Extreme contagion in global habitat clearance

Abstract

Habitat clearance remains the major cause of biodiversity loss, with consequences for ecosystem services and for people. In response to this, many global conservation schemes direct funds to regions with high rates of recent habitat destruction, though some also emphasize the conservation of remaining large tracts of intact habitat. If the pattern of habitat clearance is highly contagious, the latter approach will help prevent destructive processes gaining a foothold in areas of contiguous intact habitat. Here, we test the strength of spatial contagion in the pattern of habitat clearance. Using a global dataset of land-cover change at 50 Â 50 km resolution, we discover that intact habitat areas in grid cells are refractory to clearance only when all neighbouring cells are also intact. The likelihood of loss increases dramatically as soon as habitat is cleared in just one neighbouring cell, and remains high thereafter. This effect is consistent for forests and grassland, across biogeographic realms and over centuries, constituting a coherent global pattern. Our results show that landscapes become vulnerable to wholesale clearance as soon as threatening processes begin to penetrate, so actions to prevent any incursions into large, intact blocks of natural habitat are key to their long-term persistence.

Reducing the global environmental impacts of rapid infrastructure expansion

“…In intact habitats, avoid the fi rst cut New roads in forested areas can greatly increase deforestation, both because forest loss is spatially highly contagious [22] and because an initial road often spawns networks of secondary and tertiary roads that can greatly increase the spatial extent of habitat disruption. For instance, the fi rst paved highway across the Brazilian Amazon, linking Belem and Brasília, began in the early 1970s as a narrow cut through the Infrastructures, such as roads, mines, and hydroelectric dams, are proliferating explosively.…”

Historical drivers of extinction risk: using past evidence to direct future monitoring

“…Among general proxies of human pressures and habitat state, we also included information on levels of tree cover and tree cover change (see also [22]). While the role of these variables is probably more influential for forest-dependent than for non-forest species, it is known that habitat clearance has a contagious effect [49], and we use tree cover, a well-mapped habitat feature at a global scale [31], to estimate the general condition of natural habitats within species ranges.…”

Legislative correlates of the size and number of protected areas in Canadian jurisdictions

“…Although this may indicate a benefit of protected areas for local peoples (i.e. people congregate near protected areas), it may also pose a future threat to protected areas due to the contagious nature of land use (Boakes et al, 2010). The important role that protected areas play in local economies and livelihoods is a fundamental reason for local stakeholder involvement in protected areas planning and management.…”