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Harvard Forest Symposium Abstract 2007
- Title: Impacts of the hemlock woolly adelgid and atmospheric nitrogen deposition on forest nitrogen retention
- Primary Author: Pamela Templer (Boston University)
- Additional Authors: Heidi Lux (Harvard Forest); David Orwig (Harvard Forest)
- Abstract:
After several decades of research on forest nitrogen (N) cycling and the effects of atmospheric N deposition, there is still some uncertainty about the factors that regulate N retention and loss in forest ecosystems. For example, the hemlock woolly adelgid (Adelges tsugae), an introduced aphid-like insect from Asia, threatens hemlock (Tsuga canadensis) stands throughout the northeastern United States. This insect is responsible for up to 95% tree mortality in some forest stands of southern New England. Previous research has shown that the presence of the hemlock wooly adelgid can lead to a reduction in forest canopy cover and increased N concentrations in the soil beneath these canopies. However, it is not known whether the hemlock wooly adelgid leads to changes in forest ecosystem N retention and loss.
The purposes of this project are to measure rates of N inputs and outputs from the forest floor in intact hemlock stands, stands where the trees have been girdled and stands that have been experimentally harvested to mimic the effect of the wooly adelgid on hemlock mortality. We are measuring the isotopic signatures of incoming nitrate, as well as N that is leached out of these stands, to determine whether or not these forests have become N saturated. We have also collected soils to measure total soil microbial biomass. We expect rates of N losses and saturation to be greater in those plots without live trees, compared to plots with intact hemlock stands, due to lack of tree uptake of N. This work is being conducted at the Arnold Arboretum in Boston, MA (urban site) and Harvard Forest in Petersham, MA (rural site). This research is part of a larger project examining the combined effects of N deposition and shifts in forest tree species composition on forest nutrient cycling. - Research Category:
