PARENT SESSION
Oral Session # 40: Fire Ecology II: Forests.
Presiding: D Falk
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 102.
Effect of time since fire on growing season length and annual transpiration from boreal black spruce forests.
Ewers, Brent *,1, Gower, Stith2, Bond-Lamberty, Ben2, Wang, Chuakuan3, 1 Department of Botany, Laramie, Wyoming, USA2 Department of Forest Ecology and Management, Madison, Wisconsin, USA3 Department of Biology, Winnipeg, Manitoba, Canada
ABSTRACT- The microclimatic and successional changes during recovery from stand killing wildfires impacts growing season length and annual transpiration. We quantified growing season length and annual transpiration in 2001 and 2002 across a chronosequence of regenerating stands of boreal black spruce originating from wildfires in 1850, 1930, 1964, 1981 and 1989. In each stand, we used either Granier-type sap flux sensors (trees greater than 4 cm DBH) or Kucera-type sap flux sensors (trees less than 4 cm DBH) to quantify sap flux per unit sapwood area and scaled these up to the whole tree and stand level using site specific allometric equations for leaf area and sapwood area. The dominant species across the chronosequence consist of paper birch (Betula papyerifera), trembling aspen (Populus tremuloides), jack pine (Pinus banksiana), and black spruce (Picea mariana). We measured sap flux in six to 12 trees of each species present in the five stands for a total of 84 trees across the chronosequence. Analysis of the 2001 data showed that stand transpiration was not proportional to leaf area index across the five stands. This was explained by differences in transpiration per unit leaf area for the four species and changing species compositions across the chronosequence. In addition, black spruce, which dominated the two oldest stands, had a declining sensitivity of stomatal conductance to vapor pressure deficit with increasing age. We hypothesize that growing season length will decrease with increasing stand age but that species level differences across the chronosequence will have more of an impact on annual transpiration than growing season length.
Key words: disturbance, boreal forest, water cycling