Cushion plants are found in mountain environments all over the world, including here in the Andes (Image: Chris Mattison/Naturepl.com)

They look like comfy cushions from the outside, but inside they contain mini-ecosystems, sheltered from the harsh mountain environment around them.

One of the best ways for mountain plants to maximise their chances of survival in extremes of wind and temperature is to form a dome shape. Hundreds of species do it, including the two-flower cinquefoil (Potentilla biflora, pictured below).

Now it appears that many more species, from microbes to animals, exploit these domes too. Within each cushion plant's structure is a totally different world - a sheltered microcosm with moderate temperatures, higher moisture and good soil.

"They form a shape that can be compared to a turtle," says Fabien Anthelmeof the French Institute for Development Research based in La Paz, Bolivia, who studies alpine plants. "It allows them to develop their own microenvironment, which is moist, warm and rich in nutrients."

Working in the Altai mountains of Siberia, between 1750 and 4000 metres above sea level, Igor Volkov and Irina Volkova from the Tomsk State University found that temperatures fluctuated much less within domes than outside, where they could vary from well below freezing to 15 °C over the course of a day. Inside, it remained a relatively benign 5 to 7 °C.

The environment within the cushions favours microbial activity. Dead leaves and plant matter that gets trapped in the cushion decays rapidly, and this compost in turn encourages further plant growth.

The researchers found, for example, that soil under the two-flower cinquefoil contained 15 times as much humus as the rocky area near it. The soil was also much richer in nutrients like nitrogen and phosphorus.

Two-flower cinquefoil, one of many cushion-forming plants (Image: NPS/Jacob W. Frank)

This allows other plant and animal species to thrive within the domes, says Juha Alatalo from Uppsala University in Sweden, who studies alpine plants and climate change.

Another team, led by Yang Yang from the Chinese Academy of Sciences in Kunming, studied cushion plants in the Himalayan Heng Duan mountains in southern China.

They found that the diversity of plant species within the cushion domes is about 30 per cent higher than it is outside. Species that could not otherwise survive were able to do so within these havens.

As habitats grew more severe with higher elevations and lesser rainfall in the different Heng Duan study sites, Yang Yang's team found that the number of species found outside cushion domes decreased at a faster rate than within the domes. In other words, cushion plants were the last remaining oases of life in these frontier environments.

"Cushion-forming plants are very tolerant to abiotic stress, like drought and cold temperature," says Anthelme. As such they act as a foundation for alpine ecosystems and are able to "heal" degraded soils, he says.

"As a typical ecosystem engineer in the alpine region, cushions have cascade effects on the function of the high elevation ecosystem," says Yang Yang.

Their presence is key to preserving the biodiversity of alpine areas, he adds. (New Scientist)