The effects of thinning and soil disturbance on enzyme activities under pitch pine soil in New Jersey Pinelands

a b s t r a c t Disturbance is an important factor in changing ecological processes. Forested ecosystems undergo natural disturbances of fire and windthrow and disturbances involved in management (thinning, harvesting, control burning). Using the New Jersey pine barrens as model system for eastern US mixed forests, we have observed that under conditions of repeated physical soil disruption or control burning, the pine barrens forest understory can change from ericaceous to graminoid species dominance through suppression of the ericaceous plants. In order to predict changes in soil properties and assess the potential to maintain this alternate herbaceous layer community, replicate manipulation plots were established the Franklin Parker Preserve in the New Jersey pine barrens. The manipulations consisted of: intact forest controls (CONT), canopy tree thinning (THIN) and canopy tree thinning plus ercicaceous stem removal and soil tilling (THIN & PLOW). The manipulations were designed to increase sunlight penetration to the forest floor and to encourage graminoid plant species establishment. Soil active carbon, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN), six hydrolytic enzyme activities and two oxidative enzyme activities under three different treatments were measured. In the 0-10 cm soil depth, we observed that protease and arylsulfatase activity showed a significant decrease in the THIN and THIN & PLOW treatments compared to CONT, the activities of cellulase and phenol oxidase were significantly lower in THIN than CONT and THIN & PLOW, whereas the trend of peroxidase activity was opposite. There were no significant differences between treatments for glucosaminase, glucosidase and acid phosphatase activities. For the 10-20 cm soil depth only acid phosphatase and phenol oxidase activity significantly differed between treatments. We found that all enzyme activities except for peroxidase were significantly lower in the 10-20 cm soil horizon than in the 0-10 cm; peroxidase activity was significantly higher in the lower soil horizon. We demonstrated the activities of cellulase, phenoloxidase, arylsulfatase and protease were significantly and positively related to active C, but peroxidase activity was negatively correlated. Less expected is that only phenol oxidase was related to soil MBC, whereas the correlations between peroxidase, phenol oxidase, arysulfatase, protease activities and soil MBN were obvious. By understanding the relationships between microbial activity (enzyme production) and disturbance, we can determine the beneficial effects of many management practices on the potential nutrient availability for subsequent tree growth, since these enzymes are key to nutrient mineralization and carbon dynamics in soil.