P.I.(s): E.H. (Ted) Hogg -- Forestry Canada
Co-I(s): P.A. (Rick) Hurdel, Ian Campbell, Thierry Varem-Sanders -- Forestry Canada
Objectives: Regional climate-vegetation relationships indicate that the southern limit of the boreal forest is presently governed by moisture stress. This investigation aims to use a combination of field studies and modelling to predict how forest communities at the boreal forest's southern limit could respond to future changes in climate. The investigation includes short-term measurements of transpiration, photosynthesis, stem respiration and LAI, plus longer term studies of stand development, growth (tree ring analysis) and regional forest composition (palynology). This work will also form part of an ongoing Canadian study (BFTCS) of climate change effects on the functioning and carbon balance of the Canadian boreal forest.
To compare ecophysiological responses of aspen to environmental conditions across a climatic moisture gradient from the aspen parkland to the southern boreal forest.
Known Problems and Caveats:
Interruption of sap flow by the heater and sensors causes a consistent underestimation from theoretically calculated values (by 45-55% based on heat transfer modeling and published analyses).
Comparison of sap flow at mixedwood with those made by Saugier have been completed. Comparison of sap flow and canopy transpiration at PANP OA will be made once Zimmerman and Black send us their data. We are planning to present our HPV work at 1995 ESA meeting in Utah. Main result is that midday sap flow increases linearly with VPD up to ca. 1 kPa, then remains remarkably constant over VPDs from 1-2.8 kPa. There was no evidence that sap flow was limited by soil moisture, but 1994 was wetter than average. Significant night-time sap flow in aspen occurred on warm, dry nights, especially in June. Sap flow in aspen was almost negligible after Sep 27 at both PANP and mixedwood, but in spruce continued through at least Oct. 20.
Tree-ring density and width measurements on biometry and allometry material.
Cores were collected by various teams including Tom Gower and the biometry crew. Cores have also been submitted by D. Lawrence (H. Shugart). Total involves an estimated 2000 cores (biometry and D. Lawrence) and 1500 disks (allometry). Material is being analyzed by x-ray densitometry for ring width and density using a system developed at the Northern Forestry Center of CFS (DendroScan). Resolution is in most cases 0.005 mm.
Places and Times of Measurements:
Most tower sites, allometry sites, and biometry sites. Additional sites collected by D. Lawrence. Collection during 1993 and 1994.
Known Problems and Caveats:
Some cores/disks mislabeled in the field; some incomplete; some breakage during transport or analysis. Problems are noted with each sample individually. Percentage latewood calculated as percentage of ring formed after (max. density + min. density)/2.
Data to be supplied to BORIS from biometry and allometry sets: mean (of two radii per tree where available) ring widths, mean maximum density, mean minimum density, mean percentage latewood. Submission is expected after the completion of quality control, in late summer 1995. Other data will be available from Ian Campbell and Thierry Varem-Sanders; this includes the entire density traces, but will be readable only with DendroScan software (expected available for purchase in fall 1995). Data for material from D. Lawrence will be submitted to BORIS by D. Lawrence.
Tree-ring studies using x-ray densitometry, examining all the tree cores and cross-sections collected by the various biometry and allometry teams, totaling approximately 3,000 pieces of wood, most of which have now been processed. We expect to have a series of reports ready starting around January. All ring data will also be contributed to the International Tree-Ring Data Bank in Tucson,
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Last Updated: October 29, 1997