Beatty, Susan W.听1
1听University of Colorado, Dept. of Geography
Common fine-scale disturbances in eastern deciduous forests include treefalls, animal burrows, and effects of invasive species such as earthworms. The remnant effect of treefall disturbance is a microtopography of mounds and pits that comprise up to 60% of the forest floor. Mound microsites are substantially different in soil characteristics than adjacent pits, in that mounds are drier, coarser in texture, have little or no A-horizon or leaf litter layer, are more acid, lower in available nutrients, and subject to frost heave. Pits can become small vernal ponds during snow melt or high rainfall events. Plant species richness is four times as great on mounds versus pits. Exotic plant species colonize both mounds and pits, as do natives, however in the face of environmental variation exotics are more likely to become locally extinct, followed by recolonization in subsequent years. Native species show less variation in population size over time. This is due to differential survivorship in microsites in wet versus dry years, but with some individuals surviving and reproducing in at least one microsite. The invasion of exotic earthworms threatens to radically alter the decomposition and erosion rates in deciduous forests, as well as increase leaching loss of nitrates from the soils. Down stream water quality may be threatened as a result.