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The mixed conifer type of southwestern Oregon is perhaps the ecologically most diverse of the forest types occurring in Oregon. The great variability in species mixture, climate, soils, and topography require careful planning of regeneration procedures if

TABLE 6 Estimated shelterwood requirements for adequate regeneration in the true fir-mountain hemlock zone. Density of residual stand indicated in square feet of basal area per acre.

.	Site Condition
Anticipated Species Dominance	Favorable	Severe
With 30 percent or more area in mineral seedbed and a seed source present, noble fir, Douglas-fir, white pine, other true fir species, and Engelmann spruce will regenerate. Without a seedbed the true firs, except noble fir, and Engelmann spruce will predominate.	80-100 ft.2	100-140 ft.2
Hemlock species and true fir, except noble fir, will predominate.	Over 100 ft.2	Over 140 ft.2

silvicultural disasters are to be averted. The difficulties of obtaining successful regeneration in this region are indicated by the high rate of regeneration failures. With proper planning and execution of silvicultural procedures, natural regeneration can become a valuable supplement to artificial regeneration. Natural regeneration can provide substantial benefits, especially at higher elevations where planting seasons are short and access is often difficult

Although numerous regeneration failures suggest that clearcutting is not a practice favorable for natural regeneration in the interior of southern Oregon because of the extremes of heat and drought common to this region, recent studies of advance regeneration of Douglas-fir and white fir suggest that harvests designed to minimize damage to residual regeneration can result in thrifty stands. In the absence of viable advance regeneration, however, clearcutting is not recommended for natural regeneration in this area.

Shelterwood cutting is probably the most promising method where topography and conditions of stands permit its use. Little information exists concerning required density of the shelterwood. Basal areas of at least 80 square feet per acre should probably be maintained in the overstory until regeneration is established. This figure may have to be revised upward considerably depending upon species mixture and site. If stands are heavily infested with dwarf mistletoe, shelterwood can still be used, but the residual overstory will have to be removed as soon as regeneration has become established.

Selection cutting appears to be a less desirable method of harvesting because few stands are truly all-aged. It may be employed, however, where mixtures of species with different degrees of shale tolerance occur and an all-age structure of stands is wanted.

The western Siskiyou Mountains and the southern Oregon Coast Range have a more favorable climate than the interior portions, and here natural regeneration can be obtained with clearcutting. Natural regeneration sometimes is more abundant on clearcuts than on partially cut areas. In the mountains where site index is high for Douglas-fir, Douglas-fir is an aggressive competitor and is being favored by clearcutting. Other more shade-tolerant species such as cedars, western hemlock, and true firs appear to be favored by partial cuts on such sites. On the coastal terraces where site index is much lower for Douglas-fir than in the mountains, cedars and western hemlock seem to have a competitive advantage even on clearcuts. Shelterwood cutting in old-growth stands is undesirable for still another reason. Such stands are highly vulnerable to blowdown if opened up by partial cutting.

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