Between 1951 and 1975, range forage interrelationships and food habits of black-tailed deer and domestic sheep were studied on the Hopland Field Station of the University of California. Other nearby areas with contrasting covertypes were compared.

Data were collected on percent of volume and frequency of occurrence of forage plant species in samples of rumen contents taken from animals collected on the various range types. Browse preferences were compared in a series of “cafeteria” feeding trials with penned animals, and correlations with phosphorus and protein content were tested.

Little significant forage competition between deer and sheep was found, although chaparral browse was limited. In general, diets of these animals were complementary, with deer relying primarily on browse, and sheep on grass. In other range types, deer had a wide latitude in their dietary patterns, depending upon availability of preferred forage species.

In browse preference feeding trials, where grasses were excluded from the diet of sheep, both deer and sheep tended to select or reject the same browse species; their palatability did not correlate with phosphorus or protein content when measured on a dry weight basis. However, deer preference ranking correlated significantly with plant protein content determined on a green weight basis.

Relationships between forage consumption and forage production on the field station were also evaluated. Production of all forage classes except chaparral browse exceeded estimated consumption by wide margins. However, combined browsing by sheep and deer substantially reduced oak seedlings and will eventually lower browse, mast, and lichen production. Sheep grazing on Hopland Field Station maintains grassland in a productive seral stage, which raises the carrying capacity for deer over that which would exist without livestock.