Protected Area Connectedness Index

The Protected Area Connectedness Index value of each protected cell in relation to other cells that are protected or contain primary vegetation in the surrounding non-protected landscape is scored using the cost-benefit analysis (CBA) technique described by Drielsma et al. (2007). Each of the protected cells of interest is first assigned a “benefit” value, representing the proportion of that cell included in protected areas or covered by primary vegetation (outside reserves) (Santini et al. 2015; UNEP-WCMC 2016; WDPA). Each cell in the surrounding landscape is also assigned a “cost” value, indicating permeability to dispersal through that cell, scaled from 0.1 for cells with no protection or primary vegetation through to 1.0 for cells fully protected or covered by primary vegetation. The primary vegetation is based on statistical downscaling of remotely-sensed MODIS land cover data (Friedl et al. 2010; Hoskins et al. 2016), abiotic environmental attributes, and Hansen et al.’s (2013) Landsat-based Global Forest Change dataset.

The connectedness of each protected cell is calculated as a weighted sum of the benefit values of all cells in the surrounding landscape weighted by the probability of dispersal associated with the least-cost path between the protected cell of interest. This probability of dispersal is a function of the permeability values of cells along the least-cost path (Drielsma et al. 2007; Santini et al. 2015). The resulting weighted sum for each protected cell is expressed as a proportion of the maximum possible sum if that cell were surrounded by a continuous expanse of protected cells within a 500km radius, thereby yielding a connectedness score for that cell between 0 and 1.  The Protected Area Connectedness Index is then derived by summing these scores across all protected cells within the unit, and dividing this sum by the number of protected cells, thereby expressing overall connectedness as a proportion, also ranging between 0 and 1.