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.
We all know tropical rainforests are the world's biologically richest ecosystems and are rapidly disappearing.
Many species, including apes, monkeys, and forest elephants, are being killed off by rampant overhunting and the commercial bushmeat trade
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.
For some, his outlook is too optimistic.
While few dispute that urbanisation is occurring, it may not lead to much forest recovery.
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.
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.
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
The Green Room is a series of opinion articles on environmental topics running weekly on the BBC News website
Do you agree with Dr Laurance? Is nature more resilient than we give it credit for? Can secondary growth in tropical forests sustain the vast majority of biodiversity? Or do we need to ensure that old-growth forests are protected from exploitation?
Urbanization won't stop deforestation- it will put even greater pressures on forest resources- the way forward is to understand that 'rampant consumption' led society will ultimately create havoc for the world.
Sushant Pandit, New Delhi, India
The decline of old growth forests on the earth needs to be looked at as one of the most important issues on the planet. As in, our disappearing forests should have bigger headlines than the economic slump of our economy. With no life their will be no economy to complain about. but the significance of second growth should not be overlooked. The second growth can be looked at as a sort of "refugee camp" for outcast animals, who will will at least be able to fair longer than with no forest at all. Forest growth takes place on a very macro level and as humans it hard to imagine a time span of 400 years or more. These aged forests are of course more desirable as they offer a far greater amount of biodiversity for ecosystems to be built upon. All in all, the ancient forests need to be protected, as do second growth, because they are the beginning to the future of life here on earth, though they may not yet provide the necessities to maintain the vast ecosystems of their elders, they will eventually.
evan sztricsko, vancouver canada
Few researchers know tropical forests like Dr. Laurance does. His point is absolutely right. What I don't understand is the optimism of Dr. Wright in the face of the current deforestation rates worldwide. I don't know how much forest cover will remain by 2050, but what if Dr. Wright is wrong? What if people stops moving to cities and/or they increase ANYWAY their unsustainable use of forest's goods and services? We can't afford more mistakes with these wonderful ecosystems.
Luis G. Morales, Caracas, Venezuela
All I know is that if we don't do something, our world can change.We need to come together and do what's right for our polluted earth.
Lela Culpepper, Houston,Texas, America
Too many people and not enough space.There are only a certain amount of resources and when they cannot sustain humanity a dark period beckons.First goes the forest,then the animals in it.Only the generalists and pests survive like rats, cockroaches,cane toads etc etc
Jay Cobden, Colchester,UK
All secondary grown forests that I know are less diverse than the original ones. That is especially true to amphibians. In recent years, a huge decline in the populations of these animals has been reported. And also, if we give enough time for secondary growth forests to grow old, some species won't reappear, because of local extinction. So, if we continue with the current rates of deforestation and natural resources consumption, the extinction trend we now observe will only worsen.
Ulisses Imianovsky, Pomerode, Brazil
This article prompted a lot of thought. I remembered the temperature differences between second growth and old forest areas from when I was a kid and how dense a hedge row or the edge of forest could be. The way even the little streams didn't dry up in the old forest and how different types of trees had to fight it out with nasty weeds and vines to grow back. I'd imagine there are quite a few similarities where ever a forest tries to grow back but the scale of deforestation in the tropics has to be taking its toll. Now with a click of the mouse people can get information on seed dispersal in tropical forests and how species rely on each other to keep the forest whole. I think new leadership in my country does indeed know how things are interconnected and how tropical forests play a part in keeping our planet whole.
Dale Lanan, Longmont, Colorado, USA
I feel totally sick that here in Australia, our governments talk about saving tropical forests in other countries to help the planet, yet we are allowing the wholesale destruction of our own extraordinary forests. The Tasmanian and Victorian governments have long been infiltrated by an 'economic rationalist' insane wish to industrially harvest native forest as a point of principle. The ruination of our wild places and river catchments is rudely ignored. International pressure would be most appreciated. Tasmania's majestic forests cry out for world attention to stop the destruction. Help us, please.
Angela Halpin, Trentham, Victoria, Australia
I agree with Dr Laurance, we can not limit ourselves to think what is going to happen in the future, we all have to act now, if we allow it happen, we will not can fix it, and it is not to fix, it is to prevent how fast the global warming increase. We need to protect old-growth forest, it will not only save endangered species in the forest; by storing carbon, they help to support the earth temperature and save marine habitats.
Daniel Francisco Bernal Galeano, Bogotá Colombia
Of course we need to stop all old growth loss.The age of ever increasing human economic/population growth must end.The alternative is an unsustainable nightmare.
steve johnson., Whitwick Leics.
I am sorry, I do not agree. I cannot understand how we just stand by & let this all unfold. Its like Bush with global warming - "Its not happening, etc". What will happen when its all gone & we roast???
Roger Southall, Wolverhampton
Nature may be resilient over the short term but global health over the long term requires a delicate harmony that old-growth forests exude and we barely understand.
Larry Mather, Cathedral City, United States
How can we reduce deforrestation when all our human pressures are up up up; why are the natives leaving the forest margins for cities; to make more money, to buy more stuff; to have more people, who want more timber, and cut down more trees. . . . We've run out of stuff folks ! - we've run out of all the stuff because we've run out of Planet. And until we stop - that's spelled S T O P; look it up in the dictionary ! - we are going to kill all the trees, kill all the other species; then the bugs that are left will all prey on us; and we are going to kill ourselves. CO2, deforrestation, biodiversity; these are all symptons. The problem is "us" And til we get our heads around the problem; "human activity" - til then, we are going to trash the lot ! Trees, apes, water, air; we are going to trash the lot !
Steven walket, Penzance
There is already plenty of evidence from around the world that "regenerating" forest generally lacks the specialists of old forest (although the plant species may look much the same or be more diverse). Even if there were no such evidence, a precautionary approach should be adopted: we should assume impoverishment and loss of integrity unless proven otherwise, especially in the tropics where such losses are more likely to be permanent. Good article - and thanks for your efforts!
Clive Hambler, Oxford, UK
A few plant and animal species may thrive in a dramatically altered ecosystem; however, the vast majority of species will be driven extinct if current rates of rain-forest destruction continue. Rain-forests are a highly complex and inter-woven environment in which animals/plants have adapted very gradually over thousands of years. A dramatic example is the destruction of Brazil's Atlantic rainforests, which has resulted in the extinction of thousands of life forms. Why should we expect other tropical forest areas to be any different? How many more broken links in the chain of life can Mother Nature endure before the entire system implodes? At the current rate we are soon to find out. Thank you.
Frank Friedrich Kling, Woodstock, IL
Global WArming also leads into Weather disruptions regarding rainfall and other elements. It impacts on the forest survival and recovering and can do stronger damage, which would also impact on secondary forests. In Areas like amazon the amount of good soil is kept due the forest diversity. It is common in many areas the subsequent desertification which comes before the time to develop the secondary forest. Of course, for the cases when it develops, most of the diversity have been killed or got into strong competition through the food chain. Something will survive but hardly to say the exact % of it. Forests is a delicated balance between flowers, fruits, insects and protection. When everything have been whipped out, local nature have a severe damage what takes longer to recover itself which will be adpted into the new balance based on the species which had survived their local own apocalipse.
Carlos Frohlich, London
If President Obama achieves nothing else designed to help the environment this year, I hope that he will find an effective and fair way of protecting the world's rainforests as part of the next version of Kyoto.
Dr Matt Prescott, Oxford