Adaptive Silviculture: An Alternative for Nonindustrial Private Forests

In many cases, neither clearcutting nor selection harvesting is acceptable to nonindustrial private forest (NIPF) owners (Smith 1986). Many NIPF owners reject even-age silviculture for aesthetic as well as financial reasons. It is difficult to provide an even flow of products on small forest tracts using even-aged management. Uneven-age systems require a long-term commitment and great skill to apply, and they tend to regenerate the less valuable shade-tolerant species. Hicks (1998) points out that NIPF owners in the central hardwood region often take the economic certainty of a timber sale over the uncertainty of "best" silvicultural management. Silvicultural plans for NIPF owners should take into account not only forest biology, but also the economic realities of the owner (Hicks 1998).

An adaptive silvicultural approach, where management goals remain flexible, offers a means for NIPF owners to improve their stands at reasonable costs. Adaptive silviculture can be tailored to meet landowner objectives and constraints, to take advantage of favorable market conditions, to exploit good crops of desirable regeneration, and to respond to insect or disease outbreaks. The adaptive silvicultural approach becomes "management" when plans are developed and goals are set. Three cardinal rules must be adhered to in adaptive silviculture: (1) cuttings should not degrade species composition; (2) regeneration should always be considered; and, (3) the harvest should be designed to remove only the growth (Hicks 1998).

Smith (1988) discusses several ways of rejuvenating central hardwoods that are practical and adaptable to landowner objectives:

Alternatives to Clearcutting (for Even-Aged Management)

• Leave residual trees-such as occurs with deferment cutting or two-age management (Hicks 1998).
• Utilize more shelterwood management. An irregular shelterwood (Smith 1986) may be applied in stands of mixed species where some species have a much longer rotation age than the others (Hicks 1998).

Alternatives to Single-Tree Selection (for Uneven-Aged Management)

• Extend the cutting cycle for selection management to permit greater harvest volume at each entry (Hicks 1998).
• Consider removing pole-sized trees in silvicultural operations, even in the absence of markets for small products. In central hardwood sawtimber stands, pole-timber trees often are of inferior species or low vigor. Such trees should be culled when valuable sawtimber is being harvested to prevent them from dominating the future stand. Where composite markets exist, they make it more economically feasible to eliminate such trees (Hicks 1998).
• Apply a financial maturity concept. This method of selection management, developed by Trimble and others (1974), involves harvesting trees when they reach their financial maturity diameter. Financial maturity is based on expected rates of return. With this technique, Trimble and others (1974) reported obtaining adequate regeneration over 20 years, but shade-tolerant species were favored. Smith (1988) recommends adjusting minimum cutting diameters based on experience, with diameters of undesirable or short-lived species adjusted downward and those of valuable and long-lived species adjusted upward (Hicks 1998).
• Use differential diameter-limit cutting (Smith 1986). Diameter-limit cutting, the practice used by most NIPF owners, can be made silviculturally acceptable with proper modifications such as raising the diameter limit to 16-18 inches for valuable sawtimber species; harvesting no more volume than can be sustained by growth; and applying appropriate cultural practices (improvement cutting, thinning, presalvage) during each entry, irrespective of diameter. Although diameter-limit methods do not provide specifically for regeneration, regeneration often occurs under canopy openings. The "adaptive silviculture" approach enables the manager to favor desirable regeneration and discourage or kill undesirable regeneration as it develops (Hicks 1998).

Alternative to Group Selection (for Uneven-Age Management)

• Smith (1986) recommends dropping "group selection" terminology in favor of a "small opening" concept, with the size of openings tailored to fit the silvical characteristics of the species to be regenerated. Small openings can provide edge and habitat for wildlife and are generally aesthetically acceptable to most owners. He suggests a relatively long cutting cycle of 20-40 years, which creates a less patchy appearance of the forest. These longer cutting cycles may make it necessary to perform intermediate cuttings within the small groups. Such cuttings can be done when mature trees are harvested (Hicks 1998).