Climate change is making the European Alps greener: detailed long-term studies have shown that snow cover is retreating and species richness increasing at high elevations. But what kinds of plant are best able to take advantage of this changing environment? To answer this question a team from the WSL Institute for Snow and Avalanche Research SLF in Davos and the Université de Lausanne in Switzerland re-surveyed plant species on 120 Swiss mountain summits (ranging in height from 2449m to 3418m) one century after the first surveys were carried out.

They found that species numbers increased for all the plant traits that they considered, but one trait in particular gave plants a major leading edge when it came to colonizing summits. This favourable trait was 'pappus' – seeds (such as dandelions) that have hairs on that help the seed to fly in the wind.

"On mountain tops the wind is generally stronger and more frequent than in lowlands and the ability to disperse efficiently in the wind probably helped the species to colonize new summits," explained Magalì Matteodo, lead author of the research, which is published in Environmental Research Letters (ERL). "Moreover, this pappus allows heavier seeds to be carried, and hence there are more nutritive reserves in the seed for establishment in harsh, mountain conditions."

Many summits are now marked by the yellow of the Alpine dandelion (Taraxacum alpinum) and Swiss Hawkbit (Leontodon helveticus), both of which have pappus seeds. So what exactly is it that has made these mountain tops more hospitable to these traditionally lower alpine species? Matteodo and her colleagues think that temperature is the most important driver.

"Warmer temperatures decrease the length of the snow cover and increase biological activity, an important factor in these cold conditions where growth is often limited by low temperatures, even in summer," she told environmentalresearchweb. "Hence, plants can start to grow earlier and grow quicker."

Other plants were also gaining ground but much more gradually. Cushion plants (slow-growing species with a compact, hemispherical shape) and species with capsule fruits (where multiple seeds release from a pod, such as poppy) were slower than pappus plants to colonize the warmer alpine summits, but were still increasing in number.

Ultimately, the change in plant species will result in a new ecosystem establishing in high alpine environments. Small and large herbivores, and their predators, will likely follow the plants. "Already we have indications (unpublished Masters’ thesis) that the distribution of grasshoppers has changed in parallel to plant distribution but the results are not clear yet," said Pascal Vittoz of the Université de Lausanne.

So, plants with pappus seeds appear to be the current winners but what kind of plants are losing out? Matteodo and her colleagues couldn’t see a clear correlation between any particular plant traits and disappearing species. Instead, extinctions to date seem to reflect rather random processes.

Do these changes in high-altitude flora matter? Should we be doing anything about it? The scientists will be considering these questions and many others at their upcoming conference: "Faster, Higher, More? Past, Present and Future Dynamics of Alpine and Arctic Flora under Climate Change" on 22–25 September 2013, at Kurhaus Bergün, Grisons, Switzerland.

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