Expert Opinion on Environmental BiologyISSN: 2325-9655

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Research Article, Expert Opin Environ Biol Vol: 7 Issue: 2

Bifurcated Response of a Regional Forest to Drought

Chuixiang Yi1,2*, Guangwei Mu1, George Hendrey1,2, Sergio M Vicente-Serrano3, Wei Fang1, Tao Zhou4,5, Shan Gao1,4,5 and Peipei Xu1,4,5

1School of Earth and Environmental Sciences, Queens College of the City University of New York, New York, 11367, USA

2Department of Earth and Environmental Sciences, the Graduate Center of the City University of New York, New York, NY 10016, USA

3Instituto Pirenaico de Ecología, Consejo Superior de Investigaciones Científicas (IPE-CSIC), Zaragoza 50080 Spain

4State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing 100875, China

5Academy of Disaster Reduction and Emergency Management, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China

*Corresponding Author : Chuixiang Yi
Professor, School of Earth and Environmental Sciences, Queens College of the City University of New York, New York, 11367, USA
Tel: 718-997-3366

Received: February 27, 2018 Accepted: April 03, 2018 Published: April 06, 2018

Citation: Chuixiang Yi, Guangwei Mu, Hendrey G, Vicente-Serrano SM, Fang W, et al. (2018) Bifurcated Response of a Regional Forest to Drought. Expert Opin Environ Biol 7:2. doi: 10.4172/2325-9655.1000153


Several lines of evidence suggest that forest growth in many regions is declining as a consequence of changing climate. To predict the fate of forests in the future, a quantitative understanding of how the key climate variables (insolation, precipitation and temperature) interact with forests to cause the decline is a pressing need. Here we use a regionally-averaged tree-ring width index (RWIr) to quantify forest growth in the Southwest United States (SWUS). We show that over a period of 90 years, SWUS RWIr bifurcated into forest stands with enhanced (healthy) and reduced (declining) branches when regressed on shortwave-radiation and temperature, respectively. The reduced branch was controlled overwhelmingly by drought as measured with a regionally-averaged precipitationevapotranspiration index (SPEIr). As SPEIr approached -1.6 (previously shown as a tipping-point for SWUS conifer forest growth), RWIr approached zero and in extreme drought years, wide spread tree mortality has been observed. Modeled trends in SPEI based on four IPCC-GHG scenarios predict SWUS SPEIr falling below -1.6 more or less continuously within a few decades. With drought expanding north- and eastward over larger areas, tree mortality may become a semi-continental phenomenon with coniferous forests transitioning to more xeric ecosystems. Our results provide insights into how to differentiate functions of climate impacts on forest growth and how to identify tipping-point control parameters for forest regime transitions.

Keywords: Forest growth decline; Tree rings; Tipping point; Bifurcation; Tree mortality; SPEI

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