Human development, land conversion, fire and storms are causing the forests worldwide to become increasingly fragmented, to the degree that 70% of the Earth’s remaining forest is within 1 kilometre of a forest edge today. The world’s most intact forest landscapes are found in the tropics, but fragmentation of tropical forests is predicted to accelerate over the next decades.
In the face of this reality, researchers are trying to understand how to make best use of the remaining intact habitat for the purpose of wildlife conservation. In a study published in Science today, ASE Asst Prof Eleanor Slade and co-authors shed some light on this issue: “Everyone knows habitat loss is bad for animals, but there’s been a longstanding debate about fragmentation – the arrangement of remaining habitat,” said co-corresponding author Matt Betts, a professor in the OSU College of Forestry and the director of the Forest Biodiversity Research Network. “How do we design wildlife reserves? Do we make many small ones, or fewer big ones, or do we make corridors?”
The study looked at over 6,500 animal species globally and found that tropical animals are particularly dependent on large areas of continuous, unfragmented forest landscape. Tropical animals are as much as six times more vulnerable to disturbance, and it is a historic legacy of low disturbance in tropical rainforests that have resulted in species being less adapted to changing environmental conditions. “Biodiversity of vertebrates increases massively toward the equator, but even accounting for that, a greater proportion of species are more sensitive to fragmentation,” Betts said. “Sensitivity increases six-fold at low versus high latitudes. That means that not only should we care about the tropics because so many species are found there that are found nowhere else on Earth, but those species are also more sensitive to how we treat the forests.”
At higher latitudes, for example in temperate forests, a larger proportion of animals can tolerate significant changes in the landscape, due to having evolved through glaciations, frequent wildfire, hurricanes etc. This does not mean that temperate forests are not sensitive to fragmentation, but the consequences for wildlife are less severe compared to tropical forests.
The study has implications for the formation of reserves, while in temperate forests the configuration patterns of preserved forest is less important than preserving the right kind of habitat, in tropical forests preserving continuous areas of unfragmented forest landscape is more important.
Sunbear (Helarctos malayanus) – one of the tropical mammal species found to be negatively affected by forest edges in Malaysian Borneo (photo: Matt Betts)
Steller’s Jay (Cyanocitta stelleri), a forest bird of the western US and Canada whose abundance was found to be positively influenced by edges. (Photo: Hankyu Kim)
Steller’s Jay and Chestnut-sided warbler (Setophaga pensylvanica), a forest bird of the eastern US and Canada whose abundance was found to be positively influenced by edges. (Photo: Mike McDowell)
Unfragmented tropical forest in Costa Rica (top) and recently burned temperate forest in southern Oregon (bottom). Species that evolved in landscapes with little large-scale disturbance – like this one in the tropics – tend to be more sensitive to deforestation and edge effects than those that have persisted in landscapes with disturbances such as fires and windstorms. Photos: Matt Betts
Read the original article: Extinction filters mediate the global effects of habitat fragmentation on animals
Commentary in The New York Times: Fractured Forests Are Endangering Wildlife, Scientists Find
Perspective in Science: Lasting signature of forest fragmentation