Vegetation, Biomass, and Nitrogen Pools in a Spruce-Fir Forest of the Great Smoky Mountains National Park

Unlike most forests, Picea rubens-Abies fraseri forests of the Great Smoky Mountains appear to be saturated with nitrogen (N). However, studies of N cycling in these forests have been carried out only in a few small plots. To expand these data to a landscape scale, studies of N dynamics were initiated in 1991 in an unlogged 17.4 ha watershed. An initial phase of these studies, presented here, was the estimation of overstory species composition, biomass, and standing N pools, and their spatial distributions, in that watershed. Picea comprised most live basal area and biomass and showed no obviously unusual mortality or health symptoms. Abies, although formerly abundant, was a minor overstory component, consisting mostly of small individuals at the highest elevations. Most Abies have been killed by an exotic insect pest, Adelges piceae. Biomass of Betula alleghaniensis was high on low-elevation east-facing slopes near streams. Picea contained 71% of the live overstory N, while Abies contained less than 2%. Although Picea foliage comprised only 6% of live biomass, 37% of the total N content was in Picea needles. Overall, some species distributions reflect well-known landscape patterns (e.g., increasing Abies importance with elevation); distributions of other species (e.g., Picea and Betula) reflect smaller-scale topographic and possibly disturbance-oriented patterns. The watershed is large enough to encompass vegetation patterns at several spatial scales, all of which will influence N storage and dynamics.