Altitude-dependent responses of dryland mountain ecosystems to drought under a warming climate in the Qilian Mountains, NW China

Abstract

Climate warming has intensified drought severity in many areas of the globe. Dryland mountain ecosystems are sensitive to climate variability. However, the response of mountainous vegetation to drought has high uncertainties due to the rugged terrain and varied local climate and is still not well understood. In this study, the Qilian Mountains (QLMs) in northwestern China, which have a typical dryland mountain ecosystem and experienced intense climate change, are selected as a case study area. We utilized a downscaled normalized difference vegetation index (NDVI) product and climate data to explore the spatiotemporal dynamics in vegetation greenness and the climatic drivers for the period 1982 ∼ 2018. We studied the response of different vegetation types to drought at different altitude gradients Results suggest that most areas in the QLMs displayed an upward trend in greenness and the greening rate was greater in the southeast, while vegetation degradation occurred in the western part. The grass and shrub communities showed a decreased sensitivity to drought at the medium altitudes and increased sensitivity at the lower and upper limits of their distribution altitudes. The broadleaf forests showed intensifying drought sensitivity at all elevations. Coniferous forests and alpine meadows respectively displayed decreasing and increasing trends of sensitivity to drought along elevations. A combination of the fastest warming and mildest wetting trends over the lowest (<3200 m) and highest (>4200 m) elevations are likely exacerbating the vulnerability of vegetation to drought. By contrast, the medium elevations (3200 ∼ 4200 m) have experienced rapid wetting and relatively slower warming, and the vegetation is expected to be less affected by drought if the current climate change trends continue. These findings help to better understand how these dryland mountainous vegetation communities respond to drought under a changing climate and provide some insights into the protection of these vulnerable ecosystems for the local managers.