Transcript Clear-cutting

How we use and abuse our greatest natural resource
Leading question
What methods do we use to manage our
forests?
Objectives:
To identify and discuss forestry practices
Harvesting Wood
There are essentially two different methods to harvest wood. These are:
Selective cutting and Clear-cutting.
Selective cutting — Forest harvesting in which only certain species or
sizes of trees are removed from an area, often for use as timber or to
make pulp for paper.
Under the heading of selective cutting there are also two sub-categories.
Shelterwood cutting is a method of forest harvesting in which up to
70 percent of trees are cut, leaving small patches of old growth standing
to provide seeds for regeneration.
Strip cutting is when only a long narrow strip of a selected block is
harvested, leaving many older trees to continue to grow and reproduce
on the land.
Harvesting Wood
Clear-cutting — Forest harvesting in which all of
the trees in the area are cut for use as timber or to
make pulp for paper.
This is the most common method of harvesting
wood. Approximately 90% of wood harvesting is
done in this manner. Large scale logging operations
often utilize this method of harvest.
Clear cutting
As mentioned above clear cutting
has been, and continues to be the
number one method of harvesting
wood in Canada, meaning that this
is not an uncommon view at most
large scale harvesting operations
across Canada.
In most cases after a clear cutting
operation occurs the ground is
either left to re-grow on its own, or
it is replanted.
Selective cutting
This is a selective
cut in it’s least
destructive form.
Notice that only a
few mature trees
have been
removed, and
much of the
canopy remains,
providing shade
for much of the
forest floor.
Selective cutting
Notice that not
all the trees
have been
removed from
this cut. Most
of what has
been left is
hardwood, and
these are left in
small clumps.
This is a take on
shelterwood
cutting.
Selective cutting
This is an example
of a strip cut. The
cuts are made in
narrow, long paths.
The areas left fully
treed on either side
of the swath help to
provide partial
shade and new
seeds to the
recently cleared
area.
Regeneration of a forest
Forest Succession: The gradual
supplanting of one community of
plants by another, usually as a
result of differences in shade
tolerance.
Regeneration of a forest
Each tree species has a particular tolerance to the
environment factors around it. For example, some trees do
well in full sun, while others require only indirect light to
grow well. Some trees do well in wet area, some thrive in dry
conditions. Soil composition may even determine which
trees are successful in a particular area.
When trees are removed from the forest, even in relatively
small numbers, the growth of new, smaller trees of different
varieties is greatly affected, and the overall make-up of the
forest and its inhabitants is changed over time.
A look at succession
The following slides help to describe
the process of forest succession in the
average clear cut situation. Try to
think of clear cuts that you have seen
in your own experiences in the woods
of New Brunswick. Do the animations
make sense?
Imagine this as a recently clear cut forest. Pioneer
species are those that begin to grow rapidly following a
clear cut operation occurs.
Pioneer species quickly occupy a site following clearing. They grow rapidly
to compete with grasses and shrubs.
As the crowns of pioneer species close, seedlings from these trees are
unable to survive in the resulting shade.
Different species then begin to grow beneath the pioneers. The
resulting undergrowth, or understory, is often dense.
As the short-lived pioneers near the end of their life spans, understory begin to
take over the site. The result is a major change in plant and animal species.
Softwood begins to take over a hardwood dominated site as the shortlived pioneer crowns thin with aging.
Beneath the second successional stage species, that often form thicker
crowns than pioneers, new species that are even more shade tolerant
become established.
The process of succession continues until the most shade-tolerant species suitable for
the site (climax species) become established.
Seedlings of highly shade tolerant climax species thrive in the shade of their
parents. Because of this, climax species will persist until disturbance sets back
the succession process to the pioneer or some other stage.
Disturbances can include a number of events such as clear
cutting, pest infestation, or forest fires.
The results of a forest fire in a
previously heavily shaded forest.
The results of the Pine Beetle
infestation in British Columbia.
The beetle attacks the pines,
killing them off leaving a dry and
dangerous landscape
The clearcut site looks barren immediately following harvest.
Similar area, two years following harvest, showing that grass has covered
the site. Young pine seedlings are barely visible in the foreground.
At ten years following harvest young pine trees, that have sprouted from
seeds present in the soil and spread by wind and wildlife, are well
established.
In early summer 1988, as today, much of Yellowstone park was
covered by aging stands of lodgepole pine. Many trees had been
killed by frequent outbreaks of the endemic Mountain Pine Beetle.
This condition led to the Great Yellowstone fire, 1988
Vast areas of lodgepole pine and other forest types were killed.
Eleven years later showed a landscape again dominated by lodgepole pine
that had sprouted from seeds present in the soil.
Aspen harvest site one year following clear cut harvest.
A good site several years following harvest. 50,000 to 100,000 stems per
acre from stump sprouting.
Mature aspen
stand. 65-70 years
old. Approximately
200 stems/acre.
When reproduction of species with medium to high shade tolerance is desired
following logging, selective harvest or thinning methods can be used.
Pros and cons of forest management practices
Clear cutting
Pros
Selective Cutting
Pros
– less disruptive to the forest
– less expensive as the entire area is environment than others
– harvesting only mature trees of
cut down all at once
– provide wood at a more competitive desired size/type/quality
– less soil erosion and runoff into local
price
streams
– safer for workers
– company can choose which type of – no disruption of fish spawning areas,
nesting areas and other wildlife habitat
tree to replant
– less surge of nitrates entering the
water, increasing the growth of algae
– no ground exposed to sun,
increasing the warming of the area in
the summer and cooling in the winter
– less water loss from soil
Cons
– all trees are cut regardless of their
age, size or maturity
– damage the entire forest ecosystem,
changing it to farm like conditions
rather than a forest
– greater warming and cooling of the
area because there is no ground cover
changing the microclimate
– soil erosion and runoff of materials
into local streams and lakes
Shelterwood Logging
Pros
– clear cutting only part of an old
growth forest
– small groups of seed-bearing trees
are left standing so that their seeds
will regenerate the logged area
– less disruptive to the natural
environment than clear cutting the
entire area
– protection from soil erosion and
runoff materials
Cons
Cons
– costly because extra care / time
– specific areas of the forest
taken to cut down trees
ecosystem are disturbed
– costly to replace the trees
– microclimates will now vary in the
– prices for the consumer would not be forest changing a variety of animal and
as competitive
plant species habitats
Silviculture – Re-growing the forest
Growing Canada's forests
Companies that harvest Canada's public forests must
also ensure they are properly regenerated.
Silvicultural practices often address ecological issues
as well as timber production. Natural regeneration is
the most common silviculture system in Canada
where most of the forests are even aged. Planting is
also commonly used, but the results are very different
than what one would see in a natural regeneration
site.
Silviculture – Re-growing the forest
The most common trees planted in New Brunswick are: Black
Spruce, White Spruce, Red Spruce, Norway Spruce, Jack Pine,
White Pine, and Red Pine. Virtually no Cedar or Larch are
being grown and planted after harvesting occurs.
Silviculture – Re-growing our forest
When natural regeneration occurs, the results are often
similar to what was demonstrated above in the animation.
That is if the former cut is not managed. If it is managed
actions like thinning, or herbicide spraying may occur to
eliminate certain undesirable species.
When planting occurs the results are often a monoculture,
or an area with only one dominant species present. This is
often the desired outcome from the point of view of pulp and
paper companies, for example.
A clear-cut operation near Doaktown.