 Mixedwood Plains Ecozone
Changing Forest Landscape Conditions
Health of sugar maple: Analyses of sugar maple
within this ecozone and in portions of the Boreal Shield and the
Atlantic Maritime ecozones, reveal no difference in growth and vigor
between stands managed for maple syrup and unmanaged stands (Lachance
et al. 1995). The total number of taps has increased 12% from
1994 to 1995, while the area of maple stands managed as sugarbush
has decreased 2% (Parent 1996).
Results from the North American Maple Project (NAMP) (Lachance
et al. 1995) and the Acid
Rain National Early Warning System (ARNEWS) (Bowers and
Hopkin 1997) show that forests are healthy. However, some stands,
located in high level areas with frost, disease and insect damage,
high ozone levels, and high sulfate and nitrate deposition in exceedance
of critical loads have shown some decline (Bowers and Hopkin
1997). Some locations show poor tree condition and these generally
occur in areas characteristic of soils that receive acidic deposition
at levels above their buffering capacity. A direct link between
poor growth and acid rain is unclear, as these areas are also considered
to be naturally poor growing sites, where higher levels of damage
would be expected (Bowers and Hopkin 1997).
A fragmented forest: Europeans have settled in
the St. Lawrence River Valley since the 17th century.
Over the years, land-use practices have modified the landscape (Bouchard
et al. 1989). Forests, in large part, have been replaced by
agricultural fields and urban areas. Today, less than 10% of the
original forest cover remains (Ecological Stratification Working
Group 1996). The remaining forests are so greatly fragmented,
due to land conversion for urban and agricultural purposes, that
long-term viability of these ecosystems is threatened (Savard
1994). Very little old-growth forest remains (Brisson et
al. 1994). Introduced diseases, such as beech bark disease
(Brisson et al. 1996), have begun to attack the remaining
forest.
Changing Biodiversity
Entry for introduced species: Settlement of Europeans,
as well as heavy maritime and railway traffic, have contributed
to the introduction of numerous non-native, usually invasive, vascular
plants along the St. Lawrence River axis (Catling and Cayouette
1996, Rousseau 1968). More than 600 000 white elms have disappeared
from the St. Lawrence Lowlands since the introduction of Dutch elm
disease in 1944 (Pomerleau 1961). Chestnut blight has almost
eliminated American chestnut from the Lake-Erie Lowland (Farrar
1996). The butternut
canker, a more recent invader, is killing butternut (Innes 1998).
The European race of scleroderris
canker and white
pine blister rust are continuing threats to species such as
red or white pine. Pine false webworm, a common pest on pines, is
increasing its range since its introduction into southern Ontario
in 1961 (Lyons et al. 1993).
Threatened forest ecosystems: Carolinian forests
in southern Ontario, and hickory-sugar maple and basswood-sugar
maple forests in southern Quebec have been reduced substantially
in size following settlement and deforestation (Catling and
Cayouette 1996). Tree species such as white pine, red oak,
eastern hemlock, and American beech were harvested to such an extent
that the composition of the forest has changed (Bouchard et
al. 1989).
Fragmentation of forests, invasion of forest edges by non-native
plants, harvesting of old-growth forest, and an increase in plantations
have resulted in a decrease in numerous bird species, including
wild turkey, red-headed woodpecker, and Kirkland warbler. Rare birds
such as the Acadian flycatcher, Louisiana water thrush, prothonotary
warbler, and Cerulean warbler are directly threatened by the decreasing
area of Carolinian forest (Brunton 1996).
Lack of forest habitat has eliminated wolverines, cougars, and
wapitis from this ecozone. Populations of snowshoe hare and Canada
lynx are declining because of deforestation. Other mammals, such
as the gray wolf and American marten can be found only along the
northern edge of the ecozone adjoining the boreal forest. Some species
have benefited from deforestation and harvesting practices: eastern
cottontail, woodchuck, eastern grey squirrel, meadow vole, coyote,
northern racoon, striped skunk and white-tailed deer (Smith
and Smith 1996).
Changing Atmospheric Environment
High pollutant levels: Pollutant deposition is
generally higher than in other ecozones (Miller et al. 1990).
This ecozone is located along one of the major storm tracks of North
America, and wind and clouds carry over it pollutants produced in
the American Midwest. There are also many large urban settlements
and industrial areas within the ecozone that are sources of air
pollution (Ecological Monitoring and Assessment Network, Environment
Canada 1996).
Measurements of sulfate deposition by the Quebec
Department of Environment (Boulet and Jacques 1989, 1992,
1993a, 1993b; Grimard 1984, 1985; Jacques and Boulet 1988, 1990;
Jacques and Grimard 1987) show that sulfate deposition currently
ranges from 21 to 38 kg/ha/yr and has been decreasing steadily by
about 3% per year since 1984. Current nitrate deposition varies
from 16 to 25 kg/ha/yr. Rain acidity has a mean annual pH ranging
from 4.1 to 4.5.
Ground-level ozone: Ground-level
ozone reaches the highest peaks in Canada in this ecozone (Thomson
1992). From April to September 1986-1993, there were 127 days
with episodes reaching harmful levels of smog in this ecozone, the
highest in Canada. Concentrations during some episodes were high
enough to induce immediate, short-term damage in sensitive plant
species (Pearson and Percy 1997). For example, in 1988,
there were regional episodes of 4, 5, 7, and 9 days' duration.
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