PARENT SESSION
Poster Session # 9: Herbivory.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Testing the plant vigor hypothesis in an intensively-managed forest.

Coyle, David^*,1, Coleman, Mark¹, Nowak, John^*,2, Fettig, Christopher^*,3, Booth, Donald^*,4, ¹ USDA Forest Service, New Ellenton, SC, USA² USDA Forest Service, Asheville, NC, USA³ USDA Forest Service, Davis, CA, USA⁴ Bartlett Tree Research Laboratories, Charlotte, NC, USA

ABSTRACT- The plant vigor hypothesis (PVH) states that herbivores preferentially feed on more vigorous plants or plant parts. This presents a dilemma in agricultural or intensively-managed forest systems, as silvicultural, chemical, and genetic manipulations are often employed to increase plant vigor and ultimately production. Plant vigor is directly related to plant growth and productivity in intensively-managed forest systems. Few studies have examined the PVH in this environment. The Short Rotation Woody Crops Cooperative Research Program operates a 55 acre fertigated tree plantation in South Carolina. Pest feeding and the resulting plant injury from several arthropods were evaluated on trees receiving one of four silvicultural treatments: irrigation only, fertilization only, irrigation + fertilization or an untreated control. Arthropods studied included the cottonwood leaf beetle, cottonwood leafcurl mite, and various ambrosia beetle species on eastern cottonwood; and the Nantucket pine tip moth on loblolly pine. In general, pests of cottonwood supported the PVH while the Nantucket pine tip moth did not. Due to the unnatural environment created, intensively-managed forests are more susceptible to pest outbreaks than are natural ecosystems. A thorough understanding of pest populations and injury as they relate to tree vigor is essential for effective management of these systems.

Key words: Populus deltoides, plant vigor hypothesis, Pinus taeda