Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Wildland Resources

Committee Chair(s)

Peter B. Adler


Peter B. Adler


Thomas C. Edwards


Nancy J. Huntly


David N. Koons


Thomas A. Monaco


Rapid climate change presents humanity with a number of big problems. Foremost among these is the sad fact that the climate we will pass on to our children will likely be nothing like the climate that we inherited from our parents. Ecologists have collected solid evidence that climate change has already begun to affect the living things around us and the ecosystems humans depend on. Unfortunately, predicting the future effects of climate change on life on earth is not easy. We focused on three research goals as part of an effort to improve our ability to predict how plants and animals will be affected by climate change.

First, we studied the effects of yearly variation in temperature on an important shrub from the western US: sagebrush. We found that sagebrush abundance increased in cold places after relatively hot years, but decreased in warm places after hot years. In contrast, we did not see the same pattern for precipitation—sagebrush actually decreased in dry places in response to wet years and increased in wet places in response to wet years. This pattern hints that sagebrush is limited more by temperature at the edges of its range than by precipitation.

Second, we studied how the growth and survival of thousands of individual grasses and shrubs varied from year to year at field site in eastern Idaho. Using this information, we developed a model that related plant growth and survival in each year to the amount of rain and snow that year. Next we set up an experiment to directly control the amount of water available to plants. We ran the experiment for five years and then we used the plant growth and survival model we built from the observational data to predict how each species would respond in the experiment. We found that we could predict two out of the four species responses to the experiment. Overall we found that the direction that species responded to the experimental treatments was generally the same as how they responded to natural precipitation.

Third, we used mathematical models to examine the indirect effects of climate change on competing plants. Climate change can affect a species directly by decreasing or increasing its population growth rate. But climate change can also affect its competitors. If competition is strong then it is possible that an environmental change with positive direct effects on the first species, but that also causes positive direct effects on its competitor, can actually be a net negative for the first species. This complicated back and forth among competitors can make predicting the effects of climate change difficult. Fortunately, we show that some mathematical properties of species competition can help predict when indirect effects are large. One benefit of this work will be helping researchers figure out when the response of species to climate change can be safely predicted from single species population models rather than complicated multi-species models.