Logged forests retain considerable biodiversity in Borneo providing conservation opportunity

A new study in the Proceedings of the Royal Society B finds that forests which have undergone logging in the past, sometimes even twice, retain significant levels of biodiversity in Borneo. The researchers say these findings should push conservationists to protect more logged forests from being converted into oil palm plantations where biodiversity levels drop considerably and endangered species are almost wholly absent. Given that much of Borneo's forests have been logged as least once, these long-dismissed forests could become a new frontier for conservationists.

"Whilst the value of primary habitat is undisputed and efforts to protect them are vital, the area of primary forest remaining in Borneo is rapidly diminishing and is increasingly fragmented," lead author David Edwards explained to mongabay.com. "It is only with the inclusion of logged over, degraded forests that large-scale networks of protected areas can be maintained and the long-term viability of Borneo's biodiversity guaranteed,"

Edwards and his team surveyed birds and dung beetles—the most "cost-effective indicator" species of biodiversity—in a primary forest, a forest logged once (where all the large marketable trees are removed), and in a forest logged twice in the Malaysian state of Sabah in Borneo. They found that over 75 percent of species remained even after two rounds of logging, although about half of the species experienced abundance changes.

"Logging rainforest shifts the make-up of species found, and in turn, relogging causes further changes," Edwards says "However, despite these shifts in species, we find that relogged forests harbor similar numbers of bird and dung beetle species to primary forests and that over three quarters of the species found in primary habitat remain after relogging."

Edwards adds that he was surprised that biodiversity remained so high even after a forest was logged twice.

"The forest structure and canopy height of relogged rainforests are so dramatically different to primary forests that it is hard to believe that biodiversity will remain in high levels. But that is exactly what we do find."

The study also found that birds endemic to Borneo (found no-where else) were unaffected by the first round of logging, but nearly half were impacted by the second. IUCN Red List threatened birds were also impacted by logging, but not nearly as much as by conversion into palm oil. According to the study, endangered birds had "a two hundred-fold higher abundance" in logged forest than in palm oil plantations.

While once or twice logged forests are often considered 'degraded lands' and so handed over to palm oil and other plantation companies for conversion, Edwards says this new study shows that logged forests hold vital conservation potential.

"Converting relogged forests to oil palm would come at a dramatic loss of biodiversity. Just focusing on the total numbers of species present would reveal a reduction from about 140 species in second rotation forest to about 30 species in oil palm. And those species lost include the vast majority of IUCN Red-listed species found in relogged forests."

There is also the potential that once or even twice logged forests might eventually see the return of lost species. Edwards says that if, over time, logged forests begin to regenerate "then hopefully the 20-25% of bird and dung beetle species that are currently absent/very rare will also begin to recolonize and recover. Such an understanding of forest regeneration will also indicate whether degraded forests will need some assistance to aid their recovery via forest restoration techniques."

The island of Borneo contains some of the Earth's most biodiverse rainforests—over 16,000 species have been identified not including insects—but has lost half of its forest cover in the last 50 years to logging, plantations, and subsequent fires.

CITATION: David P. Edwards, Trond H. Larsen, Teegan D. S. Docherty, Felicity A. Ansell, Wayne W. Hsu, Mia A. Derhé, Keith C. Hamer and David S. Wilcove. Degraded lands worth protecting: the biological importance of Southeast Asia's repeatedly logged forests. Proc. R. Soc. B published online 4 August 2010. doi: 10.1098/rspb.2010.1062.