The variety of soil microsites created by tree falls

Abstract

The uprooting of forest trees leads to the formation of microsites on the forest floor, contributing to fine-scale heterogeneity in soil properties. We found the types of microsites formed depended on the way the tree fall occurred. Tree falls were classified as either hinge or rotational types. Hinge tree falls formed when the root mat of a tree and the surrounding soil were uplifted vertically, leaving an adjacent pit in the soil. Hinge tree falls varied as to thickness of the root mat and angle of uplift. Rotational tree falls were usually a result of a ball and socket motion of the root mat and soil, which positioned the tree bole over the newly created pit. The tree falls disrupted and redistributed surface soil organic matter and subsoil. In rotational tree falls, the surface material remained intact, covering some of the pit and the adjacent side of the mound. In hinge tree falls, the surface organic matter was deposited on the throw side of the mound, leaving subsoil on the other side and in the pit. With time, however, hinge-type pits accumulated litter and eventually had more organic matter than mounds. Old mounds from both hinge and rotational tree falls had lower concentrations of calcium and magnesium, lower pH, and less moisture than pits. The tree fall process creates long-term soil patterns and maintains microsite heterogeneity in forest communities.