Litter Invertebrate Responses to Variable Density Thinning in Western Washington Forest

Abstract

We evaluated the response of forest floor invertebrates to variable density thinning (VDT) of the Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forest overstory at Ft. Lewis, Washington, during 2000 and 2001 (7-8 years post-thinning). We placed pitfall traps at 8-12 random grid points in each of four thinned units and four control (unthinned) units in each of two sites (blocks) representing different management histories. Most taxa showed significant seasonal trends, with peak abundances during summer. ANOVA indicated strongly significant effects of site for 9 of 39 species and combined taxa, probably reflecting factors associated with management history; only two taxa showed significant responses to the thinning treatment or to block ϫ treatment interactions. Indicator analysis revealed three spider species as potential indicators of thinning treatment. Detrended correspondence analysis (DCA) and cluster analysis for 85 species indicated that the thinning treatments altered the invertebrate assemblage in different ways, depending on initial structure. Multiresponse permutation procedure (MRPP) confirmed that species assemblages, but not combined taxa or functional groups, in treated units differed significantly from those in control units and from each other. Therefore, VDT affected forest floor invertebrates in the short term, but the effect was strongly modified by site (block) factors, especially management history. These results indicated that previous management history is an important determinant of treatment effect and that compensatory shifts in relative importance among species within functional groups may maintain ecological function during environmental changes.

Arthropods as bioindicators of sustainable forest management, with a focus on plantation forests

“…Arthropods are good bioindicators of ecosystem change and habitat modification due to their small body size, short generation time (Kremen et al, 1993), high sensitivity to temperature and moisture changes (Schowalter et al, 2003), and provision of ecosystem services (Longcore, 2003). These characteristics make arthropods suitable indicators of the integrity of forest management practices (Samways, 1994;New, 1995New, , 1998Progar and Schowalter, 2002;Maleque et al, 2006a).…”

The ant (Hymenoptera: Formicidae) communities of the central interior of British Columbia: Adaptations to a temperature-constrained environment.

“…These data may be calculated from tallies of total individuals or from simple presence-absence (incidence) observations. It is common in the myrmecological literature for tallies of total individuals captured to be used to derive relative abundance data Bestelmeyer et al 2000;Parr and Chown 2001;Wang et al 2001b;Schowalter et al 2003;Borgelt and New 2005;Dunn et al 2007). The natural history of ant species and the manner in which they are distributed in the environment, however, should make myrmecologists wary of this approach.…”

Effect of thinning on flying insect communities using window traps in young douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests in the Pacific Northwestern America

“…Multi-response permutation procedures (MRPP) were conducted with the software PC-ORD, a nonparametric protocol for testing the null hypothesis of no differences among groups of thinning treatments in the data matrix. MRPP is useful when analyzing ecological data because it does not require assumptions of normality and constant variance (Biondini et al, 1988;McCune and Mefford, 1999;McCune and Grace, 2002;Schowalter et al, 2003). Values for indicator species were calculated according to the method of Dufr6ne and Legendre (1997) -this is a simple, intuitive solution for identifying which species may serve as an indicator(s) of a particular environmental condition.…”