Grassland forage production under five different grazing management schemes (on natural areas and areas grazed by domestic livestock and wildlife) was compared after 20 years of treatment in the Edwards Plateau region of Texas, southwest USA.
The grazing regimes (initiated in 1949) were:
1) continuous heavy grazing with cattle, sheep and goats at 48 AU (animal units)/section (640 acres; 259 ha);
2) continuous light grazing with cattle, sheep and goats at 16 AU/section;
3) no livestock grazing, deer grazing only (livestock exclosure);
4) no livestock or deer grazing (deer-livestock exclosure);
5) moderately grazed 4-pasture deferred rotation system stocked with cattle, sheep and goats.
Forage yields were estimated by clipping 20 (9.6 ft²; 0.89 m²) plots in each pasture in autumn, air drying and weighing. Samples were divided into four groups: decreasers (i.e. species which decrease under excessive grazing pressure); increasers and others; forbs, and weeds.
Forage yields (live plants and litter) were lower on a natural area than under deferred rotation or light grazing. More decreaser plants were found in deferred rotation pastures. Forbs and weeds on the heavily grazed pasture were of little forage value, and were comprised 90% bitterweed Hymenoxys odorata (a native herb, poisonous to livestock, especially sheep).
Forage yields (lb/acre) by grazing regime (1-5) were: 1 - 958; 2 - 1,988; 3 - 1,795; 4 - 1,422; and 5 - 2,195.
Overall, the 4-pasture deferred rotation system allowed development of a highly productive herbaceous vegetation community and was considered to produce (maintain or improve) the most desirable livestock and wildlife habitat on the study grasslands.