SPATIAL GRADIENTS AND PATCH STRUCTURE ON 2 PUERTO-RICAN LANDSLIDES

We measured spatial variation of important abiotic and biotic factors inflencing landslide regeneration, contrasted variation among transects and microhabitats within a landslide with variation between two landslides, and tested for spatial gradients and patches in those factors. In addition, we performed multiple regression, principal components analysis, and canonical correspondense analysis to identify those factors important in defining patch structure and to investigate their ability to predict the current vegetative structure. We found that total daily photosynthetic photon flux density was 50 times greater in the landslide compared to the surrounding forest, but similar between landslides. The red:far red ratio was homogenous in the open areas of the landslides, but in areas covered by vegetation it was similar to those ratios found in the forest border. The soil had average extractable phosphorus of 0.108 g/m(2) to 9 cm depth. Nitrogen was .10 percent of average soil mass, carbon was 1.83 percent of average soil mass, and there was a 69 percent average moisture content. Seed rain averaged 31 seeds per trap with the seed pool showing an average of two seedlings per sample. Vesicular-arbuscular mycorrhizal fungi covered 7 percent of the average length of roots sampled, and the vegetation (dominated by species Cyathea arborea, Cecropia schreberiana, Miconia spp., and Nepsera acuatica) had two structural levels on average. For these factors, the strongest gradient was from the forest into the landslides from the side rather than from she top of the landslide to the bottom or between landslides. Evidence of distinct patches was found where patch structure was defined by levels of light, seed pool, fungi, vegetation, soil N, and soil C. In addition, light, the key abiotic factor, showed very significant negative correlations with the key biotic factors of mycorrhizal fungi and vegetation, implying causal relationships.