Plant community response to changes in grazing and precipitation timing in the Shortgrass Steppe

Background/Question/Methods

Changes in climate have caused precipitation events to switch from smaller, more frequent events to larger, less frequent events in the Shortgrass Steppe. Following these large, late-season events, there is a green-up of the plant community. Land managers work to make management decisions that allow for flexibility in case of a drought year. This includes switching from traditional, season-long continuous grazing system to a rotational one that uses short-duration, high intensity grazing style. This style means managers can move livestock based on the quality and quantity of forage available in each pasture, giving the plant community time to regrow following the disturbance. The goal of this study was to 1) determine if differences in grazing timing allow for greater regrowth of plants compared to ungrazed areas, and 2) assess growth of plant communities following a large, late season precipitation event. To answer these questions grazing cages were established in six pastures in a rotational grazing system. For each pasture, half the cages were removed for grazing, then replaced after a set time period. Two of the pastures received additional moisture treatments to simulate a late season storm event. Pin frame measurements were taken to estimate biomass throughout the growing season.

Results/Conclusions

Initial analyses show that regrowth of plants is greater when grazing occurs early in the growing season versus later. We also found that the effects of late season rainfall showed stronger effects on forage quality, causing greening of vegetation, than on forage quantity. We observed an interaction between grazing and increased rainfall, such that plots that were grazed showed a larger plant growth response under increased precipitation than plots that were not grazed. These findings highlight the need for managers implementing rotational grazing systems to switch timing of grazing events from year to year, and that attention should be paid to late season rainfall events due to their capacity for extending forage greenness.