Forest Fires and Old-Growth Forest Abundance in Wet, Cold, Engelmann Spruce-Subalpine Fir Forests of British Columbia, Canada

摘要

The amounts of old-growth forest present under current and pre-harvesting era disturbance regimes in the dominant higher elevation (900-2300 m) forests in eastern British Columbia (B.C.) - wet cold Engelmann spruce (Picea engelmannii Parry ex Engelm.) - subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forests (ESSFwc), and one important group of ESSFwc forests, the Northern Monashee (ESSFwc2) biogeoclimatic variant - were quantified using a GIS forest age database, with the assumption that old-growth forests were forests > 140 years old. This was done in order to inform natural disturbance based management in this part of British Columbia. Database constraints restricted the analysis to the post 1800 period only and resulted in estimation of a range of old growth for any time period. The oldest trees in old-growth forests do not necessarily indicate when the forests were last disturbed by fire, as ~(14)C dating of charcoal indicated that, for two of five 210- to 320-year old stands sampled, the most recent fire event probably occurred over 1000 years ago. The amount of old growth in both ESSFwc and ESSFwc2 forests, since 1800, decreased to a minimum in the mid to late 1800s, then increased. In the case of the ESSFwc2, this increase occurred until the 1960s before the amount of old growth decreased again. Amounts of old growth in 2003 (58-59% of the forested area) were within the pre-harvesting era range of 30-60% in ESSFwc2 forests, but may be above the range of 20-50% in ESSFwc forests. Old-growth forests have dominated most subalpine landscapes in eastern B.C. for at least the last several decades. If management of ESSFwc forests is to emulate historical disturbance regimes, greater protection of old-growth ESSFwc forests than at present will be necessary.