Uneven-aged Management - A "Natural" Approach to Timber

treesWith timber prices down for many products, less interest in investing in costly regeneration after harvest, and greater interest in a more natural approach to forest management, many landowners are looking for alternatives to the traditional plant, thin and harvest approach of timber management. Uneven-age management is an alternative that sustains the forest cover, provides income at more frequent intervals, minimizes regeneration costs and provides many wildlife habitat and recreational benefits.

An uneven-aged stand is a group of trees that differ significantly in ages; by convention, the spread of ages exceeds 25% of the planned life span for an age class. 

In uneven-aged management, we remove mature trees, or groups of them, leaving gaps and young trees to grow, allocating a portion of the growing space to regeneration.

To contrast, we remove all of the trees when harvesting an even-aged stand in order to allocate all of the growing space to regeneration. When growing southern pines for timber, an even-aged management scheme is commonly used. To see the advantages and disadvantages associated with using these reproduction methods, visit our Even- vs. Uneven-Aged Reproduction Methods page.

In both cases, we are opening up a temporary void in the ecosystem so that the space can be occupied by a new age class to replace the one removed in the harvest.

For more information on converting an even-aged stand to uneven-age, read the University of Florida Extension Publication, Opportunities for Uneven-age mangement in second growth longleaf pine stands in Florida.

Structure of an Uneven-Aged Stand

A balanced uneven-aged stand contains age classes which occupy roughly equal amount of ground space per acre.

Each cutting in a selection system must: 

  1. regenerate a new age class
  2. harvest mature trees and excess numbers in each age class
  3. balance the age class distribution

Balance among age classes in uneven-aged stands can be achieved by influencing the distribution of diameter classes through tending operations.

During each cut, remove: 

  • the mature age class and replace it with regeneration of a new age class
  • the excess trees per diameter class so that the growing space is allocated equally among residuals of each class

The immature trees to leave standing: 

  • those of best quality, soundness, and vigor
  • those having the best chance for survival and growth
  • the species you wish to include in your mix

To improve the quality of the stand over time, cut among the immature age classes according to the following priority: 

  1. remove the defective and diseased trees
  2. remove high risk trees that might not survive another cutting cycle
  3. remove low value trees of any species
  4. thin the least desirable species (see our Thinning page for more information).
  5. remove excess numbers of desired species

If we were to make a graph showing the diameter (in inches) class distribution of a balanced uneven-aged stand, with diameter classes on the x-axis and the number of trees per acre on the y-axis, the curve would resemble an inverse "J".  This structure is called an Arbogast structure.  View a sample Arbogast distribution from Davis and Johnson, 1987.

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The Selection System

The selection system is a silvicultural program which creates and maintains an uneven-aged stand.

The selection system includes:

  1. a selection method to harvest mature trees and regenerate a new age class to replace them
  2. tending (thinning) of the immature age classes

In the selection system, regeneration, tending, and harvesting all take place concurrently.

Individual Tree Selection

Individual or single tree selection is a selection system in which openings are created to regenerate a new age class in the space previously occupied by individual mature trees.

Individual tree selection will result in gaps with relatively low light levels. Therefore, this method is best suited to regenerate shade-tolerant species.

Group Selection

Group selection is a selection system in which openings are created to regenerate a new age class in the space previously occupied by groups of 2 or more mature trees.

The gaps created by a group selection cut will usually receive sufficient light levels to regenerate shade-intolerant species, given an adequate seed source.

When using the group selection system,

  1. identify family groups of mature and immature trees
  2. harvest groups of mature trees from cutting area
  3. thin the immature trees to maintain a balanced stand structure (see the Structure of an Uneven-Aged Stand)

All selection systems share the following features: 

  • mature trees are removed from a roughly fixed proportion of the stand area
  • a new age class is regenerated in the space previously occupied by mature trees
  • regeneration, tending, and harvest occur concurrently


CAUTION!

Important note about terminology: Selective cutting is not the same as the selection system!

You may hear the word selective cutting used but selective cutting refers to: 

  • culling or high-grading
  • it is an exploitive cutting that removes only certain selected species, size classes, or high value trees without regard to the future stocking or health of the stand

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