Mass elevation effect (MEE) has been qualitatively considered to influence the elevational distribution of treelines in large mountains. Prof. ZHANG Baiping’s mountain GIS research group at the Institute of Geographic Sciences and Natural Resources Research (IGSNRR) of the Chinese Academy of Sciences, quantitatively found the contribution of MEE to the high treeline distribution in the Rocky Mountains in North America. MEE of the target region is further modeled with three factors of mountain base elevation (MBE), latitude, and hygric continentality. This work has been published in Physical Geography.

MEE is virtually the heating effect of mountain massifs and can be defined as the temperature difference on a given elevation between inside and outside of a mountain mass. However, this effect and its implications for mountain altitudinal belts have not been well studied until recently.

Researchers developed MEE models with three factors of MBE, latitude and hygrometric continentality on a global scale. As a result, the altitudinal distribution of global treelines can be more accurately modelled when taking MEE into account. MBE usually acts as the primary factor for the magnitude of MEE and, to a great extent, could represent MEE. "MEE leads to higher treelines in the interior than in the outside of mountain masses,” said ZHANG.

“It makes montane forests to grow at 4800–4900 m and snowlines to develop at about 6000 m in the southern Tibetan Plateau and the central Andes, and large areas of forests to live above 3500 m in a lot of high mountains of the world”, he said.

The result shows that MEE contributes the most to treeline distribution pattern. Without MEE, forests could only develop upmost to about 3500 m above sea level and the world’s ecological pattern would be much simpler.   

ZHANG's mountain GIS group, supported by the National Natural Science Foundation of China, has carried out in-depth research on the conceptualization and quantification of MEE in the world’s main mountain ranges and plateaus including the Tibetan Plateau, the Alps, Scandinavia, the Andes, the Rocky Mountains and the New Zealand mountains.

The Rocky Mountains are the highest and most extensive in North America. Their MEE should be strong and responsible for the high elevations of treelines in the interior of the mountain range.    

Under ZHANG's guidance, Ph.D. student WANG Jing calculated the temperature difference (ΔT) between the inner and outer Rocky Mountains at the same elevation and developed a MEE model for the Rocky Mountains. They found that ΔT was mostly between 2.1 and 4.1°C in the Colorado Rockies and the southern Wyoming area. Their study showed that treeline was higher in the interior than in the outside of the mountain range, by 700–1400 m.    

It was further revealed that MBE contributed most to MEE both in the whole range (45.65%) and in the Colorado Rocky Mountains (55.21%).

This work was supported by the Innovation project of State Key Laboratory of Resources and Environmental Information System (LREIS) and the National Natural Science Foundation of China.