Timber management is often the means by which forest stewardship is
implemented. It can be used to improve wildlife habitat, increase
the aesthetic value of a forest, increase biological diversity, and
provide a landowner with additional income. Timber
management is more than just cutting trees. It is the manipulation of forest resources to grow higher quality trees in a shorter period of
time on a continual basis.
The art and science of growing trees is called silviculture.
Silviculture serves to provide optimum growing conditions for desirable
species (intermediate treatments) and to regenerate the forest after
harvesting occurs (reproduction cuttings). Individual tree species
respond differently to various silvicultural treatments, therefore an
understanding of a tree's biological
and environmental limitations (its silvics) is essential to proper
timber management. Let's take a brief look at the various
silvicultural systems and their intended results on a forest.
Intermediate Treatments
Similar to gardening, landowners should conduct intermediate treatments
to provide optimal growing conditions. For a tree to reach its full
potential, it must have access to sunlight, nutrients, and water.
These
limiting factors are what cause tree mortality to occur naturally in a forest. As trees compete for these resources,
their growth is slowed until the competition is removed, either by natural
death or by thinning. Thinning, as depicted below, allows trees to
grow more rapidly than they would among competing trees, and, like
weeding a garden, thinning provides for a better
crop. Thinning, in itself, can provide some income for landowners;
however, oftentimes it is only enough to cover the cost of the actual
thinning. As a result of the cost, thinning should be viewed as a long term
investment. The true monetary benefits of thinning will not be
realized until the final crop tree harvest.
Trees of Equal Age but Different Thinning Occurrences
Reproduction Cuts
There are several methods of regenerating a forest. The approach
a landowner takes depends on their objectives for tree species composition
and the physical structure of the forest. It is important to note
that harvesting a forest is not deforestation, but rather a means by which a
new forest is regenerated. Forests can be regenerated as an even-aged
or an uneven-aged forest. As their names imply, even-aged
reproduction cuts simply mean managing a forest so that only trees of
similar ages exist, while uneven-aged cuts have multiple age classes.
Even-aged Reproduction Cuts
Clear Cut: With the clear cutting silvicultural
system, all trees in a stand are cut at one time. Seeds from surrounding
trees, root sprouts, or artificial seeding or planting are used to
regenerate the stand. This timber management strategy will be
discussed in more detail at station 9.
Seed Tree: The seed tree system removes most trees
from the forest while leaving a few high quality, desirable trees standing
to provide a seed source for the next forest generation. This
technique is often used when little advanced regeneration exists in the
forest. It is the goal of this technique to provide seed to the site
that will produce high quality trees that resemble the seed source
trees. Similar to a clear cut, a seed tree cut favors trees that are
not tolerant of shade. The
seed trees are usually removed after seedlings are well established.
Shelter Wood Cut: The shelter wood system is
similar to the seed tree system in that trees left behind provide the seed
source for the next generation of trees. Unlike the seed tree cut
however, the shelter wood cut favors more shade
tolerant species because there is a greater density of large
trees. The shelter trees provide protection from direct sunlight and
other extreme conditions. After a forest is regenerated, the shelter
providing trees are harvested to complete the system.
Clear Cut
Seed Tree
Shelter Wood
Uneven-aged Reproduction Cuts
Single Tree Selection:
In single tree selection, a forester evaluates every tree in the
stand. Undesirable trees are removed, overly dense areas are
thinned, and mature trees are harvested, leaving a stand with
multiple age classes and much vertical structure. Seedlings of
shade-tolerant trees develop wherever they can find space.
Cuttings are more frequent, providing income on a regular basis but
at a lower return per harvest to the landowner. Damage to the
remaining trees is a consideration.
Group Selection: The group selection system harvests
small groups of trees rather than individual trees. It is similar to
creating small clear cuts across the forest, allowing multiple age groups
to be very close to each other. Using this method a logger is less
likely to damage near-by trees than they are with single tree selection.
WHAT NOT TO DO!
Selective Cutting: Selective cutting, also known as
creaming, culling, or high-grading, is a method used by too many
landowners in the U.S. Selectively cutting a stand removes the best,
most desirable trees from the forest, leaving poor quality trees to serve
as a seed source for the next generation. It has been shown that this
degrades the genetic quality of the forest over time and, as a result, causes much environmental degradation. It is like pulling out all
of the greyhounds from the dog race so that they can be sold and leaving Chihuahuas
to race. You may have made good money from the
greyhounds, but in the long run you won't be making any money off the Chihuahuas because they
are not good for racing.
