The wonderful world of alvars.
What in the world is an alvar? Most people have heard of wetlands, forests and prairies, but there is an equally important type of habitat that isn’t so well known. An alvar is a naturally open habitat with a thin covering of soil (or no soil at all), over a base of limestone or dolostone.
Upon first glance, it may appear as if these are barren landscapes with little to no life inhabiting them, but in fact the opposite is true. Alvars are home to many rare and unusual flora and fauna, and at a small scale they are among the most species-rich communities in the world.
Across the globe alvars are only present in certain areas including the coast of Sweden, the eastern European Baltic region, the United Kingdom, Ireland and the North American Great Lakes Basin. Some alvars are also located in Manitoba, Newfoundland, Quebec and the Northwest Territories.
Over 60 per cent of the Great Lakes Basin alvars are located in Ontario. The Nature Conservancy of Canada (NCC) and other environmental groups believe that because of this, Ontarians have a responsibility to conserve these globally significant habitats and their specialized species communities.
Types of alvar habitats.
There are five main types of alvar: alvar shrubland, alvar grassland, alvar savannah, alvar pavement and alvar woodland. The different types are determined by the amount of soil present. Location, soil moisture and the length of drought period determine which types of vegetation grow there.
Alvar pavement is a type of habitat that occurs on exposed rock, which may be cracked or fissured and has less than 2 centimeters of soil. The vegetation is patchy and mosses and lichens are dominant. This type of alvar may have the most plant diversity. Plant communities take root in bedrock cracks and in depressions where rainwater gets caught.
Alvar shrubland has a moderate to high cover of shrubs, low tree cover, and it appears stunted. Creeping juniper, ground juniper, and fragrant sumac are some species that live there.
The most uncommon alvar type is alvar savannah. Scattered trees of oak or pine cover 10-25 per cent of the land, providing habitat for birds and mammals.
Alvar grassland supports grasses, sedges and more continuous vegetation, as this type of alvar is more meadow-like. The soil depths range from 1-10 cm, and the species can vary depending on the extent of flooding in the spring. Species include tufted hairgrass, poverty oatgrass and little bluestem.
Alvar woodland has the highest tree cover of all alvar habitats and is often adjacent to other alvar types. Conifers such as eastern red-cedar, white spruce and eastern white pine are common in this habitat type.
Different alvar species.
Many of the species that survive on alvars are rare and aren’t found in any other habitat in the world, such as certain types of moss, lichen, birds and insects. In Ontario, 54 plant species are found mainly on alvar habitat.
The lakeside daisy is a rare vascular plant that is listed as threatened under the Species at Risk Act in Canada. It is a species that is predominantly found in alvars as they mostly grow in the cracks of limestone or on tufts of low-growing vegetation. Other plant species that inhabit alvars are false pennroyal, early buttercup, blazing star and upland goldenrod.
The eastern loggerhead shrike is a species that is listed as endangered in Canada by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), as it is one of the fastest-declining bird species in North America. This particular songbird is unique because it hunts like a bird of prey by impaling its prey on thorns or the barbed wire of fences, enabling it to tear apart and consume its prey or leave it for later consumption. There are many thorn trees present on alvars such as the Carden Alvar Provincial Park, which is a traditional nesting area for the eastern loggerhead shrike.
Alvar habitats are created where environmental extremes create naturally open landscapes. The soils of the relatively flat limestone bedrock were scraped away by ice, wind and water a long time ago. The plants and wildlife that live there have developed to live in very harsh environments.
During the summer months alvars can reach high temperatures of 43˚C at the rock surface. The winter winds turn the habitat so cold that needle ice crystals churn up the little soil that exists there. Springtime changes the landscape again into many shallow pools and bedrock pockets, and some areas remain flooded for weeks at a time. As summer approaches the land begins to dry and the flowering plants start to turn brown. The combination of flooding and drought holds off invading trees and makes it difficult for trees and shrubs to take root. Alvars sometimes display evidence of past fires such as the presence of charcoal, which is another contributing factor to their open character.
Alvar habitat locations.
Some of the most famous alvar habitats occur in the Ontario region including Manitoulin Island, the Carden Plain and the Bruce Peninsula.
Manitoulin Island is a place of incredible beauty and history. The ancient Precambrian quartzite rocks, that are the foundation of the island, were formed more than 2 million years ago. Aboriginal people who occupied the region would use the quartzite to make tools, and the region, now called Shequiandah, is considered an ancient archaeological site.
The Carden Alvar Provincial Park is one of Ontario’s newest parks. Carden is an old township in central Ontario, which is now part of the City of Kawartha Lakes. For years birders and botanists would visit the Carden Plain, and some of these visitors became concerned with the continued loss of alvar habitat. Grasslands were shrinking, causing a decline in many bird species.
Conservation began in 1996 through the efforts of many volunteers, donors and organizations including the Couchiching Conservancy, The NCC, the Ontario Ministry of Natural Resources and Forestry, Ontario Field Ornithologists and more. In the spring of 2014 Ontario Parks formalized the regulation to create Carden Alvar Provincial Park, which encompasses 1,917 hectares of permanently protected alvar habitat. There are over 400 plants, 230 bird species and 130 species of butterflies and dragonflies inhabiting the area. The public can enjoy this beautiful park by hiking on the two trails or by attending various events including the Carden Alvar Nature Festival.
Threats to alvar habitats.
There are many threats to alvars, which is why it is so important to conserve and protect these rare and delicate habitats. Rock quarries, urban and rural development, disturbance by motorized vehicles and cyclists, introduction of invasive and weedy species, and overgrazing of livestock and wildlife are all contributing factors.
Unfortunately, a lot of alvar land is still unprotected. About 50 alvar sites have been identified in the Napanee Plain and Prince Edward County areas, and less than 2.5 per cent of those areas are protected.
The good news is that you may have alvar habitat on your land! If your property consists of relatively flat limestone or if the soil is less than 15cm deep, it may be an alvar habitat. Other signs are seasonal flooding or drought, sparse or absent trees, and having alvar indicator species present such as prairie smoke, long-leaved houstonia, balsam ragwort and lichens like Cladonia pociullum.
If you discover that you have an alvar on your land, you could be supporting a habitat for rare and unique species that are not found naturally anywhere else in the world. To help take care of an alvar environment, tread lightly on sensitive habitat and graze livestock on a rotational basis to prevent overgrazing. Another option is to enter into a conservation agreement with the NCC or another land trust to protect the alvar on your property.
Anyone can do their part to help alvar habitats by being respectful of plants and wildlife. Reading more about these amazing habitats will help you appreciate the rarity and importance of alvars.
If conservation efforts continue and people help spread awareness about these important areas, then alvar communities can continue to thrive for generations to come.