CLIMATE AND DECIDUOUS FORESTS IN MARITIME CANADA

1
CLIMATE AND DECIDUOUS FORESTS IN MARITIME CANADA

Future warmer and locally drier summer climates
are projected for Maritime Canada. This will
cause changes of range of plant and animal
species in the forests. Climate change will
result in loss of habitat, decreases or
extinction of native plant and animal species,
and the arrival of more invasive species. The
effects of climate change are likely to be
compounded by other stresses, especially those
caused by human use of the land. The future fate
of the already highly stressed ecosystems of the
remnant Acadian Forest is uncertain. Changes in
ecosystems and dominant species will occur due to
changes in climate. Replacement of formerly
dominant species by new migrants from the
southwest, and increasing significance of species
present in lesser amounts today, can both be
expected. Since tree species require long
periods to migrate, most of the changes will
involve shifts in the proportions of trees that
are already present in the forests of Maritime
Canada.
Regional warming has resulted in the
progressively earlier arrival of spring in
Maritime Canada. This has lead to earlier leaf
development in deciduous trees, earlier flower
blooming and earlier bird nesting times. The
effects are greatest in interior areas, and
relatively less along the coast. Earlier spring
weather can cause problems in Maritime forests.
An early spring warm spell followed by frost can
result in dieback of the youngest shoots and
prematurely opened leaves. This is particularly
a problem for yellow birch, which has suffered
greatly from tree crown dieback. A decrease in
the proportion of yellow birch in the forests
would result in the expansion of white birch and
poplar.
Prior to the development of agriculture, much of
Maritime Canada was covered by the Acadian
deciduous forest. Broad-leaved deciduous trees,
such as beech, sugar maple, and northern red oak,
dominated the assemblage. Beech appears to have
covered more than 50 of many inland areas of
southern New Brunswick, mainland Nova Scotia, and
PEI. Other southern boreal species such as
yellow birch, white pine, hemlock, and white
cedar were also common. Originally, white birch
and jack pine were both uncommon. As a result
of the changes brought by agriculture and the
introduction of other tree species, the Acadian
Deciduous forest has been largely replaced by a
more varied assemblage of trees. The proportions
of spruce, fir, pine, and maple have increased at
the expense of beech and red oak. Future climate
change will operate on a forest that has already
undergone many changes in the last 200 years,
within the lifespan of many trees.
Yellow birch and cedar
Mulberry (left) could expand its range as climate
changes. Cedar (right) would benefit from
reduced snowfall and freezing rain.
Red Spruce
Eastern hemlock is favoured under warm climates,
but where forest fire frequency is low. In
Maritime forests, suppression of forest fires has
allowed hemlock to expand more rapidly than jack
or red pine. Hemlock was shunned by loggers, due
to its hardness and its tendency to break in
shards when cut. It is a poor choice for
firewood, as it tends to throw off shards
explosively when burned. Consequently, hemlock
has frequently expanded its geographical range
and share of the forest assemblages of eastern
Canada following logging. Hemlock is susceptible
to damage by freezing rain and ice storms,
however.
Decreased summer precipitation raises the
possibility of drought disturbance. Trees with
deep root systems are resistant to drought, but
shallow-rooting hemlock and spruce may have some
difficulty.
Lady-slipper orchids prefers moist, acidic peaty
or conifer needle-duff soil. Lady-slippers
flourish best under wetter summer conditions,
beneath mature conifer forests. Summer drought
and forest fires, which favour the growth of
pines and maples, would gradually result in the
replacement of lady-slippers with other orchid
species. Transplantation of lady-slippers is
extremely difficult, hampering re-population of
areas.
More forest fires are likely in the interior
areas of the Maritimes. Increased summer heat and
drought in some areas leading to increased
frequency of fires would affect all forest
species. Analysis of palaeo-ecological data and
climate modeling suggests that an increase in
forest fires can be expected in Atlantic Canada.
That would favour the expansion of red pine in
Nova Scotia and southern New Brunswick, and jack
pine in northern New Brunswick and Cape Breton.
In the Maritimes, most forest fires result from
human activity. Warmer and drier summers will
result in more human use of forested areas for
recreation, leading to an increase in fire
activity. A change in forest composition could
result.
Adaptation efforts for the deciduous forests
involve development of management plans,
protection of key habitats and species, and
sustainable use. Protected areas and wildlife
and forestry management policies that incorporate
climate change sensitivity and risk analysis are
important. The parks and protected areas of
Maritime Canada help to cushion the impacts of
climate change on natural ecosystems and
biodiversity. Parks also allow us to see how
ecosystems that are less disturbed by human
activity respond. Many trees in Maritime forests
live for more than 200 years. Adaptation options
are more limited within the forestry industry
over the short term. The best strategies promote
enhancement of the capacity of the forests to
cope with shifting climate conditions and
affected site conditions, and preservation of
genetic variability. Harvesting and reforestation
should be conducted with a view towards
maintaining the maximum possible degree of
genetic variability.
Sugar maple is well-adapted to both the present
and anticipated future Maritime climates. Maples
have increased in numbers over the past 200
years, as a result of cutting of other deciduous
trees.
Text and photographs by Norm Catto, ncatto_at_mun.ca