Even-aged Harvesting Methods - Shelterwood, Seed Tree, Clearcutting

Even-aged Harvesting Methods

Many tree species do not tolerate major shade during the early stages of development. These stages include early seedling germination, development and sapling growth stable enough to compete in mid-canopy. These tree species have to have some light for regenerating and ensuring future even-aged stands for that species. Most of these timber types are mostly coniferous with a few exceptions.

Commercially valuable trees that need light to naturally regenerate a new stand of the same species makes up a major part of even-aged harvesting schemes by foresters. The reproductive management of these trees in North America includes jack pine, loblolly pine, longleaf pine, lodgepole pine, ponderosa pine, slash pine. Notable intolerant hardwood species include many valuable commercial oaks plus yellow-poplar and sweetgum.

Several reforestation systems and harvesting methods can be used to create even-aged stands.  While specific treatments vary across the U.S. by tree species and climate, the basic systems are clearcutting, seed tree and shelterwood.

Shelterwood

Even-aged stands must regenerate beneath the shade provided by mature trees left from the previous stand.  It is a major harvest scheme used in all regions of the United States. This includes regenerating loblolly pine in the South, Eastern white pine in the Northeast and ponderosa pine in the West.

Preparing a typical shelterwood condition could include three possible types of cuttings: 1) a preliminary cut might be made to select high yielding trees to leave for seed production; 2) an establishment cut can be made that prepares a bare soil seed-bed as well as trees that provide seed just before seed fall; and/or 3) a removal cut of overstory seed trees that have established seedlings and saplings but would be in competition if left to grow. 

So, a shelterwood harvest would be done to leave seed-producing trees uniformly throughout the stand, in groups, or strips and, depending on seed crop and species, can have between 40 and 100 crop trees.  As with seed tree harvests, shelterwoods are sometimes interplanted to supplement natural seeding.  Red and white oak, the southern pines, white pine, and sugar maple are examples of tree species that may be regenerated using the shelterwood harvesting method.

Here are specific shelterwood terms that further explain this harvesting method:

Shelterwood Cut - Removing trees on the harvest area in a series of two or more cuttings so new seedlings can grow from the seed of older trees. This method produces an even-aged forest.

Shelterwood Logging - Method of harvesting timber so that selected trees remain scattered throughout the tract to provide seeds for regeneration and shelter for seedlings.

Shelterwood System - An even-aged silvicultural scheme in which a new stand is established under the protection of a partial canopy of trees. The mature stand is generally removed in a series of two or more cuts, the last leaving a new even-aged stand that is well developed.

Seed Tree

The seed tree reforestation method leaves healthy, mature trees with a good cone crop (usually 6 to 15 per acre) in the existing stand to provide seed for regenerating a new stand of trees.  Seed trees are typically removed after regeneration is established, especially when seedling levels are significant enough to stand some logging losses. It is not unusual for a forest manager to leave the seed trees for wildlife or aesthetics objectives. However, the primary objective of a seed tree regeneration harvest is to provide a natural seed source.

Artificial planting of nursery seedlings may be used to supplement areas where natural seeding was not adequate.  White pine, the southern pines and several species of oak may be regenerated using the seed tree harvesting method.

Clearcutting

Removing in a single cutting all of the overstory trees in a stand to develop a new stand in a shade-free environment is called a clear or clean cut harvest. Depending on species and topography, reforestation can occur by natural seeding, direct seeding, planting, or sprouting.

See my feature on clearcutting: The Debate Over Clearcutting

Each individual clearcut area is a unit in which regeneration, growth, and yield are monitored and managed specifically for wood production. That does not mean that all trees will be cut. Certain trees or groups of trees may be left for wildlife, and buffer strips are maintained to protect streams, wetlands, and special areas.

Common tree species regenerated using clearcutting include the southern pines, Douglas-fir, red and white oak, jack pine, white birch, aspen, and yellow-poplar.