Mixed-severity fire regimes in dry forests of southern interior British Columbia, Canada

• Published in: Canadian journal of forest research Vol. 42; no. 1; pp. 88 - 98
• Main Authors: Heyerdahl, Emily K, Ken Lertzman, Carmen M. Wong
• Format: Journal Article
• Language: English
• Published: NRC Research Press 2011
• Subjects: coniferous forests; dry forests; fire regime; fire scars; fire severity; fires; growth rings; Pinus ponderosa; Pseudotsuga menziesii var. glauca; trees; British Columbia
• ISSN: 1208-6037; 1208-6037

Historical fire severity is poorly characterized for dry forests in the interior west of North America. We inferred a multicentury history of fire severity from tree rings in Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) – ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) forests in the southern interior of British Columbia, Canada. In 2 ha plots distributed systematically over 1105 ha, we determined the dates of fire scars, indicators of low-severity fire, from 125 trees and inferred dates of even-aged cohorts, potential indicators of high-severity fire, from establishment dates of 1270 trees. Most (76%) of the 41 plots contained fire-scarred trees with a mean plot-composite fire scar interval of 21 years (1700–1900). Most (76%) also contained one or two cohorts. At the plot scale, we inferred that the fire regime at most plots was of mixed severity through time (66%) and at the remaining plots of low (20%), high (10%), or unknown (4%) severity through time. We suggest that across our study area, the fire regime was mixed severity over the past several centuries, with low-severity fires most common and often extensive but small, high-severity disturbances also occasionally occurred. Our results present strong evidence for the importance of mixed-severity fire regimes in which low-severity fires dominate in interior Douglas-fir – ponderosa pine forests in western Canada.