Soil Warming and Nitrogen Deposition in a Northeastern Forest
Ecosystems worldwide are faced with climate change. In the northeastern United States, climate change is coupled with nitrogen deposition from air pollution. The objective of this study is to determine how soil warming and nitrogen deposition influence species richness, diversity, and abundance of vegetation in a northeastern forest. Our study site is the chronic Soil Warming and Nitrogen Fertilization experiment at the Harvard Forest Long Term Ecological Research site. The experiment has four treatments with 6 replicates per treatment in a completely randomized block design: control, heated, nitrogen addition, heated plus nitrogen addition. In the heated plots, we warm the soil 5?C above ambient temperature using buried warming cables. In the nitrogen addition plots, we add monthly amounts of NH4NO3 equivalent to a rate of 5 g N m-2 y-1. The data consists of one year of pre-treatment data in 2006 and two years of post-treatment data in 2007 and 2008. Each year, we count the number of stems for each plant species in every plot. There are no significant differences for plant species richness or diversity between treatments. Monotropa uniflora (Indian Pipe) is more abundant in heated plots, though this difference is not statistically significant. Mycoheterotrophs, such as M. uniflora, have unique life histories by which they acquire nutrients by parasitizing fungi. The increase in M. uniflora in the heated plots may coincide with an increase in the abundance of its mycorrhizal host fungi. Our results suggest that after two years of soil warming and nitrogen addition, there may be differences in the relative abundances of particular plant species with unique life histories although overall species richness and diversity remain unchanged.