September 14, 2011
Primary rainforests are top conservation priority
The research, which was led by Luke Gibson of the National University of Singapore and Tien Ming Lee of the University of California at San Diego and involved scientists from a range of international institutions, examined 138 scientific studies across 28 tropical countries. It found consistently that biodiversity level were substantially lower in disturbed forests.
"There's no substitute for primary forests," said Gibson in a statement. "All major forms of disturbance invariably reduce biodiversity in tropical forests."
The research found that certain groups are more affected by forest degradation than others. Mammals seem to adapt more readily than birds and insects. The study did not assess the impact of degradation on freshwater fish, reptiles, or amphibians — groups known to be particularly sensitive to ecological change.
The findings are important because primary forests continue to fall at a rapid rate. According to the FAO, old growth forest cover declined by a minimum of 42 million hectares (162,000 square miles) — an area nearly the size of California — during the 2000s. Much of the loss was the result of selective logging, which while less damaging to biodiversity than outright conversion for agriculture, increases the vulnerability of forests to fire and future deforestation. Logging roads cut into remote forest areas typically grant access to developers, small farmers, and hunters.
Excluded from these charts are countries that lack primary forest data, including the Solomon Islands, Laos Argentina, Paraguay, Myanmar, Malaysia, Nepal, Guyana, the United States, Canada, and India.
The authors nonetheless agree that selectively logged forests do have some conservation value and are worth protecting. A study published earlier this month in Conservation Letters argued the same point.
"As selective logging is rapidly expanding throughout the tropics, ecological restoration of such areas might represent an effective strategy to alleviate threats to biodiversity," said co-author Lian Pin Koh of ETH Zurich.
But to conserve the maximum amount of biodiversity, the authors say old-growth forests should be a priority. They argue protected areas—despite their shortcomings—offer the best hope for primary forests.
"Primary forests are irreplaceable for sustaining tropical biodiversity," the authors write. "Consequently, we strongly urge their protection by enhancement of enforcement in existing protected areas, expansion of the current network of reserves and the curbing of international demand for forest commodities obtained at the expense of primary forests."
Impact of various disturbance regimes on biodiversity in tropical forests. Chart based on Gibson et. al 2011. Photo by Rhett Butler. Click to enlarge
"A growing number of reserves are being degraded, downsized, if not entirely degazetted, so holding on to the last remaining large tracts of primary forests within existing reserves will be a crucial part of the conservation mission this century”, said co-author Carlos Peres of the University of East Anglia.
"Improving mechanisms for delivering and sustaining the social, financial and technical support necessary to achieve such goals continues to present one of the greatest challenges to tropical biodiversity conservation in the twenty-first century," the authors conclude.
‘Primary forests are irreplaceable for sustaining tropical biodiversity’ by Luke Gibson, Tien Ming Lee, Lian Pin Koh, Barry W. Brook, Toby A. Gardner, Jos Barlow, Carlos A. Peres, Corey J. A. Bradshaw, William F. Laurance, Thomas E. Lovejoy & Navjot S. Sodhi was published online on 14 September 2011 in Nature and is available at www.nature.com/nature (doi: 10.1038/nature10425).
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