Global survey of anthropogenic neighborhood threats to conservation of grass-shrub and forest vegetation.

The conservation value of natural vegetation is degraded by proximity to anthropogenic land uses. Previous global assessments focused primarily on the amount of land protected or converted to anthropogenic uses, and on forest vegetation. Comparative assessments of extant vegetation in terms of proximity to anthropogenic land uses are needed to better inform conservation planning. We conducted a novel comparative survey of global forest and grass-shrub vegetation at risk of degradation owing to proximity of anthropogenic land uses. Using a global land cover map, risks were classified according to direct adjacency with anthropogenic land cover (adjacency risk), occurrence in anthropogenic neighborhoods (neighborhood risk), or either (combined risk). The survey results for adjacency risk and combined risk were summarized by ecoregions and biomes. Adjacency risk threatens 22 percent of global grass-shrub and 12 percent of forest vegetation, contributing to combined risk which threatens 31 percent of grass-shrub and 20 percent of forest vegetation. Of 743 ecoregions examined, adjacency risk threatens at least 50 percent of grass-shrub vegetation in 224 ecoregions compared to only 124 ecoregions for forest. The conservation threats posed by proximity to anthropogenic land cover are higher for grass-shrub vegetation than for forest vegetation.