Increasing bitterbrush nutrient quality with 2,4-D, mowing, and burning in southcentral Wyoming.

Effects of burning, mowing, and 2,4-D on antelope bitterbrush (Purshia tridentata Pursh.) nutrient contents were evaluated in southcentral Wyoming. During the first growing season following treatments, spraying of 2,4-D increased bitterbrush nitrogen (N) contents from 1.5 to 1.9%, phosphorus (P) from 0.12 to 0.15%, and in vitro digestible dry matter (IVDDM) from 44.1 to 48.4%. Mowing increased N from 1.5 to 1.7%, P from 0.12 to 0.16%, and IVDDM from 44.1 to 46.1%. Burning increased N from 1.4 to 1.9%, P from 0.11 to 0.17%, ash from 3.7 to 5.3%, and IVDDM from 47.4 to 51.0%, and decreased gross energy from 4,640 to 4,380 kcal/g. There were no differences in N and IVDDM contents among treatments at the end of the second growing season, but P content was still greater in mowed bitterbrush regrowth than on untreated bitterbrush. Ash contents were not affected by treatments, but were higher in summer (3.9%) than in winter (2.4%). Gross energy contents varied only 5 to 10% among all treatments and seasons. Correlation coefficients between N, P, ash, and IVDDM contents varied from +0.54 to +0.76, and all of these nutrients were negatively correlated with gross energy. Bitterbrush nutrient contents can be increased by shrub management practices, but short-term responses require that small portions of the total area be treated annually in a rotational shrub management program.