Intermediate Silvicultural Treatments

Summary of Intermediate Stand Treatments

• Thinning

• Release

• Improvement cutting (TSI)

• Sanitation and Salvage

• Fertilization

• Pruning

• Prescribed Fire

How intermediate treatments fit into a silvicultural system

Components of even-aged

silvicultural systems

Stand Initiation

How intermediate treatments fit into a silvicultural system

Textbook Chapters by Topic

• Thinning: Ch 17, 18, 19

• Release Treatments: Ch 16

• Improvement, Sanitation and Salvage: Ch 22

• Pruning: Ch 20

Thinning

What is Thinning?

• Defined by Nyland as:

“A treatment to increase the diameter increment of residual trees, improve stand quality and health, and increase stand level production by cutting excess and potential mortality trees without permanently breaking the crown canopy”

When we thin a stand…

• We are reallocating growing space to the residual trees

• Which residual trees you choose depends on your objectives

Why do we thin?

• Residual trees increase DBH faster, maintain larger crowns and higher vigor

• Reduces rotation length (age) required to produce trees of a given diameter• Typically improves average quality of trees (more valuable)• Provide intermediate income• May avoid stagnation in densely crowded stands• Reduce wood losses to mortality • Reduce a stand's susceptibility to insect infestation• Increase potential seed production• Improve wildlife food production and availability• Improve aesthetics, by creating a more open, park-like appearance

Effects of Thinning on Individual Growth

• Thinning increases diameter growth

1969 19791959

Effects of Thinning on Individual Growth

Effect of Thinning on Stand Growth

Production function for an even-aged stand thinned three times

Effect of Thinning on Stand Growth

Effects of Thinning

• Four major factors influencing long-term growth following thinning:1. Timing of each thinning

2. Crown condition and position of residual trees

3. Post-thinning spacing and its influence over crown vigor and development

4. Interval between successive thinnings

• Period of post-thinning growth increase vary due to spacing and a tree’s competitive position.

Effects of Thinning

• Some potential negative impacts from thinning– Tends to reduce total biomass production– Damage residual stems and site– May increase insect attack and disease losses– Temporarily increase wildfire hazard due to increased fuel load– Reduce tree quality due to increase limb retention and epicormic

branching– Increased danger of wind and ice damage due to sudden exposure

What is epicormic branching?

Methods of Thinning

• Primary thinning methods

1. Low thinning

2. Crown thinning

3. Selection thinning

4. Geometric thinning

5. Free thinning

Methods of Thinning: Low Thinning

• Low thinning– Trees are removed from the lower crown classes

– Must be very heavy or done early and frequently to appreciably increase growth of upper crown class trees

– Most applicable in stands which nearly all trees are merchantable

Methods of Thinning: Low Thinning

• Low thinning intensities– Grade A (very light): remove overtopped

– Grade B (light): remove overtopped and intermediate

– Grade C (moderate): remove overtopped, intermediate, and some co-dominant

– Grade D (Heavy): remove overtopped, intermediate, and most codominant

• Other names for low thinning:

Methods of Thinning: Crown Thinning

• Crown thinning

– Removes trees from upper crown classes to favor the best trees in those classes

– Unlike low thinning, no matter how lightly applied, principle cutting is made in the upper crown classes

– Can provides greater income than low thinning

– Other names for crown thinning

Methods of Thinning: Selection Thinning

• Selection thinning

– Removes dominant crown class trees in order to favor the growth of trees in lower crown classes

– Most commonly used to remove poorly formed dominant trees

– Applied in some two-layered stands to remove taller layer

– Repeated selection thinning is only appropriate for shade tolerant and negatively geotropic conifers

Methods of Thinning: Geometric Thinning

• Geometric thinning– Trees to be cut are chosen strictly on the basis of spacing or pattern

with no regard to crown class

– This results in removal from all crown classes and retention of trees in all crown classes

– Most appropriate where there is little differentiation in crowns or in tree quality

– Usually applied only as a first thinning in young stands

Methods of Thinning: Geometric Thinning

– Row thinning removes strictly by rows in a plantation

A geometric thin performed by removing every 5th row in a 14-year-old slash pine plantation in Georgia. Photo Credit: David Moorhead, UGA, Bugwood.org

After 5th row thinning with thin from below in leave rows in a 14-year old stand. Initial Basal Area = 140 square feet per acre, Residual Basal Area = 70 square feet per acre.

Methods of Thinning: Geometric Thinning

– Strip thinning (or corridor thinning) cuts trees in a strip of set width

Aspen stand, 15 ft wide machine corridor, first summer post-harvest.

Methods of Thinning: Free Thinning

• Free thinning– Objective is to select the best trees, regardless of canopy position, and

release them

– Differs from crown thinning in that spacing across the site need not be uniform

– Typically, a set number of crop trees are released (e.g. 50 or 100)

Thinning Regimes

• Whether to thin?

• When to thin?

• How much to thin?

• What thinning method do we use?

Often tough questions. Objectives, economics, growth rates, and current stand conditions will drive the decision.

Timing of Thinning - When do we thin?

Merchantability

• To avoid capital investment, a commercial operation is desirable rather than pre-commercial

– Southern pines: Commercial thinning tends to be possible at about age 12 (depending on site index and initial density)

– Upland hardwoods: in general commercial operations come much later than for conifers (slower diameter growth in dense stands and higher minimum size requirements)

• 20-25 years if a pulpwood or fuelwood market is present

• 30-50 years for small sawtimber

Timing of Thinning - When do we thin?

Objectives

• Pulpwood: thin late or preferably not at all

• Sawtimber: concentrate growth on best trees as soon as possible

• Density must be sufficient to encourage self pruning to at least 17 feet

• Wildlife: in general, thin early, frequently, and heavily from below to increase light levels in the understory and increase growth of shrubs, grasses, and forbs.

Timing of Thinning - When do we thin?

Site Quality• May chose to thin only on better sites

Live Crown Ratio• The best simple indicator of tree vigor and ability to respond to release

– Southern pines:

• First thinning, attempt to keep most potential crop trees at least above 35% LCR; 40-45% is better for a high growth rate, but this slows self pruning

• For older stands, seek to keep LCR above 30% (higher for more diameter growth)

How much do we thin?Choosing a Residual Density

Objectives• Pulpwood: maintain high residual density (light or no cut)

• Sawtimber: lower residual density to keep diameter increment higher

• Wildlife or grazing: low density to encourage understory vegetation

How much do we thin?Choosing a Residual Density

Live Crown Ratio• If crowns are small, thin lightly and frequent

Site Quality• More flexibility in residual density is possible on good sites

Stand Density and Stocking

Quantitative tools for determining how much we should thin

• Stand density is an absolute measurement based on basal area or number of trees per acre

• Stocking is a relative term that relates a given stand density to a management objective

– Because size-density relationships influence the amount of available growing space in a stand

Simple Measures of Stand Density

• Trees per acre

• Basal area per acre– Basal area is a combined measure of both, number of trees and their

size

– Widely used because it is:

Stocking

• Stocking Chart for Upland Hardwoods (Gingrich 1967)

– A graphical tool to allocate growing space on a relative basis for upland hardwood stands in the Central Hardwood Forest Region

Properties of the Upland Hardwood Stocking Chart

Average Maximum Density (A-Line) is set at 100% Stocking

Shows the upper limit of a fully stocked stand

Properties of the Upland Hardwood Stocking Chart

Area between the A-Line and B-Line indicates that a stand is fully stocked

A similar level of merchantable volume produced within the range of full stocking

Properties of the Upland Hardwood Stocking Chart

B-Line identifies the minimum density of full site occupancy

Typically, residual stocking for thinning in upland oak stands would be at or just above B-Line

Below B-Line risks increasing epicormic branching

Properties of the Upland Hardwood Stocking Chart

C-line is the lowest stocking that will grow to the B-line within ten years

Thinning in the Central Hardwood Forest Region

• Silvicultural approaches:

1. Area-wide thinning to a target residual stocking

2. Crop tree release

Area-wide Thinning in theCentral Hardwood Forest Region

• When to thin

– Commercial thinning may begin as early as 30 years in upland oak stands on site index 80 or better

• Age of first commercial thinning could be between 40 to 50 if no market for small diameter (< 12 in) wood exists

Area-wide Thinning in theCentral Hardwood Forest Region

• How much to thin– Regardless of the site, the first thinning in young stands should be as

heavy as possible.

– Typically, residual stocking for area-wide thinning in upland oak stands would be at or just above B-Line

– The stand should approach average maximum density (A-line stocking) before subsequent thinning

– Aim for a well stocked stand with at least 50 high quality trees per acre for the final harvest cut

Area-wide Thinning in the Central Hardwood Forest Region

• How Often to Thin

– Frequency of thinning depends on the intensity of the first and subsequent cuts, site index, and rotation age

– Rotation age varies with site index if our goal is to produce high quality sawlogs

Area-wide Thinning Mature Stands in the Central Hardwood Forest Region

• Foresters generally consider upland oak stands mature when they are 80 to 100 years old or have reached a specified rotation age

• However, by the time stands are 50 to 60 years old and in the large pole/small sawtimber size, they have generally slowed in height growth, their annual basal area growth has leveled off, and except for size, they have many of the characteristics of older stands

Area-wide Thinning Mature Stands in the Central Hardwood Forest Region

• In older stands with 80 percent or more stocking, a very light thinning or improvement cut can be used to remove some cull trees, undesired species, or some short-lived species or old residuals from past logging– Do not reduce stocking below 75 percent and do not make large holes

in the stand

Area-wide Thinning Mature Stands in the Central Hardwood Forest Region

• If current stocking is 60 to 80 percent, it is usually best to hold off on thinning– Any cutting in such stands will probably not benefit the entire stand

and may allow an unwanted understory to develop rapidly

Crop Tree Release in the Central Hardwood Forest Region

Miller, G.W., J.W. Stringer, and D.C. Mercker. 2007. Technical guide to crop tree release in hardwood forests. University of Kentucky, Cooperative Extension Service. Southern Regional Extension Forestry Publication, Professional Hardwood Notes, FOR-106. 23 p.

Crop Tree Release

• What is Crop Tree Release (CTR)?– CTR is an intermediate silvicultural treatment and type of free thinning

– CTR is intended to provided increased growing space through the removal of crown competition from adjacent trees

– CTR assures most site resources are focused on a small number of selected trees rather than being widely distributed among all residual trees

Crop Tree ReleaseIncreasing growing space available to individual trees

Crop Tree Characteristics by Management Objective

How Crop Trees Respond to Release

• Increased growing space provides more light, water, and nutrients

• Released crop trees respond with faster root and crown growth, then faster dbh and volume growth

• Although CTR can produce a significant response in the first growing season, maximum growth usually occurs 2 to 3 years after release

Approach to Releasing Crop Trees

• “Crown-touching” release applied to deaden or fell adjacent competing trees whose crowns touch that of the crop tree

Approach to Releasing Crop Trees

• Lower crown class trees need not be removed

Intensity of Release and Crop Tree Growth

Crop Tree Release

• How many crop trees to manage?

• Release strategies:– Full crown-touching release for rapidly growing species and young

trees in the sapling/pole stage

– Less than a full crown-touching release (at least three sides released) for small sawtimber to limit the risk of epicormic branching

– Sub-canopy trees retained to protect crop trees and add other benefits to the stand, unless they conflict with management objectives

Economic value in hardwood stands found in a relatively small number of trees

Timing of Crop Tree Release Treatments

• Best time for application is when canopy begins to close or within 10 to 15 years following canopy closure

• Can be successful used in large poletimber and sawtimber stands to promote vigor in selected crop trees

Application Techniques for Crop Tree Release

• Mechanical fell or fell and herbicide stump treatment – Difficult to fell trees in young stands

• Chainsaw girdle: double girdle 1” deep, 6 in apart– Diffuse porous trees are poor candidates for girdling without herbicide

due to there resilience to girdling

• Cut surface herbicide application• Basal bark spray (trees < 6 in)

• Cost: $40 to 60 per acre ($100 to $150 per acre contract cost)

• Focus on best available crop trees regardless of spacing

Benefits of Crop Tree Release

• Increase diameter growth and volume of crop trees

• Increases stand value by increasing the proportion of high-value crop trees

• Greatest economic gains are when large differences exist between values of crop trees and their competitors due to species or quality

Risks Associated with Crop Tree Release

• Epicormic branching

• Windthrow or damage from ice or snow