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Selective logging changes character of tropical forest

Editor’s note: this story should have been published 12/12/2011 but due to a technical glitch never went online. We just noticed its unpublished status today. Our apologies to Velho and Krishnadas (2011).

Selective logging is usually considered less harmful than other forestry practices, such as clear cutting, but a new study in’s open access journal Tropical Conservation Science has found that even selective logging has a major impact on tropical forests lasting decades. Comparing trees in two previously logged sites and two unlogged sites in northeast India, researchers found less tree diversity in selectively logged forests with trees dispersed by birds proved especially hard-hit.

“We found significant differences in species richness and diversity between logged and intact forest… Consistent with previous studies, trees in logged forests were smaller, although overall density was not different between the two treatments. We posit that selective logging might have pervasive effects on functional aspects of tropical tree communities, which appear to persist even after two decades of logging cessation,” the authors write.

The forests, located in and around Pakke Wildlife Sanctuary and Tiger Reserve, were selectively logging in the 1970s and saw some illegal logging thereafter. But in 1996 logging was banned in the area.

Photo by Rhett A. Butler

The researchers found that selective logging drastically changed the composition of the forest. In logged areas, there were far fewer species that depended on animals, such as birds, for dispersal; whereas there were more species dispersed by abiotic forces (non-living actors) such as wind.

“Canopy openness following logging is expected to favor the growth of small-seeded pioneer species, many of which are wind-dispersed, a change in community composition that persists decades after logging,” the authors write.

They add that the loss of old, animal-dispersed trees to logging makes it harder for fruit-eating birds and mammals to survive.

“Many old-growth trees are also important fruiting resources for animals, which in turn disperse the seeds of these species,” they write. Less fruit means less animals, which in turn means less chance for seed dispersal. In essence, the entire character of the forest is changed to favor wind-dispersed trees over animal-dispersed.

Given their findings, the authors recommend a review of selective logging practices in unprotected forests and surveys of biodiversity after logging occurs.

“[The local forest department] has instituted a variety of co-management schemes which include creation of village forest reserves and community conservation areas in many parts of the state. Given that these areas are still open to timber and firewood extraction, which directly impact local livelihoods, our study is of particular relevance and indicates that the present timber extraction patterns may be unsustainable,” the authors write, warning that “the moist forests of northeast India continue to suffer high pressures from logging, hunting, and large-scale felling for agriculture.”

CITATION: Velho, N. and Krishnadas, M. 2011. Post-logging recovery of animal dispersed trees in a tropical forest site in north-east India. Tropical Conservation Science Vol. 4(4):405-419.

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