28 January 2009

Reality check for deforestation debate

Some researchers have suggested that tropical forests' biodiversity may be more resilient than previously thought, says Dr William Laurance. However, in this week's Green Room, he warns against thinking that many tropical species can survive the current levels of deforestation.

By William Laurance, BBC News, 27 January 2009

Dr William Laurance

Secondary growth rainforest (Image: Robin Chazdon)

"Many species, including apes, monkeys, and forest elephants, are being killed off by rampant overhunting and the commercial bushmeat trade"

We all know tropical rainforests are the world's biologically richest ecosystems and are rapidly disappearing.

If rapid forest loss continues at the current rate, some believe, we could soon face a mass extinction event; a loss of life so devastating it might rival the catastrophic disappearance of dinosaurs and other species 65 million years ago.

However, others disagree, such as my fellow Smithsonian colleague, Joseph Wright. He says tropical deforestation will be less severe than many believe, and species extinctions far fewer.

Dr Wright's views have kicked off one of the most heated scientific controversies in the past decade, and were the subject of a recent major public debate at the Smithsonian Institution in Washington DC.

In a nutshell, he suggests that, as part of a global trend toward increasing urbanisation, many slash-and-burn farmers in tropical countries will leave the forest frontier and move to cities, where economic opportunities are greater.

This, he argues, will alleviate pressures on forests by slowing the loss of old-growth forest and allowing secondary forests to regenerate on abandoned farmland.

Such trends will reduce species extinctions, Dr Wright believes, because less old-growth forest will disappear and because some endangered species will survive in secondary forests.

Rose-tinted rainforests

For some, his outlook is too optimistic.

While few dispute that urbanisation is occurring, it may not lead to much forest recovery.

Pasture land with a few remnant trees (Image: Robin Chazdon)

Young secondary forests are scrubby and sparse, differing dramatically from old-growth rainforest

This is because large-scale corporations - industrial logging, agribusiness, biofuels, and oil and gas industries - and globalisation are increasingly causing more forests to be lost.

Indeed, a single bulldozer can clear as much forest as dozens of machete-wielding farmers, so rates of forest loss may accelerate in the future, not slow down, even if rural populations should decline.

In addition, many question Joseph Wright's assumption that endangered species can survive in secondary forests.

In regions such as the Amazon, the average age of secondary forests is just six to seven years.

Young secondary forests are scrubby and sparse, differing dramatically from old-growth rainforest, which has towering canopy trees, a uniquely dark and moist microclimate, and literally thousands of plant and animal species per hectare.

Typically, young regrowth forests sustain many generalist and weedy species, few of which are likely to be endangered.

Future threats

Finally, tropical species face perils above and beyond habitat destruction.

Many, including apes, monkeys, and forest elephants, are being killed off by rampant overhunting and the commercial bushmeat trade.

Road leading into an old-growth forest (Image: Robin Chazdon)

Habitat destruction and climate change are both dire threats to rainforest species

Others are being driven to extinction from exotic pathogens, such as the deadly chytrid fungus, that has wiped out hundreds of tropical amphibians.

Rainforests are also being degraded by selective logging, habitat fragmentation, and surface fires, all of which harm disturbance-sensitive species.

And global warming could be a far greater peril to the tropics than many realise; indeed, Dr Wright himself has begun to emphasise the importance of global warming.

In the tropics, where temperatures are nearly constant throughout the year, many species are thermal specialists.

Those living in the hot lowlands may already be dangerously close to their thermal maximum, whereas those in the cooler mountains will have nowhere to go as conditions get hotter.

Hence, habitat destruction and climate change are both dire threats to rainforest species.

What are the implications of our Smithonian debate?

Firstly, the controversy has highlighted a need for more research in a variety of areas.

For instance, we need to know which species will survive in secondary forests, and how different environmental factors such as habitat loss and global warming will interact to threaten species.

Even Dr Wright's staunchest critics credit him with bringing new perspectives to tropical conservation.

Secondly, we need to promote international carbon trading to slow deforestation and promote forest regeneration.

At the moment, landowners in tropical nations usually receive nothing for conserving their forests, which perform vital ecosystem services that benefit us all - such as storing carbon, helping to regulate the global climate, and conserving biodiversity.

Carbon trading provides a mechanism whereby wealthy nations can bear some of the costs of forest protection, a vital goal given that tropical deforestation produces a fifth of all greenhouse gas emissions today.

Lastly, we direly need the US to ratify the Kyoto Protocol (or a similar international framework) to limit its carbon emissions.

This will not only slow global warming but it will greatly increase the demand for carbon credits, some of which can be used to help slow deforestation.

Reducing deforestation will not only help our battered climate, but it will preserve some of the most imperiled species and ecosystems on earth.

Our debate in Washington occurred just days before the inauguration of President Obama.

With many Washington insiders and political staffers in our audience, we are hopeful our message was heard in high places.

Like many others, we are counting on the Obama administration to have more forest- and biodiversity-friendly policies than we've seen in recent years.

Dr William Laurance is a scientist for the Smithsonian Tropical Research Institute, Balboa, Panama

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