In the Interior Plains of North America, aspen parkland extends as an arc some 200 to 250 km wide from the foothills of the Rocky Mountains across the Canadian Provinces of Alberta, Saskatchewan, and Manitoba. It is a vegetation zone unique both to North America and the world, bounded in Alberta by the boreal forest to the north and the grasslands region to the south. It is so named because it naturally consists of a mosaic of groves of trembling aspen (Populus tremuloides) and open grassland, dotted with wetlands in low-lying areas. Its flat or undulating topography is a legacy of glacial debris deposited at the end of the last glaciation; silt from glacial lakes, till from in situ glacier melting, windblown sand dunes or glacial outwash from meltwater channels. Grasslands developed in the drier sites, woodlands in the wetter ones.
Aspen parkland proved ideal for European settlement with its fertile soils. Today only 6% of its original prairie is left, the rest consumed by agriculture, the oil and gas industry and, most recently, urban and suburban development. Most of its remaining grasslands are small, isolated, and few and far between.
Nisku Prairie is one such remnant (Figure 1). Twenty-three acres in extent, it is an L-shaped parcel of largely native grassland bordered and intruded by aspen groves. It is situated on the west-facing, gently terraced slope of the Gwynne Outlet Channel, which is incised about 20 m into the surrounding plain. This broad, shallow valley was eroded when Glacial Lake Edmonton discharged through it some 10,000 years ago. On the other three sides, Nisku Prairie is bordered by a road and acreage residences. The municipality of Leduc County has preserved it as a municipal reserve, allowable under the Municipal Government Act of Alberta, which requires that 10% must be set aside as public land when private land is subdivided for development.
In 1993 a local acreage owner “discovered” the prairie with its rich assemblage of native flora. Ecologists from the Government of Alberta and the University of Alberta testified to its ecological value as a rare remnant, and Leduc County was persuaded to beef up its protection of the reserve. With the approval of local residents, the County staked out the boundaries more carefully and erected a fence along all but the western perimeter, along with a horse gate for access, and appropriate signage. This arrangement has been successful in keeping out all-terrain vehicles, a major recreational menace in rural areas, including supposedly protected natural areas and reserves. On the public side, a volunteer management committee was established. This cooperation was later formalized in a Stewardship and Management Agreement co-signed by Leduc County and the Native Plant Council of Alberta, whose local members contribute to the pool of volunteer stewards.
A Diverse Grassland Flora
Small differences in topography, including boulder outcrops, in soil type and moisture, such as in shallow draws and west-facing slopes, contribute to a diverse flora of over 180 species (including woodland species). The dominant grass of the grassland component of aspen parkland is plains rough fescue (Festuca hallii), one of three rough fescue species that comprise what was formerly considered a single entity, the Festuca scabrella complex, now recognized as the provincial grass emblem because of its ecological importance and cultural significance as the basis of the ranching industry in Alberta. Nisku Prairie’s large cover of rough fescue grass (F. hallii) indicates conclusively that it is an original grassland remnant, as this grass does not regenerate once land has been plowed. Somewhat enigmatically, which seems to be true of many of the prairie remnants in our area, Kentucky bluegrass (Poa pratensis), considered to be an introduced species, is also a major component. Nisku Prairie’s soils belong to the Chernozemic and Solonetzic orders, the former releasing Ca2+ ions from weathering of the glacial sediments the latter Na+ ions, with consequences for soil structure and vegetation. Large patches of intermediate oat grass (Danthonia intermedia) and mat muhly (Muhlenbergia richardsonis) indicate solonetzic soils; in small spots where the solonetz develops into hard pans lacking vegetation, thickspike wheatgrass (Elymus lanceolatus subsp. lanceolatus) is present. (Many of our northern prairie remnants occur on solonetzic soils because they were difficult to cultivate; this protection does not unfortunately apply to rapid urbanization.)
Our most prized grass is Canadian ricegrass (Piptatheropsis canadensis), a relative rarity in Alberta. Among the eight species of sedge (Carex) recorded, woolly sedge (Carex pellita) and graceful sedge (C. praegracilis) appear to be the most prominent, especially in the moist solonetzic areas. Dudley’s rush (Juncus dudleyi) is common throughout the grassland (Figure 2).
Among our typical herbaceous species of the grassland are prairie crocus (Anemone patens), much esteemed as a harbinger of spring when it blooms in early May, three-flowered avens (Geum triflorum), two buttercups, prairie (Ranunculus rhomboideus) and heart-leaved (R. cardiophyllus), and heart-leaved alexanders (Zizia aptera). A succession of flowers occurs throughout June and July, including two species of Arnica, slender blue beardtongue (Penstemon procerus), golden-bean (Thermopsis rhombifolia), field mouse-ear chickweed (Cerastium arvense), northern bedstraw (Galium boreale), and veiny meadow-rue (Thalictrum venulosum). Richardson’s alumroot (Heuchera richardsonii) and the white and graceful cinquefoils (Drymocallis arguta and P. gracilis) are also common, as is bastard toadflax (Comandra umbellata). Petaloid monocots include prairie onion (Allium textile), common blue-eyed grass (Sisyrinchium montanum) and wood lily (Lilium philadelphicum). In wet years we see a few specimens of the beautiful calciphile white camas (Anticlea elegans). Mid- to late-season blooms consist mostly of Aster family members: five asters (Canadanthus and Symphyotrichum species), five goldenrods (Solidago species), two sunflowers (Helianthus spp.), meadow blazingstar (Liatris ligulistylis), and narrow-leaved hawkweed (Hieracium umbellatum). Three Artemisias are the latest representatives of the family to flower. Two other late bloomers of note are the annuals felwort (Gentianella amarella) and the hemi-parasite yellow owl’s-clover (Orthocarpus luteus) (Figure 3). Shrubs are well represented in the moist soils of Nisku Prairie. With the exception of a few willows, all are of low stature. They include swamp gooseberry (Ribes hirtellum), saskatoon (Amelanchier alnifolia) and common wild rose (Rosa woodsii). Narrow-leaved meadowsweet (Spiraea alba) forms extensive patches in the wetter areas and is at its western limit at the longitude of Leduc. Western snowberry (Symphoricarpos occidentalis), a major colonizer of poorer-quality grasslands in aspen parkland, forms occasional patches, especially on moist, west-facing slopes.
The Challenges of Managing a Prairie
Before European settlement of the aspen parkland, grazing by bison, and fire (caused by lightning or by aboriginal hunters), maintained grassland at the expense of suckering aspen. Both these management methods are difficult for small steward groups to employ and the agricultural departments of municipalities often have other priorities than their natural areas, as well as little expertise in burning for ecological purposes. Haying has been employed by Leduc County in the past and we hope to start a program of haying with litter removal again next year. We have also established two sets of experimental plots to determine the effect of litter removal on plant growth. Even after 20 years of intervention in the Prairie, weed control continues to be a major management requirement. The great bane of natural areas throughout Alberta is the introduced forage grass, smooth brome (Bromus inermis), an aggressive colonizer of disturbed open areas that can also happily coexist as understory in aspen woodland. Attempts at control of brome colonies in the grassland have consisted mostly of herbiciding with glyphosate. The resulting patches of dead litter require repeated herbicide applications pending regeneration with natives from surrounding grassland or with transplants. Over the last half-dozen years meadow foxtail (Alopecurus pratensis) has become well established, likely getting its start in the wet bottomlands of the Gwynne Outlet and spreading up into the grasslands. We are cutting and herbiciding it. A heavily disturbed area near the gate where rocks excavated from nearby fields were dumped and then removed has been the focus of volunteer efforts for the last few years. The soil here is now so disturbed that we essentially have a “garden,” with a seemingly inexhaustible seed bank supply of annual and perennial weeds such as stinkweed (Thlaspi arvense), hemp-nettle (Galeopsis tetrahit), Canada thistle (Cirsium arvense), and sow-thistle (Sonchus arvensis), along with smooth brome. We have transplanted here seedlings and plugs grown by volunteers from seed collected on site or from the general area. The transplants resemble those of the intact prairie community neither in composition nor form. We grow species that germinate easily and are robust in habit, with the objective of creating as much native ground cover as quickly as we can: three-flowered avens, Richardson’s alumroot, slender blue beardtongue, asters and goldenrods, and various grasses. Natural succession would eventually take care of the annuals, and indeed patches of the perennial colonizer Solidago canadensis complex are extensive, but we assume that thistle and brome would persist indefinitely among the natives if we did not remove them. We have not planted plains rough fescue, despite the dominance of this grass in mature prairies as its seedlings are unthrifty and uncompetitive in early successional situations. Moreover, our Nisku populations have not flowered significantly in four years, and other sources of seed are few and far between (Figure 4). We are concerned that a number of native species appear to have disappeared over the years, usually those that were present originally in small numbers. Examples include leathery grape fern (Botrychium multifidum), Hooker’s oatgrass (Avenula hookeri), long-leaved bluets (Houstonia longifolia), and Drummond’s thistle (Cirsium drummondii). All of our grassland species are wide-ranging in North America, so their loss is only of local significance. Of perhaps even greater concern is our suspicion that numbers of commoner species are declining, which raises the question of whether this is due to natural attrition, or our amateurish and inconsistent management activities! Our plans are to pay more attention to grassland health in the coming years, and to develop a more scientific basis for assessing changes in plant diversity. (A single-year inventory is not sufficient. This year we had no appreciable rain until late July, and several species did not flower or flowered only in small numbers as a result.)
Conservation of Grasslands
In many ways, the challenges of managing Nisku Prairie are typical of those of small natural areas on publicly owned, provincial, or municipal land. While the government can prevail upon private industry to restore disturbances caused by pipelines and other industrial activities, public money is not available for natural remnants whose purpose is conservation or nature-oriented recreation. The priority of urban municipalities is the maintenance of parks and urban forests; for rural ones it is agriculture and rural subdivisions. Consequently, much of the stewardship work falls on volunteers, who have their own limitations: lack of equipment, appropriate contacts and networks, expertise, time, and availability. A somewhat brighter conservation and management picture is that of the newly thriving land trusts, although even they depend to a considerable extent upon volunteers for management (Figure 5). The connectivity of small remnants to larger natural landscapes is now recognized as of supreme importance for the long-term viability of vegetation communities. Geographically, Nisku Prairie is “connected” to the Gwynne Outlet, which extends south into a deeper valley supporting natural grassland communities. However, most of the acreage owners have extended their properties, often used for grazing horses, right down to the Channel edge, severing an ecological connection. We must likely accept that Nisku Prairie can make no significant long-term contribution to the conservation of grasslands in the aspen parkland zone or in Alberta as a whole. Perhaps its most important role then is anthropocentric rather than ecocentric: to serve as a “living museum” for public education and appreciation and for scientific study and experiment, likely involving students from our various post-secondary institutions. The continued engagement of volunteers, especially younger ones, is also vital, and we should be making greater efforts at outreach. Older people with farming backgrounds have nostalgic ties to iconic species such as prairie crocus, associations that can only lessen in predominantly urban-raised populations. Our stewardship goal should be to maintain the health of the Nisku Prairie ecosystem for as long as possible so that succeeding generations can appreciate our ancestral landscapes. Such appreciation is basic to fostering attitudinal changes that could mean that conservation of both small and large landscapes will eventually be given the focus and the funding it deserves.
