1. Multiaged Systems Uneven-aged and Irregular Silviculture

2. Uneven-aged Regeneration Systems
Uneven-aged regeneration systems often referred to as selection systems
Not equivalent to "selective" cutting
“Selective" logging and "select-cut" merely means harvest is not a clearcut
Terms are imprecise as they could refer to systematic silvicultural methods or exploitive high-grading

3. Characteristics of Uneven-aged Systems
Selection methods produce an uneven-aged stand (with at least 3 age classes or distinct cohorts)

4. Characteristics of Uneven-aged Systems
Maintains continuous high forest cover
Typically emphasizes sawtimber production
Regulation methods allow sustained yield at recurring intervals
If balanced, each harvest removes amount equivalent to growth produced since the last harvest
Useful for putting an irregular stand under productive management without losing existing stocking

5. Characteristics of Uneven-aged Systems
Rotation length is the average time period required to obtain trees of 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

6. Characteristics of Uneven-aged Systems
Intermediate treatments should be completed to ensure continued recruitment and favorable growth among residual trees
For sustained yield, systems requires frequent and accurate inventory

7. Potential Objectives/Benefits in Using a Selection System
Maintains structural diversity within stand
Maintains good site protection
although frequent logging may result in increased soil damage on sensitive sites
Pleasing aesthetics without time gaps
Frequent periodic income
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

8. 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 more difficult and costly per unit area than with even-aged methods
Results in more logging damage to residual trees than with even-aged methods
Due to frequent entry of harvesting equipment
Leads to long-term depletion of growing stock if not applied carefully

9. Characteristics of Uneven-aged Systems
Uneven-aged regeneration methods provide openings for establishment and recruitment of new age classes (cohorts)
Selection methods are traditionally classified as either
Single-tree selection
Group selection
In practice, selection methods can create a continuum from very small to large regeneration openings

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

12. 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

13. 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

14. Variations of the Selection Method
Group Selection: removes clusters of adjacent trees from a predetermined proportion of the stand area
Group selection was developed to create larger openings needed to regenerate shade-intolerant and intermediate species

15. Application of group selection
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
In the Central Hardwood Forest Region, opening sizes are typically between 1 and 2 times the height of surrounding trees
Locate harvest groups among the oldest or largest trees in the stand
Appropriate tool for other objectives—wildlife openings, aesthetics, salvage/sanitation

16. Application of group selection
Opening shape to fit the stand conditions or to maximize objectives/constraints
Rectangular openings will be more efficient for logging than circular
Rectangular openings provide more sun if oriented with their long axes east-west
Group selection is easier to plan and keep the stand balanced than with single-tree
Logging is more efficient and less damaging to residual trees than with single-tree

17. Application of group selection
Complete felling of all trees in the openings is crucial to allow for good regeneration
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

18. 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
Openings in group selection should not exceed 2 times the height of adjacent mature trees
Difficult (or impossible) to locate groups within a stand following second or third entry

19. Regulating Selection Systems

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

21. 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:

22. 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

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

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

25. Structural regulation and Guiding Curve
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

26. 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)

27. Silvicultural Approaches to Creating Irregular Stand Structures

28. Creating Irregular Stand Structures
Irregular silviculture seeks to create stands with:
Continuous canopy cover
Variation in age structure and spatial arrangement
Multilayered canopies with tree crowns at various height levels (stratum)
Practices increase or create heterogeneity within stands and allow complexity to develop through time
While uneven-aged selection systems create irregular stands, all irregular silvicultural practices do not necessarily seek to:
Balance the age classes
Maintain stable diameter distributions
Realize consistent yield at regular intervals (cutting cycles) through time

29. Creating Irregular Stand Structures
Irregular silviculture differs from selective cutting (an exploitive strategy) by:
Tending and regenerating economically and ecologically important species and sustaining values and interests through time
Practices do not compromise future production or ecological function
While irregular silviculture does not have to closely regulate spatial or temporal arrangements of age classes, it must:
Plan for deliberate regeneration of replacement trees to maintain the irregular age class and structural attributes
Invest in tending to nurture the recruitment and growth of target trees at different stages of development
Make treatments financially feasible and provide a revenue stream to pay ownership and management costs

30. Creating Irregular Stand Structures
First step in developing irregular stand structures is to create a two-aged stand
Irregular silviculture practices are referred to as:
Continuous cover forestry
Femelschlag
Dauerwald
Close to nature forestry (Pro Silva Europe)
Ecological forestry
Variable retention harvesting
Methods utilized in irregular silviculture include: selection systems (group and single-tree), irregular and group shelterwoods, variable density-thinning, “free” selection

31. Creating Irregular Stand Structures

32. Creating Irregular Stand Structures

33. Creating Irregular Stand Structures

34. Two-Aged Silviculture

35. 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

36. Benefits of a Two-Aged System
Increased structural diversity and retention of habitat components compared to even-aged methods
Production of a wide range of forest products from pulp to large-diameter sawtimber in the same stand at the same time
Ability to regenerate shade-intolerant and intermediate shade-tolerant species
Improved aesthetics compared to clearcutting

38. Benefits of a Two-Aged System
Increased initial revenue compared to other types of non-clearcut regeneration techniques
Development of old-growth structural characteristics
Maintenance of seed production in reserve trees throughout the entire rotation
Ability to “life boat” species that would otherwise be eliminated if the area was clearcut

39. 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

40. 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

42. 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

43. Two-aged Regeneration Methods
Two-aged stands can be created in a single treatment or through multiple entries
Single entry: deferment or leave-tree methods
Multiple entry: Reserve shelterwood
Basal area of reserve trees (i.e., the oldest age class) does not typically exceed 25 ft2 ac-1

44. Deferment or Leave-Tree Approach
Uncut Stand
Reserve trees (10-15 ft2 ac-1 BA)

45. Deferment or Leave-Tree Approach

46. Reserve Shelterwood Uncut Stand Establishment Cut* (45-60 ft2 ac-1 BA)
Reserve trees (10-15 ft2 ac-1 BA)
*Similar to the uniform shelterwood (even-aged), an optional preparatory cut may proceed the establishment cut

47. Variable Retention Harvesting

48. Variable Retention Harvesting
Variable retention harvesting aims to retain legacies from the past and enrich the new community with structural features reminiscent of older forests
With regeneration units of older stands,
Retain large and decedent trees, maintain course woody debris, and reduce disturbances to forest floor
Retained attributes as dispersed elements or aggregated in small patches of residual forest
Results in an irregular forest of at least two ages

49. Variable Retention Harvesting
In intermediate aged stands
Intermix thinned patches with variable levels of residual stocking
Stimulates residual tree development, creates horizontal heterogeneity in stand conditions and structure, and establishes gaps of various sizes to establish and release regeneration
Attempts to mimic disturbances considered natural for the region

50. Variable Retention Harvesting
Dispersed Retention

51. Variable Retention Harvesting
Aggregated Retention

52. Irregular Shelterwood Systems
Three general classifications:
Expanding-gap irregular shelterwood
Continuous cover irregular shelterwood
Extended irregular shelterwood

53. Irregular Shelterwood Systems
Expanding-gap irregular shelterwood -
“Aims to regenerate new cohorts in groups that are gradually enlarged until the stand is totally removed”

54. Expanding-gap irregular shelterwood

55. Expanding-gap irregular shelterwood
Initial Gaps

56. Expanding-gap irregular shelterwood
Preparatory/establishment cutting around gaps

57. Expanding-gap irregular shelterwood
Preparatory/establishment cutting following gap expansions

58. Expanding-gap irregular shelterwood
Final removal of areas receiving preparatory/establishment cutting

59. Expanding-gap Irregular Shelterwood

60. Irregular Shelterwood Systems
Continuous cover irregular shelterwood –
“Sequence of cuttings is applied more freely in space and time, which permits maintenance of a multicohort structure and a continuous forest cover ”

61. Continuous cover irregular shelterwood

62. Irregular Shelterwood Systems
Extended Irregular Shelterwood –
“Aims to regenerate the whole stand while … two cohorts are maintained for at least 20% of the rotation length”

63. Extended irregular shelterwood

64. Other Partial Cutting

65. 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

66. Other Partial Cuttings (non-silvicultural treatments)
Non-silviculture, exploitative partial (selective) 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

67. 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

68. Rehabilitating Cutover Stands
Stand assessment initial step in rehabilitating cutover stands
Assessment determines:
Abundance and distribution of suitable residual trees and their potential
Status of advance reproduction
Patterns of interfering understory vegetation
Characteristics of suitable residuals
At least lower codominant
> 20 to 25% live crown
No (to few) epicormic branches on lower bole
No apparent decay or damage of the main stem
< 25% of major branches dead or dying
< 10% lean

69. Rehabilitating Cutover Stands
High degree of stocking variability and patchiness makes stand-wide treatments impractical in many cases and prescription may use combination of methods within a stand

70. Silvicultural Methods for Rehabilitation
Complete tree removal as regeneration method for places lacking acceptable growing stock
Liberation cutting to release a younger age class already in place
Leaving widely space trees as shelterwood establishment cut or initiate a two-aged arrangement

71. Silvicultural Methods for Rehabilitation (cont.)
Thinning even-aged patches with acceptable growing stock
Releasing widely spaced crop trees within main canopy without additional tending between (i.e., crop-tree release)
Low-density selection systems for cutover uneven-aged areas