should focus on understanding the interactions among grazing management (which can affect population size structure), winter precipitation regimes and population dynamics in order to forecast the effects of climate change on the structure and function of the sagebrush steppe ecosystem.