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Harvard Forest Symposium Abstract 2006

  • Title: A comparison of transpiration in black birch and eastern hemlock stands
  • Primary Author: Michael Daley (Boston University)
  • Additional Authors: Julian Hadley (Harvard Forest); Justin Pettijohn (Boston University); Nathan Phillips (Boston University)
  • Abstract:

    Eastern hemlock (Tsuga canadensis) is a foundation tree species found in forests across northeastern, USA. Eastern hemlock is a long-lived and shade-tolerant species that often develops into dense stands creating unique microclimates. Unfortunately, the status of this foundation species is currently threatened due to the invasive pest hemlock woolly adelgid (HWA; Adelges tsugae Annand). As HWA kills eastern hemlock trees, the replacement species in dead and dying hemlock stands are largely deciduous species, mainly black birch (Betula lenta). This transition from a coniferous to deciduous stand represents an extreme change in the morphological, phenological, and physiological characteristics of the ecosystem. This study utilized whole-tree transpiration measurements to investigate changes in ecosystem water use due to the loss and replacement of eastern hemlock from HWA infestation. Whole-tree measurements provide a tool to understand transpiration processes in individual species and their relative contributions to overall stand evapotranspiration. During the peak growing season, daily transpiration from black birch was 5-6 mm and 1.6 times greater than eastern hemlock transpiration. However, by late August, this relationship shifted and transpiration was nearly equal in the two species around 3 mm per day. The validity of our scaling approach was assessed by comparison with eddy covariance data and estimates were found to be significantly correlated in both stands. Our results indicate that a transition from a hemlock to a black birch dominated stand will result in a significant increase in transpiration, particularly during the peak growing season, and affect the catchment water balance.

  • Research Category: Forest-Atmosphere Exchange
    Invasive Plants, Pests & Pathogens
    Watershed Ecology