Patterns in tropical leaf litter and implications for angiosperm paleobotany

Abstract

One hectare of undisturbed Amazonian forest, containing about 175 species of trees larger than 10 cm diameter at breast height, was studied to determine the relationship between high-richness forest and the autochthonous litter produced by the forest. Litter samples contained up to 52 species, of which one-third represented epiphytes, vines, and lianas.These modern leaf litter studies from southeast Amazonian Peru indicate that reconstructions of ancient high-diversity forests are possible using autochthonous leaf litter deposits. In comparison to temperate litter samples, however, more sampling must be done to recreate fairly simple descriptors of ancient communities such as species richness and heterogeneity. Samples must be large, relatively closely spaced, and maintained as distinct collecting localities to retrieve the maximum amount of data from rich, angiosperm-dominated localities. There are many advantages justifying more intensive collections. For example, biomass contribution of major life-form categories in the source forest is reflected in leaf litter accumulating under tropical forest canopies. Tropical forests, because of their extreme heterogeneity, also can provide the opportunity to reconstruct individual species characteristics from litter signatures. The relative rarity of most species creates distinct leaf shadows from which the canopy breadth and volume of many individuals can be estimated. The principles derived from modern tropical litter studies can be applied to existing fossil collections; however, their power lies with those collections originating from autochthonous assemblages, for which spatial control during collecting has been maintained, and time averaging has been kept to a minimum. These reflections of community structure available from the leaf litter provide a means for paleobiologists to contribute significantly to the study of community evolution and stability.