Disagreement over rainforest recovery

Will rainforests survive? That was the topic of a debate at the Smithsonian Institution’s National Museum of Natural History.

Satellite data and other research has revealed that huge tracts of abandoned tropical forests, which were once logged or farmed, are regrowing.

This evidence has prompted a contentious exchange of views and theories among scientists around the world.

One camp suggests that the regrowth of rainforests has been overlooked, resulting in the current “biodiversity crisis” argument, which fears that half of the world’s species could be lost in the coming decades, is too pesimistic.

However, another school of thought contends that only about half of the plants species originally found in rainforests will return to the areas, and that many animals will not survive the transition.

Others warn that the continuing expansion of netoworks of access roads into rainforests will make it easier for poachers and loggers, threatening the existence of tropical species even further.

Cristian Samper, director of the National Museum of Natural History, who presided over the debate, said: “By bringing together the world’s most foremost authorities on different aspects of rainforest sicence, we hope to achieve new insights into a situation with potentially profound implications for all species, including ours.”

Using a combination of satellite data and field research, estimates suggest that:

  • ten million square kilometres have been cleared of at least half of their wood cover for human uses, includingtimber and agriculture
  • five million square kilometres have been selectively logged, often with high-impact methods that leave forests degraded
  • Of the intact forests remaining, about 275,000 square kilometres – an area bigger than the UK – were felled in five years (between 2000 and 2005)
  • approximately 350,000 square kilometres  (about 2% of original forested areas) are in some stage of regrowth, primarily in South Asia and Latin America.

According to Greg Asner from the Carnegie Institution, deforestation was the most profound change underway in tropical rainforests.

However, he added, land abandonment was the second most important trend, with the majority of the abandonment occurring in upland areas that offered marginal farming opportunities.

Often, the inhabitants departed to pursue better income opportunities in lowlands and cities.

He added that regrowth was relatively quick:  the forest canopy closed after just 15 years; after 20 years, about half of the original biomass weight had grown back.

Joseph Wright, from the Smithsonian Tropical Research Institute, noted that more than 20% of all land within 10 degrees of the equator had acquired protected status, and that the tropics had a percentage of protected land greater than North America, Europe or Japan.

He and colleague Helene Muller-Landau asserted in a 2006 study: “Large areas of tropical forest cover will remain in 2030 and beyond.

“We believe that the area covered by tropical forest will never fall to the exceedingly low levels that are often predicted.”

They added: “Extinction will threaten a smaller proportion of tropical forest species than previously predicted.”

Their position was partly based on UN predictions of growing urbanisation and slower population growth.  As a result, the abandoned areas will recover and tropical species spared, they contend.

But William Laurance, also from the Smithsonian Tropical Research Institute, argued that secondary and degraded forests would sustain only a fraction of existing animal species.

He added that birds and mammals were more vulnerable to the altered habitat than insects and other small organisms.

Forest destruction in years past was largely the result of land being cleared for small-scale farming, he observed.

However, trade globalisation was fostering large-scale industrial agriculture, logging and mining; all of which was accelerating forest destruction.

The world was now losing the equivalent of 50 football fields of old-growth forest every minute, he warned.

“Rainforest regrowth is indeed occurring in regions but most old growth is destroyed,” he said.  “In biodiversity terms, this is akin to a barn door closing after the horses have escaped.”

The findings from the debate, and the evidence presented by the speakers, will be published as papers in a special edition of the journal Conservation Biology.

Source: Smithsonian press release

Date: 12/01/2009

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  1. […] Disagreement over rainforest recovery […]

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