Endangered ecosystem: 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.

Prairie revival
“The tallgrass prairie movement in Ontario has really blossomed,” says Allen Woodliffe, district ecologist (Aylmer District) for the Ministry of Natural Resources, “especially when you consider that in the 1970s and mid-1980s, there were only a handful of people in Ontario who even knew what was meant by prairie.”

Now, there is a provincial organization devoted to prairie research and conservation (Tallgrass Ontario), and prairie restoration work is being carried out by landowners, stewardship councils and park managers. Many people involved in restoration urge caution, however: “The more we know, the more we realize that there is a lot we don’t know,” says Woodliffe. “We’re in the infancy of understanding what prairie is all about.” For example, while prairie burns – crucial to any restoration or maintenance effort – have become relatively common, Woodliffe warns that we lack data on the ecological ramifications and long-term impacts of fire. In Ontario, prescribed burns tend to take place during a very narrow window of opportunity in spring, whereas the natural fire regime would have been more varied.

Larry Lamb, adjunct lecturer and manager of the ecology lab at the University of Waterloo, whose suburban backyard prairie was the first effort in Canada to recreate a full-scale prairie system on a home landscape, likewise urges caution: “We’re putting prairie where it doesn’t belong – planting species at risk left and right, using them indiscriminately in the landscape and using genetically inappropriate seeds. We’ll never know where the real populations of species at risk are.”

“There is a lot of enthusiasm for prairie restoration,” says Graham Buck, program coordinator of Tallgrass Ontario, “but we sort of put the cart before the horse.” Buck favours the admittedly more time-consuming work of rigorously evaluating all existing prairie remnants first: “Let’s get the mapping done, figure out where prairies are, then look at the landscape and see where we can do significant restoration work to enlarge and enhance these remnants.” The goal of Tallgrass Ontario is to continue their inventory in 2008, but Buck admits that it’s a “massive undertaking,” in part because “the more you look, the more you find.” Although many remnants are “tucked into obscure, hard-to-get-to places, often on private land,” Buck also points to some surprises staring us right in the face: “I found a new remnant approximately one hectare in size – in London!”

There may indeed be a lot we don’t know, but as Buck says, “the most encouraging thing is that prairies are incredibly resilient.”
Lorraine Johnson

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. Carden is home to the highest concentration of breeding shrikes in Ontario. In 2007, 12 breeding pairs were documented in the area, representing over half of the province’s breeding population.

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, prairie-smoke, 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.

Learn more about the organizations involved with alvar protection in Ontario:

Ontario Nature

Canada’s IBA Program

Carden Field Naturalists

Couchiching Conservancy

Nature Conservancy of Canada

Orillia Naturalists’ Club

Toronto Ornithological Club

The Couchiching Conservancy organizes two annual events to explore, celebrate and protect the Carden Plain. In 2008, the Carden Challenge, a 24-hour birding fundraiser, will be held on May 30 and 31. The Carden Nature Festival will run June 6 to 8, in partnership with Ontario Nature, the Carden Plain IBA, Carden Field Naturalists, Orillia Naturalists’ Club, Kawartha Field Naturalists and the City of Kawartha Lakes. For more information on the festival, visit www.cardenguide.com/festival.


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