| Sustainable development of forest
resources is one of the key goals and concerns of forestry
practitioners and researchers. They are working to improve
forestry practices to ensure the sustainability of these resources
and preserve the full diversity of plant and animal species,
while respecting the natural dynamics of forest ecosystems
(i.e., the collective processes involved in the evolution
of the forest).
A number of researchers feel that forest management should
emulate the natural dynamics of ecosystems and associated
processes, as this can improve our capacity to maintain or
even increase the productivity of forest resources. This is
the concept of ecosystem, or multi-resource, management, based
on natural dynamics and disturbances.
Forest mosaic of a mixt boreal forest. |
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| A
DIVERSIFIED LANDSCAPE |
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The dynamics of forest stands are strongly influenced by
natural disturbances such as forest fires. In the boreal forest,
wildfires generate a multitude of stands of variable composition
and age, collectively called a mosaic. They are therefore
partly responsible for the diversity observed at the landscape
scale. Some researchers have embraced the idea that the maintenance
of biological diversity—a crucial component of sustainable
forest development—should be envisaged at the landscape
level and entails preserving the forest mosaic.
Researchers at the Laurentian Forestry Centre (LFC) of the
Canadian Forest Service (CFS) in Quebec, particularly Dr.
Sylvie Gauthier, have been working with Université
du Québec researchers for a number of years now to
enhance knowledge on the composition and diversity of the
natural forest mosaics shaped by wildfire and to compare them
with managed forest stands.
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| MAINTAINING
THE FOREST MOSAIC |
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A forest area that has reached equilibrium with its fire
cycle has a different age class distribution from that of
a managed forest. In the first case, the age of the stands
is determined by the fire cycle, that is, the length of time
necessary for an area equal to the study area to burn. For
a 100-year fire cycle, for instance, the interval between
fires is 100 years on average, but some sectors may burn several
times during this period, whereas others will be spared. As
a result, the stands in the region will be of different ages
and their area will decrease over time, as shown in Figure
1.
Figure 1: Class age
distribution for stands. |
Studies conducted in the boreal forest, particularly in western
Quebec, show that there are huge tracts of forest that are
composed of very old fire-origin stands, some of them dating
back more than two centuries. These old stands may harbour
flora and fauna that are essential to the equilibrium of the
forest environment. Furthermore, two thirds of the stands
correspond to age classes that are younger than the fire cycle,
while the others are distributed among age classes older than
the fire cycle.
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Fires in decline for well over a century
Forest fires are the main type of disturbance in
the boreal forest. For this reason, many studies have
been carried out in recent years in various regions
of the boreal forest with a focus on fire regimes
and cycles. The fire cycle is defined as being the
length of time necessary for an area equal to the
study area to burn.
Studies conducted in the boreal forest of western
Quebec indicate that the fire cycle may vary over
time, as a result of the effect of climatic change.
One recent period that provides evidence of this and
that is characterized by a lengthening of the fire
cycle coincides with the end of the Little Ice Age
(around 1850). There has been an increase in the amount
of summer rainfall since 1850, a phenomenon which
could explain the observed decrease in fire frequency.
Furthermore, it appears that the global warming trend
that began at the end of the Little Ice Age has promoted
conditions that are less conducive to forest fires
in the eastern part of the Canadian boreal forest.
This interpretation supports the predictions that
have been made regarding a decrease in fire frequency
in the future. Indeed, simulation models based on
the assumptions of climate warming and increased CO2
levels predict an even more pronounced lengthening
of the fire cycle in the boreal forest of Eastern
Canada. Climate change represents a major challenge,
and the Canadian Forest Service plans to triple its
research efforts in this area over the next three
years.
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In in a forest managed for sustained yield, the goal is to
obtain equal areas of each of the age classes so as to ensure
a steady supply of timber over time (Figure 2). Assuming that
the silvicultural rotation is set at 100 years, all stands
in this age class would be harvested. In actual fact, the
silvicultural rotation rarely exceeds 100 years in the boreal
forest. Hence, forests older than this that originated from
a natural disturbance cycle and that have known benefits for
maintaining biodiversity cannot exist in a context of managed
forests. It would therefore be wise to modify the prevailing
management concepts so as to promote the conservation of old-growth
forests and their characteristics.
Figure 2: Class age
distribution for stands. |
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| NATURAL
SUCCESSION AFTER DISTURBANCES |
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The distribution of age classes and stand types that exists
across the landscape reflects the disturbance regime particular
to a given region. Thus, in the mixed boreal forest, shortly
after the passage of fire, young deciduous forests dominate
the landscape. They are replaced by deciduous-dominated mixed
forest as the coniferous regeneration becomes established,
and then later by conifer-dominated mixed forest until about
200 years post-fire, when coniferous stands occupy the entire
area. The natural dynamics of the mixed boreal forest is therefore
characterized by a successional sequence that goes from deciduous
stands to coniferous stands, as long as the time period between
fires is long enough. By seeking to maintain variety in the
age classes and composition of stands, forest managers can
emulate natural processes. This should be a forest management
objective.
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| EMULATING
NATURE |
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Fires in the boreal forest may encompass small surface areas
or thousands and even hundreds of thousands of hectares. Their
size and intensity are highly variable. Although large fires
are considered a fairly rare phenomenon, they have a profound
impact on the structure of the forest landscape. Within the
fire zone, islands of vegetation of varying size are left
intact throughout the region; these islands play a very useful
role as a seed source for regenerating the forest and as shelter
for wildlife.
The spatial pattern of stands in fire-origin mosaics differs
greatly from that created by current forestry practices. Researchers
feel that innovative forestry practices should be applied
in an effort to mimic certain key characteristics of landscapes
originating from disturbances such as fires, if we want to
respect natural ecosystem dynamics. These characteristics
include the age class distribution, diversity of surface areas,
the spatial arrangement of stands and their species composition.
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| INNOVATIVE
FORESTRY PRACTICES |
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The application of these new management practices should
permit the attainment of several objectives: conservation
of stands older than the silvicultural rotation, maintenance
of the structure and composition of old-growth forests within
a portion of managed forests and emulation of the spatial
pattern of stands that exists in mosaics originating from
natural disturbances. All of this can be achieved without
compromising the sustained production of fibre essential for
the economy.
The real challenge that forest managers and researchers face
is developing practices that will respect the key characteristics
of natural mosaics while minimizing the effects on the rotation
for a given region. Practices of this type are being tested
in Quebec in the mixed boreal forest, and CFS researchers
are among those involved in this undertaking.
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