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The natural eco-system out of which High Park was carved by the
European settlers is called an oak savannah or oak woodland. A
“savannah” is broadly defined as a discontinuous canopy of tree
cover with a ground layer of grasses and wildflowers, and is
considered to be a transition zone between prairie and the eastern
deciduous forest. It is the combination of the two habitats that
gives oak savannah its own unique identity. Savannah is a globally
endangered vegetation community. Human settlement has reduced it to
0.01% of its original extent.
Only at High Park can you still get a glimpse of the variety of
habitats which once occurred throughout Toronto. It is our
connection to Toronto’s wilderness past, but it has not escaped
unscathed. It has lost more than half of its rare plant species
over the last 90 years and one-third of its nesting bird species
over the last 50 years, as well as many of its rare insect species
such as the Karner Blue butterfly. Despite the loss of natural
areas to make way for other uses, High Park still supports a
remarkable variety of rare flora and vegetation communities.
High Park is the last sizeable natural area remaining on
Toronto’s Iroquois Sand Plain. These sands were laid down on the
shores of glacial Lake Iroquois, the larger version of Lake
Ontario, that was formed when the glaciers retreated from our area
about 12,800 years ago. The coarse, sandy soils are relatively warm
and dry. This “edaphic” feature has allowed savannah plants to
successfully colonize and expand their range well to the east of
the traditional warm and dry prairies of central North America.
The oak savannahs of High Park are considered “continentally
significant” by virtue of their location, at the northern edge of
the geographic zone of occurrence, and the size, nature and
characteristics of the remnant ecological community they comprise.
These ecological features are nonetheless impoverished. For
example, the dominant Black Oak trees, over 150 years of age, are
not regenerating. Regenerating is used rather than reproducing
because the oaks do set viable crops of acorns. It is from that
point onward that the life cycle of a Black Oak is impaired. At
least 50% of these Black Oaks are diseased or heart- rotted. In
recent years, successive dry summers coupled with successive Fall
Cankerworm infestations have contributed to the demise of a
substantial fraction of these old oak trees. The Parks Department
has embarked on a program which includes acorn collection and
germination as well as insect and squirrel population monitoring so
as to curtail the demise of this tree species.
As well as identifying eco-system features there should be an
understanding of eco-system function. A function that is
characteristic to savannah is fire. The whole host of savannah
flora and fauna are in some way fire-dependant. For instance, young
Black Oak trees tolerate fire by exhibiting a unique ability to
resprout stems following top kill by fire, when their competition
can not. Also, large Black Oak trees develop a fire resistant,
insulating bark which gives them a competitive advantage. The Parks
Department recognizes the necessity of fire, and has thus conducted
several controlled, or prescribed burns in the past few years.
Results have been encouraging, and the Department will continue to
use the services of professional fire practitioners for years to
come.
Forty species of the park’s native plants are known to occur in
only four other places in Metro Toronto. Four of these species
(Wood Betony, Shrubby St. John’s-Wort, Wild Lupine and Cup-Plant)
are known to occur in four other places in Canada. What we have in
High Park is truly unique and rare.