Can we restore the rainforests?
By John Pickrell
ABC Environment | 8 Mar 2011
Humans can recreate destroyed rainforests, but the question is whether they ever live up to the original. Credit: iStockphoto.
As the world recognises the value - both financial and intangible - of rainforests, efforts are being made to recreate them from scratch. But can they ever be the same as the original?
THE AIR IS LADEN with moisture and somewhere high above distant canopy the sky is heavy with cloud but down here near the rainforest floor it's dark enough that you can't tell. The hum of insects is all encompassing. I'm standing on the side of a jungle trail, batting at a variety of biting flies and watching a troop of macaques, full of cocky bravado, as they clamber over boulders surrounding a stream.
The rainforest here at Kepong, 16 kilometres north of Malaysia's capital Kuala Lumpur, seems timeless, ancient - the scale of the trees makes it hard to imagine anything else. Which is why it's hard to believe that 90 years ago the hilly landscape had been stripped bare by tin mining and vegetable cultivation. Today the Forest Research Institute of Malaysia (FRIM) has a rainforest regeneration experiment that covers 500 hectares and is more than 80 years old. Since the experiment began, under British colonial rule in the late 1920s, the researchers have a largely unbroken record of the number, diversity and size of rainforest trees in the area.
"It was a degraded area prior to 1928 that was replanted," says Dr Shamsudin Ibrahim, director of FRIM's Forestry and Environment Division. "We just plant trees hoping that the rest of nature will come back by itself." The experiment has taught them which species of trees to plant and when; how to distribute the seedlings; and which plants and animals will naturally recolonise by themselves. In recent years, large animals such as gibbons and hornbills have moved in.
Despite the lush appearance, even after 80 years, the forest still has a long way to go. Shamsudin estimates that there are perhaps a quarter of the species in untouched lowland rainforest. "To bring the area back to a natural state - to a pristine primary condition - will take another 100 years or more, but at least what we have done over the last 80 years is a testimony that through effort we can plant the right species, and also invite the invasion of other tree species to bring the rainforest back," he says.
Bill Laurance, who holds the Prince Bernhard Chair for International Nature Conservation at James Cook University in Queensland, says he doesn't know of any examples of rainforest regeneration in Australia that are greater than 50 ha in size or 30 years old - in those respects FRIM is globally unique. But how close is the rainforest to the real thing - and what's the difference anyway?
What does a forest do?
For a start, rainforests support enormous biodiversity - and a large portion are species of insects, understory birds and plants that lead highly specialised lifestyles. According to the WWF, one 6.5 hectare patch of surveyed Borneo rainforest had over 700 species of tree - more than are found in the entire eastern US. "Rainforests are the only place where such extremely large numbers of species are found," says Carla Catterall professor of ecology and rainforest regeneration expert at Griffith University in Queensland.
Virgin tropical forests are also made up of large numbers of gargantuan trees that can each be 500 to 1000 years old, locking up huge quantities of carbon. Furthermore, says Laurance, these forests stabilise soils, filter water, provide myriad natural products and pharmaceuticals, and are "amazing cloud-making machines, via the process of evapotranspiration. The clouds reflect a huge amount of solar radiation back into space, helping keep the world cool."
Humans can definitely help to speed up forest regeneration by planting trees, he says, "but the resulting forest will be a rather simplified caricature of a real primary rainforest, with lower species diversity and ecological complexity...Full forest recovery will take from a few centuries to perhaps a millennium, depending on local soil fertility and whether there are local sources of seeds and seed dispersers."
It may take hundreds or thousands of years to produce forest with the full range of complex nuances. However it's possible within a few decades to restore sites that capture many of the "ecological properties" of such forests, says Catterall - and these are properties that we value such as water regulation, biodiversity and carbon.
One Brazilian study came to similar conclusions. Detailed in the journal Biological Conservation in 2008, researchers at the Federal University of Paraná looked at different patches where previously cleared tropical forest was regenerating along the Atlantic seaboard. To measure the recovery they looked at the number of species, the height of trees, the number of shade-loving plants and the number of tree species dispersed by animals. Large animals are some of the last to return, and old growth forests are characterised by many trees with animal-dispersed seeds. The study found that within just 65 years, 80 per cent of tree species were the animal-dispersed type. However, though much of the function had returned, the study predicted that it would take up to 4,000 years for the full range of species to return.
Different ecological functions return at different points, says Catterall. Her team have found that some aspects of forest structure such as canopy cover, soil process and the covering of leaf litter on the floor may return within a decade with intensive replanting and monitoring. In Australia at least, as much as half the diversity may return over the same period in diverse replanted forests that border old-growth patches - but the remaining 50 per cent are more specialised species that take a lot longer to come back, says Catterall. "Our current work on birds in the Wet Tropics suggests perhaps a century...but this varies enormously from one place to another."
Not everyone agrees that the full range ever will return. Another report, in the Proceedings of the National Academy of Sciences in 2007, detailed an enormous survey of Brazilian rainforest which showed that of many plants and animals surveyed across 15 groups, around a quarter were never found outside primary rainforest and may not be equipped to move between isolated patches.
Lending a hand
At FRIM they've found that planting a limited number of key trees can get rainforest regeneration kick-started, but you have to be prepared to wait for many species to return themselves. "The only thing here is the time," says Ibrahim. "If you had the luxury of time to wait you could see for yourself the recovery."
"You really need to have another primary rainforest close by, as that's the crucial source of seeds and seed-dispersing animals, and you need a long, long time," agrees Laurance. One strategy is to plant trees attractive to fruit-eating animals, such as fruit-doves and flying foxes, he adds. "These frugivores tend to bring a lot of seeds into the regrowth with them."
So it really is possible for humans to regenerate rainforest - we just need the right ingredients and patience. Unfortunately, the timescales are much longer than a human lifespan. If we want our children, or even our children's children to enjoy the world's rainforests, then we need to find ways to conserve what we have now, rather than simply fixing the problem later.
"We should be doing both," says Laurance. "In areas where forests are still being destroyed apace, such as Indonesia, Malaysia and Papua New Guinea, we should focus on protecting existing forests. In areas where most of the original forests have already been cleared, such as the Philippines, Java, Madagascar, the Brazilian Atlantic forest, and parts of north Queensland, we should focus on helping forests to regenerate."
There's also an important synergy between the two approaches, says Catterall, because restoring rainforest around old-growth patches helps maintain them, while also speeding up regeneration. "The value and integrity of rainforest that's left can't maintain itself unless we put back some of what has been cleared...Although restored rainforest initially contains only part of the diversity of old-growth forest, it's presence helps the remnant patches persist, while simultaneously becoming more valuable itself as time progresses."
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