The effects of man-made and natural disturbance events upon soil microbial biomass, soil fauna, soil nutrient cycling, and litter decomposition in the southern Appalachians.

摘要

Ecosystems of the world today have been greatly affected by both man-made and natural disturbance events. No matter what the origin, disturbances to an ecosystem typically cause changes in ecosystem properties and function. The overall effects of a disturbance event are often dependent upon the severity of the disturbance. By comparing soil properties both before and following disturbance events on Watershed 55 at the Coweeta Hydrologic Laboratory, we were able to examine several soil properties which were likely to be sensitive to disturbances affecting both the vegetation and the soil system. The main objectives of this study were to: (1) quantify the effects of rhododendron removal and hurricane windthrow damage upon soil microbial biomass nematode trophic groups, soil phosphorus levels, N-mineralization, and litter decomposition in pre- versus post-disturbance soils, (2) compare these aforementioned variables between three temperate hardwood forested ecosystems (Coweeta, Harvard Forest, and Hubbard Brook) in order to examine changes in soil nutrient levels under differing conditions of temperature, moisture, and litter quality.; Soil properties were examined for data sets collected 1.5 years pre-disturbance and 2 years post-disturbance. The effects of disturbance events upon the soil system were highly variable in the short term, causing minimal changes in soil temperature, moisture, microbial biomass, nematode abundance, and soil phosphorus pools versus the larger effects measured in decomposition rates, net N-mineralization and nitrification rates. These minimal changes in soil properties were likely due to the low levels of disturbance to the soil system following rhododendron removal and the hurricane windthrow event. In addition, low levels of erosion and high levels of organic matter remaining for two years following the disturbance events have likely maintained these ecosystem processes over the short term.; In a cross site comparison study of Coweeta, Harvard Forest, and Hubbard Brook, the following soil parameters were measured: microbial biomass, nematodes, and soil phosphorus levels. In these studies, both Harvard Forest and Hubbard Brook sustained significantly higher levels of microbial biomass, nematodes, and soil phosphorus than Coweeta. Levels of higher organic matter, root biomass, soil C and N content, and increased grazing pressure from nematodes likely contributed to the elevated productivity throughout the soil system at Harvard Forest and Hubbard Brook. In contrast, factors such as soil temperature, soil moisture and litter quality seemed to have less effect upon the soil properties measured.