Recovery Plan for the Northern Spotted Owl - DRAFT

log and snag density was likely lower than at present because of frequent fires.At age 250+years, the structure of this stand may meet the old-growth criteria,having developed in a very different way than wet site Douglas-fir stands.Such stands usually will be intermixed with others that have experienced astand-replacement event during one of the intermediate fires, so that the landscapeis more patchy than in wetter Douglas-fir forests.Along the coast, redwood forest exists along a fog belt and may extend upvalleys with slopes dominated by Douglas-fir/hardwood forests. Veirs (1980)suggests fire return intervals in the northern redwood forests at 50 to 500years, but other investigators working to the south suggest more frequent firereturn intervals: 31 years at Humboldt Redwoods State Park (Stuart 1987), 20to 29 years at Salt Point (Finney and Martin 1989), and 22 to 27 years at MuirWoods (Jacobs et al. 1985). The pattern of fairly frequent presettlement fireand moderate fire severity apparently existed almost to the coast in areassouth of Eureka.WindInsectsDiseasesWind appears to be an important disturbance factor primarily along the coastin the Klamath subregion. In coastal Humboldt County, average timber lossesfrom windthrow exceeded the combined losses from fire, insects, and diseases(Oswald 1968), and Zinke (1988) noted wind-flagging along the coastal rivers inthe redwood belt. Further inland, wind is not mentioned in a discussion ofDouglas-fir/hardwood and mixed hardwood forests (Thornburgh 1982, Sawyeret al. 1988). Whittaker (1960), in his extensive monograph on these forests,does not include discussion of wind, although he recognizes the importance offire. However, in ridgeline areas within the White Fir Zone of the SiskiyouMountains, wind was implied to be an important disturbance factor (Agee1991b).Insects have historically caused disturbances in this subregion in associationwith fire. In natural forests insect populations were probably higher thanthose in the West Cascades subregion because of higher stress. However,there is a great deal of ecosystem variability across the landscape and themixed species nature of the forests may have kept defoliator and bark beetlepopulations lower than anticipated. There is also a great deal of variability inthe fire regime in this subregion.Root diseases were probably important agents of disturbance in this subregion.Armillaria probably killed stressed pines but wide tree spacing may havereduced its rate of spread through the soil. Pheffinus weirff and Heterobasidionannosum incidences would have been related to development of susceptibleDouglas-fir and true firs. H. annosurn, although capable of causing root rot ofpines, probably only attacked the most stressed individuals.Dwarf mistletoe infections would have been lower in areas with frequent firesand slightly higher in areas with lower fire frequency. Natural rust populations,especially western gall rust, were lower and of course white pine blisterrust was absent. Foliage diseases also would have been low. Butt rot and boledecay would have been important disturbance agents in older forests.456