WSP10790 - Laserfiche WebLink

Home Browse Search

Management Situation by Revision Topic l Douglas~fir is more shade tolerant than the pines and aspen, but less tolerant than Engelmann spruce or subalpine fir. Since Douglas-fir can grow under itself, old stands of pure Douglas-fir are usually uneven-aged rather than single-aged. These pure stands originated from fire, but can resist subsequent low-intensity fires. This is because Douglas-fir has rapid growth, a thick corky bark, and the ability to form adventitious roots (roots produced on stems or various types of leaves). Older Douglas-fir stands are rarely more than 400 years old, although some may potentially reach an age of 700 years if stand-replacing fires are excluded. Douglas-fir stands on this Forest are usually Jess than 335 years old (Table 1/1-4). ,. White fir is an important component in the upper elevations of the montane zone. White fir is more shade tolerant than Douglas-fir, so in time it can become a prominent part of the community. This portion of the montane zone is sometimes referred to as the mixed conifer type. Historically, natural fires have probably been important in thinning or removing white fir. Douglas-fir is much more resistant to fire than white fir. Two important seral community species are aspen and lodgepole pine. Aspen generally grows on sites that are moister than sites that support lodgepole pine. Aspen and lodgepole pine can replace ponderosa pine arid Douglas-fir forests where the latter have been removed through disturbance (fire, insects, disease, windstorms, logging, or other disturbance). Sometimes, if a burn is severe and large enough, aspen or lodgepole pine can become a climax community. Essentially, a burn under these conditions removes the seed source and makes invasion by ponderosa pine and Douglas-fir extremely slow. Opinions vary, but aspen and/or lodgepole pine in these conditions has been termed a 'subclimax' community because succession has been interrupted for an extended period. Both species can be seral dominants in the montane zone up through the subalpine zone. ~ Aspen is more shade intolerant than lodgepole pine. Most aspen regeneration is by sprouting or suckering, rather than by seed. Aspen stands can reach an age of 160 years plus, but the average life span may be 125 years or less. On this Forest, 73 percent of the aspen stands are between 66 and 125 years old (Table 1/1-4). lodgepole pine's occurrence on this Forest represents the southern geographic range of the species. Older lodgepole pine stands that are 350 to 400 years old can exist, but this is uncommon. The average life span of lodgepole pine is probably closer to 250 years or less because of past stand-replacing disturbances such as fire. lodgepole pine stands on this Forest are generally less than 275 years old (Tilble 111-4). Crane (1882), Wright (1990), Stokes and Dieterich (1980), and Dr. Phil Omi of Colorado State University (personal communication January 8, 1992 with Dean Erhard) suggest from other research done in the West that the natural fire frequency may have been as follows: 5 to 20 years in dry ponderosa pine stands, 7 to 25 years in wet ponderosa pine stands, 10 to 50 years in dry mixed-conifer stands, and 30 to 150 years in wet mixed-conifer stands. The frequent, low-intensity fires that were common in the ponderosa pine type, has generally been stopped. This may be allowing Douglas-fir to establish itself and fncrease its range at lower elevations in this zone. There also may be a higher probability of large, stand-replacing fires now. \ Foothill Zone The foothill zone is that area where the San luis Valley meets the base of the mountain ranges up to the point where the first forest is encountered -- just below the ponderosa pine 111-22 t'~2435