Live, mature, interior Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) leave-trees dispersed throughout cutblocks after harvesting show inconsistent survival in the Sub-Boreal Spruce biogeoclimatic zone of central British Columbia. Government policy is to maintain appropriate levels of leavetrees on cutblocks to meet provincial biodiversity objectives. Douglas-fir is retained because its populations are naturally fragmented at the northern edge of its natural distribution. In historical disturbance regimes, dominant and veteran Douglas-fir trees that survive fire persist to ages of 300?500 years, while younger cohorts of spruce, lodgepole pine, subalpine fir, and Douglas-fir often establish beneath them, which makes Douglas-fir ecologically an appropriate candidate as a leave-tree. Water relations for large and/or old Douglas-fir trees retained after harvesting were measured by sampling typical mature Douglasfir leave-trees in a clearcut (CC) and an adjacent unharvested (UN) unit at two sites that differed in age since harvest: one was harvested in 1998, the other in 2003. Xylem water potential and micro-environmental data for soil and evaporative demand suggest that differences in water relations between treatments and sites may be contributing factors in leave-tree mortality. At the 1998 site, surviving trees may have acclimated to their new environment, as there was little difference in water potential between CC and UN trees. However, sample trees in CC treatments, primarily at the 2003 site, reached water potentials that may be lethal on more occasions than those in the UN treatments. Furthermore, in terms of the success of this green-tree retention system, the projected effects of climate change in this region may very well exacerbate the influences responsible for direct and indirect modes of mortality for Douglas-fir and other species of leave-trees.
Bruce J. Rogers, Christopher D.B. Hawkins. 2021. Hydraulic Response in Mature Interior Douglas-fir Retained in Clearcuts in Central British Columbia. FLNRORD. Technical Report (FLNRORD). TR134
Keywords: hydraulic resistance, hydraulic sufficiency, leave-tree retention system, harvest retention, vapour-pressure deficit, water potential, water stress, plant moisture stress
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