ECONOMIC-ASSESSMENT OF UNGULATE HERBIVORY IN COMMERCIAL FORESTS OF EASTERN OREGON AND WASHINGTON, USA

Four forest stands in eastern Washington and Oregon, USA, containing e xclosures to prevent or impede ungulate herbivory, were modeled to for ecast timber yields and soil expectation values (SEVs) at harvest. Con trasts of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) growth and yield inside and outside exclosures show that ungulate herbivory may e ither promote or depress tree volume growth. Projected income from sta nds with more intensive stocking management and with inclusion of regu lated livestock herbivory was higher than that of less intensively man aged stands without livestock for scenarios with projected rising stum page price levels for 2040. Under an assumption of future stumpage pri ces held constant at 1990 levels, the reverse was true. Ungulate herbi vory plus planted stock and prescribed fire in site preparation provid ed the highest stand value at two sites. Sites without prescribed fire fared better when fenced to prevent livestock or big game herbivory. The results illustrate that ungulate herbivory alone is not the determ inant factor of the economic yield of stands, but ungulate herbivory c an have substantial impact on site productivity when used in conjuncti on with prescribed fire, stocking control, and species selection.