Shrinking Habitats Have Adverse Effects on World Ecosystems

An extensive study of global habitat fragmentation – the division of habitats into smaller and more isolated patches – points to major trouble for a number of the world’s ecosystems and the plants and animals living in them.

The study shows that 70 percent of existing forest lands are within a half-mile of the forest edge, where encroaching urban, suburban or agricultural influences can cause any number of harmful effects – like the losses of plants and animals.

The study also tracks 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 fragments of habitat.

The study, led by a researcher from North Carolina State University and involving about two dozen researchers across the globe, is reported today in a paper published in Science Advances.

The researchers assembled a map of global forest cover and found very few forest lands unencumbered by some type of human development.

“It’s no secret that the world’s forests are shrinking, so this study asked about the effects of this habitat loss and fragmentation on the remaining forests,” said Dr. Nick Haddad, William Neal Reynolds Distinguished Professor of Biological Sciences at NC State and the corresponding author of the paper.

“The results were astounding. 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 study also examined seven existing major experiments on fragmented habitats currently being conducted across the globe; some of these experiments are more than 30 years old.

Covering many different types of ecosystems, from forests to savannas to grasslands, 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.”

Haddad points 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 agricultural efficiency; and focusing on urban design efficiencies.

“The key results are shocking and sad,” Haddad said. “Ultimately, habitat fragmentation has harmful effects that will also hurt people. This study is a wake-up call to how much we’re affecting ecosystems – including areas we think we’re conserving.”

The study was supported by the National Science Foundation.

– kulikowski –

Note to editors: An abstract of the paper follows.

“Habitat Fragmentation and its Lasting Impact of Earth’s Ecosystems”

Authors: Nick M. Haddad, North Carolina State University, et al

Published: March 20, 2015, in Science Advances

Abstract: We conducted an analysis of global forest cover to reveal that 70% of remaining forest is within 1 km of the forest’s edge, subject to the degrading effects of fragmentation. A synthesis of fragmentation experiments spanning multiple biomes and scales over five continents and 35 years demonstrates that habitat fragmentation reduces biodiversity by 13-75% 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.