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These climax or sub-climax ponderosa pine communities (e.g., the ponderosa pine/Arizona <br /> fescue, ponderosa pine-juniper/blue grama, and ponderosa pine/mountain muhly plant <br /> associations) have no early-seral tree species available for management.Therefore, large clear <br /> cuts or fire-caused openings will support an extremely persistent seral stage of grasses, forbs, <br /> and shrubs. Conifer forest will eventually replace these non-forest stages, but hundreds of <br /> years may pass first! <br /> Old-growth ponderosa pine/bunchgrass stands tend to be uneven-aged with a groupy or <br /> clumpy structure. This condition is a result of wildfire patterns, previous selective timber <br /> harvest, or episodes of sporadic or intermittent natural regeneration.Tree regeneration is <br /> sporadic because optimal seedbed, seed sup-ply, and germination conditions seldom coincide <br /> (Cooper 1960, White 1985). <br /> Douglas-fir Plant Communities <br /> Many stands in the upper montane zone have a ponderosa pine overstory and a Douglas-fir or <br /> white fir understory. A long period of effective fire suppression has allowed the shade-tolerant <br /> Douglas-fir to get established under the shade-intolerant ponderosa pine.The magnitude of <br /> this successional progression is demonstrated by comparing the last two forest inventories for <br /> the Pike and San Isabel National Forests—Douglas-fir ranked third of the five major forest types <br /> in 1958; by 1980, its ranking had improved to first! <br /> Douglas-fir has more ecological amplitude than any other tree species of the Pike and San <br /> Isabel National Forests,forming ecotones with foothills (pinyon-juniper), other montane <br /> (ponderosa pine), subalpine (spruce-fir), and non-forest plant communities. This characteristic <br /> has silvicultural implications because all 15 species with considerable amplitude, regardless of <br /> lifeform (tree, shrub, or herb),tend to have a broad genetic base, which provides considerable <br /> potential for genetic improvement. <br /> Douglas-fir's affinity for steep, north-facing slopes often results in 'butt sweep' or 'pistol butts' <br /> as soil creep tips trees away from a vertical orientation. Since conifers are geotropic,they will <br /> try to regain a vertical orientation as quickly as possible, and this response is what causes a <br /> sweep or pistol butt to form. Quaking aspen has misshapen boles too, but the cause is generally <br /> from snow bend or rotational slumping more often than from soil creep. <br /> Shrubs are dominant in the undergrowth of most Douglas-fir forests. Highly productive sites <br /> often feature mountain ninebark, mountain snowberry, cliff Jamesia, Rocky Mountain maple, or <br /> myrtle pachistima in the undergrowth plant union. Sites of intermediate productivity may have <br /> creeping mahonia or russet buffaloberry as common shrubs, although some examples of the <br /> Douglas-fir/creeping mahonia plant association are reasonably productive. <br />