Assessing Impacts of Grazing Management on Pollinator Conservation in Rangeland

View the project final report

Commodities

• Animals: bees, bovine

Practices

• Animal Production: grazing management
• Crop Production: pollinator habitat, pollinator health

The purpose of this project is to quantify the contributions to pollinator conservation of different grazing management strategies. Pollinators are critical for healthy rangelands. They enable production of food for both people and livestock, and help maintain healthy water and soil (Black et al. 2011). While bees are the most important pollinators in many grasslands, other insects including beetles, flies, butterflies, and moths make significant contributions (Hanberry et al. 2021; Lichtenberg et al. 2024). Rangelands cover almost a third of the US land area with largely natural land (Havstad et al. 2007). Thus, they have strong potential to support pollinators by providing critical food (e.g., pollen, nectar, larval host plants) and shelter (e.g., bare ground for ground nesting species, woody cavities, pithy stems) habitat. Indeed, state and national initiatives target grassland management as critical for pollinator conservation (e.g., Pollinator Health Task Force 2015; USDA 2021). However, extensive overgrazing, and conversion to row crops or developed areas, have degraded rangeland habitat.

One management strategy that aims to increase grazing sustainability is rotational grazing. This strategically incorporates periods of rest to enable plant regeneration, and distributes cattle impacts across the entire landscape rather than a small number of preferred locations. Compared to continuous grazing, rotational grazing can reduce soil compaction, decrease erosion, increase nutrients available for plants, and improve cattle forage availability and quality (Teague et al. 2011; Byrnes et al. 2018; Harmel et al. 2021). Two common rotation categories are high and low frequency. The former is often referred to as high-intensity, low-rotation or adaptive multi-paddock grazing. High-frequency rotation seeks to mimic historic bison grazing by frequent rotation of cattle herds among many smaller paddocks. Each paddock receives several months of rest after a short period (often several days) of intense grazing. Low-frequency rotation includes the Merrill system (three herds rotated among four pastures), the switchback system (one herd, two pastures), and many variations that involve rotating among pastures every few months. Research to date on the sustainability of rotational grazing has focused almost entirely on cattle forage and production. However, rangelands as functional ecosystems must support various ecosystem functions and services, in addition to meeting production goals.

There is a particular need to study grazing impacts on pollinators. The properties of ranchland that are most sensitive to management – vegetation cover and composition, and soil structure (Havstad et al. 2007) – are the same properties that determine the fate of many pollinators. Thus, while ranchlands have high potential to support pollinator conservation, this can only be achieved through increased understanding of how specific management strategies affect pollinators and the resources that support them. This project will advance this goal by determining how adoption and intensity of rotational grazing, impacts pollinator habitat – including food and shelter resources – and communities.

To determine how grazing management contributes to pollinator conservation, it is necessary to (1) quantify pollinator communities on ranchland and (2) determine relationships among grazing management, specific food and shelter resources, and pollinators. There is great opportunity for sustainability-oriented grazing strategies to promote beneficial insects. Determining pollinator occurrence and the underlying mechanisms, in relation to specific management strategies, is essential to meet this goal. It is also critical to determine how grazing management simultaneously affects pollinators and livestock.