Sclerophyll shrubs such as Arctostaphyllos viscida Parry (Ericaceae; whiteleaf manzanita) are often considered obstacles to afforestation. The establishment of conifer plantations in southwest Oregon presents challenging problems for initial seedling survival and subsequent growth. This region is characterized by hot dry summers, cool moist winters, and rocky, shallow soils at low elevations. The growth of competing hardwoods within conifer plantations creates the traditional problem of undesirable competition for the silviculturist. Accumulation of manzanita biomass also contributes heavily to fire hazard while at the same time providing biomass of potential value as biofuel. This study describes productivity of whiteleaf manzanita stands of varying density growing within the confines of Pinus ponderosa Dougl. ex C. Lawson var. ponderosa (Pinaceae; ponderosa pine) plantations of the same age on poor sites. We explore the ability of this shrub to generate biomass as a potential energy source. Growth prediction equations are for height, basal diameter, biomass per individual, and biomass per hectare by stand density. The accumulated biomass after 14 yr of growth ranges around 43 metric tons/ha, and represents a strong negative influence on the supposed productivity of interplanted pines of the same age. Energy content of biomass amounts to an accumulation rate of 1.6 × 106 megajoules/ha/yr on such sites, indicating a large biofuel potential by age 14 or more. Harvesting the manzanita will also provide a potential benefit to productivity of the pines.
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Vol. 56 • No. 4