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Hastings Cty. - Protecting nature’s rock gardens
June 28th, 2005
by Louise Livingstone
Most people are aware of the importance of wetlands to hold water, improve water quality and to support a large variety of wildlife . Woodlands get good press too, because of all the benefits they provide, timber production, recreation, wildlife habitat, and air quality improvement.
However, few people see thin, bare, limestone pavements (alvars) as anything but parking lots in waiting. A few people recognize their true worth and see alvars as nature’s rock garden.
Professor Dale Kristensen from Queen’s University has spent many years studying alvars. He spoke to land owners about alvars at a recent workshop at Roblin organized by Ontario Nature and the local stewardship councils.
Seventy-five per cent of North American alvars are found in the Great Lakes Region and are concentrated in Ontario. The main area is around northern Lake Huron, Georgian Bay and on Manitoulin Island. The other area is in this area of eastern ontario on the Napanee Plain.
Manitoulin Island has some of the most famous alvar communities in the World. These are found on thin soils on flat limestone or marble with less than 60 per cent tree cover. The top soil was scraped off during glaciation and specialized plant and animal communities have developed over thousands of years, adapted to the extreme conditions found on alvars.
Alvars are exposed environments with temperatures as high as 90 to 100° Celsius in summer and 38 to 40° Celsius in winter. In summer there are drought conditions and in winter frost and ice damage occurs especially in the cracks in the rocks. Only very hardy organisms can survive.
“Alvars are below the radar and are not immediately
charismatic habitats,” said Kristensen.
“Drought, fire, flooding and ice action prevent soil from building up. Soil build up is a bad thing for an alvar as incoming species will survive and will out compete with alvar species.
“Alvar vegetation is regulated by drought, flooding, and ice action in the crevices. Fire is believed to be a major factor in some alvars,” said Kristensen. “The name alvar comes from Sweden. There are alvars on some Swedish islands and also in the Burren in the west of Ireland.”
(There is a saying. The Burren, where there are no trees to hang a man. Where there is not enough water to drown him. And if you finally succeeded in killing him, it's too rocky to bury him.)
Grazing pressure is important in grassland alvars especially cattle grazing which prevents trees taking over, however, cattle can carry seeds of alien species.
There are many colourful plant species typical of alvars such as Indian paint brush, brown knapweed. early saxifrage, blue eyed grass, prairie smoke, heath asters, dwarf hackberry, side oats gamma. Kristensen showed slides and It is not surprising he describes alvars as nature’s rock gardens.
He explained how aggressive non-native species like daffodils, lilac and blue cilla can invade and how one can start losing native species. “Lilacs love limestone. Plants were brought in by pioneers 150 years ago. Lilac now invades alvars. They drop leaves and add to the soil which encourages other non alvar species to come in,” said Kristensen.
He described the three types of alvar: open alvar, alvar savannah with scattered trees and wooded alvar saying mosses and lichen define open plate alvar.
He also said, “There are 12 globally imperiled plant communities found on Ontario alvars, and ecotourism is a growing area of the economy. People are interested in seeing habitats and see the rare birds that live on alvars.”
Chris Groome from Ontario Nature later showed slides of birds found on alvars and grasslands. The rare loggerhead shrike breeds on the limestone grasslands of Tyendinaga. This strange bird has a beak like a bird of prey and feet like a song bird. It attaches its prey, insects and small birds, onto thorns and barbs on fences to hold it firm while it eats them.
There are many threats to alvars such as urbanization and recreational uses. Flat areas attract the ATV crowd. The tire ruts fill with water in spring and this changes the hydrology of the area.
Alvars are a climax community and if not stressed can be sustained for thousands of years. Ontario Nature has a project to identify new sites, map rare species distribution and to promote stewardship education and restoration.
If you own an alvar or are interested in finding out more about how to protect alvars, please contact Jim Pedersen, Hastings Land Stewardship Co-ordinator at (613) 478-6875.