Andy's Northern Ontario Wildflowers
Alvar Types and Flowering Plants
- Manitoulin Island -
Manitoulin Island, on the north shore of Lake Huron, is the home of some of Ontario finest alvars. Illustrated on these associated pages are some alvar types found on Manitoulin Island and some of the flowering plants that occur on those alvars and adjacent lands. My perspective is through the eyes of a geologist.
What is Alvar?: Alvar areas are globally unusual because they occur only in localized areas of the world. Within the Great Lakes area, alvars occur in the Great Lakes region of Ontario, Michigan, New York, Ohio and Wisconsin. Elsewhere in the world, alvars, Quebec (Canada), United States, Stora Alvaret (Sweden) and in Estonia (Europe). The word alvar is a Scandinavian term that is now also used in North America to describe these limestone and dolomite bedrock habitats.
Alvars are formed, and are maintained, by local geological history, water conditions, local temperature conditions related to the local micro-climate, and related landscape processes such as fire. Alvars have the following characteristics that are challenging for many plants:
The term "alvar" was first used in North America in the late 1960s to define similar habitat found around the Great Lakes (Catling and Brownell 1995). Alvar habitat is interesting to many because:
Manitoulin Geology Relevant to Alvar Habitat:
There are several detailed, technical and non-technical, descriptions of the geology of Manitoulin Island. Please refer to those works for a more comprehensive discussion of the geology.
Bedrock: The foundation to Manitoulin Island are ancient, Precambrian quartzite rocks (Lorrain Formation, Huronian Supergroup, for the technically inclined). Geologists estimate that the quartzite formed about 2,100 million years ago! The ancient quartzite rocks are quite rare on the island, but are spectacular La Cloche Mountains around Willisville to the north. The quartzite was a very source of material used by early Aboriginal people who occupied the area near what is now called Shequiandah - the site of an ancient archaeological site (see "The Sheguiandah Site" reference).
Lying on top of the ancient quartzite rocks are limestone deposits, which were deposited during the what geologists call the Ordovician Period, formed about 440 to 499 million years ago! Shales occur within the Ordovician limestone rocks. These limestone rocks are most common along the north shore of Manitoulin Island. The central and south shore of the island is underlain by dolomite rocks that formed during the Silurian Period about 416 to 444 million years ago. The Ordovician and Silurian rocks contain ancient coral fossils and ancient reef structures, not dissimilar to those that form today in warm oceans. Geologists use this type of observation to infer that the Ordovician and Silurian limestone, dolomite and shale rocks formed in an ancient warm ocean close to the Earth's equator. In the recent history, these limestone rocks have weathered to form karst structures that enhance cracks and are often the foothold for plants.
Glacial deposits: Overlying the rocks on Manitoulin Island are sands, gravels, and tills that were deposited by glaciers that covered all of Ontario up to about 25,000 years ago. The stage of glaciation, called the Late Wisconsinian age, is responsible for the shape of the land and the deposition of the land-based materials on the island. Some of these deposits include material that formed on the bottom of lakes during the retreat of the glacier. In general, the composition of the till reflects to composition of the underlying bedrock - not surprising given that the till represents bedrock eroded and ground up by the passing glacier.
Manitoulin Earth, Fire, Water, Air: Relevance to Alvar:
Micro-climate: The temperature, moisture, and wind conditions are related to the local micro-climate. These conditions affect the plant (and fauna) that grow on the alvars.
Fire: A summary of the relationship between fire and alvar formation and maintenance is given by Brownell and Riley. Although many questions appear to remain, fire has influenced the creation and sustenance of some alvars.
Rock geochemistry: The composition of the bedrock and the glacial deposits directly affects the chemistry of soils and the groundwater that sustain the plants. The composition of the glacial deposits reflects the limy composition of the bedrock, so the "soil" or growing medium is also limy. The limy, basic (higher pH) conditions of the rocks, soils and associated groundwater on the alvars creates difficult conditions for many plants to grow. Those plants that survive are calciphile plants - those that tolerate these limy conditions - include Yellow Lady's Slipper. Contrast this with the presence of blueberry bushes on the acidic quartzite rocks. Plants like blueberries are calcifuge plants that do not tolerate alkaline limy soils. So, in a simple way, we see a direct influence between geochemistry of the bedrock and soil and the plant community.
Geological History: The relevant geological history began about 450 million years ago when the limestone rocks were deposited in a warm ocean. This was the origin of the limestone and dolomite rocks that underlie much of Manitoulin Island and the rocks that constitute the foundation for the alvar today. That geological history was augmented by the geological processes that marked the end of the last great period of glaciation to affect the area, about 10,000 years ago. During this post glacial period, conditions were such that the alvar pavements were created and washed clean of soils and land bridges with local climate encouraged the influx of many different plant species (see below).
Manitoulin Island Geological History - Implications for Plants on Manitoulin Island
Exhaustive descriptions of the flora of Manitoulin Island, John Morton and Joan Venn (University of Waterloo) and Manitoulin alvars (Vivian Brownell and John Riley) relate the distribution of many flowering plans to the natural history, including the geological history, of Manitoulin Island. The geological history of Manitoulin Island has been a significant factor that influenced the presence and distribution of plants on the island. For example, the limestone and dolomite bedrock is the foundation of the alvars and the presence of calciphile plants. The presence of the rare Precambrian quartzite supports calcifuge plants. The end of the most recent glaciation, at about 10,000 years ago, is marked by the melting and retreat of the glaciers and profoundly influenced the types of flora of Manitoulin Island:
So, it is clear that the geological history, the geochemistry of the limey, carbonate-rich soil and bedrock, the melting glaciers, the associated changes in lake levels, the incursion of a marine sea, changes in temperature and rainfall, and temporary land bridges, and the wave washing that removed much soil from what is now alvar, all conspired to create conditions suitable for plants on Manitoulin Island that represent 8 of Canada's 9 floristic regions. Present on Manitoulin Island are plants from: Arctic, Alpine, Prairie, Boreal, Northern Mixed Forest, Great Lakes - St. Lawrence, Deciduous Forest and Maritime floristic regions.
From the perspective of a geologist, the geological history of Manitoulin Island, which began about 450 million years ago, had a very important role laying the foundation for the very rare and special habitat call alvar and its associated rare and distinctive plant communities.
Different flowering plants may occur in a range of alvar habitats. I have illustrated the plants where I have seen them. This habitat association is not the result of a comprehensive study - just anecdotal observation.
There are several classifications of alvar types. A comprehensive classification is provided by Brownell and Riley. There are transitions between different alvar types and an island of one type may occur within another. For simplicity, the following are the alvar classifications used on this website:
Manitoulin ROCKS!: Rocks, Fossils and Landforms of Manitoulin Island (2006): M. Coniglio, Karrow, P., and Russell, P, Earth Sciences Museum, University of Waterloo in partnership with the Geological Association of Canada and the Gore Bay Museum, 123p.
The Flora of Manitoulin Island and the Adjacent Islands of Lake Huron, Georgian Bay, and the North Channel (2000): J.K. Morton and Joan M. Venn, 3rd edition, No. 40; 390 pp including distribution maps and coloured illustrations; Biology Series, Department of Biology, University of Waterloo, WATERLOO, ON. Canada. N2L 3G1.
The Sheguiandah Site: Archaeological, geological and paleobotanical studies at a Paleoindian site on Manitoulin Island, Ontario; edited by Patrick J. Julig, Mercury Series, Archaeological Survey of Canada, Paper 161, Published by Canadian Museum of Civilization, 314 p.
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August 3, 2010