Availability of cavities for avian cavity nesters in selectively logged subtropical montane forests of the Andes

Abstract

Tree cavities play a critical role in the life history of cavity-using species and thus are an important structural feature of forests. Furthermore, some common forest management practices can have a profound negative effect on cavity quantity and quality. This is the first study to address cavity resources in Neotropical montane forests and with this information we hope to develop approaches to sustainable forest management that will assure the conservation of cavity nesters. Our study design consisted of two treatments (control and harvested forest) in both piedmont and cloud forests of the subtropical montane forests of the Andes. This study indicates that cavities are an uncommon feature even in control sites with only 3% of the trees harboring cavities in both forest types. Even more uncommon are potentially usable cavities for avian cavity nesters: only 0.15% of the trees have a potentially usable cavity in the piedmont forest and only 0.42% in the cloud forest. In logged forests there is a significantly lower density of potentially usable cavities (4.12 vs. 0.51 cavities/ha in piedmont forest and 3.91 vs. 1.64 cavities/ha in the cloud forest). Furthermore, we documented a high loss rate of potentially usable cavities (from 23 to 40%/year) that differs between tree species and DBH classes. More specifically, in the piedmont forest, large, decaying Calycophyllum multiflorum have a relatively greater probability of having potentially usable cavities, while in the cloud forest potentially usable cavities are disproportionably found in large, decaying Blepharocalyx gigantea. In both forest types, snags are also very likely to harbor a potentially usable cavity. In order for harvested stands in the subtropical montane forest of the Andes to regain some of their ecological value, it is necessary to retain trees that have potentially usable cavities and also trees with the highest probability of becoming usable cavity trees.