Fire and Disturbance Ecology
© Parks Canada |
Why is fire important?
Fire is a natural disturbance agent that has helped create the landscapes
we see in the Mountain National Parks today. Some areas of the park, like the
montane grasslands, have been subject to frequent fires over many centuries
and are considered fire-dependant. These ecosystems require fire in
order to restore and maintain ecological integrity.
Fire is such a powerful and pervasive ecological force that areas
within the Mountain National Parks that experience fire only once every few
centuries have plant communities that reflect their fire history. Some
of these places are high elevation alpine meadows and subalpine forests.
What is the role of fire in an ecosystem?
Fire plays many important ecological roles in ecosystems that cannot
be duplicated by any other natural process. Fire affects the processes
that occur in an ecosystem (=function), what species live in the ecosystem
(=composition) and how those species, particularly plants, are arranged
(=structure).
© Parks Canada
Creates mosaic |
Fire produces a mosaic of plant communities of different
ages and species composition on the landscape. Typically, fires
burn with variable intensities across the landscape due to changes
in terrain, wind and other factors. Areas where the forest is completely
consumed by fire are interspersed by patches of unburned and lightly
burned forest. In this way fire increases the structural diversity
and species diversity of ecosystems over time. |
| |
© Parks Canada
Reduces Fuels |
Periodic fire reduces the amount of accumulated fuel on the forest
floor (woody debris, dead trees, forest floor litter). This reduces
the potential for extremely large, hot fires, which can damage soil
and result in increased erosion, and loss of soil fertility. |
© Parks Canada
Stabilizes insect and disease populations |
Fire has variable effects on insects and disease
that infect trees and other vegetation. Some insect populations
are directly destroyed in a forest fire, while other populations
are reduced following fire due to changes in vegetation and soil.
Wood-boring insects may increase due to increased availability of
food in the standing dead trees. Pathogenic fungi and parasitic
plants (e.g. dwarf mistletoe) may be at least temporarily removed
from an area following a forest fire.The potential for large outbreaks
of disease and insects (e.g. mountain pine beetle) is generally
reduced in ecosystems with intermittent fire because the resulting
vegetation mosaic breaks up contiguous patches of suitable host
trees. |
© Parks Canada
Recycles nutrients |
Fire releases nutrients bound up in litter and woody debris on
the forest floor. Fire reduces woody fuels to ash and consumes the
organic layer of the soil. Some of the nutrients are lost to the
atmosphere as smoke but fire also releases many nutrients into the
soil. This "flush" of nutrients is then available to plants
that re-establish in burnt areas. This function of fire is particularly
important in the Mountain National Parks where the rates of decomposition
and nutrient cycling are low. |
© Parks Canada |
How do plants survive fire?
It is often thought that fire destroys all plants and leaves nothing
but charred, barren ground in its wake. However, in areas with periodic
wildfire, plants have evolved many adaptations for surviving fire and
some actually need fire to reproduce. Plant adaptations to fire include
increased seed release, increased flowering and fruiting, fire resistant
bark and buds, and vegetative re-sprouting from undisturbed root systems.
© Parks Canada |
In the fire-dependant montane forests of the Mountain National Parks, the
seeds of lodgepole pine (Pinus contorta) are only released
from their serotinous cones following a forest fire and the seedlings
establish quickly on the exposed soil. Trembling aspen in these areas
will regenerate vegetatively by producing abundant sprouts from the
root system following fire. Some of the sprouts will produce new aspen
stems provided that browsing pressure by ungulates is not too high.
© Parks Canada
|
The open grasslands in the low elevation areas of the park were created
and are maintained by the presence of frequent fire. The fire removes
encroaching trees and shrubs and stimulates a flush of new growth in
the grass species following post-fire release of nitrogen and other
nutrients.
© Parks Canada |
How is wildlife affected by fire?
The affect of fire on wildlife varies according to the intensity and
duration of the fire, season of burning and the ecosystem that is burned.
In general fire increases the abundance of shrubs and grasses that herbivores
such as elk and deer feed on. Fire also results in increased availability
of berries that form an important part of the diet of grizzly and black
bears.
© Parks Canada |
Fire affects the quality and quantity of habitat for wildlife. In general
the amount of cover for animals is reduced when the forest is opened
up by fire. However moose, elk, and deer benefit from the increased
amount of "edge" created by the post-fire vegetation mosaic.
This patchiness of vegetation following fire also increases the diversity
of habitat types across the landscape.
The habitat of many small mammals is temporarily destroyed by fire.
Old forest dependant species such as caribou, marten, and fisher are
negatively affected by fire due to loss of cover and food resources.
Other small-scale disturbance agents
Fire is not the only natural disturbance agent that shapes the landscape
of the Mountain National Parks. Other disturbance agents such as insects, disease,
avalanches, wind and flooding work on a local scale to create and maintain
diversity in park ecosystems. These disturbance agents fall into two
main categories: biological (living) and physical (non-living).
Insects and disease: the biological disturbance agents
Forest insects and disease produce patches of dead and dying trees
across the landscape which create gaps in the forest cover. Unlike fire,
these disturbance agents generally work on a smaller scale to create
openings that range from a few trees to several hectares. These disturbance
processes normally play a larger role in structuring ecosystems like
subalpine forests where fire only occurs every few centuries than the
montane areas of the park where fire is the pervasive disturbance agent.
- Gaps colonized by young, fast-growing plants and trees
- Characteristics of vegetation in gaps:
- Increased growth rates
- Increased species diversity due to higher light levels
- Increased structural complexity due to young seedlings
and dead and dying trees
© Parks Canada
Mountain Pine Beetle Galleries |
Common species: Mountain pine beetle
(Dendroctonus ponderosae), spruce beetle (Dendroctonus
rufipennis), northern lodgepole needleminer (Coleotechnites
starki), two-year budworm (Choristoneura biennis)
Effect on park ecosystem: Create patches of
dead and dying trees. Effects on host trees range from minor deformities
to severe stress and death. Fire reduces the risk of severe insect
outbreaks by physically destroying insects and by breaking up contiguous
areas of suitable host trees.
|
© Parks Canada
Dwarf mistletoe on lodgepole pine |
Common species: Aspen cankers (Hypoxylon
mammatum),dwarf mistletoe (Arceuthobium americanum),
Armillaria root rot (Armillaria mellea), false tinder fungus
(Phellinus tremulae)
Effect on park ecosystem:
Create patches of dead and dying trees which eventually form gaps
in the forest canopy. Effects on host trees range from minor deformities
of leaves to root rots that kill the tree. Canopy openings created
by root rot are often regenerated by tree and shrub species that
are resistant to the pathogen that created the gap. This contributes
to the increased species diversity frequently observed in regenerating
disease centres. |
Physical disturbance agents
Physical agents such as windstorms and avalanches also cause disturbance
in forested areas. Windstorms and avalanches are relatively rare events
that can create large openings in the forest in a very short time. This
is in contrast to insects and disease, which are widespread in the forest
and cause sporadic, ongoing disturbance
© Parks Canada
Avalanche path |
Effect on park ecosystem: Create
large, vertically oriented openings on mountain slopes where the
trees are taken down by snow as it comes off the mountain. When
avalanches come down in the same place each year, low-growing shrub
and forb communities are created in these areas. The vegetation
in avalanche paths provides important forage for grizzly bears and
moose in mountainous terrain. |
© Parks Canada
Trees blown over by wind |
Effect on park ecosystem: Creates large openings
or can topple individual trees. Severe windstorms can cause large
areas of 'blowdown' where all trees are blown over by the wind.
Wind also causes small-scale disturbance across the landscape by
breaking tree stems or uprooting trees that have been predisposed
to wind damage by insects and disease. |