Intensity of precommercial crop-tree release increases diameter and crown growth in upland hardwoods

In 1988 seven study areas were established in Connecticut to examine the effects of precommercial crop tree release on bole and crown growth. Each study area has 27 8x8 m plots centered on a northern red oak, black oak, or scarlet oak identified as a potential crop-tree (PCT). The 27 plots at each study area were divided into 3 treatments: no cutting, removal of all stems with crowns within 1 m of the crown of a PCT, and removal of all stems with crowns within 1 m of the crowns of a PCT and 2 other potential crop-trees. After cutting, 7191 stems remained. A consequence of crop-tree release is the partial release of trees surrounding crop-trees. The percentage of release of these surrounding trees was assessed in 25% increments. Diameter growth increased with amount of release and crown class. Relative to unreleased trees, 4-yr diameter growth of northern red oak increased by 86%, black/scarlet oak by 65%, red maple by 56%, and black birch by 52%. Release slowed height growth of dominant and codominant oaks for only the first 2 yr. In sapling stands with few oaks in upper canopy positions, precommercial release could be used to augment oak density. Survival and diameter growth of oaks in the intermediate and suppressed crown classes increased with release intensity. Release also increased height growth of northern red oak in the suppressed crown classes.