silviculture kenneth williams fisheries extension specialist langston university aquaculture...

SilvicultureSilviculture

Kenneth WilliamsFisheries Extension Specialist Langston University Aquaculture Extension Program

Elements of Forestry


- “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.


Silviculture practices may be designed to mimic natural processes in forest development but often in ways that speed natural development.

Even-aged stand developmentEven-aged stand development

Begins with sudden removal of the tree canopy by logging or by natural means such as fire or wind storms.


Seedlings quickly establish themselves on the open, sun lit ground.


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.


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.


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.

Classification of even-aged Classification of even-aged stands by sizestands 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.

SeedlingSeedling

SaplingSapling

PolePole

MatureMature

Even-aged standsEven-aged stands

Rotation age – The age of the stand at the time of a planned harvest.

Competition in even-aged standsCompetition 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.

Crown classesCrown classes

Dominant – Trees that project somewhat above the general level of the canopy. They receive direct sunlight from above and some from the side.


Codominant – Canopy trees of average size that receive direct sunlight from above but little light from the sides.


Intermediate – Trees with crowns extending into the canopy layer but crowded on all sides. Only the top of the crown receives direct sunlight.


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.


Dominant Codominant Intermediate Suppressed

Even-aged stand maturationEven-aged stand maturationSuppressed 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.

Even-aged stand maturationEven-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.

Uneven-aged standsUneven-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.

Even-aged stand maturationEven-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.

Pure versus mixed standsPure 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.

Easier to manage pure stands.

Lower costs of cultural treatments and harvest methods.

Economic value often greater than a mixed stand.

Pros of pure standsPros of pure stands

Pros of mixed standsPros of mixed standsMore

aesthetically pleasing.

Greater carrying capacity for wildlife.

More insect and disease resistant, but not always.

Treatments to improve existing Treatments to improve existing standsstands

Spacing and stand density adjustment.

Removal of poorly formed or diseased trees.

PruningSalvaging dead or dying

treesFertilization

Treatments to improve species Treatments to improve species compositioncomposition

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.


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.


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.

Treatments to increase growth Treatments to increase growth ratesrates

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.

Tree thinning methodsTree 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.

Low thinningLow thinning

Before

After

Tree thinning methodsTree 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.

High thinningHigh thinning

Before

After

Mechanical thinningMechanical thinningTrees 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.

ThinningThinning

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.

ThinningThinning

Light thinning speeds development of a forest of large stately trees.

FertilizationFertilizationFertilization 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.

Forest stand regenerationForest 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.

High gradingHigh 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.

Natural regenerationNatural 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.

Advanced regenerationAdvanced regeneration

Natural regeneration not always Natural regeneration not always successfulsuccessful

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.


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.


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.

Artificial regenerationArtificial regeneration

Artificial regeneration is accomplished either by directly planting seeds or seedlings on a harvested site.

Artificial regenerationArtificial regenerationArtificial regeneration is used in intensively

managed forests that are harvested at short intervals.

Advantages of artificial Advantages of artificial regenerationregeneration

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.

Direct seedingDirect 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.

PlantingPlantingHigh 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.

Seedling lossesSeedling losses

Mice, other rodents and deer.Competition from shrubs and sprouting

stumps.

PlantingPlanting

Planting is a large portion of total cash investment in a forest stand.

Planting is only done when the increased cost can be justified.

Silvaculture systemsSilvaculture systems

Silviculture systems are classified by method of harvest and regeneration and generally grouped under even-aged and uneven-aged methods.

Even-aged methodsEven-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.

Even-aged methods-problems Even-aged methods-problems with natural regenerationwith 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.

Clearcutting methodClearcutting methodArtificial

regeneration preferred.

No biological restriction on cutting width.

Seed tree methodSeed 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.

Seed tree methodSeed tree method

Shelterwood methodShelterwood 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.

ShelterwoodShelterwood

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.

ShelterwoodShelterwood

Forest cut About 40% of

mature trees left After a new stand

is established the rest of mature trees are cut

Coppice methodCoppice 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.

Provision for sustained yieldProvision 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.

Uneven-aged methodsUneven-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.

Uneven-aged methodsUneven-aged methodsDisadvantages – Generally only shade

tolerant species work well.Most appropriate for tolerant speciesEx. 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.

Choice of management methodsChoice of management methods

Depends on goals and constraintsUneven-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.

Soil erosionSoil erosionLeaf litter and ground

vegetation usually prevent erosion on most sites except for steep slopes and unstable soils.

Road construction and skidding operations cause erosion.

Nutrient lossNutrient 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.

Chemical UseChemical Use

FertilizerHerbicideLittle use of either in most situations.

Natural precedent for harvest Natural precedent for harvest methodsmethods

Uneven-aged systems - natural death of mature trees.

Even-aged management – Fire, wind storm or insect damage.

Timber stand improvementTimber stand improvement

Removing inferior trees, diseased, poorly formed, rotted, weed species, dead trees.

Improvement cuts made every 5-7 years.Avoid high grading

Thinning a young standThinning a young stand

Remove low value treesRemove crooked treesRemove forked treesRemove poorly spaced trees

Growing treeGrowing tree

Full crown with a peak

Mature treeMature tree

Crown well rounded or flat on top, indicates growth has slowed.

time to harvest this tree

Signs of a sick treeSigns of a sick tree

Deep fire scarsGalls and conksBroken limbs or topsMetal items embedded in trees

FirewoodFirewood

Eastern OK , 6 cords hardwood per acre can be cleaned out of a stand to bring it under proper management

3.5 cords per yr used by avg wood burning home owner.

Need 10.5 acres to sustain annual home use of firewood.

Crop tree selection methodCrop tree selection method

Select trees that will not be cut.

Valuable crop treesValuable crop trees

Red oak, walnut, pine, hickory, gums, pecans, ashes and hard maples.

Low saw timber value trees to be Low saw timber value trees to be cut for firewoodcut for firewood

Black jack, post oak, cottonwood, willow, elms, hackberries, sycamore and locusts.

Stand densityStand density

Pole sized stands should contain 100-125 crop trees per acre.

Mature stands ready for harvest should contain 50-75 trees per acre.

Allow 3-4 ft. between the crowns of crop trees.

Eventually crop trees should be spaced about 25 ft apart.

Initial thinningInitial thinning

Concentrate on removing poorly formed, diseased, damaged and undesirable species.

Technical advice: contact Ok Dept Ag. Forestry Division.

HarvestingHarvesting

Avoid damaging adjacent trees.Most valuable part of tree is in the first 12

ft.

Black locust for firewood Black locust for firewood plantationsplantations

Can produce firewood in 6-7 yrs. Max. production not reached until 10-12 yrs.

Advantages: sprouts from stump after harvest, fixes soil nitrogen, reduces erosion, durable fence posts.

Other firewood speciesOther firewood species

Osage orange, catalpa, thornless honeylocust, cottonwood and green ash.

Species depends on site and soil conditions.

THE ENDTHE END

silviculture kenneth williams fisheries extension specialist langston university aquaculture...

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