Saskatchewan's Alvars

Alvar is a globally imperiled and unusual group of calcareous habitats characterised by shallow mineral soils over limestone or dolomite bedrock, a natural lack of trees, abundant rare species populations, and an unusual prairie-like plant community. It occurs in only five countries worldwide. In Canada, almost all known alvar is found in the Great Lakes Basin in Ontario, though it is also known from Manitoba, Quebec, Newfoundland, and the Northwest Territories.

Last year, while acting as the Botanist for the Saskatchewan Conservation Data Centre, I set out to find out whether alvar existed in Saskatchewan. It had never been found there before, and few people familiar with the habitat would have expected it to be — limestone and dolomite bedrock are quite uncommon in Saskatchewan, and much of the area where alvar could occur is very remote and densely covered with boreal forest, making access extremely challenging.

Nonetheless, my prior work in Saskatchewan had left me with a strong sense that there was still much to discover there, so I spent several weeks flagging possible alvar clearings using remote sensing. Because alvar patches can appear extremely similar to boreal wetlands and no predictive method exists yet to identify them, I focused on areas with known or modeled limestone/dolomite bedrock, since these are essential pre-conditions for alvar. I excluded boreal wetlands by only selecting clearings that had no apparent hydrological context which could suggest that they were boreal bogs or fens. I also used the presence of trees growing in unusually straight lines to select target sites, as limestone and dolomite tend to fracture in long, straight cracks and trees confined only to these cracks suggest that soils are shallow — another diagnostic feature of an alvar.

Finally, after weeks of planning, my long-suffering girlfriend Sabina and I were dropped off by boat at a remote lake several hours southwest of Flin Flon, where we began our hike. I felt that the odds of successfully finding alvar in Saskatchewan were so low that the first expedition had to happen the hard way, on foot.

After two days of bushwhacking to reach the first suspected site, we broke out of the boreal forest into the first clearing. It is a remarkably surreal feeling to walk out of the buggy northern boreal forest into a broad, grassy clearing dominated by wildflowers and dotted with prairie onions and wild chives. It is like being instantly transported somewhere completely different, and very far away from where you actually stand.

There was soon no doubt that the clearings were indeed alvar, after checking the soil profile and looking closely at the plant community (see the next page for photos of several indicator species). What might easily have been mistaken for just another wetland from the air was in fact solid ground, and a new habitat for Saskatchewan — likely the rarest in the province.

Above and beyond the rarity of the habitat itself, surveys at Saskatchewan's alvars ultimately confirmed extraordinarily high levels of rare species diversity, including at least five new species and one new genus to Saskatchewan. Nearly 45% of the species identified in 2020 are rare species or new species to the province, underscoring the extremely high conservation value of the sites.

Several species discoveries were particularly exciting, including Cypripedium reginae, the ‘showy ladyslipper’, which was found at the Limestone Lake site. This population is only the third known site in the province and an apparent rediscovery of the species, as it was thought to be extirpated from Saskatchewan. Two populations of Asplenium viride, the 'green spleenwort', represent the first records of the genus for Saskatchewan and apparently the first records of the species between the Alberta Rockies and the Great Lakes. Dermatocarpon dolomiticum, an unobtrusive but very unusual lichen species, is federally critically imperiled and the new population is something like 1,600 kms from the closest sites in the Great Lakes basin. And Botrychium tenebrosum, the ‘swamp moonwort’, is a new species of these enigmatic and rare ferns for Saskatchewan.

These findings only represent approximately three days of surveys, suggesting that further work will almost certainly uncover many more exciting findings.