Demographic effects of warming, elevated soil nitrogen and thinning on the colonization of a perennial plant
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Global change is causing significant modifications to native plant communities. These effects can be direct through changes in productivity, or indirect through the spread of invading species. Identifying vital traits important for individual species’ response to environmental variation could be useful for making predictions about how entire communities may respond to global change. I studied the effects of factors associated with global change on the demography of an experimentally introduced species, Pityopsis aspera. In a Florida old-field, I investigated how warming, increased soil nitrogen and thinning of the extant plant community affected survival, growth and reproduction of P. aspera using a life table response experiment. The estimated population growth rate (λ) of P. aspera was reduced by nitrogen addition, as a result of decreased fecundity. However, λ increased in response to the warming treatment, as a result of increased fecundity. In the presence of thinning, both warming and nitrogen served to increase λ as a result of an increase in the growth of young individuals. This experiment illustrates how different vital rates contribute to the population level responses of an experimentally introduced plant to warming, and nitrogen deposition. Results also show how these demographic responses may occur via indirect effects through established species. This work highlights the importance of studying interactions among temperature, soil nitrogen and demography across the entire life cycle in order to capture the complex and, often, non-additive relationships mediating global change effects.
KeywordsClimate change Indirect effects Invasion LTRE Pityopsis aspera Range shift
Countless volunteers helped in the field under less than ideal conditions, and I cannot thank them enough. I also appreciate the help of R. Weidner for all aspects of greenhouse chamber design and construction, and my dissertation committee for guidance: T. E. Miller, A. A. Winn, N. Underwood, A. Mast, J. Chanton, and J. Hellmann. Portions of this research were funded by Florida State University.
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