Tree roosts used by an endangered bat require almost a century to develop

Abstract

As a forest-dependent species, the endangered Indiana bat (Myotis sodalis) is reliant on large-diameter tree roosts (hereafter, “roosts”), which are usually snags. Such large trees develop as a product of time and species-specific growth rates. To better understand the ecology of bat roost habitat, we explore the putative trade-offs between tree age, size, and growth rates on the development of roosts. Specifically, we quantify the age, size, and longevity of roosts of Indiana bats using dendrochronology at three study sites across the species’ range in the eastern USA. On average, roosts were alive for 97.8 years (range = 31–283), 7.4 years elapsed after tree death before bats used them as roosts, and snag longevity was 10.8 years. Bats selected roosts based on size and not age. Fast-growing, early-successional species attained desirable roost size more quickly than slow-growing, mid- and late-successional species. Early-successional species, e.g. Populus deltoides and Pinus strobus, were suitable as roosts at ∼72 years versus 130 years for late-successional species. Tree growth rate, a trait related to successional status, was negatively correlated with roost age at use, and longevity prior to falling. Consequently, fast-growing trees fell more quickly. Therefore, species’ successional status and growth rate are key factors that determine the timeframe necessary for roost development, and their longevity as snags. A lack of selection by bats for tree age indicates that desirable roost habitat can be developed within decades, by promoting early-successional trees, but speed of development must be weighed against snag longevity.