Habitat fragmentation is a serious threat to biodiversity and patches of forest worldwide (also see sections 9 and 10). As great expanses of forest are increasingly chopped into smaller blocks, edge effects alter the the flora and fauna of forests. Fragmented patches of forest are subject to drying winds that increase the frequency of tree falls. Tree falls tear gaps in the canopy, destroying its function of moderating the humidity, temperature, and heat conditions of the forest floor. These changes affect the species that inhabit the forest patch, usually reducing diversity. Many rare species that dwell in the deep primary forest are unable to cope with the new conditions and are replaced by more common, weedier species. The drier forest conditions also mean that agricultural fires set in the surrounding scrubland and savanna are more likely to burn through the forest patch. During the Indonesian and Brazilian fires of 1997 and 1998, such forest patches went up in smoke at an alarming rate. Fragmented forests also suffer a loss of biomass—up to 36 percent—in the first few years after fragmentation.

Review questions:

• Why is forest fragmentation bad for rainforest biodiversity?

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Continued / Next: Climate Change

Based on studies in the Amazon, W.F. Laurance concludes fragmented forests may lose up to 36% of their biomass in the first few years after fragmentation ("Dynamics and biomass of Amazonian forest fragments," ITTO Tropical Forest Update Vol. 8 no. 1, 1998).

A survey of human disturbance of world ecosystems is found in L. Hannah, et al. "A Preliminary Inventory of Human Disturbance of World Ecosystems," Ambio Vol. 23 No. 4-5, July 1994.