Uneven-aged Regeneration Systems

Vivek Srivastava

Uneven-aged Regeneration Systems

• Uneven-aged regeneration systems often referred to as selection systems also called

“Selective" logging and "select-cut" merely mean that the harvest is not a clearcut

Characteristics of Uneven-aged Systems

• Selection methods produce an uneven-aged stand

• For regeneration, trees are harvested as individuals or in small groups

– Single-tree selection method: removing individual mature trees more or less uniformly across a stand

– Group selection method: removing mature trees in small groups or clusters

Characteristics of Uneven-aged Systems

• Maintains a continuous high forest cover

• Typically emphasizes the production of sawtimber sized trees

Characteristics of Uneven-aged Systems

• Selection is particularly useful for putting an irregular stand under productive management without losing existing stocking

• A selection system can be designed to obtain a sustained yield at recurring short intervals

Characteristics of Uneven-aged Systems

• Rotation length is the average time period required to obtain crop trees of a specified target size

• The period between harvests (in years) is the length of the cutting cycle

General Procedure in Uneven-aged/Selection Systems

• Harvest mature trees, either single trees or in small groups

• This provides openings for regeneration of a new age class

• "cut the worst, leave the best"

Balance vs. Irregular (unbalanced) uneven-aged stands

Uneven-aged Regeneration Methods

Variations of the Selection Method

Single Tree Selection: removes individual trees of all size classes more or less uniformly throughout the stand to maintain an uneven-aged stand and achieve other stand structural objectives

Variations of the Selection Method

Single Tree Selection

• More commonly applied in:

– Shade tolerant species

Depiction of Uneven-age Stand Managed Using Individual Tree Selection

Variations of the Selection Method

• Group Selection: removes clusters of adjacent mature trees from a predetermined proportion of the stand area

– Group selection was developed to regenerate shade-intolerant and intermediate species

– Group selection is easier to plan and keep the stand balanced than with single-tree (if area regulation is used)

– Logging is more efficient and less damaging to residual trees than with single-tree

Group Selection Method

Two-Aged (Hybrid) Silvicultural Systems

Two-Aged Silviculture

• Two-aged management is a hybrid between even-aged management and uneven-aged management

• Regeneration is accomplished (in general) two times over a standard rotation.

• Referred to as: irregular shelterwoods, reserve shelterwoods, leave tree systems

Benefits of a Two-Age System

• Development of large-diameter sawtimber or veneer trees

• Production of a wide range of forest products from pulp to veneer in the same stand at the same time

• Ability to regenerate shade-intolerant and intermediate shade-tolerant species

• Improved aesthetics compared to clearcutting

• Increased structural diversity and retention of habitat components compared to clearcutting

Irregular/Reserve Shelterwood

Uncut Stand

Reserve trees (10-15 ft2 ac-1 BA)

Establishment Cut

(45-60 ft2 ac-1 BA)

Two-age stand development

Reserve Tree Criteria

• Long-lived commercial species• Appropriate crown characteristics• Stem form and maintenance of potential veneer or high-quality

saw timber• Ability to withstand harvest• Located to avoid wind-throw and other post-harvest

perturbations

Other Partial Cuttings

Other Partial Cuttings

• Timber harvesting vs. Silviculture

– Timber harvesting extracts a product

– Silviculture involves a determined effort to regenerate mature trees or tend immature ones and to provide by the future by using harvesting to recover products that become a byproduct of systematic management

Other Partial Cuttings (non-silvicultural treatments)

• Non-silviculture, exploitative partial cutting treatments

– Commercial clearcutting: removal of only commercially salable trees

– High-grading: removal of choice species or trees larger than a specified diameter limit if they fit common utilization standards

– Diameter-limit cuttings: removal of all trees larger than a specified diameter

Disadvantages of Non-Silviculture Partial Cuttings

• Does not move forests toward a controlled age or size class distribution that ensures long-term sustained yields at predicable levels or intervals

• Does not ensure adequate regeneration in terms of number, species, or distribution

• Ignores silvical requirements of desired species with respect to regeneration and long-term growth

• Removes acceptable growing stock and leaves defective and unhealthy trees