Effects of above- and belowground partial harvest disturbance on growth and water status of residual sugar maple.

Partial forest harvesting is known to modify both above- and belowground resource availability and may result in direct and indirect stress to the residual trees as a result of machinery traffic and sudden changes in irradiance. We studied sugar maple (Acer saccharum Marsh.) trees in stands that had undergone a selection harvest 11 years before sampling to verify whether sudden increases in light availability and soil disturbance caused by machinery influence growth rates and lead to water stress. We selected trees that had experienced either no disturbance from partial harvest, soil disturbance only, sudden increases in light availability only or both disturbances. We analyzed stem radial growth rates and stable carbon isotope composition (delta(13)C) of stem wood with an annual resolution from 10 years before partial harvest until 10 years after partial harvest. Disturbances from partial harvest did not negatively affect growth rates or tree water status. Although trees that experienced increased light availability had higher (less negative) delta(13)C after harvest (indicating increased water-use efficiency), they also had higher growth rates, suggesting that they experienced no pronounced water stress. Trees subjected to soil disturbance showed no sign of water stress. These results may partly be associated with favorable growth conditions (abundant precipitation and mild temperature) in the years following harvest and could differ from results that would be observed under more severe climatic conditions.