While pollinator management has become a reality for those working in agricultural areas, it is also a very important part of maintaining healthy rangeland ecosystems. Hoffman Black et al. demonstrate the important role pollinators, especially bees, play in maintaining food cycles in wild rangeland as well as their benefits to adjacent agricultural areas. Given the threats urbanization, insecticides and pathogens pose to today’s bee species, rangeland pollinator management is an opportunity to provide refuge for vulnerable bee populations and the flora and fauna that depend upon them. While evidence suggests declines in wild and domesticated bee populations, these researchers argue providing wild rangelands as a safe habitat may help slow this trend.–Michael Landsman
Hoffman Black, S., Shepard, M., Vaughan, M., Rangeland management for pollinators. Rangelands, 33(3):9-13. 2011.
Hoffman et al. argue bees and rangelands have a symbiotic relationship which should be supported to maintain bee population numbers. In California, for example, shrubland and scrub habitats in rangelands provide important shelter for dwindling bee populations. In fact, chaparral communities have some of the highest levels of bee diversity per unit in the world. Thus, resource management in rangelands must take into account the health of the pollinator populations. Hoffman et al. look at issues of grazing, prescribed burns and herbicide applications.
In recent years, researchers have discovered strong links between unsustainable grazing practices and drops in bee populations. Uncontrolled sheep grazing in the Sierra Nevada rangelands has been shown to decimate host-plant species enough to nearly eliminate bee pollinator communities. Scientists have also suggested insects in the Southwest have not developed alongside large ungulates and introducing buffalo or other species into these rangelands can put severe pressure on pollinators. However, Hoffman et al. argue grazing can play an important role in rangeland ecosystems as long as it is managed, with enough time between grazing periods to replenish plant-pollinator numbers.
While prescribed burns have long been a part of natural management in US prairie systems, they have the capacity to decimate bee populations. Burning in small, isolated habitat fragments has been shown to have a consistently negative effect on bee population numbers, given the inability for colonizers to reach these areas and replenish them. Butterflies, another important pollinator species, have also been observed to be negatively effected by widespread burns. This article calls for more responsibility in planning fires, allowing colonizers to return to the area so as not to indiscriminately remove all pollinating species. It can take two to three years for a pollinator species to fully recover from a large prescribed burn, given how isolated the area is.
Finally, this paper takes issue with the harm herbicides have caused natural pollinator species. The widespread use of nonselective herbicides has been shown to kill the floral species upon which bees are dependent. Numerous studies over recent years have shown higher levels of invertebrates in unsprayed plots than those treated with herbicides. Kevan et al. linked rapid bee loss in France to the loss Asteraceae and Lamiaceae flowers due to indiscriminate herbicide spraying. Furthermore, the same paper observed how herbicides killed many of the plants important to blueberry pollinators, reducing their numbers as well. Hoffman et al. argue for the use of selective herbicides along with a mechanical management of shrubs and small trees which provide shelter for plant-pollinators. They also argue for minimal spraying in rangelands, allowing as much of the wild, untreated ecosystem to remain. Thus, natural resource management in rangelands should prioritize policies which preserve plant pollinators.