By Ben Lampman, Long-term Agro-ecosystem Research (LTAR) Network
A long-term study from the University of Nebraska shows last year's weather may already be shaping this year's grasses in the Nebraska Sandhills.
The two-part study published in Rangeland Ecology & Management in 2024 and 2025, analyzed data collected from 2007 to 2023 in the semiarid Sandhills grasslands. The research was designed to provide land managers with up-to-date information to help inform grazing strategies in the Sandhills.
Researchers gathered biomass and species composition data twice each growing season at the university’s Gudmundsen Sandhills Laboratory in the study period. They measured total plant biomass and tracked the composition of cool- and warm-season grasses and forbs—or nonwoody, non-grass, leafy plants such as sunflowers. The team then analyzed the vegetation data alongside on-site weather station records.
Over time, the team documented a steady decline in both mid-June and mid-August of the proportion of warm-season grasses, alongside a rise in cool-season grasses. In general, the biomass of cool-season grasses peaks in June, and warm-season grasses’ biomass peaks in August.
They said the shift is likely linked to earlier and extended spring growing conditions driven by rising regional temperatures, particularly during the early growing season.
Researchers also observed an increase in forbs, such as lamb's quarters and annual sunflowers, following a year with severe drought. Reduced competition from grasses and increased soil nitrates after a drought creates favorable conditions for forb growth.
In addition, they found that cool-season grasses produce less biomass following a dry year, while warm-season grasses were more dependent on the current summer's rainfall.
Biquan Zhao, a postdoctoral researcher in the Department of Animal Science and in Biological Systems Engineering, said it is important to consider these trends and patterns for effective land management.
"The grassland is important for grazing, so people benefit by understanding that dynamic," he said. "If we have a warm spring, for example, we can expect an early start to the growing season."
Beyond livestock production, the Sandhills offer Nebraskans safe water, wildlife habitat, carbon sequestration, tourism opportunities and many other benefits, said Tala Awada, professor in the School of Natural Resources and associate dean in the Agricultural Research Division.
Awada said predicting how plant communities respond to grazing and environmental changes is key to identifying possible harmful tipping points and ways to protect this fragile ecosystem.
Despite the importance of these seasonal and year-to-year patterns, the study said there has been limited long-term understanding of how shifting seasonal conditions affect the Sandhills.
Maintaining a project of this scope requires sustained commitment. Zhao noted that long-term monitoring presents logistical challenges such as long-term access to remote grassland sites.
Zhao said future research could incorporate GPS tracking to pinpoint exact sampling locations and link them with satellite imagery for more precise analysis.
Ultimately, Awada said these studies are challenging and require sustained resources to bring to fruition. She said long-term grassland monitoring is important to ensure the sustainability of the Sandhills for livestock production and their many other benefits.
The study received funding from the USDA-ARS Meat Animal Research Center and had two parts: Part One | Part Two