INTERACTIVE INFLUENCES OF SILVICULTURAL MANAGEMENT AND SOIL CHEMISTRYUPON SOIL MICROBIAL ABUNDANCE AND NITROGEN MINERALIZATION

The purpose of this study was to determine whether soil acidification, a widespread. chronic mode of disturbance and forest thinning, a site specific acute disturbance, produced interactive effects capable of p roducing changes in more general ecosystem properties and processes. T wo forested sites in the Daniel Boone National Forest, KY which were s imilar in history, management, and parent material but which differed in the degree of soil acidity were selected for study. In each forest site we sampled two plots that were experimentally thinned in the 1960 's and two adjacent unmanaged plots for soil chemical characteristics, microbial abundances, N mineralization and nitrification. There were significant differences between forest sites: and significant effects of management for all soil chemical parameters, fungal biomass, N mine ralization (site only) and nitrification. Soils from managed plots wer e generally higher in pH, nutrient availability and nitrification rate s. There were significant interactions between site and management for NO3, pH, Ca, Ca:Al ratio, and nitrification resulting from the greate r magnitude of the management effect at the less acidified site. Addit ionally, there were interactive effects of site and management in orga nic C, NH4 and fungal hyphal length because plots at the two sites sho wed dissimilar effects of management. Modeling using path analysis det ermined that N mineralization was most strongly predicted by combinati ons of organic C. Al, Ca:Al ratio, and fungal:bacterial ratio, while i norganic N availability and Ca:Al ratio were the main factors for nitr ification. Fungal hyphal length was most strongly predicted by Al and pH; in contrast, path analysis failed to produce a model for bacterial abundance. These results suggest (1) that acute and chronic modes of disturbance have the potential to interact in a significant and ecolog ically meaningful manner and (2) that research to assess forest health should be based on key ecosystem processes, such as N mineralization and nitrification. (C) 1998 Elsevier Science B.V.