Ranchers need to provide alternative livestock feeds when herbaceous forages become limiting in summer. We determined foliar yield components and nutritive value (in vitro digestibility [IVDMD], total nonstructural carbohydrate [TNC], N, robinin, and mimosine) of transplanted Robinia pseudoacacia (black locust) and Albizia julibrissin (mimosa) trees pollarded at 50 cm in Arkansas, USA. Black locust exceeded mimosa for every yield component (foliage mass tree^-1, leaves shoot^-1, shoots tree^-1, shoot mass tree^-1, basal area, and biomass tree^-1) except mass leaf^-1. Projected foliar yields were 1900 and 1600 kg foliage ha^-1 for black locust and mimosa, respectively, assuming a population of 12300 trees ha^-1. Mimosa foliage had greater IVDMD, TNC, and N digestibility than black locust. Mimosa foliage exceeded the nutritional N requirements of growing cattle (Bos taurus) and goats (Capra hircus), but protein supplementation would be needed for growing goats grazing black locust foliage. Concentrations of robinin and mimosine were below detectable limits in black locust and mimosa, respectively. The extract of black locust bark, but not foliage, was toxic to bioassayed monkey (Cercopithecus aethiops) cells. Either black locust or mimosa could provide moderate quantities of high quality, rotationally grazed forage for cattle or goats during summer months when herbaceous forage may in short supply