lakeside daisy, manitoulin island, copyright 2006 Andy Fyon

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Alvar Types and Flowering Plants

- Manitoulin Island -

 

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Habitat:

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.

Open pavement alvar, copyright 2010 Andy Fyon, www.ontariowildflower.com

Typical Open Pavement Alvar, Manitoulin Island, Burnt Harbour area.

 

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:

  • are naturally open areas - high solar incidence;

  • have thin soil that overlie flat-lying limestone or dolomite rocks - limy soil, when present, which is hard on many plants;
  • vegetation is sparse;
  • trees are absent or uncommon due to fire or shallow soil and if present, do not form a continuous canopy;
  • the area is subject to flooding in the spring and fall and subject to severe drought in the summer;
  • shrubs are short or creep along the ground.
  • winter frost may have an important impact on the surface conditions due to the thin soil conditions.

The term "alvar" was first used in North America in the late 1960’s to define similar habitat found around the Great Lakes (Catling and Brownell 1995). Alvar habitat is interesting to many because:

  • alvars comprise a small percentage of the Earth's ecosystems by land extent;

  • approximately 120 alvars exist in the Great Lakes region, but they constitute only 0.2% of the land area there
  • alvars support rare and unusual flora and fauna.

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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).

Lorrain quartzite outcrop located to the west of the Sheguiandah archaeological site, Manitoulin Island.

Date: April 3, 2010

Lorrain quartzite inlier, copyright 2010 Andy Fyon, www.ontariowildflower.com

Patrick Julig, Department of Anthropology, Laurentian University, copyright 2010 Andy Fyon, www.ontariowildflower.com

Dr. Patrick Julig holding an historic tool made from Lorrain quartzite at the Sheguiandah archaeological site, Manitoulin Island.

 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.

stromatoporoid fossil, copyright Andy Fyon 2010, www.ontariowildflower.com

An Ordovician stromatoporoid fossil of the type that builds ancient coral reefs, Verulum Formation, Goat Island.

A Silurian coral fossil impregnated with hydrocarbon from the Manitowaning Bioherm, Manitoulin Formation, southwest of Manitowaning, Manitoulin Island.

Coral, copyright 2010 Andy Fyon, www.ontariowildflower.com

Coral, copyright 2010 Andy Fyon, www.ontariowildflower.com

A Silurian coral fossil of the type that builds coral reefs from the Manitowaning Bioherm, Manitoulin Formation, southwest of Manitowaning, Manitoulin Island.

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.

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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.

  • Air Temperature: In a general sense, the cold waters of Lake Huron are an important moderating influence on the temperature of the coastal regional of Manitoulin Island. In the spring, the air temperature remains cool in the spring, but remains warmer as winter sets in, compared to inland regions. This temperature difference influences the location of some plants (e.g., the presence of Alpine / Arctic plant species on the south shore of Manitoulin Island) and when some plants bloom.

  • Ground temperature: On open alvar pavements, the temperature can get very hot on a summer afternoon as there is virtually nothing to stop the solar incidence.  In addition, the light coloured limestone and dolomite rocks can reflect the light back up to affect the underside of leaves and plants. Winter temperatures can be conversely cold and frost can extend deeply into the ground where snow cover is shallow. These temperature conditions limit the types of plants that can grow.

  • Moisture: In the spring and fall, most alvars on Manitoulin Island are flooded by snow melt and fall rains. However, this moisture soon disappears; rain water quickly runs off the flat rock surface. Close to lakes, where the ground water is close to the surface, plants that take root in cracks in the rock or in the very shallow soil are sustained by the higher moisture available. The spring and fall flooding, contrasted by the dry hot summer conditions, creates a challenging growing habitat on the alvars.

  • Wind: along the shore alvars, there is almost constant wind blowing off Lake Huron along the south shore of the island. This wind helps keep the temperatures on the land cool and is suitable to low-growing plants.

  • Lake ice: Along the south shore of Manitoulin Island, lake ice during the winter scrapes along the shore, cleaning off exposed soil and plants. Therefore, there is commonly a zone devoid of soil within several meters of the shoreline. Plants that grow in this region of the shore alvar are commonly rooted in cracks where a small amount of soil has accumulated.

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).

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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:

  • at about 11,000 years ago, the higher parts of the island emerged from beneath a glacial lake to become islands - plants could get a foothold

  • a marine sea formed along the St. Lawrence and Ottawa rivers - allowed maritime plants to migrate inland to the Manitoulin area
  • the ice front was still close to the north so the climate was likely cold, dry and similar to present-day Arctic - this lead to the growth of Arctic / Alpine flora in the region
  • between 9,000 and 6,000 years ago, the lake level had dropped even more and then rose again, ancient Manitoulin Island was briefly connected to the Bruce Peninsula, the glacier had melted back, the climate was warmer - plants from the southern deciduous forest origins and western prairie regions migrated into the Manitoulin area
  • between 5,000 and 4,000 years ago, temperatures fell to below today's and lake levels dropped again and resulting wave action removed much of the soil and till that had been deposited when the glaciers melted away; this material was washed in to the remain lake that covered parts of the ancient island to become fertile valleys today; the wave-cleaned limestone plains became the alvar areas.

Ancient shoreline, copyright 2010 Andy Fyon www.ontariowildflower.com

An ancient shoreline preserved in the glacial deposits, north of Sheguiandah, Manitoulin Island. This shoreline was formed when the lake level of Lake Huron (as we know it today) was much higher when the glaciers started to melt. This is the type of evidence that geologists use to infer that lake levels changed as the glaciers melted.

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.

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Alvar Classification and Flowering 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:

  1. Shoreline alvar: bare limestone and dolomite along the lake shore;

  2. Open alvar pavement; (Flowering Plants of open alvar pavement, inland from shore alvar);
  3. Open alvar grassland; <25%tree and shrub cover and >50% herbaceous cover with grasses and grasslike graminoid plants such as sedges (family Cyperaceae) and rushes (family Juncaceae);
  4. Alvar Woodland >25%, but <60% trees

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Relevant References:

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 Alvars of Ontario: Significant Alvar Natural Areas in the Ontario Great Lakes Region (2000): Vivian R. Brownell and John L. Riley, Federation of Ontario Naturalists, Don Mills, Ontario, 269 p.

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.

Sources of Information on Alvars

Alvars of Ontario - Nature Conservancy of Canada

Alvar - Wikipedia

US Environmental Protection Agency

Click here for more habitat information:

 

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For more information email: andy@ontariowildflower.com
URL: http://www.ontariowildflower.com/manitoulin_limestone_beach.htm
© 1999-2010 Andy Fyon
Sudbury, Ontario

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Andy Fyon

August 3, 2010

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