Evaluating the long-term effectiveness of terrestrial protected areas: a 40-year look at forest bird diversity

Designation of protected areas has become one of the primary approaches to reducing biodiversity loss, with the number of new set-asides growing in the last decades largely from the addition of small protected areas to the global portfolio. Information on the effectiveness of protected areas to stave off species extinction is surprisingly scarce, with almost nothing known about the long-term fate of biodiversity in smaller protected temperate forests. Here we use an uncommonly complete biodiversity inventory of a small protected deciduous forest to evaluate its performance over a 40-year time span. We tracked bird compositional changes using a within-season repeat sampling protocol allowing us unusual accuracy in documenting species gains and losses through time. We found that nearly half the species found in the forest at the time of initial protection are now extirpated, and that yearly forest species composition is highly dynamic. Ground nesting and migratory species were more likely to be extirpated than were canopy breeders, cavity nesters, and year-round residents. Regional population declines explained differences in extirpation probability across species indicating that the study population, to some extent, mirrored larger regional dynamics. However, a substantial number of species declined in abundance within the forest while experiencing no regional declines, or even regional increases, in abundance. Our results reinforce that even with protected status, small forest fragments may not provide the conservation benefits that protection is meant to provide.