Canopy arthropod responses to density and distribution of green trees retained
after partial harvest

Tim D. Schowalter*, Yanli Zang, and Robert A. Progar
Department of Entomology, Oregon State University, Corvallis, OR 97331

*Current address: Department of Etomology, 404 Life Sciences Bldg.,
Lousiana State University, Baton Rouge, LA 70803. Phone: 225-578-1634
tschowalter@agcenter.lsu.edu

(for full paper click here).

Abstract. We measured canopy arthropod responses to six contrasting green-tree retention treatments at six locations (blocks) in western Oregon and Washington as part of the Demonstration of Ecosystem Management Options (DEMO) study. Treatments were 100% retention (uncut), 75% retention with three 1-ha harvested gaps, 40% dispersed retention, 40% aggregated retention with five 1-ha uncut aggregates, 15% dispersed retention, and 15% aggregated retention with two 1-ha uncut aggregates. Arthropods were ampled from upper, mid-, and lower crown levels of one overstory Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and from three understory vine maple (Acer circinatum Pursh) in each treatment unit during June and August each year to assess seasonal variation in abundances. Pretreatment data were collected in 1996 and posttreatment data in 1999– 2000. Arthropods showed little evidence of response to treatments, but the abundance of arthropods on both plant species showed significant variation among blocks, reflecting responses to environmental gradients at a regional scale. Arthropod abundance also varied significantly over time in unmanipulated (control) treatments, suggesting sensitivity to annual changes in weather. Our results suggest that disturbance at this intensity or scale has little influence on canopy arthropods in the short term. Future sampling will be necessary to evaluate the extent to which arthropods respond to changes in environmental conditions created by these treatments over longer time periods.