The Aspen Parkland: A Biological Perspective
by W. Bruce McGillivrayThe 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 Region 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. 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.
Evidence 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.
Trembling aspens are well-suited to parkland. They can withstand fire by producing suckers from horizontal roots even if the “mother” tree is destroyed. The characteristic uniform height of trees in Aspen groves reflects the common age of the individuals that likely developed from suckers after a disturbance. In many instances, the grove has a uniform genetic make-up as well, as all trees could be clones of the same parent. Aspen produce seeds every year (about 1.5 million from a mature tree produce the poplar fluff or “cotton” of late May or early June) but they require cool moist soil and no competition for light to germinate and grow. This combination is rarely found in parkland, hence the preferred form of reproduction is vegetative suckering (cloning). The genetic uniformity of aspen groves means that most trees in the grove look alike. Variation between groves is common, however, as they originated from different parents. The shape of the trees, bark colour (from white to grey), leaf size, and leaf shape can differ considerably among groves. In large stands of aspen, genetic differences in phenology (timing of flowering, leafing) are noticed in early spring when a group of trees are in leaf while the rest are just budding out.
As placid as a parkland scene may be, there is an ongoing battle being fought between the grasses and the aspens. After a fire, it is a race to see which can get to the sun first – grass or suckers – but grass usually wins. The large leaves of suckers, relative to those on a mature tree, are designed to be efficient light catchers. In wet years, though, the aspen can encroach relentlessly on the grasses, and in dry years the trees may hold their gains. Some suckers can appear 25 metres from the parent plant and grow 3 metres in a single year. Prolonged drought weakens aspens, however, and leaves them susceptible to fungus invasion. Groves can die and the grasses will take back their lost territory. Ideal growing conditions for Aspen are found in the southern mixed-wood boreal forest, just north of the Aspen Parkland. Ironically, most of the Aspen Parkland is a bit too dry for aspens to really thrive.
The history of the Aspen Parkland is one of competing interests. There is a tension between the trees and the grasslands. The local winner in these contests reflects long-term climatic conditions, as well as the effects of fire, topography, and serendipity. Other contests pit fur traders against the fur bearers; farmers, ranchers and engineers against nature; and loggers against common sense. These contests continue to be a feature of the parkland. There have been both winners and losers in these contests. Of the 7.35 million original hectares of Aspen Parkland in Alberta, 90 to 95 per cent has been altered or destroyed, primarily to support agriculture. Most remaining samples of original Parkland are less than 1,000 hectares in area and are on marginal soils. Morainal areas and those with solonetzic soils are relatively unproductive and have resisted development.
Contact with settlers has affected numerous animal populations. Early fur traders were remarkably efficient at eliminating fur bearers from the Parkland. After a few years in an area, catches declined and new areas were explored and trapped. Conservation was unknown. Bison (Bison bison) were gone by about 1870. They were soon followed by the wolf (Canis lupus), grizzly bear (Ursus arctos), and magpie (Pica pica). Beaver (Castor Canadensis) were virtually extinct by 1900. In fact, the turn of the century saw an all-time low in big game, including mule deer (Odocoileus hemionus), elk (Cervus elaphus), moose (Alces alces), and pronghorn (Antilocapra americana). Despite a relatively small population, there were enough Albertans hunting for food or commerce to essentially eliminate game. A lack of game meant anything else was worth eating, and species such as whooping crane (Grus americana), passenger pigeon (Ectopistes migratorius), prairie chicken (Tympanuchus cupido), and sharp-tailed grouse (T. phasianellus) were either eliminated or threatened with extinction. An irrational and misguided hatred of predators took its toll on hawks, owls, coyotes (Canis latrans), and badgers (Taxidea taxus), and left prey populations such as ground squirrels with few natural enemies.
For a number of reasons related to changes in animal populations, scarcity and value to collectors, and increasing leisure time, Albertans began systematic study of their natural world. Francis La Grange Farley settled in Camrose in 1907, at the age of 37, and spent a lifetime studying the birds of Alberta. He wrote hundreds of articles in local newspapers, but also published 36 scientific papers in peer-reviewed journals. His influence is still felt as the donor of many ornithological books to Provincial Museum of Alberta's library and as a mentor to the authors of the first Birds of Alberta. The value of his documented observations as a yardstick to measure change in our landscape is apparent from a 1919 paper by Percy Taverner, Dominion ornithologist, who recounted his 1917 collecting expedition to central Alberta. Taverner was thrilled at spotting (and as a good museum ornithologist, collecting) a black-billed magpie. He quoted Frank Farley: “No one knew this bird 10 years ago [yes, this is our ubiquitous magpie) …. I never saw or heard of one farther north than 10 miles from Camrose.”
Besides Farley, there is a relatively short list of naturalists who documented parkland habitats before they were modified so extensively. Bits and pieces can be gathered from the writings of egg collectors and naturalists such as Archibald Henderson, Tom Randall, Charles Horsbrugh, Evan Thompson, N.V. Fearnhough, Elsie Cassels and Norman Criddle. William Rowan, who began his career at the University of Alberta in 1920, made Beaverhill Lake an internationally known birding spot and worked to establish many of the bird conservation measures we have in place today. J. Dewey Soper provided details on mammal populations and wrote The Mammals of Alberta. To my knowledge, these works have never been summarized in an overview that discusses the effects of settlement on habitats and wildlife in the Parkland.
Ironically, despite massive loss of original parkland habitat after 1900, many animal populations are in far better shape than they were at the turn of the century. Magpies are back, thanks to cattle and urbanization. Ungulate populations are at all-time highs. However, there has been a change, as the white-tailed deer (Odocoileus virginianus) has moved in from the east and south and supplanted the Mule Deer from much of its range. Elk and bison can be found, but usually in parks and game farms. With all the clearing of trees, white-tailed Jackrabbits (Lepus townsendii) moved north from the grasslands. Coyotes have thrived, as have red fox (Vulpes vulpes), particularly in the last decade. Our cities are a source of warmth and food and have disrupted the normal life history of many birds, including Canada Geese (Branta canadensis) and various ducks that overwinter. Various gulls, magpies, merlins (Falco columbarius), house sparrows (Passer domesticus), Starlings (Sturnus vulgaris), cliff and barn swallows (Hirundo pyrrhonota and rustica), purple martins (Progne subis), Rock Doves (Columba livia), and Blue Jays (Cyanocitta cristata) nest, feed or overwinter near us, thanks to our buildings, feeders, gardens, and garbage.
The conundrum of wildlife and habitat (or ecosystem) conservation is that change does not affect all species equally. All too often, single species are used as evidence for or against the “value” of change. Ecosystem health cannot be measured by the success of single species. Healthy white-tailed deer populations do not mean healthy Aspen Parkland habitats. The debate has to be about what constitutes “real” Aspen Parkland. Is it what existed in 1830? 1900? 1950? 1994? What price are we willing to pay to create and maintain it? An important point in this debate, especially in a transition zone, is that change is natural. Droughts, fires, floods, temperature increases and glaciers change landscapes just as we do.
The value of preserving historical landscapes can be measured in biological terms such as biodiversity, gene polls and seed banks. The human cost of loss of biodiversity and genetic diversity is perhaps unknowable. We have no way of predicting final outcomes of incremental biological changes in the environment on societies. What about our personal loss? Does it matter that there is little land left that is as our ancestors discovered it? Surely, as much as our museums and archives tell us our sense of place, so too does the character of the land. Do we teach our children to recognize their land and distinguish it from other places? How is a sense of place born? Perhaps our memories cheat, and modified landscapes can serve as our land. Can a golf course fill the bill? Once the last patch of native fescue grasses in the Parkland is ploughed or the last slough drained, we may find out.
A final note on the preservation of habitats comes from Zolati and Vitt, who speculate on the impacts of warming on plant distributions. Given an atmospheric load of (carbon dioxide) that is twice present levels, the southern boundary of Alberta’s Aspen Parkland will be north of Edmonton. Therefore, in their model, in 100 years all of the former Aspen Parkland that graced central Alberta will have been replaced as grass. What then becomes of our “place”? Life in a transition zone is really life on the edge. A few degrees of temperature change or a consistent change in moisture levels and our environment is threatened. This north-south, wet-dry or hot-cold tension may be the defining characteristic of Aspen Parkland life. Does it shape the people? I do not know, but I will bet the folks in Calgary have a different view than I do in Edmonton.
The immense flocks of Passenger Pigeons that once darkened the air were one of the wonders of America. The descriptions of their number, if they were not circumstantial and well vouched for by men of undoubted veracity, would sound like wild stretches of the imagination; flocks, so dense that haphazard shots into them would bring down numbers, travelled rapidly with a front miles in width and so long that it took hours to pass a given point.
- Percy A. Taverner, Birds of Western Canada, 1926