Divergent Seasonal Patterns of Qinghai Spruce Growth with Elevation in Northwestern China

Yanfang Wan,Xiaoqing Li,Xiande Liu,Yanhui Wang,Bin Wang,Pengtao Yu,Shunli Wang,Lei Zhang,Yipeng Yu

doi:10.3390/f13030388

Abstract

Dryland montane forests are important agents for soil and water resource conservation. The growth of these forests under climate warming is strongly affected by local environmental factors. However, how environmental factors impact intra-annual stem growth dynamics across environmental gradients in these regions remains unclear. This work focused on assessing seasonal patterns of stem growth across different elevations and how environmental factors impact stem growth in the Qilian Mountains, northwestern China. The stem growth of 50 Qinghai spruce trees was monitored for two years across an elevation gradient from 2500 m to 3300 m above sea level (a.s.l.). We found that growth initiation occurred later as the elevation increased, and growth commenced when elevation-specific temperature thresholds were reached. However, growth cessation presented large elevational differences: cessation occurred much earlier at low elevations (2500 m and 2700 m a.s.l.). Exceptionally early growth cessation occurred predominantly at 2700 m a.s.l., which was correlated with seasonal drought/insufficient rainfall and low soil moisture occurring since mid-July 2015. Temperature and soil moisture were the key factors governing the daily rate of stem growth in the beginning, rapid growth, and end stages. Overall, due to effects of seasonal drought and low temperature on growth cessation and growth rate, the annual growth of Qinghai spruce was rather low at both low (2500–2700 m a.s.l.) and high (3100–3300 m a.s.l.) elevations; middle elevations (approximately 2900 m a.s.l.) might be the most favorable Qinghai spruce growth. Our results implied that tree growth will likely decline at low elevations and that the optimal elevation for Qinghai spruce growth in northwestern China is expected to shift upward under future climate warming.

Highlights

Climate changes, dramatic warming and severe drought events, have occurred around the world [1], most notably in northern China [2,3]
To assess the impacts of future climate change on forest growth, it is crucial to study the climatic forcing of tree growth at annual and seasonal time scales
Studies on seasonal growth responses to climate changes are urgently needed, it can help our understanding of tree growth at annual or multiyear time scales

Summary

Introduction

Dramatic warming and severe drought events, have occurred around the world [1], most notably in northern China [2,3]. These changes exert a strong influence on forest dynamics and growth [4–6]. To assess the impacts of future climate change on forest growth, it is crucial to study the climatic forcing of tree growth at annual and seasonal time scales. A number of studies about growth-climate relationships were mostly based on tree-ring-based investigations [7–10]. Such studies do not fully explain the effects of climate conditions on tree growth and do not capture seasonal growth changes and relevant growth-limiting factors. Studies on seasonal growth responses to climate changes are urgently needed, it can help our understanding of tree growth at annual or multiyear time scales

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