Research helping land managers weather drought on mixed-grass prairies

Just outside Badlands National Park in west central South Dakota, the Buffalo Gap National Grassland offers hiking, biking, and camping among rugged sandstone — as well as acres of forage for livestock and habitat for plant and animal species found only in the Great Plains. Increased periods of drought are impacting the productivity of the mixed-grass prairies in this region and prompted range managers to ask researchers to help them find ways to adapt and maintain long-term health of the plants that livestock and wildlife depend on. 

Jacqueline Ott, research ecologist with the USDA Forest Service Rocky Mountain Research Station, is partnering with Dr. Amy Symstad from the U.S. Geological Survey and Dr. Troy Ocheltree at Colorado State University to embark on a four-year study of this grassland’s response to different drought scenarios. Scientists aim to create tailored tools to help range and livestock managers adapt to droughts by knowing when and how to adjust grazing practices in order to maintain productivity and the unique biodiversity of mixed-grass prairies long into the future.

The Buffalo Gap National Grassland accounts for “some of the most intact grasslands in the world” explains Ott. 

The mixed-grass prairies like those of the Buffalo Gap support some of the largest cattle production in the country. These prairies and their forage productivity are shaped by a highly variable climate, fire, and grazing. The timing and intensity of drought influences the productivity of grasses and other plants, but the exact ways climate patterns influence plant development and drought recovery within these mixed-grass prairies isn't fully understood. It turns out some of the answers lie below the ground and how different types of grasses "breathe" and grow.

The experiment focuses on the different responses of cool-season grasses and warm-season grasses, which fill different roles within the Great Plains. Although all grasses are capable of growth throughout the growing season from March through October, cool-season grasses tend to grow more during the cooler periods of the season (spring and fall) while warm-season grasses tend to grow more during the warmer periods (summer and early fall).

Depending on the timing of a drought, these two groups of grasses may be affected differently, so much so that the overall forage production during and after drought will depend on which types of grasses are in a pasture.

To provide insight, the research team installed 46 rainout shelters to simulate drought in a more controlled experimental way. These partial roofs keep half of all rainfall off covered plots. The team is also simulating grazing and trampling by livestock in the experimental plots to evaluate the effects of two potential grazing strategies during and after a drought. To do this, Ott and her team first use lawnmowers to remove forage, then guide horses across the experimental plots to approximate the effects of cattle hooves on the plants and soil surface.

Throughout the growing season, the team has returned to the field to measure the response of the grasses and other plants to the simulated drought and grazing scenarios. The research team has been measuring plant community composition, forage productivity, belowground bud production, soil moisture, and stages of grass developmental.

Ott is looking closely at the impacts of partial-season and season-long droughts on the grasses using indicators like delays in plant development, the number of below ground buds produced, which is the primary way these grasses regrow following drought, and changes in stem recruitment. 

“Our job as researchers is to provide the best available science for both public and private land managers,” says Ott. “Land managers often have to make difficult decisions on whether to maintain their herd size during drought conditions. Through this research, we can provide managers additional confidence in how their grasslands will recover forage productivity potential following drought.”

This is also an opportunity to encourage and help "grow" new scientists. Interns from the Chicago Botanic Gardens are assisting with the ongoing field studies led by Ott and Symstad. Students from Colorado State University, under guidance from Ocheltree, will conduct greenhouse studies to examine physiological responses of dominant grass species to drought. 

The Rocky Mountain Research Station filmed some of the work last spring and talked with scientists about what inspired this collaboration, the design of the field experiment, and how the research will help managers navigate drought conditions. Find out what the 2024 growing season had in store for them, providing an even greater variety of drought treatments than they had planned!