Microsite Variation and Soil Dynamics within Newly Created Treefall Pits and Mounds

Abstract

We studied early soil dynamics, environmental conditions and plant colonization of microsites within 28 recently created treefall pits and mounds in a catastrophic windthrow. Pit and mound sizes were proportional to the size of the fallen trees, and deposition of eroded soil in the center of pits occurred at a decreasing rate over 2 yr. Instability of the substrate contributed to low plant abundance in the pits resulting in lower total plant cover than in the intact soil microsites adjacent to the pits. Larger pits revegetated more slowly than small ones. We recognized four microsites associated with the exhumed roots of each treefall: mound, pit, wall, and intact forest floor (no soil disturbed). Both growth forms and individual species differed in their colonization among microsites, resulting in lower species diversity and total cover on mounds relative to other microsites. Small-seeded, wind-dispersed species colonized the center of pits more readily than species that relied on vegetative spread. Species that are rare in intact forest were common on the disturbed soil of pits and mounds. During two successive years, we documented significant differences among microsites in light, soil moisture, and soil temperature. The species of fallen canopy trees had little influence on the plant community after disturbance, except in the intact soil microsite. We conclude that differential colonization of microsites within forest disturbances occurs at a finer scale than previously recognized and that this facilitates the maintenance of species diversity in the plant community.