Date of Graduation
College of Creative Arts
James B McGraw
Ecological response to recent climate change has been documented for a multitude of species worldwide. Climate models predict further increases in temperature, as much as 8 times the degree of warming that has already occurred. Given observations of species response to contemporary climate change and the unprecedented degree of warming expected over the next century, climate change will no doubt determine future ecosystem composition and affect global species diversity. In order to prevent loss of biodiversity, it is necessary to understand and accurately project species' response to climate, and to identify species that are vulnerable to climate change driven extinctions. In this thesis, I asked the question "How will climate change affect American ginseng (Panax quinquefolius L.) demography?". In addition to mean temperature increase, climate models predict an increase in anomalous weather events, such as late spring frost. In Chapter 2, I examined the effects of the 2007 spring frost on ginseng demography. Frost negatively impacted ginseng survival, growth, and reproduction, and could depress long-term population growth rates. In Chapter 3, I took advantage of a long-term, spatially extensive dataset to examine range-wide variation in demographic response to climate. Results indicated that populations of ginseng are adapted to local temperature regimes, and form population-specific thermal optima. In Chapter 4, I modeled the effect of climate change on ginseng extinction risk using Population Viability Analysis (PVA). Climatic warming increased extinction risk and decreased viability of ginseng populations. Because ginseng populations are adapted to local temperature regimes, a relatively small degree of warming (1°C over a 70 year period) significantly increased extinction risk for all populations throughout ginseng's range. In order to experimentally test for adaptive differentiation of populations with respect to climate, I conducted two reciprocal transplant experiments; one in a controlled growth chamber environment (Chapter 5) and one in a natural setting along an elevational gradient (Chapter 6). Results from Chapter 4 indicated that populations were adaptively differentiated with respect to temperature. However, the expected 'home-site' advantage response of fitness-related traits was rarely observed, indicating that environmental covariates of temperature, such as soil moisture and disease, may be critical to understanding adaptation to temperature. In Chapter 6, confounding environmental factors that varied among transplant gardens precluded accepting or rejecting the hypothesis of local climatic adaptation. In both transplant experiments, warmer climatic conditions negatively affected ginseng reproduction. This research provides compelling evidence that climate change will negatively impact long-term persistence of ginseng and other ecologically similar species.
Souther, Sara, "Demographic response of American ginseng (Panax quinquefolius L.) to climate change" (2011). Graduate Theses, Dissertations, and Problem Reports. 4793.