Treeline Dynamics on Southern Vancouver Island, British Columbia
Colin P. Laroque, David H. Lewis
and Dan J. Smith*
Department of Geography—Ring Laboratory University of Victoria Victoria, BC V8W 3P5
This paper describes the nature of treeline dynamics and upper-elevation tree establishment patterns on southern Vancouver Island, British Columbia. We examined tree growth, climate and seedling relationships at three upper-elevation locations using standard dendroecolog- ical approaches. Our data suggest that this habitat has experienced species-specific pulses of tree establishment that have had a major impact on the character of the local treeline boundaries. The stem data collected within quadrats at Gemini Mountain and Haley Bowl show that seedling establishment within the last three cen- turies was episodic and linked to historical climatic pat- terns. Successful mountain hemlock establishment in this setting is restricted to periods characterized by either cool summers and shallow winter snowpacks, or warmer than normal summers and moderately deep snowpacks. The establishment of amabilis and subalpine fir seedlings appears restricted to intervals with cool growing seasons and moderately deep seasonal snow- packs. Episodic seedling establishment in the 20th cen- tury has resulted in a gradual infilling of the local tree- line and the development of a more structured parkland belt that is expected to have habitat implications for endangered Vancouver Island marmot.
Keywords: dendroecology, subalpine meadows, seedling establishment, tree rings, Vancouver Island, Vancouver Island marmot.