Hydraulic responses to environmental perturbations in Tsuga canadensis and Betula lenta
Michael J. Daley (1, 2), Nathan G. Phillips (3), Justin C. Pettijohn (3) and Julian Hadley (4)
1. Science and Mathematics Department, 1844 Commonwealth Avenue, Lasell College, Newton, MA 02466, USA / 2. Corresponding author () / 3. Geography Department, 675 Commonwealth Avenue, Boston University, Boston, MA 02215, USA / 4. Harvard Forest, Harvard University, 325 North Main Street, Petersham, MA 01366, USA / Received November 30, 2007; accepted April 4, 2008; published online July 1, 2008
Summary
Eastern hemlock (Tsuga canadensis (L). Carr.) is a late-successional species found across the northeastern United States of America that is currently threatened
by the exotic pest, hemlock woolly adelgid (Adelges tsugae Annand). Because whole-tree physiological characteristics may scale to influence ecosystem processes, we considered whole-tree
hydraulic controls in eastern hemlock and the replacement species black birch (Betula lenta L.). Through a series of misting perturbations, whole-tree resistances (R), capacitances (C) and time constants (τ) were determined from time series sap flux data in eastern hemlock and black birch. Black birch trees
responded more rapidly to environmental perturbations than eastern hemlock. Utilizing the step function after applied treatments,
whole-tree τ ranged between 9.4 and 24.8 min in eastern hemlock trees compared with 5.9 to 10.5 min in black birch. Species
was not a significant predictor of R or C when controlling for tree size. In both species, R decreased with sapwood area and C increased. Our τ results indicate that the loss and replacement of eastern hemlock by black birch will decrease the lag between
transpiration and absorption of water from the soil and potentially alter the diurnal pattern of carbon and water uptake.
Keywords:
birch, capacitance, hemlock, resistance, sap flux, time constant.
