Twenty-Five Year Response of Non-Crop Trees to Partial Release During Precommercial Crop Tree Management

by

Jeffrey S. Ward

Chief Scientist, Department of Forestry and Horticulture, 123 Huntington Street, The Connecticut Agricultural Experiment Station, New Haven, CT 06504

Abstract – An underappreciated component of precommerical crop tree release (PCT), indeed any crop tree release, in the inevitable partial release of trees other than selected crop trees (i.e., non-crop trees). While the response of released crop trees is increasing understood, few studies have examined the response of the 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. Each area had nine 26 ft x 26 ft plots for each of two treatments: PCT and unmanaged controls. Sixty-three crop trees per acre were released by cutting all stems that had crowns adjacent to the crop trees. This resulted in the inadvertent partial release of 380 upper canopy, non-crop trees per acre. Diameters and crown classes of all stems (DBH > 0.8 inches) were measured annually (n=4,828). For those stems in upper canopy at canopy closure, partial release did not increase the proportion that remained in the upper canopy, excepting a small increase for red maple. Partial release increased proportion of both intermediate and suppressed oaks that ascended into the upper canopy. Partial release reduced mortality of both oaks and birches in the intermediate and suppressed crown classes. Partial release had no (oak) or minimal (<0.4 inch for red maple, birch) effect on 25-year diameter growth. Precommercial crop tree release can be used to increase survival and growth of quality oak saplings without deleteriously impacting stand diversity and growth.