Climate 'causes leaves to narrow'

Herbarium sample of narrow-leaf hopbush (Image: Greg Guerin/Haixia Wen/Andrew Lowe) Herbarium samples helped the researchers compare leaf widths over more than a century

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Leaves are getting narrower on some plant species as a result of changes to the climate, a study has suggested.

A team of Australian researchers studies specimens from the wild and from herbarium collections stretching back more than 120 years.

Analysis of the herbarium samples found that leaf width had decreased by two millimetres.

The findings of the study, described as the first of its kind, appear in the Royal Society journal Biology Letters.

Lead author, Greg Guerin, from the University of Adelaide, said the team chose narrow-leaf hopbush (Dodonaea viscosa subsp. angustissima) as it appeared to display different leaf characteristics in different climates.

"We followed this up by examining exciting herbarium collections before beginning to gather [field] data," he told BBC News.

The researchers looked at more than 250 herbarium specimens collected from one region: Flinders Ranges, southern Australia's largest mountain range.

Dr Guerin observed: "Historical herbarium collections provide immediate access to wide sampling throughout a geographic region and through time.

"You just can't replicate that kind of sampling, covering hundreds of kilometres... from one region over 130 years."

To support this data, the team gathered 274 field samples from a mountain, collecting specimens at every 50m drop in altitude.

"This gave us information on variation within populations and the local influence of altitude on leaf shape and size," Dr Guerin explained.

The analysis revealed a two-millimetre decrease in leaf width over 127 years across the region.

Between 1950 and 2005, the team added, there had been a 1.5C (2.7F) increase in the maximum temperatures in the region but there had been little change in rainfall patterns.

Next steps

Dr Guerin said: "The next step is to test whether similar patterns are emerging in other species and in other regions."

He acknowledged that because the study was the first of its kind, there was no comparable data at this stage.

"We chose a likely candidate species - one that appeared to vary in leaf shape with latitude - but given that the first species we tested revealed strong change over time, it may well be that similar shifts are occurring more widely."

Dr Guerin said that the shift in leaf shapes could, in some cases, have wider ecological consequences.

"The study is a new example of significant climate change responses to date," he said.

"We now know that every degree of warming is ecologically significant and generating ecological disequilibrium.

"There is some good news here in that some Australian plant species may have the potential to respond to and cope with increasing temperatures."

But he warned that other species might be less well suited to adapt.

"These species may rely more heavily on tracking favourable climate through migration.

"A recent study by a student in our group (the Andy Lowe laboratory) looked at the climate change sensitivity of a habitat-restricted plant species endemic to the same Flinders Ranges region in South Australia.

"The species had low adaptive capacity because of a combination of low genetic diversity and small, isolated populations.

"This is a problem because its current climate niche is predicted to shrink over this century."

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