Document: RIC-3-69-3

Effects of treefalls and topography on species composition and diversity at different spatial scales in a NW Argentina neotropical montane forest.

RICARDO GRAU, H.*

University of Colorado, Boulder, CO, 80309, USA 1

Abstract:
I describe tree species composition (5 cm DBH), Slope, Aspect, and treefall regime (using dendroecological techniques) in six hectares of subtropical montane forest. Time-since-gap showed spatial autocorrelation (Moran's I) at spatial scales 5000 m2. Point pattern analysis (Ripley's K) showed that recent treefalls (1990-1997) are spatially aggregated at 500 m2, and are spatially associated with previous treefalls (1978-1987) at spatial scales of 1500-3000 m2. Ordination scores (NMDS) of plots (species composition) correlated with Slope at 400 m2, and with Aspect at larger spatial scales. At scales of 2500 m2, the factors best correlated with ordination axes were Number of treefalls and Time-since-gap. At the scale of individual gaps ( 500 m2), however, the treefall regime descriptors were not correlated with species composition. Both correlation of species richness with treefall regime and discrimination of light-demanding and shade-tolerant species in the ordination analysis increased abruptly at scales 2000 m2. At scales corresponding to individual gaps, composition and diversity were unrelated with treefall regime, but at the scale of aggregations of several treefalls, treefall regime was a good predictor of species richness and composition of regeneration groups. This can be attributed to the fact that treefall aggregations increase the probability of new treefalls being colonized by light-demanding species. The results emphasize the importance of scale in interpreting the relationship between canopy disturbances and forest composition and diversity.

Keywords: diversity, treefall gaps, subtropical montane forest, Yungas, Argentina, spatial analysis, forest dynamics

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This abstract is being presented at: 11:15 AM in session:
Oral Session #42: Disturbance Ecology: Effects of Storms.