Evaluating the consistency of understorey vegetation response to forest thinning through synthetic analysis of operational-scale experiments

Abstract

We attempted to extend the inference scope of several detailed songbird habitat restoration studies in western Oregon to the broader region through a reanalysis and synthesis of five large-scale management experiments. This previous work demonstrated the importance of understorey vegetation to songbird habitat. However, individual studies have shown conflicting results regarding how vegetation responds to restoration thinning. Understorey vegetation covers 4-6 years after thinning was strongly related to pre-treatment conditions (indexed by the unthinned control treatment). Baseline models that accounted for the pre-treatment conditions showed that herbaceous cover consistently, but only slightly, increased following thinning. Shrub cover, however, tended to decrease following thinning when the pre-treatment cover was >30 per cent. Each study had limited replication and most had limited geographic and environmental conditions, leading to the inconsistent findings when analysed separately. The reanalysis approach allowed us to test the repeatability of specific finding and demonstrated the applicability of restoration thinning for enhancing habitat in western Oregon. © Institute of Chartered Foresters, 2009.