A regional paleolimnological assessment of the impact of clear-cutting on lakes from the west coast of Vancouver Island, British Columbia

The impact of forest harvesting on lakes within the temperate rainforest on the west coast of Vancouver Island was examined in a paleolimnological stu dy of four lakes that had 35-92% of their watersheds progressively clear-cu t over a period of 15-30 years (impact lakes) and four lakes that had exper ienced little or no known anthropogenic disturbance in their watersheds (re ference lakes). Changes in diatom species composition and percent organic m atter in the Pb-210-dated sediment cores were compared over the last 100 ye ars in each of the impact lakes before and after the onset of forest harves ting, which began in 1950, and before and after 1950 in the four reference lakes. Only one impact lake showed significant changes in percent organic m atter. Significant changes (p < 0.05) in species composition following fore st harvesting were detected in all four impact lakes and in one of the four reference lakes. However, the changes in diatom species composition follow ing clear-cutting in the impact lakes were small, with changes in the relat ive abundance of the most common species being maximally 20%, but more typi cally 3-10%.