An experiment was established in 1961 to determine the influence of bearmat (Chamaebatia foliolosa Benth.) competition on ponderosa pine (Pinus ponderosa Laws.) survival and growth. Ponderosa pine seedlings were planted in bearmat which was: (A) untreated, (B) sprayed with a mixture of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and (C) eliminated by a combination of herbicide, clipping sprouts, and trenching to prevent root and rhizome invasion. Ponderosa pine survival after 19 yr averaged 9%, 66%, and 90%, respectively, for the three treatments. Tree height after 19 yr averaged 1.6, 1.9, and 5.7 m for treatments A, B, and C, respectively. Soil moisture use was initially less on the herbicide-treated than on the untreated plots, but bearmat quickly sprouted after application to compete with the pine seedlings for moisture. After 19 yr the bearmat was more dense and appeared to be more vigorous on the sprayed plots than on those receiving no treatment. We estimate that 75% reduction in net wood production could result after 50 yr on this site from bearmat competition.
