5/12/2019----Competitive Exams: Forestry: Selection Cutting- Translation in Hindi, Kannada, Malayalam, Marathi, Punjabi, Sindhi, Sindhi, Tamil, Telgu -
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Competitive Exams: Forestry: Selection Cutting
Selection cutting is the silvicultural practice of harvesting a proportion of the trees in a stand.
Selection cutting is the practice of removing mature timber or thinning to improve the timber
stand. This system may be used to manage even or uneven-aged stands. Management objectives
can include the protection of forest soils, maintenance or improvement of wildlife habitat, the
increase of individual stem productivity, encouragement of regeneration/species diversity or the
improvement of the visual amenity of plantations. Selection cutting may include opening up
areas to allow tree species that require greater light intensity to grow but that are not large
enough to meet the legal definition of a clearcut.
Selection cutting it is not recognized as a valid silvilcultural term since it does not define the
objectives of cutting, such as, to improve the quality of trees in the residual stand (also known as
an “intermediate treatment” ), or for the purposes of regenerating the stand (also known as a
“regeneration treatment ‘). The term,” selection--or selective--cutting “means nothing more or
less than the fact that someone has designated trees for harvest. Often the term is used to’
selL'the concept of harvesting to reluctant owners who usually then discover--after the fact--that
only the best trees were ‘selected'leaving a largely defective stand in its wake. Used correctly, the
term’ selection silviculture ‘implies the use of an uneven-aged method--either’ single tree or
group selection'--to begin regenerating, or reproducing, a stand usually to more late-
successional, or ‘climax’ species. Anyone who uses the term” selection cutting “or” selective
harvesting" should be challenged to define his or her terms and, moreover, to identify the
overall silvicultural purpose of harvesting trees.
Single-Tree Selection
The most common type of selection system is Single Tree Selection, in which scattered
individual trees are marked and harvested. Typically, in north America, trees are selected for
harvest using the Arbogast Method (after the method's creator). This is also known as the DBq
method. Under this method, a harvest is specified by defining a maximum diameter (D), a
residual basal area (B), and a q-ratio (q). The q-ratio is the ratio of the number of trees in a
diameter class to the number of trees in the next larger class. Typically diameter classes are
either 4 centimeters or 2 inches.
Given the required DBq, a residual curve is computed. This tells the forester how many trees in
each size-class should remain in the stand. An inventory of the stand is conducted, and excess
trees are marked for harvest. The goal here is to regulate the diameter distribution into a form
that is known to be sustainable. A distribution is sustainable if enough trees remain post-
harvest that they can grow back all that was harvested before the next harvest. Sustainable
distributions can provide a steady even-flow of timber over an infinitely long time-horizon.
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5/12/2019----Competitive Exams: Forestry: Selection Cutting- Translation in Hindi, Kannada, Malayalam, Marathi, Punjabi, Sindhi, Sindhi, Tamil, Telgu -
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Conducting a full stand inventory is rarely practical, and tracking the number of trees in small
size-classes is tedious in the field. A typical single-tree selection harvest will involve an
inventory from a number of sample plots, which is used to estimate which size-classes contain
excess trees. Based on this estimate, and the smooth residual curve, a marking-guide is
constructed based on larger, more tractable size-classes.
On the ground, the forester will use the techniques of Bitterlich Sampling to determine the basal
area around a fixed point. If it is higher than the desired residual, trees are marked to bring it
down. Whenever possible, they are marked from the surplus classes indicated on the marking
guide. The result matches very closely the one given by a full inventory, but is much faster and
more practical.
If production of high-quality sawlogs is a management goal, then crop tree management may be
an appropriate technique. Under this method the highest grade trees are selected and then
“released” by removing lower grade trees which would otherwise compete with the selected tree
for sunlight and water. The selected tree is frequently pruned to grow logs with maximum value.
A similar approach, known as the ‘Frame Tree’ system, is employed in Western Europe. A
number of high quality stems are identified at an early stage of the stand development and
successive thinning interventions are aimed at releasing the growth potential of these trees.
Commonly the final crop trees are harvested when they reach a specified size in order to
maximize the financial return to the grower. Throughout the process natural regeneration is
encouraged to infill the ground that has been opened up. This “continuous cover” approach can
be seen as an alternative to clearfelling.
Another common but sometimes controversial method of selection is diameter limit, the
removal of all trees above a certain diameter. Poorly planned diameter limit cutting is
considered high-grading by some.
Group Selection
A popular variation of Single-Tree selection is Group Selection. Under this system, a number of
‘group openings’ are created in addition to the harvest of scattered individual trees. If the
groups created are large enough, and if seed-bed conditions are favorable, this can allow species
which are intolerant of shade to regenerate. Under typical single-tree selection, it is rare for
shade-intolerant species to do well.
Sometimes these group openings can be quite large, prompting critics to say that group
selection is tantamount clearcut.
Overstory Removal
Overstory removal or shelterwood cutting is a variation of selection cutting. In this method all
the large trees are taken and the understory of saplings and smaller trees are left for
regeneration. Overstory removal requires care be used to avoid residual stand damage.
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At least in the midwest region of the US, it is typical for shelterwood cuts to be a two-step
process. The first step is a thinning down to ~75% crown cover. This provides growing space for
new and vigorous regeneration, without removing the benefits of a forest-floor micro-climate
and abundant seed source. After the new regeneration layer is well established (25 − 30 years),
the residual overstory from the first step is removed. Once this new tree layer reaches maturity,
the process is repeated.
The retained trees can be damaged by and otherwise impede the logging operation,
necessitating a higher density of logging roads and skid trails. Depending on the regional
topography, it is sometimes economical to use cable logging or helicopter logging as an
alternative to skidding logs.
High-Grading
The practice of high-grading, which targets only the highest-quality trees, is commonly confused
with Selection System Silviculture. This gives higher income at first but lowers the quality of the
remaining forest by leaving undesirable tree species standing, as well as poorly formed trees
from desirable species. This can create conditions where no substantial quality timber will
naturally grow for many decades.
High-grading most often occurs when foresters employed by the logging company mark the
stand or in cases where no forester is employed. The logging company gets more profit from a
higher-volume harvest, so it is in their economic best interest to take as much as they can. A
small minority of logging companies operate this way; it is by no means the norm. However, the
effects of this mistreatment are long-lasting, so only a few ‘rogue’ companies can do quite a bit
of damage to the landscape.
One way to avoid high-grading is to contract with an independent forester to mark the stand.
Typically marking contracts pay the forester a flat-fee for any marking job. This removes the
economic incentive to over-harvest a stand. More than that, there's an economic incentive to
practice responsible management so that the forester might receive another contract the next
time a particular stand is harvested.
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