In selective cutting, each tree must be individually assessed
to determine whether it will be cut, left, measured, counted, or marked. The
single most important factor used to determine what trees get harvested is
economics. Other factors closely scrutinized include rate of growth, the
potential for future growth, health and quality of a tree, spacing, and species
type.
Trees selected for harvesting are then cut at specific intervals. This process
is referred to as a cutting cycle, meaning the trees cut are those one third or
less than the maximum age of the oldest age class of tree within a stand. The
trees harvested can either be individual trees scattered throughout the stand or
small pockets of trees grouped together. Trees are spaced, thinned, or weeded in
such a way that enough sunlight can reach ground level and allow for the natural
regeneration of desired tree species to take place. Managing an uneven forest
canopy as well as three distinct age classes of tree species within a stand is
common of selective cutting.
Some
of the advantages of selective cutting are:
It supports more varieties of wildlife than clearcutting
It is more resistant to disease and insect manifestations than clearcutting
It leaves a lighter ecological footprint
It creates a more natural-looking forest stand after harvesting
At higher elevations and in northern forests, it encourages growth of desirable
shade tolerant tree species
Clearcutting
Clearcutting is a harvest system that removes all the trees in a stand at the
same time. The size of the stand may vary greatly. A few clearcuts are as little
five acres. Large clearcuts of 40 to 200 acres are called patchcuts. In order to
make sure that the area continues to produce desirable trees, foresters usually
re-plant or reseed soon after cutting.
People disagree over the use of clearcutting in some forest areas, especially
where a large acreage is involved. Clearcutting allows higher wood production of
intolerant species. It also a I lows those trees that need much sunlight (such
as the Douglas fir) to grow more quickly without competition from other tree
species. These kinds of trees are important to some forms of wildlife. But large
patch cuts without proper care bring increased danger of soil erosion.
The great change in tree species during harvest and
re-planting can greatly change the habitat for various forms of wildlife. The
ecosystem is much simpler, and the forest is more likely to be harmed by disease
or insects.
Selective Cutting
In this type of harvesting, individual trees or groups of trees are
harvested from time to time on a regular basis over a longer period of
time. Timber harvesters make a number of light cuttings as the trees mature. In
selective cutting the forest keeps trees of different ages. This is cal led an
all-aged forest. An all-aged forest supports more varieties of wildlife and can
better resist natural attacks of disease and insects.
Most softwood varieties of trees, such as pine, fir and
redwood, do not regenerate as well under this system. They are naturally
replaced by climax species that are more tolerant to shade. Another problem is
that wind and ice storms can damage the open stands that are left behind after
cutting. In general, timber production is less under this system than under
clearcutting.
Both clearcutting and selective cutting are good forms of harvesting in certain
areas. The forest manager must decide when to use which system of harvesting.
