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Impacts of Grazing on RWB Wetland Seed Production

Research involved counting seeds available for shorebird forage. Photo by D. Varner

Research involved counting seeds available for waterfowl forage. Photo by H. Hillhouse

(Posted 5/8/18) Since 2012, the Rainwater Basin Joint Venture has helped fund research focused on better understanding the potential for and the impacts of cattle grazing in wetlands. The first project (2012-2014) focused on the impacts of cattle grazing on seed production in Rainwater Basin wetlands. An article based on the research was accepted recently for publication by the journal, Wetlands. Titled “Timing and Protocols for Estimating Seed Production in Moist-Soil and Phalaris arundinacea Dominated Areas in Rainwater Basin Wetlands,” the article by H. L. Hillhouse, L. Zilli and B. E. Anderson describes the timing of seed production within Rainwater Basin wetlands.

 

Developing estimates of seed production is important for understanding how effective management strategies are at producing the seeds that are critically needed by spring migratory waterfowl. Traditionally, plant-based seed production estimates are conducted once a year, at the time of estimated peak seed production, which provides a one-time snapshot of the wetland seed production. This project utilized the traditional one-time sampling, and also collected seed production samples throughout the growing season.

The dual sampling technique allowed an understanding of how seed production is distributed throughout the growing season and how the timing of sampling could affect estimates of seed production. With this knowledge, management activities might be more accurately timed to better achieve desired results. For example, to increase seed available for waterfowl, managers could avoid active management, such as grazing or mowing, when seed production by annual plants is most vigorous. Or, to control undesirable species such as reed canarygrass, managers carry out active management timed to disrupt seed production.

The second part of the 2012-2014 project focused directly on the impacts that cattle grazing had on seed production and reed canarygrass biomass in Rainwater Basin wetlands. As is common in the area, grazing was initiated in the spring, and was excluded from individual plots by installation of grazing exclosures at specific times throughout the growing season. A manuscript reporting the results of this work is currently under consideration for publication.

Exclosures allowed researchers to examine ungrazed plants. Photo by D. Varner.

Exclosures allowed researchers to examine ungrazed plants. Photo by H. Hillhouse

The results showed that grazing during the growing season tended to result in reduced seed production in areas with moist-soil vegetation, and the longer the grazing continued, the greater the reduction in seed production. In contrast, although grazing longer in areas dominated by reed canarygrass did result in reduced biomass, it had minimal impacts on seed production, probably because most reed canarygrass seed production occurred very early in the grazing season and seed production by other species was limited. This suggests that managers or landowners managing wetlands to promote seed production should be cautious about grazing during the growing season, and should consider restricting cattle to areas with reed canarygrass during the growing season.

Although the 2012-2014 project raised some concerns about grazing impacts in wetlands, that’s certainly not the whole story with respect to grazing in wetlands. Research used in developing the Rainwater Basin Joint Venture’s Best Management Practices (BMP) document was in progress at the same time as the final analysis for the 2012-2014 grazing impacts study, and taking both of those documents into consideration, a different picture emerges. The research that was the basis for the BMP, conducted by the RWBJV and its partners, found that grazing is important for reducing the cover of invasive species and it can, under the right circumstances, promote more favorable (i.e., native) plant communities. Further research is needed to better understand many of these relationships, and work is already underway to help us better understand the complexities. Among the challenges associated with grazing wetlands is lack of information about the quantity and quality of forage available at different times of the year. That research is currently underway. The results will be released in the form of a Nebraska Extension document, most likely during the summer of 2018.