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Harvard Forest Symposium Abstract 2019

  • Title: Seasonality of Species-specific Radial Growth Responses to Moisture Variability Determines Support for the Isohydricity Water Use Framework
  • Primary Author: Tsun Fung Au (Indiana University - Bloomington)
  • Additional Authors: Justin Maxwell (Indiana University - Bloomington); Neil Pederson (Harvard Forest); Richard Phillips (Indiana University - Bloomington)
  • Abstract:

    Extreme drought has profound impacts on the eastern deciduous forests of United States. Based on a water use framework continuum, sugar maple (Acer saccharum) adopt a more isohydric strategy while more anisohydric strategy is observed in white oak (Quercus alba) in response to water deficit conditions. In order to disentangle whether drought sensitivity of radial growth is consistent with the isohydricity water use framework, we sampled 781 tree cores from 418 individual trees in 18 forests where both sugar maple and white oak co-exist. We analysed the growth-climate relationship between the two species using maximum temperature (Tmax), precipitation (PCP), standardized precipitation evapotranspiration index (SPEI) and vapor pressure deficit (VPD) with Pearson’s correlations. We found both species respond significantly to all climate variables in June, including positive responses with PCP and SPEI and negative responses with Tmax and VPD (p<0.05). We also determined drought and legacy effects by using climate data to predict radial growth. Our results suggested soil moisture in June was the dominant factor influencing radial growth of both species. White oak generally had higher correlation coefficients to all climate variables than sugar maple during early growing season, although they were not significantly different. However, when examining the entire growing season, sugar maple was significantly more sensitive to drought. Our findings suggested the ability of isohydricity water use framework explaining species-specific differences in radial growth-climate responses is dependent on the portion of the growing season that is examined. For the month of June, both species are equally sensitive. However, we found support for the isohydricity explaining species-specific responses when examining the entire growing season. The differential seasonality responses indicated future drought impacts will be dependent on both forest compositions and drought timing. In a forest that shifts from oak to maple dominated, future drought in the earlier portion of the growing season will remain important but drought in the later portion will increase in importance, indicating that future drought could have a large impact on carbon sequestration.

  • Research Category: Physiological Ecology, Population Dynamics, and Species Interactions; Historical and Retrospective Studies; Forest-Atmosphere Exchange