Heterogeneous Responses of Alpine Treelines to Climate Warming across the Tibetan Plateau

Abstract

The Tibetan Plateau hosts a continuous distribution of alpine treelines from the Qilian Mountains to the Hengduan Mountains and the Himalaya Mountains. However, not much is known about the broadscale alpine treeline dynamics and their responses to climate warming across the Tibetan Plateau. Herein, we collected a total of 59 treeline sites across different forest regions of the Tibetan Plateau and the related field data (i.e., upward advance magnitude, tree recruitment and height growth), expansion potential (i.e., elevational difference between the current treeline and the tree species line (EP)) and vegetation TI (an index of species interactions) from the published references. Site characteristics (e.g., elevation, slope and aspect) and the related environmental factors were used to analyze the relationships between treeline shifts and environmental variables. Despite increases in the recruitment and growth of trees at most treeline sites, alpine treeline positions showed heterogeneous responses to climate warming. Most treelines advanced over the last century, while some treelines showed long-term stability. EP was significantly and positively linked to the summer warming rate and treeline shifts, suggesting that the position of current tree species line is of crucial importance in evaluating treeline dynamics under climate change. In addition, warming-induced treeline advances were modulated by plant–plant interactions. Overall, this study highlighted the heterogeneous responses of regional-scale alpine treelines to climate warming on the Tibetan Plateau.

Chapter 4: Effects of a changing cryosphere on biodiversity and ecosystem services, and response options in the Hindu Kush Himalaya

“…Similarly, an overall advancement of the treeline in the Tibetan Plateau and adjacent mountain regions in China has also been reported (Wang et al, 2022). Wang et al (2022) have recorded rapid advancement (>10m) of the treeline across the Tibetan Plateau for 50.8% of the sites studied over the past century while they have recorded slow advancement (0-10m) for 16.9% of the sites, and a stable treeline for 32.2% of the sites. Researchers have also observed an advancement of tree species including Pinus wallichiana in glacier-retreated sites in the HKH (Sigdel et al, 2020).…”

“…Permafrost, an important component of, and contributor to, the alpine ecosystems has been less studied. The interactions and links between permafrost and alpine ecosystems remain under explored in the region (Wang et al, 2022).…”

Fifty years of change in the lower tree line in an arid coniferous forest in the Qilian Mountains, northwestern China

“…During adaptation to climate change, forest ecosystems may fill in their interiors rather than shift the position of the tree line [ 51 – 53 ]. In a study of the forest line in the Himalayan Mountains (including the Qilian Mountains), the changes in forest line exhibited high heterogeneity, with 67.7% of the tree lines shifting upward, 73% of the forest lines exhibiting an increase in tree recruitment, and 67.8% of the forest lines presenting acceleration of tree growth rates [ 4 ].…”

“…line in the Himalayan Mountains (including the Qilian Mountains), the changes in forest line exhibited high heterogeneity, with 67.7% of the tree lines shifting upward, 73% of the forest lines exhibiting an increase in tree recruitment, and 67.8% of the forest lines presenting acceleration of tree growth rates [4]. One survey showed that Picea crassifolia Kom.…”

“…Tree lines are apparent vegetation boundaries, commonly defined as the elevational limit of trees greater than 2 m in height [1][2][3][4]. The area extent of tree lines has geological and ecological significance, and changes in tree lines play an important role in the development of mountains and regional ecology [5][6][7].…”