Heat stress is killing forests

Woodlands at risk as mercury climbs http://www.theage.com.au/environment/climate-change/woodlands-at-risk-as-mercury-climbs-20141223-124s2a.html December 24, 2014 – Peter Hannam

Trees – even Australia’s hardy eucalypts – can take only so much heat, writes Peter Hannam. Trees are dying from heat stress in the forests of Europe, Asia and North America and it is inevitable rising temperatures will start to damage even Australia’s hardy woodlands, says Derek Eamus, a plant physiologist at the University of Technology, Sydney.

“At 50 degrees, you just start to see massive mortality in the canopy, even in the eucalyptus,” Eamus says.

Many studies have focused on how vegetation initially benefits from increases in carbon dioxide – a plant food – provided adequate water and soil nutrients are available. Less understood, though, is how trees cope with higher temperatures, particularly when humidity drops. That gap is partly because humidity conditions have been difficult to replicate at large scale.

“Stomata of all plants respond to decreased humidity by closing their apertures so they can reduce the amount of water they have to spend,” Eamus says. Less transpiration, though, means ambient temperatures are hotter.

Droughts will make the problem worse as eco-systems are already under stress. “The incoming solar radiation can’t evaporate the water from soil and leaves, [so] it heats the canopy, ground and air,” he says.

Some species are less adapted to rising temperatures than others, so the biodiversity balance will shift. Eamus predicts alpine forests – which are forecast to see some of the biggest temperate increases – “are going to be first ones to keel over”.

December 24, 2014 - Posted by Christina Macpherson | Uncategorized

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