A Tundra-Steppe Transition on Kathul Mountain, Alaska, U.S.A.

Abstract

Paleoecological data do not permit a definitive characterization of the treeless vegetation that covered unglaciated interior Alaska during the last glacial period. Knowledge of the potential ranges of modern taxa can help determine which species could have comprised full-glacial plant communities. Azonal grassland (steppe) communities that currently occupy steep south-facing bluffs within the boreal forest of interior Alaska contain species that may have been more widespread during the full glacial. In order to investigate the potential ecological range of steppe taxa we studied the vegetation at Kathul Mountain, where continuous treeless vegetation occurs from low elevation to alpine tundra. The results from 27 vegetation plots placed along an elevational gradient from 290 to 910 m suggest a gradual transition from steppe to tundra. Species responded individualistically to changing elevation, and steppe and tundra taxa were intermixed over a broad zone of intermediate elevation. Two important steppe taxa, Agropyron spicatum and Artemisia frigida, were consistently present to elevations over 800 m. Regression of DCA scores on environmental variables indicated that both the interaction of slope and aspect and elevation were important factors controlling vegetation composition. Assuming that changes in elevation, slope, and aspect cause a change in temperature and growing-season length, it appears that some steppe taxa could have survived full-glacial conditions, at least on lower-elevation slopes with a south-facing aspect. The vegetation on such sites during the last glacial period may have been similar to that of the tundra-steppe transition seen today at Kathul Mountain.