Abstract

Alpine treelines are projected to shift upslope in response to climate warming, but empirical studies have yielded inconsistent results, with both upshifted and stable alpine treelines. Additionally, treelines on different slope aspects of the same mountain can differ. Thus, for a better understanding of the mechanisms of treeline formation and treeline responses to climate change, we need to elucidate the population dynamics at treelines on different slope aspects. Here, we quantified the population dynamics of Balfour spruce (Picea likiangensis var. rubescens) at treeline ecotones on contrasting north- and east-facing slopes on the eastern Tibetan Plateau based on field surveys. The alpine treeline positions of Balfour spruce have not advanced toward higher altitudes on the contrasting slopes in recent decades. Compared with the east-facing slope, more recruits occurred on the north-facing slope above the present treeline, indicating a more favorable regeneration condition. However, on the north-facing slope, the individual growth rate of Balfour spruce was lower, and the number of adult trees above the present treeline was higher than that on the east-facing slope. Thus, slope aspects mediate a trade-off between the growth and survival of treeline species, explaining the absence of an impact of slope aspects on treeline responses to climate change. Our results highlight the importance of considering the effect of topography on population dynamics in predicting alpine treeline dynamics under the scenario of climate change.

Highlights

  • IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations

  • Previous studies have reported that some alpine treelines advanced to higher altitudes in response to climate warming, but others did not respond or even decline to lower elevations [3,4,5]

  • We addressed two questions: (1) Does the alpine treeline elevation shift under climate change? (2) Do tree regeneration and growth at alpine treeline ecotones differ among different slope aspects?

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Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Alpine treelines represent one of the most obvious vegetation boundaries in the world [1]. Treeline trees acclimate to harsh living conditions close to their physiological limits [1]. Alpine treelines are highly sensitive to climate warming and are frequently used as an indicator of climatic changes [2]. Previous studies have reported that some alpine treelines advanced to higher altitudes in response to climate warming, but others did not respond or even decline to lower elevations [3,4,5]

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