The creation of protected areas provides potential solutions to the loss of biodiversity posed by land development. However, due to limited money and land availability, protected area designation has shifted away from governments towards local and non-governmental organizations. This shift in responsibility for protected area establishment is a global trend picking up steam over the past two decades, but New Jersey adopted this mode of protected area acquisition in the 1960s. Within the urbanizing forests of the New Jersey highlands there are now over 4,400 protected areas, with most areas being 500ha or smaller. Given their size and number, these protected forests are embedded in a very complex matrix of human-modified land uses (e.g., residential development, industrial use, and agriculture). To assess the value of these protected areas in terms of their contribution to regional bird diversity, we documented how the size (ha) and surrounding land use influenced protected area bird diversity. We wanted to know if there was a threshold protected area size below which the bird community became indistinguishable from the community utilizing surrounding human-modified habitats.
We suggest that any protected area below a threshold is not functioning to preserve unique forest bird communities, but is instead a simple extension of surrounding land use types. Our results show that such size thresholds exist in New Jersey, and that where this threshold lies varies per surrounding land use types. For conservation planners our results suggest that, if the goal of designating land as ‘protected’ relates to biodiversity preservation, there are clear size and locational constraints that will prohibit goal achievement. For ecologists, our results emphasize that protected area size interplays strongly with landscape context, thus shaping the ecological value of the growing number for small locally-managed protected areas.