. Estimating productivity on sites with a low stocking capacity. Forests and forestry Mensuration; Forest site quality. of how well the productive potential of the site is being utilized. However, stock- ing estimates obtained in this manner are again only valid for areas that fall within the range of conditions sampled to develop the stocking standard. Areas with patchy stands, nonforest inclusions, and sparse stands on the forest fringe are situations that evidently were not sampled by the makers of yield tables. Meyer's (1961) ponderosa pine (Pinus ponderosa}— yield table is based on a samp
. Estimating productivity on sites with a low stocking capacity. Forests and forestry Mensuration; Forest site quality. of how well the productive potential of the site is being utilized. However, stock- ing estimates obtained in this manner are again only valid for areas that fall within the range of conditions sampled to develop the stocking standard. Areas with patchy stands, nonforest inclusions, and sparse stands on the forest fringe are situations that evidently were not sampled by the makers of yield tables. Meyer's (1961) ponderosa pine (Pinus ponderosa}— yield table is based on a sample which excluded all plots with a stand density index of less than 250 (250 trees per acre when quadratic mean diam- eter is 10 inches). Data collected by q/ Hall—' in the Blue Mountains of eastern Oregon suggest that substantial areas of ponderosa pine type will not support this many trees. Data gathered for this study suggest a similar situation in California. Stock- ing capacity also is obviously limited, possibly because of soil toxicity, in stands of Jeffrey pine (Pinus jeffreyi) growing on serpentine (peridotite and serpentinite soils) in southern Oregon and northern California (fig. 3). We have observed similar restrictions on stand density in stands of other species growing on dry sites, and Wikstrom and Hutchison (1971) report the condition to be widespread in the intermountain and Rocky Mountain regions. The assumption, implicit in most yield tables, that stocking capacity is constant for a given site index has been questioned by several European authors. Assmann (1959) found substantial varia- tion in Norway spruce (Pioea exoelsa) 2/ — Names of trees according to Little (1953). —I Frederick C. Hall, unpublished data on file at the Regional Office, U. S. Forest Service, Portland, Oreg. yields that he was unable to explain by site index. Bavarian spruce yield tables (Assmann and Franz 1965) reflect these findings by dividing each site index class into three pr
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