Remote sensing methods for the biophysical characterization of protected areas globally: challenges and opportunities

Protected areas (PAs) are a key strategy to reverse global biodiversity declines, but they are under increasing pressures from anthropogenic activities and concomitant effects. Thus, the heterogeneous landscapes within PAs, containing a number of different habitats and ecosystem types, are in various degrees of disturbance. Characterizing habitats and ecosystems within the global protected area network requires large-scale monitoring over long time scales. This study reviews methods for the biophysical characterization of terrestrial PAs at global scale by means of remote sensing (RS) and provides further recommendations. To this end, we first discuss the importance of taking into account structural and functional attributes, as well as of integrating a broad spectrum of variables, to account for the different ecosystem and habitat types within PAs, considering examples at local and regional sale. We then discuss potential variables, challenges and limitations of existing global environmental stratifications, as well as biophysical characterization of PAs, finally offering some recommendations. Computational and interoperability issues are also discussed, as well as the potential of cloud-based platforms linked to earth observations to support large scale characterization of PAs. Using RS to characterize PAs globally is a crucial approach to help ensure sustainable development, but requires further work before such studies are able to inform large-scale conservation actions. This study proposes 14 recommendations in order to improve existing initiatives to biophysically characterize PAs at global scale.