PARENT SESSION
Oral Session #55: Fire Ecology. Presiding: M. Moritz.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas H.
Historical mixed-severity fire regimes in the southwestern interior of British Columbia, Canada.
Heyerdahl, Emily1,2, Lertzman, Ken2, 1 2
ABSTRACT- Mixed conifer forests historically sustained fires with a range of severities. However, spatial variation in the mix of severities across the landscape is poorly understood. We reconstructed historical fires (1712-1997) of all severities in mixed-conifer forests in the unroaded Stein River watershed in the southern interior of British Columbia. We sampled fire scars (163 trees) and establishment dates (1165 trees) on a grid of 44 points in a remote 700 ha area. Douglas-fir is equally common across the study area but ponderosa pine is less common in the mesic western portion of the area, where the understory layer is relatively productive. The variation in mesoclimate that drives this gradient in vegetation did not drive a similar gradient in low-severity fires, which were equally frequent across the study area, occurring roughly every 20 years. In contrast, moderate- and high-severity fires, inferred from establishment dates, were more likely to burn in the mesic western portion of the study area than in the drier eastern portion. This decoupling of spatial variation in fires of different severities probably resulted from variation in fuel loads across the study area. The mesic forest to the west likely had higher fuel loads, and more fuel ladders, than the drier forests to the east so that, during periods of extreme fire weather, fires to the west were more likely to be severe than fires to the east.
KEY WORDS: fire history, mixed-severity fire regimes, British Columbia