Silvicultural effects on functional processes of a boreal wetland.

摘要

Wetlands are an important component of commercial forests in boreal regions of the Great Lakes basin. This study was designed to investigate the effects of different silvicultural practices on the functional processes of a forested wetland. The treatments were selected to provide a range of disturbances, they were: whole-tree harvesting (WTH), WTH plus disk trenching, and WTH plus bedding. The treatments were applied in 1988 using a Latin square design, which permitted the assessment of treatment effects and gradient factors within the wetland. An adjoining undisturbed stand was used as a reference. Studies of organic matter decomposition, N-mineralization, soil nutrient and C pools, and water quality were conducted for 16 months following disturbance.; The Cotton Strip Assay showed that organic matter decomposition increased in accordance to the degree of site disturbance. The increase in soil temperature was the factor primarily responsible for the decomposition response. Nitrogen mineralization was studied using four in situ methods: sequential-core, core-ion exchange resin with and without vegetation uptake, and closed-core. Net N-mineralization during the 10 week incubation on the bed treatment exceeded annual estimates from similar undisturbed wetland sites. Nitrogen immobilization was measured on the reference, harvest-only, and trench treatments. There was no difference in estimates of net N mineralization or immobilization among the different methods. Soil nutrient pools were measured on a unit volume basis. The disturbance treatments caused a reduction in soil K and C pools, and the site preparation treatments caused an increase in acidity and Al. Bedding was effective at concentrating soil nutrients in the tree planting line. Analyses of vadose and groundwater samples showed increased concentrations of K, NO{dollar}sb3{dollar}-N, NH{dollar}sb4{dollar}-N, and electrical conductivity as a result of harvesting and site preparation. Nitrate was the dominant form of inorganic N in the water column in the late summer and fall. Position within the wetland affects measurements of organic matter decomposition and water quality, and it must be considered when interpreting results. This boreal wetland was sensitive to disturbance, and long-term monitoring is recommended to evaluate recovery of the wetland and the regeneration response.