Leaf litter effect on plant species composition of deciduous forest treefall pits

Abstract

In deciduous forests of central New York, treefall pits have rich soil, but low plant species richness. To test whether leaf litter limited species distributions, we removed litter in 10 randomly chosen pits in 1983 and compared them with controls over 3 years. Wire cages prevented litter accumulation in experimental plots. By year 1 (1984) litterless pits were significantly warmer and less moist than controls. From years 1 to 3 the average Coefficient of Community (CC) index between experimental mounds and pits increased 10-fold. No changes occurred in controls. Species composition of experimental pits became different from the controls. Species richness increased in litterless pits, with no change in other plots. Experimental and control mounds were similar in species composition all years, indicating no effect of the cage. Species responses to litter removal included: (i) enhanced germination, (ii) establishment, and (or) (iii) no change. All herbs showing increased germination or establishment were species previously restricted to mounds. The species that did not change were those already inhabiting pits. No species declined after litter removal. Litter removal in pits allowed several species to expand their distributions from mounds into litterless pits, without affecting existing pit species. The spatial heterogeneity accentuated by leaf litter accumulation does not facilitate coexistence of species in the forest community, but only limits species population sizes and spatial distributions.