Climate change is shrinking Australian plant leaves

If your plan for escaping climate change is to hide in the shade of a tree, you might be out of luck. It turns out the leaves of some plants are shrinking in response to the warmer weather.

But bad news for shade-lovers may be good news for plant conservation. The changes could indicate that plants are evolving rapidly to changing conditions, suggesting they have a better chance at survival.

"Often we consider that climate change is something that is going to happen in the future," says Andrew Lowe, a plant conservation biologist at the University of Adelaide in Australia and a key investigator on the study. "But we've already seen substantial changes in the Earth's climate and so we should expect that there have been changes to the Earth's plants."

While earlier studies have observed climate-change-induced alterations in plant's flowering time and animal migration patterns, this is the first evidence of changes to plant shape, Lowe says.

Analysing about 500 historic and new samples of a type of Dodonaea viscosa ? an Australian shrub in the Lychee family ? Lowe and colleagues found average leaf width has shrunk by 2 millimetres, or 40 per cent, over the past 127 years.

Across the region, the northerly, warmer areas tend to have plants with wider leaves on average. A narrowing of leaf width of 2 millimetres is equivalent to a difference in latitude of 300 kilometres.

Ray of hope

"There is some good news here in that some Australian plant species may have the potential to respond to, and cope with, increasing temperatures," says co-author Greg Guerin, also from the University of Adelaide.

The changes to the leaf size could be due to "plasticity", where individual plants shrink their leaves in response to warm weather. Alternatively, it could be due to migration, where plants that used to grow further north are moving south. There is a third possibility, however: the change in leaf size could be an evolutionary adaptation to climate change, says Guerin.

Although this might be good news for some species, Guerin points out that adaptation is unlikely to help some of the most vulnerable species.

"Other species have less potential to adapt. These species may rely more heavily on tracking favourable climate through migration but this can be problematic in a landscape fragmented by human activity," he says.

The next step for the team is to figure out whether other features of plants are also changing to cope with warmer weather and to find out how widespread these changes are among different species.

"The value of historical collections is huge. You can't replicate that kind of sampling."

Journal reference: Biology Letters, DOI: 10.1098/rsbl.2012.0458

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