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The Aspen Parkland: A Biological Perspective

by W. Bruce McGillivray

Page 1  |  

A stand of Trembling Aspen (Populus tremuloides): The Aspen Parkland as transition between grasslands and boreal forest, between foothills and prairie. The relationships between human cultures and their environments are both close and complex. The great diversity of aboriginal cultures worldwide is, in part, a function of environmental differences that shaped life histories. Unquestionably, the land determined hunting practices, settlement patterns, shelters, agriculture and recreational activities. The Aspen Parkland of Alberta is not a great biome, such as a tropical rainforest or desert. It is better defined as an ecotone or transition zone between the arid grasslands of the south and the wetter, colder, boreal forest to the north. How its character has shaped the lives of its human inhabitants is a question better put to a sociologist. As a biologist, I want to explore the natural aspects of the land. Perhaps from this perspective, we can begin to understand our feelings for the place we call “home.”

The Parkland Natural Region1 is a north-south transition zone between dry grasslands and boreal forest. It also is an east-west transition zone between the foothills and grasslands. With only a few minor exceptions, it is a uniquely Canadian landscape stretching across parts of Alberta, Saskatchewan, and Manitoba. In Alberta, it covers about 10 to 15 per cent of the available landscape for a total of 60,000 square kilometres. Today, it is the most densely populated, and concomitantly, most heavily altered Alberta landscape. Geologists and botanists have conspired to further define Parkland into three types – Peace River, Central, and Foothills – but for those of us outside these two disciplines, the differences among the three areas are relatively subtle.

Natural regions are built on rock substrate and soils and modified by climate. The historical slate of Aspen Parkland substrate was wiped clean by the glaciers of the Wisconsin advance. The ice left central Alberta from 20,00 to 12,000 years ago. Even then the climate was not suited to Aspen Parkland, being initially too cold and subsequently, too continental to support aspens. The present configuration of Alberta habitats has likely existed for only a few thousand years.2 As the Aspen Parkland is a fairly new and relatively heterogeneous habitat (that is, as a transition zone, it varies considerably, especially from north to south), it is not surprising that it has not spawned unique species or cultures.

Knob and kettle landscape: Slumping ground as ice melts beneath glacial sedimentsEvidence of the glaciers’ passage is found in the surficial deposits that form the soils and shape the land of the region. When the glaciers melted, they released huge amounts of water creating lakes (and lake sediments) and powerful rivers in wide or newly carved channels. These spillways now hold dry (“lost”) rivers or chain lakes or are channels for modern rivers. Vast quantities were carried and subsequently dropped by the glaciers. Large boulders litter the Parkland as “erratics.” Mixed deposits dropped from the ice formed “moraines”- more familiar as the “knob and kettle” feature of prairie potholes. The kettle or depression, often filled with water, formed when ice buried under glacial sediments finally melted causing the ground to slump. Other glacial features left behind on the Parkland are drumlins (rounded hills) and eskers (sinuous ridges), both formed from the deposition of materials in meltwater channels. Wind-blown deposits of finely ground glacial debris and sand are scattered throughout Central Alberta. The lakes that dot the region and the rivers that cross it bear witness to the scouring of the ice and the erosive power of flowing meltwater.

Cold temperatures are a modern feature of the Aspen Parkland. In fact, with a mean annual temperature of 2 degrees C, and about 260 days with a reading below 0 degrees C, some might say that the Ice Age is still with us. The soils of the parkland are dark and rich under grassland vegetation, but lighter and grayer in the wooded areas. Solonetzic (salty) soils occur in the central Parkland, producing the familiar alkaline character of many sloughs and lakes. The south to north transition from grassland to boreal forest is mediated by climate and soils and marked by vegetation. The southern parkland is known as groveland, a region dominated by grasses but with scattered small clumps of aspens in depressions that collect moisture. As the moisture content of the soils increases to the north, so too does the frequency of trees, until at its northern limit the Aspen Parkland is a solid forest.

The dominant tree of the Aspen Parkland is the trembling aspen (Populus tremuloides). A second poplar, the balsam (Populus balsamifera), is more common in wetter areas, along rivers, near lakes, and in the north. Tent caterpillars, the scourge of the aspen and most other deciduous bushes, are unable to digest the leaves of the balsam poplar. Interestingly, deer and foresters share the same dislike for balsams. In aspen groves, the deciduous understorey has played an important role in parkland kitchens. Fruits of the snowberry (Symphoricarpos albus), saskatoon (Amelanchier alnifolia), chokecherry (Prunus virginiana), low-bush cranberry (Viburnum edule), and red raspberry (Rubus idaeus) provide a natural harvest.

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