LOBLOLLY-PINE RESPONDS TO MECHANICAL WOUNDING WITH INCREASED RESIN FLOW

The oleoresin produced by many conifers has a deleterious effect on nu merous associated herbivores, including bark beetles (Coleoptera: Scol ytidae), and may have evolved as a plant defense mechanism. Three expe riments with juvenile loblolly pine (Pinus taeda L.) used mechanical w ounding to drain resin reserves and assess the effects of prior bark w ounding on subsequent resin flow up to 7 days post-treatment. Resin fl ow returned to pre-treatment values within 2 days after wounding began and, in nearly every tree in each experiment, continued to increase o n subsequent days. On average, resin flow reached double the pre-treat ment values (mean +/- SE: 2.10 +/- 0.10 vs. 1.13 +/- 0.10 g/3 h and 2. 28 +/- 0.09 vs. 0.90 +/- 0.09 g/3 h for wounded vs. pre-treatment in e xperiments 1 and 2, respectively). Considering its timing and magnitud e, this previously undescribed response may be important in modulating interactions between pine trees and bark beetles. In addition, resin flow following treatment was greater in trees in larger crown size cla sses (thinned > edge of stand = unthinned in experiment 1; edge of sta nd > thinned > unthinned in experiment 2). This may help explain why t rees in thinned stands are less susceptible to southern pine beetle (D endroctonus frontalis Zimm.) infestation than trees in unthinned stand s.