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~ Management Situation by Revision Topic ?;?~ Engelmann spruce and subalpine fir stands have a higher percentage of ~ngelmann spruce. Engelmann spruce's life span averages 350 to 400 years with 500 plus year old trees possible. On this Forest, there are very few stands that exceed 335 years old (Table 11I-4). Trees over 250 years are not uncommon for subalpine fir, but generally most are in the 150 to 200 year range. This is because Englemann spruce is susceptible to heart rot and generally dies at an earlier age. . The subalpine zone is typically a dense, deep green expanse of forest. It is only broken by drainages, outCfOpS of fock, Of fire disturbance. Aspen and lodgepole are the major sera I species in this zone due primarily to past natural fire disturbance. South-facing slopes, which are hotter and drier environments, will have stands of Thurber fescue grassland. Open stands of bristlecone and limber pine can also be found on rocky, windswept slopes. The spruceffir forest receives the most precipitation of all the forest types on the RGNF. A great quantity of snow falls in this zone, which accumulates all winter and lasts into early summer. The trees protect the snow from melting or blowing away. Because of this, there are plants adapted to high amounts of moisture and a cold environment. Rocky Mountain whortleberry typically forms dense mats and is adapted to the cool, moist environment under Engelmann spruce. Some very delicate, fragrant flowers, like wood nymph, can be found in the sprucelfir forest. Crane (1882), Stokes and Dieterich (1980), and Dr. Phil Omi of Colorado State University (personal communication January 8, 1992 with Dean Erhard) suggest that the natural fire frequency may have been 100 to 500 years in this zone. Historically, there may have been wide deviation from this average fire frequency. The upper edge of the subalpine zone is called timberline. This is where the transition to the alpine zone begins. The growing season is short and the climate is extreme. Winter winds and temperatures are severe. Because of this, the trees at timbefline are at their tolerance fOf existence and are usually stunted and twisted. Timberline varies by topography; it will be higher on southern exposures or in sheltered draws, and lower on northern exposures or windswept ridges. Montane Zone Douglas-fir and ponderosa pine are the dominant and characteristic trees of the montane zone. Pondefosa pine generally grows in scattered, park-like stands with abundant light reaching the ground surface. Ponderosa pine is shade intolerant, so typically there can be abundant grass growth of Arizona fescue and mountain muhly in the understory. Potentially some ponderosa pine stands with trees over 450 years old may exist, but a maximum of 300 to 350 years is more common for the oldest stands in the Rocky Mountain Region. Ponderosa pine stands on the RGNF are usually less than 215 years old (Table 11I-4). Historically, frequent, low-intensity fires removed competing understory vegetation and down material. This resulted in irregular-shaped stands with uneven-aged groups of trees varying in size from a few trees to several acres. On north-facing slopes, in ravines, and with elevation gain, Douglas-fir intermingles with ponderosa pine and eventually feplaces it in this zone. Arizona fescue and mountain muhly dominate areas that are too dry for tree growth. Rocky slopes and dry, gravelly afeas will often support limber pine and bristlecone pine -- trees usually found in open stands in the upper montane and subalpine zones. 11I-21 C"~2434