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A review of the alvars of the Great Lakes region: Distribution,
floristic composition, biogeography and protection
Catling, PM | Brownell, VR
Canadian field-naturalist. Ottawa ON [CAN. FIELD-NAT.]. Vol. 109,
no. 2, pp. 143-171. 1995.
Alvars are naturally open areas of thin soil over essentially flat
limestone or marble rock with a more or less sparse vegetation
cover of shrubs and herbs with trees absent or at least not
forming a continuous canopy. Drought and extremes of soil moisture
are major factors limiting tree cover. Alvars are important as
sites for (1) the protection of biodiversity including threatened
plant communities, rare and threatened species of flora and fauna,
and germplasm of crop relatives; (2) biological research and
environmental monitoring; and (3) ecotourism. Approximately 85% of
alvar sites and more than 90% of alvar landscape area in the Great
Lakes region is in southern Ontario. With the exception of small
isolated areas, most notably western Lake Erie and Lake Champlain
area, the alvars of the Great Lakes region occur near the contact
line of the granitic Canadian Shield upland with the Ordovician
and Silurian limestones and dolomites. A list of 347 vascular
plant taxa found on alvars in seven alvar regions is included
based on examination of 59 sites in Ontario, one in Ohio and three
in New York State, as well as on the literature and on personal
communications. On the basis of floristic composition and
environmental factors, alvars may be divided into two types:
shoreline alvars along rivers and lakes and plateau alvars. Four
major plant communities related to soil depth and moisture
availability are identified on plateau alvars: alvar grassland,
alvar pavement, alvar savanna and pavement ridge. Biodiversity is
highest on the alvars of western Lake Erie, Manitoulin Island and
the Napanee Plain. The alvar floras of seven regions are apparent
as three major groups in both a phenogram and in the principal
coordinate plot derived from a matrix of Jaccard's coefficients:
(1) the western Lake Erie alvars with a proportionally high
component of plant species occurring to the south, but a
relatively small proportion occuring to the north; (2) the alvars
of the Bruce Peninsula and Manitoulin Island with a high
proportion of northern and endemic plant species at the expense of
southern species; and (3) the alvars of central Ontario, eastern
Ontario and northern New York with a moderate representation of
plant species occurring also to the north, but the major
proportion being southern species. The endemics and boreal
elements of the northern Lake Huron alvars are probable relicts of
the Picea Parkland and tundra-like environments that existed in
front of the Wisconsin glacier more than 9000 years ago. Although
some of the best alvars in the Great Lakes region are protected,
not enough sites are protected to achieve adequate representation.
 Descriptors: Article Subject Terms biogeography | endemic species | plant communities | savannahs | species diversity | Article Geographic Terms North America, Great
Lakes
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