April 2, 2015 — Seventy percent of forested lands remaining in the world are within a half mile of the forest edge, where encroaching urban, suburban or agricultural influences can cause any number of harmful effects, according to a new study involving scientists at the University of Colorado Boulder.
The research team, led by North Carolina State University, did a global survey of habitat fragmentation—the division of habitats into smaller and more isolated patches—and found the degree of fragmentation points to trouble for a number of the world’s ecosystems, from forests to savannahs to grasslands, and the plants and animals living in them.
The study also tracked seven major experiments on five continents that examine habitat fragmentation and finds that fragmented habitats reduce the diversity of plants and animals by 13 to 75 percent, with the largest negative effects found in the smallest and most isolated patches.
The study, which involved about two dozen researchers across the globe, is reported today in a paper published in Science Advances.
Kendi Davies and Brett Melbourne, assistant professors in CU-Boulder’s Department of Ecology and Evolutionary Biology and co-authors of the study, have been tracking the fates of species in a 30-year-long experiment at Wog Wog in southeast Australia, along with Australian researchers. “Big, long-term experiments in ecology are critical because we can draw very strong conclusions,” Davies said.
The researchers assembled a map of global forest cover and found very few forest lands unencumbered by some type of human development.
“The results were astounding,” said Dr. Nick Haddad, William Neal Reynolds Distinguished Professor of Biological Sciences at NC State and the corresponding author of the paper. “Nearly 20 percent of the world’s remaining forest is the distance of a football field—or about 100 meters—away from a forest edge. Seventy percent of forest lands are within a half-mile of a forest edge. That means almost no forest can really be considered wilderness.”
The seven major experiments on fragmented habitats tracked by the study cover many different types of ecosystems. The experiments combined to show a disheartening trend. Fragmentation causes losses of plants and animals, changes how ecosystems function, reduces the amounts of nutrients retained and the amount of carbon sequestered, and has other deleterious effects.
“The initial negative effects were unsurprising,” Haddad said. “But I was blown away by the fact that these negative effects became even more negative with time. Some results showed a 50 percent or higher decline in plant and animals species over an average of just 20 years, for example. And the trajectory is still spiraling downward.”
The researchers point to some possible ways of mitigating the negative effects of fragmentation: conserving and maintaining larger areas of habitat; utilizing landscape corridors, or connected fragments that have shown to be effective in achieving higher biodiversity and better ecosystem function; increasing the efficiency of agriculture; and focusing on urban design efficiencies.
The studies were supported by the National Science Foundation.