PARENT SESSION
Organized Oral Session 32: Forest disturbance regimes in the circumboreal forest zone: Natural variability and implications for forest management and biodiversity conservation
Organizer(s): S Gauthier, T Kuuluvainen, and D Kneeshaw
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 516 C, Level 5, Palais des congrès de Montréal
The disturbance ecology of northwestern Canada: Factors and consequences.
Burton, Philp*,1, Taylor, Steve2, 1 Canadian Forest Service, Prince George, B.C., Canada2 Canadian Forest Service, Victoria, B.C., Canada
ABSTRACT- The mountainous boreal and taiga ecozones of British Columbia (BC) and Yukon occupy 729,440 km2 or 13.5% of Canada's boreal forest. These ecozones consist of 47-63% mountainous terrain, with average elevations >1100 m, and with 62-70% of soils being loams and sandy loams. The boreal cordillera ecozone experiences a mean annual temperature (MAT) of -2.7 C and is 61% forested, while the taiga cordillera MAT is -7.0 C and it is 46% forested. The ecology of these northern cordilleran forests is distinctive from that of the boreal plains, shield, and lowlands to the east. Recent analysis of Canada's Large Fire Database (Stocks et al. 2002), accounting for 97% of the area burned from 1959 to 1997, indicates that fires burn less area (0.335 %/yr) in these ecozones than across boreal Canada as a whole (0.424 %/yr). Mean annual precipitation is slightly lower than found in the neighboring ecozones to the east, but a lower incidence of lightning and the interspersion of high elevation tundra (providing less potential fuel and breaks in fuel continuity) results in a lower incidence and extent of wildfires. Reduced burn rates and smaller fires should result in more old forests. However, these forests are also susceptible to insect attack and other biotic agents of tree defoliation and mortality: outbreaks of 11 widespread and 49 minor forest insect pests were mapped in Yukon from 1952 to 1995. Available data from BC illustrate distinctive combinations of fire and insect outbreaks for different ecoregions and biogeoclimatic zones. For example, eastern spruce budworm (Choristoneura fumiferana) is 14 to 18 times more prevalent than fire in some ecoregions. Because biotic mortality agents exhibit a strong dependence on particular tree species, biogeoclimatic zones and subzones (reflecting climate, elevation and climax forest types) show stronger distinctions in disturbance regime than do ecoregions spanning several forest types. Abiotic disturbances (unseasonal cold, windthrow, landslides, avalanches, floods) are also important, but their distribution and frequency are largely undocumented. Disturbance return intervals appear to be centuries longer than those of adjoining forests to the east or to the south, requiring adjustments to our thinking about nature reserve design and sustainable forest management.
Key words: boreal forest, disturbance regime, insect outbreaks, wildfire