Diameter limit cutting is a common
method used to harvest timber on private forestland. In this type of logging operation,
trees over a specific diameter are removed regardless of their species, age, quality, or
vigor. The remaining trees are intended to restock the area with seedlings and be the
future crop trees. This publication should help you understand the serious
impacts of cutting trees using this method.
Diameter Limit Cutting: A
Definition
When proper selective logging
methods are applied, the mature and high risk trees are harvested. The higher quality,
more vigorously growing trees are left on the site, resulting in improved growing
conditions and increased growth potential of the woodland. However, when
timber is harvested using a diameter limit cut, the growth potential of the woodland is
greatly reduced. This happens because the trees with the poorest growth potential are
retained on the site. Thus, when a diameter cut is made, the best trees are taken
at the expense of future timber growth.
Age and Size Relationships
Most of the nonindustrial, private
forests in northern Idaho are composed of trees of similar age but with greatly differing
diameters. The trees have diameter variations because of competition among trees, species
differences, and genetic variations. Small trees are not necessarily young trees! Therefore,
if only the larger trees are harvested, the remaining trees will tend to be the
inferior ones. These inferior trees will not have the ability to fully utilize the site,
resulting in reduced tree growth and long-term economic loss.
Figure 1. Original
timber stand before harvest.
Figure 2. The same stand after a
diameter limit cut.
Figure 3. The same stand after a proper harvest.
|
Advantages
of Diameter Limit Cutting |
Disadvantages
of Diameter Limit Cutting |
This harvest method occasionally has
limited
advantages. Please note that these advantages do not take into consideration the
development and care of the forest. The diameter limit system:
-
Is easy to communicate to logger and
landowner.
-
Is easy to administer.
-
Can convert the stand to maximum dollars
quickly with little sale preparation.
-
Is a relatively inexpensive logging method.
-
Can promote forage and brush development,
which is beneficial to livestock and wildlife.
-
Can be used to describe mature trees to be
removed if the diameter is kept large (18 to 20 inches and larger).
|
The disadvantages
heavily outweigh the advantages. This method:
- Does not consider the quality or vigor of individual trees.
The decision to cut or leave a particular tree is based solely on its diameter.
- Often results in the best-growing trees being
removed, leaving the older, smaller, poorer trees to regenerate the area. These residual
trees are of poor genetic quality, which will result in inferior new seedling trees. This
would be the same as a rancher selling his best breeding livestock and keeping the poorer
quality animals to maintain his herd.
- Disregards the future of the stand, what tree species mix
is best adapted for the site or how much timber should be left on the site for continued
high production. Future economic losses would be likely.
- Will promote leaving diseased or insect-infested trees.
These defective trees will most likely be a threat to the stand by infecting the other
trees and seedlings.
- Will lower the economic value of the land because of an
abundance of poor quality, low value trees.
- Often leaves a stand understocked. Tree planting and brush
control are often necessary.
|
Harvesting Goals.
The decision to harvest your timber will
affect both your future as well as that of the coming generations. Therefore, the decision
to harvest and the harvesting method should be carefully considered.
The timber should not be harvested
without a specific goal in mind. Consider these questions:
Is the purpose of the harvest to increase
the livestock and wildlife forage potential of the woodland?
Is the harvest designed to change the
species makeup of the stand?
Is the harvest meant primarily to thin
trees to improve their growth?
After you have determined the harvest's goal,
you can decide on a logging method. Some factors to consider are the condition of the
forest, the needs of the tree species involved, and the topography. You can make a
management plan that will both achieve your immediate purpose and be beneficial to the
remaining stand.
Because of all of the factors involved in
this process, the assistance of a professional forester is recommended in planning the
harvest. Many sources of forestry assistance are available. Your state Woodland Forester
or Extension Forester can direct you to the best source.
College of Agricultural and
Life Sciences / College of Natural Resources,
University of Idaho, U.S. Dept. of Agriculture, and Idaho counties cooperating.
To enrich education
through diversity, the University of Idaho is an equal opportunity/affirmative action
employer and educational institution.
