What’s Inside That Counts

When people talk about forest loss, they often consider only the total area of felled trees. But it’s also important to know how much “interior” forest — that is, forested spots surrounded by more forest — is vanishing, researchers argue. A new analysis in Scientific Reports shows that in 48 states, forest interior is disappearing about three to nine times faster than total forest area.

Forest interior is needed to maintain “many of the ecological values of forests,” the team writes. In other words, a forest is not just the sum of its parts: many of its inhabitants need large continuous stretches of trees to thrive.

To analyze forest interior in the U.S., the study authors examined land cover maps of all states except Hawaii and Alaska from 2001 and 2006. Then the team figured out whether each pixel of forested area on the map was interior forest. To qualify as interior, at least 90 percent of that pixel’s surrounding pixels within a given “neighborhood” also had to be forest.

Between 2001 and 2006, the states’ net loss of total forest was 1.1 percent. But 3.2 to 10.5 percent of interior forest disappeared, depending on which neighborhood size was used in the analysis. Interior losses were especially severe in parts of the Pacific Northwest and Southeast.

While states also planted trees during that time, these additions usually didn’t increase the amount of interior forest much. As people continue to fragment forests, interior sections “will become smaller and more concentrated on publicly owned land,” the authors write. Roberta Kwok | 18 September 2012

Source: Riitters, K.H. and J.D. Wickham. 2012. Decline of forest interior conditions in the conterminous United States. Scientific Reports doi: 10.1038/srep00653.

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