The surprising shapes of mountain ranges

Ask someone to draw a mountain range, and chances are they’ll sketch a series of triangles. Mountains shrink the higher you go, people assume, so montane species are particularly vulnerable to climate change. To escape rising temperatures, these animals will be forced upslope into tighter quarters, increasing their risk of extinction.

But a new study suggests that this idea is too simplistic. Mountain ranges come in a variety of shapes, and counterintuitively, many of them have more area at higher elevations. While some montane species will certainly suffer from narrowing habitats, others may encounter more space as they migrate upward.

Scratching your head? The Earth as a whole does have far less land at higher elevations, and one mountain peak has much less space at the top than the bottom. But if you look at mountain ranges, more complex patterns emerge. Steep slopes can open up to large plateaus. In a press release, one study author compares this type of landscape to “a giant table where a leg represents a steep, limited-area climb that leads to a high-altitude expanse.”

To catalogue the types of shapes, the team studied data on 182 mountain ranges around the world. About one-third of the ranges looked like a typical pyramid: the area decreased as elevation increased. But the rest had more unexpected configurations. More than a third were classified as diamonds, meaning that the area increased toward mid-elevations and shrank again at the top. About a quarter were hourglasses, slimming down toward the middle and then expanding. And 6 percent were inverse pyramids, increasing in area the higher you climb.

These findings complicate the picture for mountain species conservation. Animals near the peaks, such as snow leopards, are still out of luck. But species living on the foothills of diamond ranges will initially have more space as they move upward. Those near the bottom of hourglass ranges will be squeezed into tighter spaces before their habitat opens up, and they may require more attention during the bottleneck stage. So scientists and managers will need to tailor their conservation strategies to the mountain range’s topography. Roberta Kwok | 21 May 2015

Source: Elsen, P.R. and M.W. Tingley. 2015. Global mountain topography and the fate of montane species under climate change. Nature Climate Change doi: 10.1038/nclimate2656.

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