uneven-aged regeneration systems
TRANSCRIPT
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