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Differential Trends of Qinghai Spruce Growth with Elevation in Northwestern China during the Recent Warming Hiatus

1
Research Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Key Laboratory of Forest Ecology and Environment of the State Forestry Administration of China, Beijing 100091, China
2
State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
3
University of Chinese Academy of Sciences, Beijing 100049, China
4
Academy of Water Resource Conservation Forests of Qilian Mountains in Gansu Province, Zhangye 734000, China
*
Author to whom correspondence should be addressed.
Forests 2019, 10(9), 712; https://doi.org/10.3390/f10090712
Received: 6 July 2019 / Revised: 10 August 2019 / Accepted: 19 August 2019 / Published: 21 August 2019
(This article belongs to the Section Forest Ecology and Management)
Tree growth strongly responds to climate change, especially in semiarid mountainous areas. In recent decades, China has experienced dramatic climate warming; however, after 2000 the warming trend substantially slowed (indicative of a warming hiatus) in the semiarid areas of China. The responses of tree growth in respect to elevation during this warming hiatus are poorly understood. Here, we present the responses of Qinghai spruce (Picea crassifolia Kom.) growth to warming using a stand-total sampling strategy along an elevational gradient spanning seven plots in the Qilian Mountains. The results indicate that tree growth experienced a decreasing trend from 1980 to 2000 at all elevations, and the decreasing trend slowed with increasing elevation (i.e., a downward trend from −10.73 mm2 year−1 of the basal area increment (BAI) at 2800 m to −3.48 mm2 year−1 of BAI at 3300 m), with an overall standard deviation (STD) of 2.48 mm2 year−1. However, this trend reversed to an increasing trend after 2000, and the increasing trends at the low (2550–2900 m, 0.27–5.07 mm2 year−1 of BAI, p > 0.23) and middle (3000–3180 m, 2.08–2.46 mm2 year−1 of BAI, p > 0.2) elevations were much weaker than at high elevations (3300 m, 23.56 mm2 year−1 of BAI, p < 0.01). From 2000–2013, the difference in tree growth with elevation was much greater than in other sub-periods, with an overall STD of 7.69 mm2 year−1. The stronger drought conditions caused by dramatic climate warming dominated the decreased tree growth during 1980–2000, and the water deficit in the 2550–3180 m range was stronger than at 3300 m, which explained the serious negative trend in tree growth at low and middle elevations. After 2000, the warming hiatus was accompanied by increases in precipitation, which formed a wetting–warming climate. Although moisture availability was still a dominant limiting factor of tree growth, the relieved drought pressure might be the main reason for the recent recovery in the tree growth at middle and low elevations. Moreover, the increasing temperature significantly promoted tree growth at 3300 m, with a correlation coefficient between the temperature and BAI of 0.77 (p < 0.01). Our results implied that climate change drove different growth patterns at different elevations, which sheds light into forest management under the estimated future climate warming: those trees in low and middle elevations should be paid more attention with respect to maintaining tree growth, while high elevations could be a more suitable habitat for this species. View Full-Text
Keywords: Qinghai spruce; warming hiatus; elevation gradient; tree growth; growth-climate relationships Qinghai spruce; warming hiatus; elevation gradient; tree growth; growth-climate relationships
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Wang, B.; Yu, P.; Zhang, L.; Wang, Y.; Yu, Y.; Wang, S. Differential Trends of Qinghai Spruce Growth with Elevation in Northwestern China during the Recent Warming Hiatus. Forests 2019, 10, 712.

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