Uneven-aged Regeneration Systems

Uneven-aged regeneration systems often referred to as selection systems also called –This is not equivalent to "selective" cutting, as the term is commonly used –“Selective" logging and "select-cut" merely mean that the harvest is not a clearcut These terms are imprecise They could be referring to a thinning, to a shelterwood establishment cutting, or to a high-grading cut

Characteristics of Uneven-aged Systems Selection methods produce an uneven-aged stand (with at least 3 age classes or distinct cohorts) 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 –The entire stand remains under the influence of mature trees –Harvested opening widths are no more than 2 times the height of adjacent mature trees Typically emphasizes the production of sawtimber sized trees –Pulpwood production is relatively low

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 For sustained yield in a selection system: – If the stand is balanced, each harvest should remove an amount equivalent to the growth produced since the last harvest

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 –Harvests occur regularly at short intervals throughout the rotation –Cutting cycle is normally between 5 to 20 years

Characteristics of Uneven-aged Systems To avoid "high-grading", each cutting should include intermediate treatments among trees other than those of the target size For a sustained yield, the method requires frequent and accurate inventory

General Procedure in Uneven-aged Systems Harvest mature trees, either single trees or in small groups This provides openings for regeneration of a new age class (cohort) "Tend" the remaining cohorts to maintain approximately equal total area in each -- among these remaining sizes, "cut the worst, leave the best"

1.Area regulation 2.Volume regulation 3.Structural regulation Approaches to regulation in the selection method and maintaining a balanced stand with sustainable yield

Area regulation: this is the simplest, and is fairly easy with a group selection system, but it is difficult with the single-tree approach. –Combined area of all trees removed in each cutting cycle:

Volume regulation: harvest the allowable cut each cutting cycle -- if a stand is balanced, this is equal to the growth during the cutting cycle period

Structural regulation: use a reverse J-shaped curve of residual diameter distribution as a guide.

Balance vs. Irregular (unbalanced) uneven-aged stands

In balanced uneven-aged stands with an reverse-J shape distribution, a constant ratio exists between the number of trees in successive diameter classes. This relationship defines the shape (steepness or flatness) of the structural regulation guiding curve and is called the q factor (or quotient) q = where, Ni = number of trees in the ith diameter class Ni+1 = number of trees in next largest diameter class Structural regulation and Guiding Curve

Influence of q on Target Diameter Distribution A smaller q value more large trees and fewer smaller trees A larger q leaves fewer large trees, more smaller tree (i.e. less sawtimber)

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 Norway spruce, beech, silver fir (central Europe) Sugar maple, American beech, birch (Northern hardwoods) –Restrictive sites where pronounced seasonal water limitations favor natural monocultures Ponderosa pine Has been used for other forest types –Upland oak forests of the Missouri Ozarks (Pioneer Forest, MO) –Loblolly-shortleaf pine (Crossett Experimental Forest, AR) –Longleaf pine, southern Coastal Plain region

Variations of the Selection Method Single Tree Selection Central and southern upland and bottomland hardwoods –Generally, without intensive competitor control, single tree selection has resulted in a transition to 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

Application of group selection Locate groups to be harvested among the oldest or largest trees in the stand Uses area regulation to maintain balanced stand Openings must be wide enough to allow good regeneration establishment –Due to shading effects of edge, best success and growth of intolerant seedlings may be restricted to 2/3 or less of the area in a small opening Group selection in the Central Hardwood Region generally uses open sizes between 1 and 2 times the height of surrounding trees

Application of group selection Shape the harvested openings to fit the stand conditions or to maximize objectives/constraints considerations –rectangular openings will be more efficient for logging than circular or square ones-narrow –rectangular openings provide more sun if oriented with their long axes east-west Complete felling of all trees in the openings is crucial to allow for good regeneration

Application of group selection Control of undesirable species should be considered –Possibly pre- or post-harvest injection, basal bark herbicides, or cutting Tend the remaining uncut stand areas between group openings

Issues associated with group selection Uses area regulation for structural control Difficult (or impossible) to locate groups within a stand following second or third entry Appropriate tool for other objectives—wildlife openings, aesthetics, salvage/sanitation

Issues associated with group selection Group selection is often confused with patch clearcutting If groups are managed as an individual “stand” and tracked through time as such, you are using even-aged silviculture at a small spatial scale In group selection, harvested opening widths are no more than 2 times the height of adjacent mature trees

Potential Objectives/Benefits in Using a Selection System Can provide frequent periodic income from the stand with no long time gaps Has good flexibility; maintains a reserve of large trees on the stump (thus one can take advantage of market fluctuations) Requires only a low investment in regeneration

Potential Objectives/Benefits in Using a Selection System Maintains high diversity within the stand –usually provides good wildlife habitat for many, but not all species Maintains good site protection –although frequent logging may result in increased soil damage on sensitive sites Maintains pleasing aesthetics without time gaps

Potential Drawbacks/Disadvantages of Selection Systems Involves a high level of complexity, requires higher management costs than other methods Produces less pulpwood than other methods Harvesting is usually more difficult and costly per unit area or product than with even-aged methods Typically, selection results in more logging damage to potential crop trees than with even-aged methods, due to more frequent entry of equipment into the stand Can lead to high grading if not applied carefully

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. –Two age classes Referred to as: irregular shelterwoods, reserve shelterwoods, leave tree systems, and deferment methods

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

Benefits of a Two-Age System Increased initial revenue compared to other types of non- clearcut regeneration techniques Development of old-growth structural characteristics Maintenance of sexual reproduction in reserve trees throughout the entire rotation and the ability to “life boat” species that would otherwise be eliminated if the area was clearcut

Constraints/Undesirable Features of Two-Aged System Reducing older age classes to low densities and wide spacing increase the danger of blowdown Residual trees may be prone to epicormic branching –Reserve trees must be carefully selected Lack of appropriate long-lived species to maintain the system

Constraints/Undesirable Features of Two-Aged System Forest fragmentation and habitat effects similar to clearcutting Reduction in initial revenues compared to clearcutting Limited development of shade-tolerant species Damage to new age-class trees if a portion of reserve trees are removed prior to the end of the second rotation length

Irregular or Reserve Shelterwood: Leaves residual overstory for an extended period of time into new rotation – creates two-aged stand –In central hardwood region, reserve tree density is approximately 10 to 15 ft 2 ac -1 of basal area Has ecological/aesthetic vs. economic/operational tradeoffs Characteristics of reserve trees are important

Irregular/Reserve Shelterwood Uncut Stand

Irregular/Reserve Shelterwood Uncut Stand Establishment Cut (45-60 ft 2 ac -1 BA)

Irregular/Reserve Shelterwood Uncut Stand Reserve trees (10-15 ft 2 ac -1 BA) Establishment Cut (45-60 ft 2 ac -1 BA)

Irregular/Reserve Shelterwood Uncut Stand Reserve trees (10-15 ft 2 ac -1 BA) Establishment Cut (45-60 ft 2 ac -1 BA) Two-age stand development

Reserve Tree Criteria Long-lived commercial species Appropriate crown characteristics including live crown ratios (typically > 40 for hardwoods), well-balanced crown proportions and overall crown vigor Stem form and maintenance of potential veneer or high-quality sawtimber Ability to withstand harvest Located to avoid wind-throw and other post-harvest perturbations

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 –In the Central Hardwood Region, repeated exploitative cutting yield a degraded stand composed primary of low-value, shade-tolerant species Ignores silvical requirements of desired species with respect to regeneration and long-term growth Removes acceptable growing stock and leaves defective and unhealthy trees