PARENT SESSION
Oral Session #10: Paleoecology. Presiding: S. Hotchkiss.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.

Conifer stomates as indicators of the subarctic and subalpine treeline.

PISARIC, MICHAEL¹, ¹

ABSTRACT- Reconstructing vegetation dynamics from pollen in lake sediments is challenging in treeline environments, due to the transport of pollen across vegetation zones. Further, the differential production and preservation of some types of pollen grains can also confound the interpretation of pollen records. Analysis of the conifer stomate content within lake sediments is an important tool for tracking past changes in the position of treeline, both in the subarctic and at high elevations. To characterize the relationship between vegetation cover and conifer stomate representation in lake sediments, I analysed surface samples from 20 lakes in mountain regions of northwestern Canada and 26 lakes in the subarctic of northern Siberia. Above treeline in northwestern Canada, alpine-tundra lake sediments contained no stomates. Where trees are present in the subalpine forest-tundra and the valley forests, stomates were found in all but one lake. In contrast, north of the subarctic treeline in northern Siberia, stomates were consistently found in lake sediment surface samples from the tundra vegetation zone. These stomates were likely reworked from peat deposits surrounding many of the lakes. Knowledge of the modern relationship between vegetation and stomate deposition are important for interpreting Holocene records from these regions. Fossil stomate records suggest that alpine treeline was at least 230 m higher between 10 000 and 4000 radiocarbon years BP, while the subarctic treeline in northern Siberia shifted north between 8500 and 3500 radiocarbon years BP.

KEY WORDS: conifer stomates, treeline, northwestern Canada, Siberia