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9 In the Special component, normal rotation age will be modified to whatever age best meets the objectives of the particular area. As an example, some ponderosa pine stands along major travel routes may be preserved 300 years or more for their attractive appearance when old. Overmature Engelmann spruce trees may be preserved alongside streams to provide shade and add to the natural beauty. On the other hand, old and young trees may be removed to open up vistas along major roads. 3. Silviculture Systems A silvicu1tural system is a well-defined process using accepted biological principles whereby a forest is grown and usually harvested, and if harvested, reproduced. Si1vicu1tural systems are often identified according to the method by which trees are harvested and the stand is reproduced. The four main systems used in the United States are: (a) selection system, (b) shelterwood system, (c) seed-tree system, and (d) the c1earcutting system. All of these silvicultura1 systems and their associated harvesting methods are biologically sound under certain forest conditions. a. In the Special component, the Selection and Shelterwood Systems will be used to enhance the key values of scenic beauty, recreation and wildlife on a continuing basis. b. In the other components, silvicultura1 systems will be prescribed depending on the timber type, slope, and stand condition to protect and enhance the key values of scenic beauty, recreation and wildlife over the long run. Recreation and scenic beauty values may be adversely affected in certain areas on a short-term basis. On slopes greater than approximately 30 percent, cable logging systems will be used. The c1earcut silviculture system or the one step removal cut of the she1terwood system is normally used with the cable system. Cable logging will result in clearcut patches about BOO feet long and 250 feet wide (about five acres in size). In the ponderosa pine type on the San Juan National Forest, there have been problems in obtaining natural reproduction. These must be overcome before silvicultural treatments that do not depend on planting can be prescribed. Historical records. for the area indicate good natural regeneration in ponderosa pine occurs only when good seed years are followed by two or more years of good moisture. This combination occurs about once every 40 years. Planting nursery grown trees has only been moderately successful to date, primarily because of competition from Gambe1 oak and other vegetation. Considerable research has been done on treatment and perpetuation of ponderosa pine in other parts of the west. More work needs to be done in applying appropriate research findings from these other areas to the San Juan in an attempt to overcome the regeneration problem. Failing in this, local research work may be required. There are two options for treating the ponderosa pine type. One is to make Group SelectionZl harvest cuts in the overmature stands and gamble that reprOduction .Can be established on the cutover areas. The other option is to make intermediate cuts~ on an Individual Tree Selection basis in immature stands and make salvage cutslV in the overmature stands. The first option may result in up to 17 thousand acres of additional nonstocked acres during the next ten years, depending upon reproduction success. The second option would not increase the number of nonstocked acres, but would increase the number of acres that would shift into the overmature (121 years plus) age group. 11 Group Selection: A silviculture system in which the canopy is opened, by group cuttings, so as to create fairly evenly distributed gaps that are enlarged by subsequent cuttings as the groups of re- generation develop; regeneration is mainly natural, though often young seedlings are planted and resultant crop more or less even-aged. BI Intermediate Cuts: Any removal of trees from a regular crop or stand between the time of its 7ormation and the harvest cutting. lV Salvage Cut: The exploitation of trees that are dead, dying or deteriorating (e.g., because over- mature or materially damaged by fire, wind, insects. fungi or other injurious agencies) before their. timber becomes worthless. <