Identification of tree groups used by secondary cavity-nesting birds to simplify forest management in subtropical forests

In tropical and subtropical forest ecosystems, cavities formed by decay processes are a key but scarce resource for birds that nest and roost in them, which makes them a highly sensitive group to logging. The piedmont forest of northwestern Argentina is a complex ecosystem with 113 tree and 120 bird species. It has high logging pressure on the few, well-conserved forest remnants, complicating the delineation of sustainable management guidelines for each tree or bird species in a short time. Our objective was to reduce the complexity of subtropical forests by grouping tree species according to the characteristics used by secondary cavity-nesting birds (i.e. non excavators). In the piedmont forest, 50 plots of 0.25 ha were sampled to record cavity trees and cavity characteristics. These were then used in a cluster analysis to form tree groups. Additionally, cavities were searched to identify the bird species using the decay-formed cavities. A total of 187 cavity trees, comprising 23 tree species, were recorded, and these formed four tree groups or clusters. We recorded 86 cavities that were used by secondary cavity-nesting bird species. The four tree groups were unequally used by secondary cavity nesters. The tree group that included valuable timber species ( Myroxylon peruiferum , Anadenanthera colubrina and Calycophyllum multiflorum ) and had the greatest cavity availability represented 71% of total cavity use. Another tree group with valuable timber species ( Cedrela balansae and Amburana cearensis ), measured > 73 cm DBH and > 21 m tall, had cavity entrances > 0.10 cm 2 , and contributed 14% of all cavity use by birds. A third group had no highly economically valuable tree species, and included the snag category (i.e. standing dead trees) as well as a 15% of cavity use. The fourth tree group had a DBH