ANIMALS and plants in the Amazon are being hit far harder by people encroaching into the jungle than anyone thought. The biggest investigation to date has concluded that Amazonian wildlife is agoraphobic, avoiding even the smallest clearing in the vast sea of rainforest, and that fragmen-tation of the forest is having a massive impact on native species.
In the review, that analyses the findings of 340 separate studies, researchers found that fragmentation increased local extinction rates and altered species richness and abundance. It also disrupted ecological processes and increased the risk of fire.
Fragmentation has a much larger impact on tropical rainforests than on other ecosystems because natural clearings and fires are rare. And the immense size of the Amazon means there are many extremely specialised animal and plant species that are not adapted to life on the edge.
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鈥淚t was a surprise that even small unpaved roads can have an impact,鈥� says William Laurance of the Smithsonian Tropical Research Institute in Balboa, Panama, who led the research team. For instance, some birds that live in the lower canopy or on the ground won鈥檛 go near the edge of the forest, let alone cross a narrow road. 鈥淭here are fewer species 70 and even 100 metres from the edge of a road.鈥�
Logging, roads, pipelines and fire continue to chop the Amazon into more and more fragments. 鈥淔orest edge鈥� has increased at the rate of 19,000 kilometres per year since 1992, estimates Mark Cochrane from Michigan State University in East Lansing. And the rate of deforestation may now be worse than it was in the 1970s. Also, despite Brazil鈥檚 efforts to educate farmers and impose controls, slash and burn continues to be a common agricultural practice. In addition, over 90 per cent of accidental fires start around forest edges, he says. 鈥淭ropical forests generally don鈥檛 burn unless they are chopped into smaller fragments.鈥�
Laurance鈥檚 group report in this month鈥檚 issue of Conservation Biology that species living within forest fragments smaller than 100 hectares are doomed. While they could not determine a minimum critical size for nature reserves, the researchers believe they need to cover millions of hectares to preserve the low population densities of some species. And because the composition of species varies drastically from area to area, a large number of reserves, linked by wide corridors of primary forest, are also essential to maintain healthy levels of biodiversity.
That could prove all but impossible, as fragmentation will be on an unprecedented scale by 2020, Laurance says. Brazil has already given the go-ahead for a $40 billion 鈥淎dvance Brazil鈥� programme for new highways, hydroelectric schemes, gas pipelines and river-channelling projects in the Amazon rainforest. Even the Porto Velho-Manaus and Cuiaba-Santarem superhighways now being built will spark profound changes, as they鈥檒l bring loggers, miners, hunters and settlers into pristine areas.