Smart Cattle Grazing Turns Rangelands Into Monarch Butterfly Strongholds

The monarch butterfly has become the unlikely centerpiece of an increasingly urgent conservation puzzle, and one of the most promising solutions may be hiding in plain sight on cattle ranches across the northern Great Plains. New research from North Dakota State University, Iowa State University, and Oklahoma State University suggests that the way ranchers move and manage their herds can dramatically reshape how much milkweed and nectar-rich wildflowers persist on rangelands, with cascading consequences for both adult butterflies and their caterpillars. The study, published in Frontiers in Ecology and Evolution, offers some of the clearest evidence yet that working  livestock landscapes can double as monarch habitat, provided the grazing strategy is designed with ecology in mind.

The stakes could hardly be higher. The eastern migratory monarch population has declined by roughly 80 percent over the past thirty years in the United States, a collapse driven by the loss of host and nectar plants, land use change, and pesticide exposure. Milkweed, the obligate host plant on which monarch females lay their eggs and on which monarch caterpillars feed exclusively, has fared especially poorly in agricultural landscapes. Researchers estimate that milkweed in the midwestern United States declined by about 40 percent between 1999 and 2014, a loss of approximately 860 million stems. Because an estimated 38 percent of monarchs overwintering in Mexico originate from the Midwest, that loss has been directly correlated with declines in the overwintering population.

Conservation planners have proposed adding 1.6 billion milkweed stems across the Midwest to stabilize the overwintering population at its six-hectare target. Much of the effort to date has focused on croplands, roadside rights-of-way, and urban plantings. But rangelands, the unplowed expanses of native grasses and forbs that cover nearly twice as much land as croplands in the United States, remain an understudied frontier. Prior estimates suggest rangelands already host some 4.1 billion milkweed stems across 13.2 million hectares. The question the new study set out to answer was whether ranchers could push those numbers higher, not by taking land out of production, but simply by changing how cattle are distributed across the landscape in space and time.