Cover Story

Endangered Ecosystems: Alvars

By Andrea Smith

I’m driving through one of Ontario’s biodiversity hot spots on a sunny November day, but my timing is all wrong. According to my guides, Kyra Howes and Lou Probst (both of the Couchiching Conservancy), the best time to see the Carden Alvar is from mid-May to mid-June, when a rich palette of wildflowers carpets the plain, and grassland birds, butterflies and dragonflies abound. Still, even on this late autumn visit, the stark beauty of these limestone barrens is evident. I’m struck by the wide grassland vistas and the flat slabs of surface bedrock that characterize the area. Abandoned wooden corrals dot the pasture landscape, which is neatly bordered by old snake-rail fences.

The term “alvar” refers to shallow limestone or dolostone bedrock covered with little or no soil. The resulting landscape is typically flat and open, characterized by scattered vegetation adapted to seasonal cycles of flooding and drought. Alvars are extremely rare globally, occurring only in the Baltic region of Estonia and Sweden, in western Russia and within the Great Lakes basin of North America. More than half of the continent’s alvars are found in Ontario, including sites on the Bruce Peninsula, Manitoulin and Pelee islands, near Napanee and here in Carden Township, just east of Orillia. The 10,000-hectare Carden Alvar is situated on the Carden Plain, an area of grasslands and shrublands that stretches from Georgian Bay to Bobcaygeon.

More than 200 bird species are found on the Carden Plain, including thriving grassland bird populations, which are declining across the rest of North America. In 1998, Bird Studies Canada and the Canadian Nature Federation designated the Carden Plain a nationally significant Important Bird Area (IBA). Among the species birders flock to see are the eastern bluebird, bobolink, upland sandpiper and rare golden-winged warbler. Perhaps the star attraction, however, is the eastern loggerhead shrike, an endangered passerine requiring large open grassland scattered with hawthorn for hunting and nesting.

We drive west on Alvar Road to Lake Dalrymple and then follow the shoreline south to Prairie Smoke Ranch. The Nature Conservancy of Canada, in partnership with Ontario Parks and the Couchiching Conservancy, has been acquiring alvar on the Carden Plain since 1998. The 280-hectare Prairie Smoke property is its most recent acquisition, obtained through a federal ecogift donation in 2006.

Still, Carden Plain is not entirely safe from threats to its ecological integrity. The dominant pressure comes from quarry operators that own approximately 13 percent of the land area. Although the currently active operations produce less than 20 percent of their licensed limits, and at least a 30-year supply of aggregate is estimated to exist in reserve, quarries continue to be dug here. The shallow limestone, combined with cheap land prices, makes the Carden Plain particularly attractive to aggregate companies. As Probst dryly observes, “for those interested in conserving the alvar, it’s good news that land is cheap, but the disadvantage is that quarries can easily outbid conservation groups for the land.”

Cattle ranching is the other primary land use on the Carden Plain. While light grazing maintains grassland alvars and may actually promote their productivity, intensive grazing disturbs thin alvar soils and can lead to loss of alvar plant species and the introduction of weedy exotics, such as garlic mustard and common viper’s-bugloss. Of the approximately 2,400 hectares of protected Carden Alvar, just over 80 percent is leased to farmers for grazing. “We’re trying to reach a balance between maintaining the alvar and destroying it,” explains Howes. “We’re experimenting with cattle numbers to the point where grass is kept cut and we don’t destroy the alvars. It’s a trade-off.”

We park at the edge of a hayfield and walk through a damp cedar forest until we reach grassland again. Howes identifies a handful of the more than 400 vascular plants found on the plain: fragrant wild bergamot, Virginia (or early) saxifrage, field chickweed and upland white aster. The botanical composition of alvars is a fascinating mix of boreal, southern and prairie species, many beyond their normal range but able to survive and thrive under harsh alvar conditions. The namesake of the property, prairiesmoke, for example, is widespread in western Canada but rare and extremely restricted in Ontario. In general, alvars have high numbers of rare, specialized and endemic species and, at a small-scale, they are among the most diverse ecological communities globally.

Alas, the few existing alvars worldwide are in danger. Quarry activity threatens most alvars close to urban centres. Use of all-terrain vehicles and illegal dumping also pose problems for fragile alvar habitats.

But, explains Howes, “the Carden Alvar is considered a healthy community because of the large expanses of relatively untouched native alvar grasslands.” For now, the alvar seems to be doing well despite human pressures and is recognized as one of the most biodiverse alvars in Ontario.

By Andrea Smith