Uneven-aged regeneration systems, also called selection systems, involve harvesting trees individually or in small groups to maintain a continuous forest cover with a mix of age classes. This is done through single-tree or group selection methods. Single-tree selection removes individual mature trees uniformly across the stand, while group selection removes clusters of adjacent mature trees. The goal is to regenerate new age classes while emphasizing production of sawtimber-sized trees under a sustained yield. Two-aged systems combine elements of even-aged and uneven-aged management by regenerating stands twice over a standard rotation period.

1. Uneven-aged Regeneration Systems
Vivek Srivastava

2. 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

3. 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

4. Characteristics of Uneven-aged Systems
• Maintains a continuous high forest cover
• Typically emphasizes the production of sawtimber sized trees

5. 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

6. 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

7. 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"

8. Balance vs. Irregular (unbalanced) uneven-aged stands

9. Uneven-aged Regeneration Methods

10. 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

11. Variations of the Selection Method
Single Tree Selection
• More commonly applied in:
– Shade tolerant species

13. Depiction of Uneven-age Stand Managed Using Individual Tree
Selection

14. 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

15. Group Selection Method

16. Two-Aged (Hybrid) Silvicultural Systems

17. 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

18. 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

20. 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

21. 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

22. Other Partial Cuttings

23. 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

24. 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

25. 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