A HIGH-RESOLUTION FIRE AND VEGETATION HISTORY OF A GARRY OAK HABITAT IN COASTAL BRITISH COLUMBIA

MCCOY, M.M. (1), PELLATT, M.G. (2), AND MATHEWES, R.W. (3).

(1) Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada, (2) Parks Canada, and School of Resource and Environmental Science, Simon Fraser University, Burnaby, BC, Canada, (3) Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada.

We used fossil pollen and macroscopic charcoal (>125 µm diameter) from a 210Pb-dated lake sediment core in southwestern British Columbia to reconstruct local fire and vegetation history, from ca. 1748 AD to present, at 2-5 year intervals. Roe Lake is within the northern range limit of Garry oak (Quercus garryana) ecosystems (GOEs) which, in Canada, are restricted to the dry Coastal Douglas-fir biogeoclimatic zone of southeastern Vancouver Island and southern Gulf Islands. Prior to the arrival of Europeans, frequent low- to medium-intensity fires helped maintain the parkland structure and graminoid-dominated understorey typical of GOEs.

Charcoal accumulation rates (CHAR) were quantified in five sizes classes (0.125 - 0.25 mm, 0.26 - 0.50 mm, 0.6 - 0.75 mm, 0.76 - 1.0 mm, and >1 mm). CHAR pattern is similar for all size classes; 0.26 - 0.50 mm is the most common. Following a quiescent period pre-ca. 1775, increased CHAR activity is interpreted as increased fire activity. Two CHAR peaks at ca. 1796 and ca. 1876 are followed by increased Alnus and decreased Pseudotsuga menziesii pollen. The late 1800s activity is considered associated with logging and land clearing. A peak in Pteridium spores suggests continued disturbance into the early 1900s. A significant decline in CHAR after ca. 1930 is attributed to fire suppression.