Tallgrass prairie response to grazing system and stocking rate.

Abstract

Grazing system and stocking rate effects on standing crop of species and relative species composition of tallgrass prairies in north-central Oklahoma were evaluated from 1989 to 1993. Twelve experimental units, consisting of pastures dominated by big bluestem [Andropogon gerardii Vitman], little bluestem [Schizachyrium scoparium (Michx.) Nash], and indiangrass [Sorghastrum nutans (L.) Nash], were arranged in a completely randomized design with either a short duration rotation or continuous grazing system and stocking rates ranging from 51.5 animal-unit-days/ha (AUD/ha) to 89.8 AUD/ha. Yearling steers grazed the pastures from late April to late September. Cumulative precipitation was above average during the study period. Continuous and rotation grazing affected the major herbage components similarly over time. Standing crop of all major herbage components declined as stocking rate increased. The standing crop of the major herbage components also declined from the first to the last year of the study. The decrease in standing crop of big bluestem, indiangrass and forbs over years was greatest at lighter stocking rates. Relative composition of switchgrass [Panicum virgatum L.] increased at the lower stocking rates over time in both grazing systems. The relationship between shortgrasses and stocking rate was different between grazing systems at the start of the study but became similar between grazing systems over time. After 5 years, short-grasses were positively related to stocking rate under both grazing systems. Favorable growing conditions and the high seral state of the vegetation in the experimental pastures may have tempered the response to grazing treatments.