Document: SEB-3-34-44

Nitrogen deposition influences regeneration of coniferous and broad-leaved tree species in contrasting stand types.

CATOVSKY, S.* and F.A.BAZZAZ

Harvard University, Cambridge, MA 02138 USA ¹

Abstract:
Despite increasing levels of nitrogen deposition at temperate latitudes, no studies to date have considered how this perturbation will alter temperate forest species composition. Nitrogen deposition may affect mixed forests in particular due to differences between evergreen coniferous and deciduous broad-leaved species. We investigated regeneration responses of both types of species to nitrogen deposition, and compared these responses across coniferous and broad-leaved stand types. We addressed nitrogen effects on (1) understory seedling bank development, and (2) seedling responses to canopy gap formation. We applied nitrogen (0, 2.5, 7.5 g m^-2 yr^-1) both to replicated understory plots in three conifer and three broad-leaved dominated stands, and to seedlings growing in high light conditions in soil from each stand. We examined seedling survival and growth for three coniferous and three broad-leaved species over two years. Nitrogen differentially influenced species' regeneration patterns, although the nature of these effects depended on light environment. In the understory, changes in seedling bank structure were driven primarily by differential seedling survival, with nitrogen decreasing Acer rubrum and Picea rubens abundance, and increasing Betula alleghaniensis abundance. Under gap conditions, nitrogen predominantly increased seedling growth, with early-successional broad-leaved species responding most strongly, and coniferous species remaining relatively unresponsive. Thus, increasing nitrogen deposition will alter the composition of mixed temperate forests, but the exact nature of the change will depend on both current species composition and future patterns of disturbance.

Keywords: nitrogen deposition seedling regeneration

This abstract is being presented at: 3:15 PM in session:
Oral Session #28: Effects of N Deposition in Ecosystems.