Title: Silviculture
1Silviculture
Elements of Forestry
- Kenneth Williams
- Fisheries Extension Specialist
- Langston University Aquaculture Extension Program
2Silviculture
- - Growing trees. The biological aspect of
forest management subject to economic and
environmental constraints. - Purpose to enhance timber production, wildlife
habitat, stream flow and the aesthetic qualities
of the forest. - The manipulation of forest stands to accomplish
set objectives.
3Silviculture
- Much effort has been devoted to increasing growth
rates of forest stands. - Silviculture practices can be used to benefit non
timber values. Ex. Prescribed burning to improve
wildlife habitat.
4Silviculture
- Silviculture practices may be designed to mimic
natural processes in forest development but often
in ways that speed natural development.
5Even-aged stand development
- Begins with sudden removal of the tree canopy by
logging or by natural means such as fire or wind
storms.
6Even-aged stand development
- Seedlings quickly establish themselves on the
open, sun lit ground.
7Even-aged stand development
- In 10-20 years the seedlings have grown enough to
form a new closed canopy of trees all about the
same age. This is a young forest and is called an
even-aged stand.
8Even-aged stand development
- Existence of an even-aged stand indicates that
that the previous stand was removed over a short
period of time. Whatever the cause. - Seedling establishment can take over 10 years, so
even-aged stand trees can be 20-30 years old in a
young stand.
9Even-aged stand development
- Trees are all about the same size in a young
stand but as the stand matures, tree size varies
due to species and individual tree genetics.
10Classification of even-aged stands by size
- Seedlings less than 1 meter tall (3.3 ft.)
- Saplings taller than 1 m. up to 4 inches in
diameter. - Poles trees 4-10 inches in diameter.
- Mature 10-24 inches in diameter.
- Overmature A large number of the trees becoming
senescent.
11Seedling
12Sapling
13Pole
14Mature
15Even-aged stands
- Rotation age The age of the stand at the time
of a planned harvest.
16Competition in even-aged stands
- Competition for light and other resources is
severe in young stands. - The canopy of slower growing trees may be covered
by other trees and not receive adequate light. - Trees are often categorized by their position in
the canopy.
17Crown classes
- Dominant Trees that project somewhat above the
general level of the canopy. They receive direct
sunlight from above and some from the side.
18Crown classes
- Codominant Canopy trees of average size that
receive direct sunlight from above but little
light from the sides.
19Crown classes
- Intermediate Trees with crowns extending into
the canopy layer but crowded on all sides. Only
the top of the crown receives direct sunlight.
20Crown classes
- Suppressed Trees with crowns completely
overtopped by surrounding trees. They receive no
direct sunlight except for where small gaps in
the canopy exist. - Once a tree has become suppressed it has little
chance of regaining a dominant position in the
canopy.
21Crown classes
- Dominant Codominant Intermediate Suppressed
22Even-aged stand maturation
- Suppressed trees have a high mortality rate.
- Tree numbers in even-aged stands are reduced by
50-60 by competition in about 40 years. This is
a self-thinning process.
23Even-aged stand maturation
- Small trees growing beneath the canopy may not be
younger than much larger trees. - In fast growing stands, intermediate trees may
become suppressed in the near future.
24Uneven-aged stands
- Even-aged stands gradually become uneven-aged
stands in which 3 or more age classes are
intermixed. - By the time the stand reaches the pole stage an
understory of shrubs and seedlings has developed. - When mature canopy trees begin to die at
different ages, gaps in the canopy are filled
with understory trees.
25Even-aged stand maturation
- In uneven-aged stands, suppressed trees are often
younger than overstory trees. - Uneven-aged stands are characteristic of the
later successional stages. - Because replacement trees often grow in the shade
and in small gaps in the canopy, these stands are
often dominated by shade tolerant species.
26Pure versus mixed stands
- Under natural conditions trees may occur in
nearly pure stands of a single species or in
mixtures. - Pure stands are often even-aged and result from
some catastrophe. - When pure stands are established artificially
they are called monocultures.
27Pros of pure stands
- Easier to manage pure stands.
- Lower costs of cultural treatments and harvest
methods. - Economic value often greater than a mixed stand.
28Pros of mixed stands
- More aesthetically pleasing.
- Greater carrying capacity for wildlife.
- More insect and disease resistant, but not
always.
29Treatments to improve existing stands
- Spacing and stand density adjustment.
- Removal of poorly formed or diseased trees.
- Pruning
- Salvaging dead or dying trees
- Fertilization
30Treatments to improve species composition
- Sometimes difficult some species may be very
well adapted to the site and difficult to
suppress. - Best done when favored trees are very young and
still capable of responding to release from
competition.
31Treatments to improve species composition
- Release cuttings are performed to free desirable
seedlings and saplings from trees of competing
species that have already or probably will soon
suppress crop trees. - Release cuttings are often required in young
conifer stands if intermixed with aggressive
hardwoods.
32Treatments to improve species composition
- Improvement cuts in pole and mature stands
remove diseased or poorly formed trees and trees
of undesirable species. - Economics dictate removal only of undesirable
trees that clearly interfere with a promising
crop tree. - If crop tree already dominant, further tree
removal would have no effect on growth.
33Treatments to increase growth rates
- Stand density and tree growth are regulated
primarily by thinning. - Thinning does not effect total wood production
per acre, however, remaining trees become larger
and more valuable. - Thinning results in a more open stand of larger
trees and accelerates the natural outcome of
competition.
34Tree thinning methods
- Low thinning a light, low thinning would only
remove suppressed and intermediate trees. - A heavy, low thinning also removes some
codominant trees. This releases dominant tree
growth and is a preferred method.
35Low thinning
36Tree thinning methods
- High thinning the objective is to create
sufficient numbers of small gaps in the canopy to
stimulate growth of better crop trees. - Removal of intermediate and codominant trees of
smaller size or poor quality. - Suppressed trees usually not removed.
37High thinning
38Mechanical thinning
- Trees removed in strips regardless of crown
class. - Quick and inexpensive.
- Trees next to cut areas benefit.
- Works well in plantations. Where every 3rd row of
trees are cut.
39Thinning
- Intensively managed stands are thinned about
every 10 years. - Thinning is sometimes delayed until thinned trees
can be used as pulpwood or firewood. - Young, even-aged stands are thinned to improve
wildlife habitat and recreation.
40Thinning
- Light thinning speeds development of a forest of
large stately trees.
41Fertilization
- Fertilization is only used in areas where known
deficiencies exist. Here they can increase growth
20-100. - Fertilization is expensive and can cause
pollution problems. - Some forest types show no response to
fertilization.
42Forest stand regeneration
- In any partial timber harvest it is important to
remove some low-quality trees along with good
trees. This combines a harvest cut with an
improvement cut. - It is very important to leave a few very good
trees.
43High grading
- High grading- The removal of all good trees from
a stand. This results in lowering the genetic
quality of the stand over time, resulting in long
term damage to stand quality and economic value. - High grading degrades forests.
44Natural regeneration
- Seedlings and saplings already present under the
forest stand to be cut. Also called advanced
regeneration. - Many hardwoods sprout from cut stumps. This is an
important form of regeneration in hardwood
forests. - Natural regeneration is more successful in humid
areas than in semiarid climates.
45Advanced regeneration
46Natural regeneration not always successful
- Adequate seed production in some species may
occur almost every year but in others only at
long intervals. - Ex. Red pine seed crops every 7 years.
47Natural regeneration not always successful
- Seedling germination and survival in some species
is greatly influenced by weather. - The microclimate of the stand must be favorable
for regeneration. - Ground surface or seedbed must be in good
condition. Scarification or burning may be
necessary to remove duff.
48Natural regeneration not always successful
- Dense advance generation and shrub and sprout
layers may prevent establishment of desirable
species. - Seed and seedling predators are sometimes
responsible for regeneration failures. - Ex. Insects, mice and deer.
49Artificial regeneration
- Artificial regeneration is accomplished either by
directly planting seeds or seedlings on a
harvested site.
50Artificial regeneration
- Artificial regeneration is used in intensively
managed forests that are harvested at short
intervals.
51Advantages of artificial regeneration
- Stand establishment more reliable.
- Increases chances of prompt reforestation.
- Timing can coincide with favorable weather
conditions. - Greater control over species composition.
- Greater control over tree spacing and subsequent
growth. - Seeds and seedlings can be derived from
genetically superior stock.
52Direct seeding
- Can be done from the ground by hand or machine or
from the air. - Cheaper than planting.
- Less control over spacing.
- Lower success rate.
- Very useful for covering extensive areas by air
after a major fire or on steep or irregular
terrain.
53Planting
- High success rate with seedlings.
- Containerized better than bare root but more
costly. - Site preparation important. Mechanized equipment
usually used for this, however, steep slopes and
environmentally sensitive sites may be burned.
54Seedling losses
- Mice, other rodents and deer.
- Competition from shrubs and sprouting stumps.
55Planting
- Planting is a large portion of total cash
investment in a forest stand. - Planting is only done when the increased cost can
be justified.
56Silvaculture systems
- Silviculture systems are classified by method of
harvest and regeneration and generally grouped
under even-aged and uneven-aged methods.
57Even-aged methods
- Clearcutting regeneration by natural seeding,
direct seeding or planting. - With natural seeding, effective dispersal
distance of seeds may limit the width of the
clearcut.
58Even-aged methods-problems with natural
regeneration
- Clearcutting a shade intolerant forest that has a
dense understory of more shade tolerant species
will change forest composition. - Ex/ Southern pines with a hardwood understory.
59Clearcutting method
- Artificial regeneration preferred.
- No biological restriction on cutting width.
60Seed tree method
- Scattered mature trees are left on the site to
serve as a seed source and to provide uniform
seed dispersal. - Works best with intensive site preparation and
deeply rooted trees. - This method does not always produce enough
seedlings.
61Seed tree method
62Shelterwood method
- Seed trees left in sufficient numbers to provide
shade and shelter to seedlings. - 30-80 of crown story removed.
- After several years, the rest of the crown story
is harvested. - This method is used for species that do not
germinate well under open conditions.
63Shelterwood
- This method produces the least erosion and looks
the best of even-aged methods. - Trees retained are among the larger and better
quality trees In the stand so they will be a good
seed source.
64Shelterwood
- Forest cut
- About 40 of mature trees left
- After a new stand is established the rest of
mature trees are cut
65Coppice method
- Depends on regeneration by stump sprouts.
- Restricted to species that sprout vigorously and
sprouts can obtain a commercial size. - Ex. Aspen and oak.
- Usually managed on short rotations for pulp and
firewood.
66Provision for sustained yield
- In all forms of even aged management, yield is
sustained by cutting parts of the total property
at regular intervals so that when the cutting
cycle is complete, trees from the 1st tract will
be ready to cut again.
67Uneven-aged methods
- Advantages No need for site preparation.
natural regeneration is reliable and the only
method where sustained yield can be obtained from
a single stand of trees. - Forest canopy stays largely intact.
- Fire hazard is minimal because no piles of
logging debris. - Used by small land owners and managers of
multiple-use recreation areas.
68Uneven-aged methods
- Disadvantages Generally only shade tolerant
species work well. - Most appropriate for tolerant species
- Ex. Maple, hemlock, cedar, spruce and fir.
- Unfavorable to some wildlife species. Group
selection helps. - Difficult to prevent injury to nearby trees.
- Can resemble high grading if only best trees cut.
69Choice of management methods
- Depends on goals and constraints
- Uneven-aged methods best for sites where tolerant
species are valuable and in demand. - Does not work well for many commercially valuable
shade intolerant species. - Costs of each method must be evaluated.
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71Soil erosion
- Leaf litter and ground vegetation usually prevent
erosion on most sites except for steep slopes and
unstable soils. - Road construction and skidding operations cause
erosion.
72Nutrient loss
- Natural replenishment of nutrients work well on
long rotation cuttings. - Short rotations 40 years or less, increase
nutrient loss. - Whole tree harvesting increases nutrient loss.
Most nutrients in branches and leaves not trunk.
73Chemical Use
- Fertilizer
- Herbicide
- Little use of either in most situations.
74Natural precedent for harvest methods
- Uneven-aged systems - natural death of mature
trees. - Even-aged management Fire, wind storm or insect
damage.
75THE END