PARENT SESSION
Oral Session # 50: Forest Ecology III: Modeling; Nutrient Cycling.
Presiding: L Comas
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 100.

Neighborhood dynamics of nutrient redistribution via litterfall: Implications for population dynamics and ecosystem processes.

Canham, Charles^*,1, Bigelow, Seth^{1, 2}, ¹ Institute of Ecosystem Studies, Millbrook, NY² U.S. Forest Service - Sierra Nevada Research Center, Davis, CA

ABSTRACT- Our ability to explicitly link models of forest community and ecosystem dynamics has been hampered by a mismatch in the spatial scales typically considered by community and ecosystem ecologists. Most current models of tree population dynamics focus on fine-scale neighborhood interactions, while ecosystem models typically aggregate at a larger, plot scale. When local species effects on ecosystem processes are non-additive, there can be considerable error in using non-spatial models to predict the effects of changes in species abundance. We present a spatially-explicit analysis of redistribution of calcium (Ca), magnesium (Mg), and potassium (K) via litterfall of the dominant tree species in a temperate forest. We used inverse modeling and maximum likelihood methods to fit models of leaf litterfall for individual species. In all of the species, a lognormal distribution was the most parsimonious model of leaf litter distribution around source trees, and there was a strong wind direction effect in 5 of the 6 species. For two of the species, Fagus grandifolia and Quercus rubra, the modal dispersal distances for leaves were 7 and 11 m, respectively, well outside the radius of the crown. Leaf nutrient chemistry varied significantly as a function of both species and soil nutrient availability. Concentrations of Ca and Mg in litter of the 3 tree species that are typically found on more cation-rich soils increased asymptotically as soil concentration increased, while the species typically found on more base-poor soils had consistently low concentrations of Ca and Mg in litter. Given evidence of strong tree species effects on soil nutrient availability in this system, and non-additive effects of mixtures of different species of leaf litter, the results have implications for the competitive interactions between tree species and the development of patchiness in species distribution within stands.

Key words: nutrient redistribution, leaf litterfall, temperate forests