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Climate Change and White-Tailed Deer Impacts on the Function of Northern Temperate Forest

Samantha McClenahan, Vassar College ’13

Professor Dr. Lynn Christenson 

Our forests are currently under multiple natural and anthropogenic stresses including climate change and high densities of both native (e.g. white-tailed deer) and non-native (e.g. gypsy moth) species.  These stresses impact the structure and function of our hardwood forests.  To test the effects of climate change and white-tailed deer overpopulation on the function of a Northern temperate forest, I used an ongoing, 5 year deer exclusion study site at Vassar College combined with a laboratory soil-invertebrate freeze experiment. The field treatment provided background data for structural and functional site conditions in the presence or absence of deer.  The soil-invertebrate freeze experiment evaluated the effects of invertebrate diversity and nitrogen cycling on soils extracted from the 5 year sites after undergoing an intense freeze cycle of 10 days at -20°C.  The field treatment differed in soil pH, soil moisture, soil organic matter, NO3--N, and nitrification rates between the fenced and unfenced areas indicating a possible indirect effect of deer on soil properties. Additionally, there was a difference in soil pH, NH4+-N/NO3--N, and mineralization/nitrification rates between the Oak and Orchard site which could be due to leaf litter quality. The invertebrate communities, however, were not significantly different between sites or exclosures. Freezing negatively affected invertebrate survival in terms of both richness and abundance regardless of locational differences. Within the freeze treatment, there were also significantly lower invertebrate abundance and richness recovered from the fenced areas. Functionally, removal of invertebrates raised initial nitrogen stocks, while freezing with invertebrates resulted in higher mineralization rates.  The experiments revealed that deer presence is potentially indirectly altering soil properties and nitrogen cycling; future soil freezing events may directly alter invertebrate abundance and richness; and soil freezing events may increase mineralization rates through reduced survival rates of invertebrate populations and specific invertebrate species.