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Global Survey of Anthropogenic Neighborhood Threats to Conservation of Grass-Shrub and Forest Vegetation
Citation:
Riitters, K. H., J. D. WICKHAM, T. G. WADE, AND P. Vogt. Global Survey of Anthropogenic Neighborhood Threats to Conservation of Grass-Shrub and Forest Vegetation. JOURNAL OF ENVIRONMENTAL MANAGEMENT. Elsevier Science Ltd, New York, NY, 97:116-121, (2012).
Impact/Purpose:
Humans dominate the world, threatening the conversion and degradation of natural vegetation. Land-cover conversion to agriculture and urban land use is a globally significant driver of natural vegetation loss (Turner et al., 1990; Meyer and Turner, 1994), and croplands and pastures alone cover approximately 40 percent of the land surface area (Foley et al., 2005). Within the natural vegetation that remains, ecological functions are at risk from “edge effects” extending hundreds of meters from converted land (e.g., Murcia, 1995; Forman and Alexander, 1998; Weathers et al., 2001; Houlahan and Findlay, 2004; Harper et al., 2005; Laurance, 2008) and from “matrix effects” that permeate anthropogenic landscapes (e.g., Forman 1995; Ricketts, 2001; Ewers and Didham, 2006). Edge and matrix effects must be considered in conservation planning simply because much of the remaining natural vegetation resides in anthropogenic landscapes, (Margules and Pressey, 2000; Luck et al., 2004). Through remote sensing there has been a rapid expansion in the availability of global land-cover data to address conservation issues, but systematic analyses are needed to better inform conservation planning (Dymond et al., 2001; van Lynden and Mantel, 2001; Leper et al., 2005). Most of the available studies consider only the absolute areas of converted vegetation, remnant vegetation, or protection status within particular biomes or ecoregions. The spatial arrangement of converted land relative to remnant vegetation is a key observation that can be made from global land-cover data (Wade et al., 2003; Townshend et al., 2008), and a necessary observation to fully evaluate anthropogenic threats from edge and matrix effects.
Description:
The ecological functions of natural vegetation are threatened when it is subsumed in anthropogenic landscapes. We report the first comparative global survey of anthropogenic landscape threats to forest and grass-shrub vegetation. Using a global land-cover map derived from remote sensing, each 9-ha pixel of forest and grass shrub land-cover was examined to determine if it was adjacent to anthropogenic land cover (adjacency risk), or at the center of a 137 km2 neighborhood containing more than 20 percent anthropogenic land-cover neighborhood risk), or either (combined risk). The observations were summarized by ecoregion and biome. 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. Conservation threats posed by proximity of existing vegetation to anthropogenic land-cover are globally significant, and higher for grass-shrub vegetation than for forest vegetation.