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Harvard Forest Symposium Abstract 2017

• Title: Early-monsoon failure appears to lead to growth cessation of lower margin Picea crassifolia
• Primary Author: Shoudong Zhao (Beijing Normal University)
• Additional Authors: Manyu Dong (Beijing Normal University); Neil Pederson (Harvard Forest); Hui Xu (University of Massachusetts - Amherst ); Shoudong Zhao (Beijing Normal University)
• Abstract:

  Shoudong Zhao, Beijing Normal University, Beijing, China, zhshd@mail.bnu.edu.cn
  
  Yuan Jiang, Beijing Normal University, Beijing, China, jiangy@bnu.edu.cn
  
  Manyu Dong, Beijing Normal University, Beijing, China
  
  Hui Xu, University of Massachusetts Amherst, Amherst, MA
  
  Neil Pederson, Harvard Forest, Harvard University, Petersham, MA, neilpederson@fas.harvard.edu
  
  
  Extreme climate has been shown to be strong drivers of forest growth, dynamics, and contraction. We are studying the climatic drivers of Picea crassifolia Kom., an endemic to northwest China where climate has significantly warmed. Picea crassifolia was sampled over an elevational gradient, from its lower distributional margin to its upper distributional margin, on the Helan Mountains to test the hypothesis that growth at the upper limit is limited by cool temperatures and is limited at its lower limit by drought. We found that trees at the lower distributional margin have experienced a substantial increase in years with stem-growth cessation since 2001 compared to trees at other elevations. While all populations have a similar climatic sensitivity, trees at lower distributional margin are more sensitive to June precipitation and July vapor pressure deficit (VPD). Particular to stem-growth cessation events in trees at the lower distributional margin, early-monsoonal precipitation (June) appears to be the primary driver. Evidence indicates that July VPD exacerbates the frequency of these events. From this work, it appears that an increase in severity and frequency of early-monsoon failure could increase the frequency and severity of stem-growth cessation in the lower population and increased vapor pressure deficit and warming in the region would likely exacerbate this stress. If this occurs, it could potentially increase the mortality rate of lower distributional margin trees, especially those that are already experiencing events of temporary growth cessation.

• Research Category: International Research Projects
  Historical and Retrospective Studies