Impact of Spring Sawfly Defoliation on Growth of Loblolly Pine Stands

摘要

To estimate the impact of a single spring defoliation by loblolly pine sawfly (Neodiprion taedae lineaiis Ross), diameters of 3,006 loblolly pines from five locations in southeastern Arkansas were measured immediately after defoliation and two more times at 1-year intervals. The proportion of defoliation was assessed at each measurement. An insecticide was used in an attempt to prevent defoliation in subsequent years. Because tree growth depends on many factors, a multivariate multiple regression model was used to separate these effects. The model predicts that a single defoliation reduces annual diameter and volume increment by 17.4, 8,4, and 2,8% for the first, second, and third years after defoliation, respectively (the actual loss was 18,9 and 8.9% for the first 2 years). It was found that trees defoliated 20-40% actually grew faster than undefoliated trees. This response, called overcompensation, is a common reaction of plants to moderate stress. Potential losses from defoliation are greatestin sawtimber-sized stands between the ages of 25 and 35 years. The decision to control sawflies should take into account stand age and time to final harvest.