WELD-01-023

Structure of Forest Stands Disturbed by Wildfire and Logging in the Rocky Mountains
Sponsor: 
Weldwood
Lead Researcher: 
Daniel R. Farr, Christopher P. Spytz, and E. George Mercer
Body: 

Efforts to conserve the biological diversity of boreal forest stands disturbed by logging are constrained by a lack of information on the structural variability of such stands relative to those disturbed by natural processes such as wildfire. In this study, the abundance, size, condition, and origin of deadwood and live trees in recently burned (34-40 yr) and logged (23-27 yr) coniferous stands in the Rocky Mountains and Foothills of western Alberta was examined.

The structure of fire-origin stands was more variable than that of harvest-origin stands, as measured by live and standing dead trees > 2 m tall and down deadwood > 7 cm diameter. In stands of both origin types, > 90% of standing dead trees were derived from the cohort of live trees germinating after disturbance. Standing dead trees of post-disturbance origin were five times more abundant in burned stands (25.9 ± 4.9 trees per plot, mean ± SD) than logged stands (4.9 ± 4.6 trees per plot). Few large fire-killed standing dead trees were present in the burned stands (3.1 ± 1.3 trees per plot), with most having fallen and contributed to a large pool of down deadwood. The down deadwood derived from the previous stand was a dominant feature of burned stands, reaching volumes of over 150 m3 / ha, approximately four times the volume of pre-harvested origin down deadwood in logged stands. Stands of both disturbance types contained similar amounts of down deadwood from trees derived from trees germinating after fire or logging.

Within protected areas where prescribed fire may be the preferred management tool, the study suggests a greater range of deadwood supply. Forest managers attempting to increase the range of deadwood to maintain or emulate natural processes should retain variable amounts of standing live and dead trees during harvesting to provide recruitment of down deadwood for the future.