Recovery Plan for the Northern Spotted Owl - DRAFT

V. Forest Protection in theEast Cascades SubregionA. The Natural History of DisturbanceFireHistorical fire return intervals in the East Cascades subregion tend to beshortest in areas lower in elevation than what appears to be prime owl habitat.Moving from the sage steppe to ponderosa pine forests, neither of which isprime owl habitat, presettlement fire return intervals may be as low as 5 to 10years (Bork 1985) in low severity fire regimes. As elevation increases, a moremixed conifer forest emerges, grading from the Douglas-fir series to the grandfir series of plant associations. Douglas-fir and ponderosa pine are dominantat the lower elevations and at higher elevations on ridges, while western larch,grand fir, and other conifers are found in addition on the more mesic or higherelevation sites (Sudworth 1908).Stand replacement fires are not the most common fire severity that occurred inthe Douglas-fir and grand fir series of plant associations (Keane et al. 1990).However, higher intensity fires are an important process for natural standregeneration of western larch, lodgepole pine, and Douglas-fir, and haveoccurred in these areas at centuries-long intervals (Antos and Habeck 1981).Many intermediate fires of lower intensity and severity occur at a more frequentinterval. In Montana, on a grand fir habitat type, the intermediateinterval was about 17 years (Arno 1976). In the eastern Washington Cascadesand Okanogan Highlands, the intermediate fire interval was estimated at 22years (Finch 1984), with a range of 12 to 52 years. Fires of low to moderateseverity are the most common types of severity in the moderate severity fireregime.Unusual stand conditions created by a long fire-free interval or severe fireweather can result in a crown fire. Fuel conditions also can affect the probabilityof crown fire behavior. Pole-sized, heavily stocked stands have a high crownfire potential (Davis et al. 1980). If a young stand survives an initial light burn,perhaps due to its burning under average to moist weather conditions, subsequentunderbums act as a negative feedback mechanism for crown fires byreducing fuels that might encourage crown fire spread. A long interval betweenunderbums allows a tall understory to develop, which has a higher probabilityof crowning (Davis et al. 1980).The successional dynamics of forests in the East Cascades subregion dependon the intensity of the fire as well as the species composition and structure ofthe vegetation at the time of the fire. Low intensity surface fires encouragewestern larch and ponderosa pine canopy dominance (Arno et al. 1985), asthey are fire resisters. Their thick bark insulates the cambium against damagebetter than any of their associates, and in mature stands they are usually thetaller trees, which helps them avoid crown scorch. The deciduous habit oflarch may make crown scorch less important, especially for late season fires(Davis et al. 1980). Peterson and Ryan (1986) modeled the relative survival of amixed conifer stand after a fire under moderate fuel moisture conditions with ascorch height of 30 feet. Mature western larch and ponderosa pine suffered nomortality in the simulation, while the basal area of other species, includingDouglas-fir, declined 75 to 100 percent. After such fires, western larch radial463