Introduction

The aspen parkland is a mosaic of grassland and woodland plant communities forming a transitional zone between boreal forests and prairies of the interior plains of central Canada. The main tract of aspen parkland forms a crescent stretching from northern Montana northeastward along the foothills of the Rocky Mountains in southern Alberta, then curving through central Saskatchewan into southwestern Manitoba and adjacent areas of northwestern Minnesota (Figure 25.1). The largest area of parkland is in Saskatchewan, where it occupies about 72,000 km2 in a belt varying in width from 40 to 160 km. Trembling aspen (Populus tremuloides) is the dominant tree species throughout the parkland and typically grows in pure stands or groves (Figure 25.2). The southern boundary is fragmented, and the widely scattered groves of aspen are replaced by mixed-grass and shortgrass prairie. Grove size increases northwards, and eventually the distinctive, isolated character of the groves is lost as the trees merge with the mixedwood (conifer–hardwood) stands of the southern boreal forest. Extirpation of the bison and suppression of fire following settlement in the 1890s resulted in the spread of aspen throughout the parkland region (Archibold and Wilson 1980). Some authors (Sauer 1950; Stewart 1956) have suggested that aspen forest is the climax vegetation of the northern Great Plains; however, Looman (1979) considered the forest to be a subclimax formed by the southward extension of this pioneer boreal species.