Forests on edge: How human-fragmented landscapes are impacting animals worldwide


Reptiles, birds, mammals, and amphibians living in forests have been impacted from forest fragmentation. (AP Photo/Michael Probst)

Reptiles, birds, mammals, and amphibians living in forests have been impacted from forest fragmentation. (AP Photo/Michael Probst)

Nearly half of the world’s forests are within just 500 meters of a human-sculpted edge, impacting nearly every animal living on our planet.

A recent study published in the journal “Nature” used data on the abundance of organisms in forests worldwide and biological information on reptiles, birds, mammals and amphibians from extensive literature to show the impacts of forest fragmentation are real and tremendous.

Interior habitats within forests were almost four times more likely to harbor species listed as threatened on the International Union of Conservation of Nature’s red list of threatened species.  

Surprisingly, 11 percent more of the animals considered showed a positive response to fragmented habitats – in other words, they became more abundant as their habitats became more fragmented.

The authors caution about how this should be interpreted.

The difference between the percent of animals positively and negatively affected is small. In the greater scheme, 85 percent of the species analyzed by the researchers were impacted, whether positively or negatively, as a result of fragmented habitats.

Those impacts tremendously restructure natural forests because animals that live near the edges of habitats no longer resemble those that live near the interior.

A closer look showed animals that were positively affected were often invasive species that have been brought into habitats by humans. Invasive species have dealt a great deal of damage not only to natural ecosystems, but to the economic well-being of huge swaths of the United States, for example, by destroying our crops or eliminating once widespread forest trees.

When it comes to what kinds of animals were most sensitive to fragmentation, the study found that ectotherms are most clearly at risk. Ectotherms are animals that don’t maintain a constant internal body temperature like humans but instead depend on the temperature within their immediate environment.

Small amphibians, like frogs and salamanders, were most sensitive to fragmentation while larger amphibians were less sensitive. Amphibians are very reliant on water and can thus be extremely threatened in drier conditions. As you move toward forest edges, drier conditions result from less forest coverage and more opportunity for the sun to penetrate onto the forest floor. Amphibians toward the forest edge wouldn’t fare so well considering they need moisture to breathe and produce eggs.

Large reptiles, like lizards and snakes, were likewise very sensitive to fragmented landscapes. These animals would be too large to find adequate shade for refuge from the sun toward forest edges, so they are predicted to overheat in fragmented habitats.

While mammals aren’t ecotherms, they too were affected by fragmentation. Larger mammals require large plots of land to meet the resource needs of their bodies. Fragmented forests don’t offer enough space and force larger mammals to traverse edges, which puts them in danger of being killed by humans. The good news: Mammals with wings (like bats) and non-mammals with wings (like birds) may fare much better because they have more mobility, but they too are at risk since their food sources include other animals that are highly impacted by fragmentation.

The fact that these patterns are shown globally means human impacts on natural landscapes have and will increasingly change forest dynamics. Forest edges are like magnets to which some species will be attracted and some will not. They have far-reaching effects toward the interior of forests no matter how remote or distant wildlife may seem from our developing societies.

Forest fragmentation is just one of the many threats that will interact with global climate change, deforestation, wildfires, hunting and pollution in a complex onslaught inflicted on the environment – our job is to make sure hotspots of living diversity are protected into the future.

Diler Haji is a campus correspondent for The Daily Campus. He can be reached via email at

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