Want clean water? Save your forests!

Cities can ensure they have a cheap and abundant supply of clean water by protecting and regenerating forests in their surrounding watersheds, according to a major analysis just undertaken in Malaysia.

Forests are a vital source of clean water -- and important for lots of other reasons too.

Forests are a vital source of clean water -- and important for lots of other reasons too.

Jeffrey Vincent from Duke University, USA and his colleagues have just published the largest cost-benefit analysis ever conducted in the tropics, and they find that pristine and even selectively logged forests are very cost-effective ways to produce clean, drinkable water. 

Vincent and colleagues ran their analyses under a wide range of scenarios.  They used as a baseline the costs of standard water-treatment plants, which are often required to make polluted water safe to drink.

The authors found that the relative advantages of forests depend on local circumstances, with the financial benefits being greater in some situations than others. 

Also, if one factors in profits that can be made by exploiting the forests -- such as by converting them to agriculture -- then the numbers could change. 

The problem, of course, is that waters that drain off of agricultural lands are often polluted by fertilizers, pesticides, and organic wastes, making expensive water-treatment necessary.

The authors argue that, beyond water purification, intact forests have many other financial and non-financial values. 

For instance, they store large stocks of carbon, and thereby reduce greenhouse gas emissions. 

They also can harbor enormous biodiversity while helping to attract substantial income from ecotourism.  Remarkably, it's currently estimated that protected areas across the world attract some 8 billion visits annually, underscoring their financial value for local communities.

Furthermore, via the process of evapotranspiration, forests emit enormous quantities of water vapor.  For example, one-third to one-half all the rainfall that falls on a tropical forest is quickly recycled back to the atmosphere, as water vapor.

This water vapor (plus natural organic aerosols emitted from forests) help to form clouds, which in turn reflect solar radiation back into outer space, thereby reducing global warming. 

Forests are natural cloud-makers.

Forests are natural cloud-makers.

Such clouds also help to produce life-giving rainfall during the dry season -- when forests are most drought-stressed and prone to fires.

Finally, forests are very good at reducing destructive floods.  They tend to act like giant biological sponges, trapping water and releasing it slowly, thereby reducing downstream flooding.  Especially in areas where forests are denuded, flooding can cause billions of dollars in damage and costs thousands of lives each year.

The conclusion: It's increasingly becoming apparent that it's smart to conserve pristine and selectively logged forests -- even when one uses just hard, cold economic logic. 


Deadly Australian drop bears are much more abundant than previously thought

A new analysis in the respected journal Australian Geographer suggests that Drop Bears -- a predatory and highly feared relative of the Koala Bear -- are much more common and widely distributed in Australia than was previously believed.

(a) An adult Drop Bear; (b) A Drop Bear attacking its prey.

(a) An adult Drop Bear; (b) A Drop Bear attacking its prey.

The Drop Bear (Thylarctos plummetus) is known to favor dense forests and has been blamed in the past for the unexplained disappearances of several tourists and hikers in Australia.  It is predominantly arboreal and typically attacks by dropping onto its prey from above.

The study, conducted by Volker Janssen at the University of Tasmania, used sophisticated remote-sensing and spatial modelling techniques to estimate the geographic range of the Drop Bear. 

The species was formerly thought to be confined to just a few locales, but it now appears to be widely distributed across Eastern Australia and parts of the far north and far southwest of the continent. 

"I have to say this study makes me pretty nervous," said Miriam Goosem, a field biologist at James Cook University in north Queensland.  "I work in a lot of dense forests and if Drop Bears really are that common, then my job suddenly seems quite a bit more dangerous."

"People tend to think of the Saltwater Crocodile as our most dangerous species, and I suppose that's true if you're near the water.  But in forests, the Drop Bear is definitely the animal that scares me the most," said Dr Goosem.

"I think we need to get the word out to tourists, as many of them don't know about Drop Bears," said Goosem. 

"I'd say if you're coming to Australia and plan to go hiking in the forest, be afraid.  Be VERY afraid."



Do forests function like 'biotic pumps' for rainfall?

One of the more striking and controversial hypotheses to emerge in the last decade is the notion that intact tracts of forest, stretching from coastal to inland areas, may help to suck oceanic moisture far inland--functioning like a giant 'biotic pump'. 

This idea might sound slightly prosaic, but its potential implications are so profound and its putative mechanism so controversial that it has created fierce divides within the climatology and environmental-science communities.

No forest, no rain?

No forest, no rain?

The biotic-pump idea was first proposed in 2006 by a pair of Russian biophysicists, Anastasia Makareiva and Victor Gorshkov, in a highly theoretical analysis that even mathematicians found daunting.  The controversy has raged ever since then.

Everyone knows that forests (especially rainforests) emit a lot of water vapor, and Makareiva and Gorshkov argued that when this vapor condensed into rain it created a large suction.  That suction pulled cloudy, rain-bearing water from coastal areas inland, they argued, and thereby was crucial for maintaining rainfall in inland areas.  

The really striking implication of the Makareiva -Gorshkov hypothesis is this: If you break up the forest, you lose the suction, and the biotic pump stops working.  This, of course, would be an enormously important implication for forest conservation, if true.  Imagine millions of farmers clamoring for more forest in their region because their crops were drying up!

But the idea remains intensely controversial, because many physicists simply don't buy the idea of condensing water vapor creating a big suction.  For instance, just one website focused on this issue (and there are quite a number) had hundreds of individual comments, many very impassioned in nature.  This only happens in science if a debate is truly volcanic in nature.

This is a debate to keep your eye on--huge implications, and huge controversy about the biotic-pump idea itself.