PARENT SESSION
Poster Session #31: Climate Change.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Treeline response to climate variability, Sunwapta Pass, Alberta, Canada.

Kavanagh, Trudy¹, Luckman, Brian¹, ¹

ABSTRACT- Vegetation dynamics were reconstructed for the past 400 years at two treeline sites in the Canadian Rockies using age-structure studies. Trees, seedlings and snags were mapped in two 30m wide plots that run 275m upslope from continuous forest into alpine tundra. Despite differences in environment and vegetation structure in the plots, the synchrony in the establishment record of seed-established trees and seedlings suggests strong climatic control on recruitment. Climate effects on treeline are examined at three spatial scales: landscape, population and individual. In the south-facing plot, a severe cooling event in the late 1600s coincides with a significant tree mortality event that resulted in treeline recession. Most subsequent establishment occurred in the 20th century. In the north-facing plot, recruitment was dominated by layering and treeline has slowly advanced upslope during the past 400 years. Comparison of temporal establishment patterns with climate data found significant correlations with June, August and seasonal (JJA, JAS) temperatures, and April and June precipitation. Correlations improve markedly when climate data are averaged for 5-7 years indicating that several favourable years are necessary for seedling establishment and survival. Annual vertical growth was measured on seedlings for the period 1986-1994. Despite significant differences in absolute growth within and between plots, the relative growth pattern of seedlings over time is similar. Annual seedling growth correlated significantly with seasonal (JJA) temperature, previous July precipitation, and previous seasonal (JJA) PDSI (Palmer Drought Severity Index) data.

KEY WORDS: dendroecology, treeline, Abies lasiocaropa, Picea engelmannii