A new study out of North Carolina State University gives a stark view of the dwindling size of forests globally. The analysis of global forest cover revealed that 70 per cent of remaining forest is within 1 kilometre of the forest’s edge, subject to the degrading effects of fragmentation. A synthesis of fragmentation experiments spanning multiple biomes and scales, five continents, and 35 years demonstrates that habitat fragmentation reduces biodiversity by 13 to 75 per cent and impairs key ecosystem functions by decreasing biomass and altering nutrient cycles.
Effects are greatest in the smallest and most isolated fragments, and they magnify with the passage of time. These findings indicate an urgent need for conservation and restoration measures to improve landscape connectivity, which will reduce extinction rates and help maintain ecosystem services, the researchers say in their report.
Habitat Fragmentation
Forest fragmentation has been a point of concern for decades, largely due to fears that lost habitat and increased accessibility to predators and parasites will drive some species to extinction. Still, some have called into question the value of habitat fragmentation, on the grounds that it doesn’t capture important ecological interdependencies, or that the influence of fragmentation per se can be subsumed under the effects of habitat loss.
Centuries of forest fragmentation has been done in the name of agricultural clearing, urban development, and other human interference. As bad as that sounds, the consequences for biodiversity are perhaps even most distressing.
That controversy makes the experiments of an international team of 24 researchers all the more interesting. Led by Nick Haddad, a professor of biology at NCSU, researchers conducted two separate analyses to illustrate the significance of forest fragmentation on the environment. First, they used a recent, high-resolution global survey of forest cover to estimate just how fragmented the world’s forests are. They found that the only exceptions were the Amazon and Congo river basins, where it’s still possible to find deep forests.
The researchers found that destruction and degradation of natural ecosystems are the primary causes of declines in global biodiversity. Habitat destruction typically leads to fragmentation, the division of habitat into smaller and more isolated fragments separated by a matrix of human-transformed land cover. The loss of area, increase in isolation, and greater exposure to human land uses along fragment edges initiate long-term changes to the structure and function of the remaining fragments.
Global Forest Size
“Fragmentation experiments—some of the largest and longest-running experiments in ecology—provide clear evidence of strong and typically degrading impacts of habitat fragmentation on biodiversity and ecological processes,” the team wrote March 20 in Science Advances. That includes some surprising effects, such as surges for some species and long periods of time before fragmentation’s effects become detectable. The full report is available here: http://advances.sciencemag.org/content/1/2/e1500052 .
“In light of these conclusions and ongoing debates, we suggest that fragmentation’s consistency, pervasiveness, and long-term degrading effect on biodiversity and ecosystem function have not been fully appreciated,” they write.
The research team included Andrew Gonzalez of McGill University’s Department of Biology, and Canada Research Chair in Biodiversity Science at McGill.
The new, global analysis stemmed from a symposium of ecologists held in Minneapolis, MN, in 2013, which drew together scientists who had worked on many of the major fragmentation experiments around the world. “It was the first time everyone had been together in the same room, and there was lots of excitement over how much agreement these disparate experiments showed,” recalls Gonzalez, who had worked on a long-running study of the fragmentation of moss-covered habitats in Canada and the UK.
The findings could help inform conservation efforts to mitigate the ecological effects of deforestation for resource development. In the case of Canada’s boreal forest, for instance, setting aside large areas for protection will mitigate the impacts of development only if they are kept intact and free of the effects of forest fragmentation, Gonzalez notes.
The scientists also used the world’s first high-resolution map of global tree cover to measure the magnitude of forest fragmentation. They found that 70 per cent of the world’s remaining forest is well within the range where human activities and non-forest species may influence and degrade forest ecosystems.
“Habitat fragmentation is an ongoing phenomenon, and our analysis shows that the scenario is worsening,” says Gonzalez.
The capacity of surviving forests and other natural habitats to sustain biodiversity will hinge on the amount and quality of habitat left in fragments, the degree to which they are interconnected, and how they are affected by other human-induced influences such as climate change and invasive species, the authors note.
“Once a forest disappears, the resulting area is more exposed and experiences greater extremes of temperature, humidity, and wind – all of which negatively influence plants and animals in nearby forests”, says Doug Levey, Program Officer with the National Science Foundation and co-author of the paper.
“It’s never too late to preserve what we already have,” he says, “People have known for a long time that fragmentation is bad and it’s getting worse.”