资源环境科技发展态势分析平台

An underappreciated component of precommerical crop tree release (PCTR) is the inevitable partial release of non-crop trees. While the response of fully released crop trees is increasingly understood, few studies have examined the response of non-crop trees. The effects of precommercial crop tree release at canopy closure on upper canopy persistence, mortality, and diameter growth over 25-years were examined on seven study areas established in Connecticut in 1988. Each area had nine 8 m x 8 m plots for each of two treatments: PCTR and unmanaged controls. The equivalent of 156 crop trees per hectare were completely released by cutting all stems with adjacent crowns. This resulted in the inadvertent partial release on two or more sides of 480 upper canopy, non-crop trees per hectare. Diameters and crown classes of all stems (DBH > 2 cm) were measured annually. For those stems in the upper canopy at when treated, partial release increased the proportion of oaks, but not maples or birches, which persisted in the upper canopy. Partial release increased the proportion of intermediate oaks that ascended into the upper canopy and reduced mortality. Partial release increased 25-year diameter growth of oaks. However, releasing upper canopy, sapling oaks on only one side did not increase upper canopy persistence or diameter growth. PCTR increased the proportion of oaks among the largest 300 trees per hectare twenty-five years after treatment. Where predicted oak densities are below management goals, precommercial crop tree release should be considered as a tool to increase survival and growth of quality oak saplings. (C) 2016 Elsevier B.V. All rights reserved.