The Shelterwood Method

The shelterwood method usually is an even-aged management system, but can also be a two-age system. In it, one or more cuttings are made to begin the development of the new age class before the old stand is completely removed. Foresters use the shelterwood method where an inadequate seed supply or a sharp change of environmental conditions might preclude sufficient regeneration after clearcutting. The shelterwood method involves two or three cutting treatments extended over a 15 to 30 year period (Nyland 1996):

1. Preparatory cutting: a cutting designed to remove poor quality trees and to increase vigor and seed production among the residuals.
2. Seed cutting: a cutting performed to open the stand sufficiently to encourage the development of regeneration.
3. Removal cutting: a cutting that is done after regeneration is established to remove the overstory and to allow the new stand to grow.

The partial cuttings in the shelterwood method share similar objectives with the seed-tree method. The two approaches differ only in the amount of residual stocking left during seed cutting and the purpose of these trees. In the seed-tree method, fewer trees remain after the seed cutting and these residual trees serve only as a seed source (Nyland 1996).

Partial cuttings in the shelterwood method accomplish several goals. First, good phenotypes are selected as reserve trees with the expectation that they will contribute good genes to the next generation. Retention of the overwood ensures a seed source for a long period in case there is difficulty in obtaining regeneration immediately after cutting. Second, the opening of the canopy stimulates seed production of the residuals and provides additional light to the forest floor, promoting growth of the new regeneration (Marquis 1979). Third, shelterwood cuttings can be tailored to favor particular species by providing enough light to encourage some species but not others; regeneration under such cutting is usually composed of shade intolerant species, similar to those that regenerate after clearcutting. Finally, shelterwoods mitigate some of the adverse aesthetic effects of clearcutting while maintaining some of the qualities of mature forests, such as hard mast production. Shelterwoods are commercially attractive because a high percentage of the stand basal area is removed in the initial cut and the high-quality trees that are left have the capacity to increase in value after they are released (Hicks 1998).

Variations of the Shelterwood Method

There are several variations of the shelterwood method; some methods vary by the number of cuttings. The one-cut shelterwood method is used when adequate advance regeneration exists and preparatory or seed cuttings are not needed. This method resembles clearcutting, except that most of the new age class already is present prior to overstory removal. The two-cut shelterwood method includes only a seed cutting and a removal cutting, and the three-cut shelterwood method includes all three cuttings (Nyland 1996).

Other shelterwood methods differ in the amount of time between cuttings. In the reserve shelterwood system, the overstory is maintained for more than 20 percent of the length of the rotation. In deferment cutting, harvest of the overstory is deferred through a complete rotation of the regeneration (Miller and Schuler 1995). In the two-age silvicultural system, the overstory and new regeneration are tended as a two-aged stand (Sims 1992). It appears that the differences between these methods have more to do with their objectives than with the way they are applied or how the new stand develops (Hicks 1998). Though attractive in many respects, these systems have several operational and financial disadvantages (Nyland 1996):

• A greater chance of damaging reserve trees during cuttings
• Higher risk of reserve tree loss due to exposure, blowdown, or old age
• Difficulties in maintaining an open overstory
• Heavy losses of the new cohort during eventual reserve tree removal, and
• Higher logging costs due to multiple entries and precautions taken to minimize damage to both cohorts

Alternative approaches include the group- or strip-shelterwood systems, which vary from other methods in the shape and arrangement of cuttings. In the strip-shelterwood method, which resembles strip clearcutting, the mature age class is removed over a series of entries in narrow parallel strips not exceeding the height of adjacent standing trees. The adjacent residual strips provide seeds and partially shade the openings. To maximize seed dispersal and reduce chances of blowdown, strips can be oriented at right angles to the prevailing winds. Where side shading is more important than seed dispersal, strips can be aligned in an east-west direction to minimize direct insolation. In the group-shelterwood method, the seed cutting creates well-dispersed openings, each with a diameter not exceeding the height of adjacent trees. Once seedlings are established, a band or ring of residual trees around all or part of each opening is removed. Additional patches can be cut at each entry to create new pockets of regeneration throughout the stand (Nyland 1996).

See also: Application of the Shelterwood Method for Oak Management