PONDEROSA PINE AND UNDERSTORY GROWTH FOLLOWING WESTERN JUNIPER REMOVAL

Recent expansions of western juniper are of great concern to land managers throughout the drier regions of the Pacific Northwest. While removal of western juniper has been found to significantly increase understory plant biomass, little information is available on the effect of western juniper removal on the tree species. This research evaluated response of understory plant biomass and cover, and ponderosa pine growth following removal of western juniper. Study sites were established in the ponderosa pine/western juniper ecotone of central Oregon. Total understory plant biomass and cover increased in response to western juniper removal. However, thinning ponderosa pine and leaving western juniper reduced biomass and cover of understory groups below control levels. Ponderosa pine under 5 cm DBH (Diameter at Breast Height) had greater percent growth in the control, where no trees were removed, than trees in treatments where competing trees were removed. Removal of western juniper appears to benefit understory vegetation, but may depress growth of small ponderosa pine trees for the first few years following tree removal.