Susceptibility of loblolly pine to bark beetle attack following simulated wind stress

Abstract

Thirty-year-old loblolly pine ( Pinus taeda) trees were subjected to simulated wind stress, which included bending stems with a winch and cable system and pruning branches on the same tree to simulate crown loss. The response of treated trees was compared with that of untreated control trees to determine the effect that extreme winds, such as those from hurricanes, have on the growth and function of surviving trees. The impact of acute wind stress on the susceptibility of pine trees to attack by the bark-feeding beetle genera Dendroctonus and Ips also was investigated. The reduction of photosynthetic capacity due to 50% leaf area loss from branch pruning decreased stem diameter growth by 67% after 1 year. It also decreased oleoresin flow, a critical defense mechanism of pines against bark beetle attack. Short-term mortality of fine roots was observed for trees receiving branch pruning, but fine root biomass quickly returned to levels similar to controls. Little damage to larger roots was observed. During the year following treatment, treated pines had similar xylem water potentials compared with control trees as well as similar gas exchange rates, except for higher photosynthetic rates per unit leaf area for treated trees. Any reduction in xylem water flow caused by stem bending appeared to be offset by decreased transpirational demand due to branch pruning. A trend of greater numbers of beetles trapped near stressed trees was observed in the study, but the increase was statistically significant only for one period. Overall, the number of beetles trapped was not large and there was no evidence of successful beetle attack on any tree. Loblolly pine trees subjected to treatment similar to that received from acute wind stress were not dramatically impaired physiologically under the conditions in this study and were not immediately prone to bark beetle attack, especially where crown loss was not severe.