The Coupling of Treeline Elevation and Temperature is Mediated by Non-Thermal Factors on the Tibetan Plateau

Abstract

Abstract:Little is known about the relationships between treeline elevation and climate at regional and local scales. It is compelling to fill this research gap with data from the Tibetan Plateau where some of the highest alpine treelines in the world are found. This research question partially results from the lack of in situ temperature data at treeline sites. Herein, treeline variables (e.g., elevation, topography, tree species) and temperature data were collected from published investigations performed during this decade on the Tibetan Plateau. Temperature conditions near treeline sites were estimated using global databases and these estimates were corrected by using in situ air temperature measurements. Correlation analyses and generalized linear models were used to evaluate the effects of different variables on treeline elevation including thermal (growing-season air temperatures) and non-thermal (latitude, longitude, elevation, tree species, precipitation, radiation) factors. The commonality analysis model was applied to explore how several variables (July mean temperature, elevation of mountain peak, latitude) were related to treeline elevation. July mean temperature was the most significant predictor of treeline elevation, explaining 55% of the variance in treeline elevation across the Tibetan Plateau, whereas latitude, tree species, and mountain elevation (mass-elevation effect) explained 30% of the variance in treeline elevation. After considering the multicollinearity among predictors, July mean temperature (largely due to the influence of minimum temperature) still showed the strongest association with treeline elevation. We conclude that the coupling of treeline elevation and July temperature at a regional scale is modulated by non-thermal factors probably acting at local scales. Our results contribute towards explaining the decoupling between climate warming and treeline dynamics.

Opposite Tree-Tree Interactions Jointly Drive the Natural Fir Treeline Population on the Southeastern Tibetan Plateau

“…In essence, niche overlap for young trees but niche separation for mature trees acts as an important agent driving the distribution patterns of trees and treeline dynamics if the environment is favorable. However, owing to heterogeneous environmental conditions at different treeline sites [52], our results are different from findings in three forest regions (CD, DQ, YS) characterized by unfavorable climates (winter frost stress or seasonal droughts) or high-pressure disturbances. Collectively, the spatial patterns of trees at treeline ecotones may differ among different forest regions of the TP, thus partly supporting our second hypothesis.…”

Climatic and anthropogenic factors explain the variability of Fagus sylvatica treeline elevation in fifteen mountain groups across the Apennines

“…In recent decades, several studies have sought to shed light on the physiological and ecological factors affecting treeline altitude at regional and global scales (Harsch et al 2009;Wang et al 2017). It is widely agreed that temperature is the most important limiting factor for tree growth and development at high altitude (Körner and Paulsen 2004).…”

Fire facilitates warming-induced upward shifts of alpine treelines by altering interspecific interactions

“…Many treelines globally, however, are relatively stable despite evidence of regional warming (Harsch et al 2009). Different responses of regional treelines to warming result from variability of the local processes controlling population dynamics at particular treeline locations (Malanson et al 2007;Gou et al 2012;Kirdyanov et al 2012;Case and Duncan 2014;Lyu et al 2016Wang et al 2017;Vitali et al, 2019). For example, regional warming promoted an upward shift of undisturbed spruce and fir treelines on the Tibetan Plateau, but their rates of upslope migration were controlled largely by interspecific interactions (Liang et al 2016).…”