Forest Residues

Forest residues management involves disposal, modification, or utilization of wood products. The costs and benefits of the several alternatives available to forest managers must be evaluated in relation to land management goals and constraints in four areas: (1) unused wood fiber, (2) conflagrations, (3) impairment of forest resources, and (4) opposition to treatment of residues. Advance modification of fuels or installation of fuelbreaks on strategic locations may be the best residue management for fire control, but probable loss must be weighed against cost. A simple framework is proposed that uses quantitative data on costs, benefits, and probabilities, but the opportunity exists to use qualitative data until research results become available.

The forest manager must balance all the interacting and often conflicting factors influencing residue management and decide on the best course of action. He needs to determine optimum volume, size, and arrangement of residues to leave on an area after logging, then to select the harvesting methods and residue management alternatives that best provide these conditions. Cramer (1974) summarized environmental effects of forest residues management for major forest types in the Pacific Northwest, but types of treatment were not listed and only minor attention was given to hemlock-spruce forests. Residue management guidelines have been prepared for Oregon and Washington (Pierovich et al. 1975) but the hemlock-spruce type is not discussed as a separate entity. Alaska is not included in either report. This report provides a detailed look at residue management throughout the north Pacific coastal fog belt, including Oregon, Washington, British Columbia, and Alaska. The approach is a general look at forest residues as part of the ecosystem, then a closer look at dead and decaying material after logging, considering fire hazard and the silvicultural, physical, chemical, and esthetic effects of this material. Residue treatments are described, evaluated, and recommended. The report is intended to provide an improved scientific framework for management decisions. The coastal environment is more moist than other parts of the Pacific Northwest. Generally, fire danger is low and the need for residue treatment to reduce fire hazard is limited to special situations. Northward into Alaska, increasing summer precipitation relegates fire danger to a subordinate management problem. Hemlock-spruce residue volumes may range up to 250 tons per acre (560 metric tons per hectare) when an old-growth timber stand is defective and has a high proportion of western red cedar, but volumes may be less than 50 tons per acre (112 metric tons per ha) with more complete utilization of sound young timber. The trend is to less residue volume as defective timber is replaced by vigorous young stands and utilization improves. Residues often dominate the post-logging environment and are a major factor influencing forest regeneration. Fresh residue intercepts natural seed fall or aerially sown seed and prevents seedling establishment; but later, as it decays and with moisture present, it becomes a suitable seed bed for hemlock and spruce. Advance regeneration, usually hemlock, grows on decaying residue material and almost invariably is intermixed with fresh logging residue. Its fate is determined by residue treatment. When residue treatments expose mineral soil, they influence species composition favoring several species. These ecological relationships between forest residues and conifer seedlings can be used by forest managers to influence density and species composition of the new timber stand. A common problem in hemlock-spruce is too many seedlings. When advance regeneration is prolific, harvesting plans and residue treatments should be designed to destroy some of the seedlings. Overstocking with post-logging regeneration can be reduced if the logging operation is planned so that fresh slash covers an appropriate portion of suitable seed beds. In special situations, individual factors carry heavy weight in residue management decisions. For soils with high erosion potential, a protective mantle of organic material should be left. At least the small residue material should be left on nutrient-deficient soils to add to the nutrient capital. Residue should be kept out of stream channels. In Oregon and Washington, broadcast burning of residues in heavy brush areas helps to control the brush and open up the area for planting. Mistletoe-infested seedlings should be classed as residue and destroyed as part of disease control programs. Special attention should be given to residue management in recreation and scenic areas. Large, continuous areas of logging slash should be avoided because of fire hazard. Smoke management plans should be followed. Treatments are needed when residue volume is too great, because the residue will interfere with seedling establishment and intensive management of the new stand.