Remote sensing for conservation monitoring: Assessing protected areas, habitat extent, habitat condition, species diversity, and threats

Monitoring protected areas and their surrounds at local to regional scales is essential given their vulnerability to anthropogenic pressures, including those associated with climatic fluctuation, and important for management and fulfilment of national and international directives and agreements. Whilst monitoring has commonly revolved around field data, remote sensing can play a key role in establishing baselines of the extent and condition of habitats and associated species diversity as well as quantifying losses, degradation or recovery associated with specific events or processes. Landsat images constitute a major data source for habitat monitoring, capturing broad scale information on changes in habitat extent and spatial patterns of fragmentation that allow disturbances in protected areas to be identified. These data are, however, less able to provide information on changes in habitat quality, species distribution and fine-scale disturbances, and hence data from other spaceborne optical sensors are increasingly being considered. Very High Resolution (VHR) optical datasets have been exploited to a lesser extent, partly because of the relative recency of spaceborne observations and challenges associated with obtaining and routinely extracting information from airborne multi-spectral and hyperspectral datasets. The lack of a shortwave infrared band in many VHR datasets and provision of too much detail (e.g., shadows within and from landscape objects) also present challenges in some cases. Light Detection and Ranging (LiDAR) and Synthetic Aperture Radar (SAR) data, particularly when used synergistically with optical data, have benefited the detection of changes in the three-dimensional structure of habitats. This review shows that remote sensing has a strong, yet underexploited potential to assist in the monitoring of protected areas. However, the data generated need to be utilized more effectively to enable better management of the condition of protected areas and their surrounds, prepare for climate change, and assist planning for future landscape management.