Stealing the Rain from a Rainforest

ALERT’s Susan Laurance, from James Cook University in Australia, is leading an ambitious, million-dollar study to understand how droughts affect tropical rainforests.  Here she tells us about this challenging project and why it is so important:

Right now, much of the world is struggling to cope with a ‘Godzilla’ El Niño drought. 

The drought has been merciless, causing catastrophic fires and haze across much of Southeast Asia, unprecedented droughts and wildfires in western North America, and mass starvation from crop failure in New Guinea. 

Fiery future?

And there’s good reason to think future droughts might even be worse. 

First, leading computer simulations suggest global warming could strengthen future El Niño events and increase the frequency of serious heat waves.

Second, apparently new climate dynamics are appearing on Earth that could threaten large areas of rainforest.  Most notable among these are the unprecedented Amazon droughts – driven by exceptionally high sea-surface temperatures in the Atlantic Ocean – that occurred in 2005 and again in 2010.

Finally, human land-uses are making rainforests far more vulnerable to droughts and fire.  For instance, forests that have been logged or fragmented are drier and have much heavier loads of flammable slash than do pristine forests.

And as new roads proliferate almost everywhere, so do the number of human-caused ignition sources.  Even ecosystems where fire was once foreign — such as the world’s deep rainforests — now burn with increasing regularity.

All this means that it’s vital to understand how droughts will affect rainforests – the world’s most biologically diverse and carbon-rich ecosystems.

Big science for a big problem

As I detail in a recent article in Australasian Science (which you can download here), my colleagues and I have recently set up some 3,000 clear plastic panels to create a ‘raincoat for a rainforest’ – inducing an artificial drought over several thousand square meters of the famous Daintree region in north Queensland, Australia.

A big advantage of our experiment – one of the few ever to study rainforest droughts in this way – is that we have a 47-meter-tall canopy crane at the site, so we can assess plant and animal responses at all vertical levels of the forest, from the ground to the tops of the most towering trees.

Our study is comparative: we want to understand how different groups of plants, such as various functional groups of trees, vines, shrubs, forbs, and epiphytes, are affected by drought.

We are looking at the survival, growth, and physiology of these plants in a variety of ways, as well as at the forest soil and microclimate.  Others are studying how insects and other fauna are affected by the drought.

Among our key goals is determining whether big trees are especially vulnerable to droughts, as suggested by recent research.   If so, then this could have profound implications – because big trees store huge amounts of carbon and provide food and shelter for an entire zoo of animal species.

We also want to learn whether certain kinds of plants have strategies – such as special water-carrying vessels in their tissues or other physiological tricks – that allow them to better survive droughts.  If so, these ‘drought winners’ could increasingly dominate forests if droughts become more intense in the future.

Not easy – but worth it

This study has not been easy – in truth it’s been a logistical nightmare to steal the rain from a rainforest.  But the study is now fully set up, and in the end we think it will be worth all the sweat and hard work. 

Rainforests are the biologically richest environments on Earth.  And if we’re going to subject them to more Godzilla-like droughts, then we need to know how they’ll respond – and whether they can sustain their stunning biodiversity into the future.