Rangeland Management for Pollinators

Pollinator conservation and rangelands don’t seem like obvious bedfellows. In this era of sustainability, the connection between pollinator conservation and row crops or pollinator conservation and orchards is obvious. But pollinator conservation and rangelands? The reality is that pollinators are a key component of a healthy rangeland ecosystem. As Kevan stated, pollination is “central to all human beings, livestock, and wildlife.”1 Pollinators are essential for rangeland food production, help with nutrient cycling, and are prey for many birds. In essence, they hold a central position in wildlife food webs. For example, many migratory songbirds require a diet of berries, fruits, and seeds from insect-pollinated plants and pollinator larvae are an important component of the diet of many young birds. Belfrage et al. demonstrated that butterfl y diversity was a good predictor of bird abundance and diversity, apparently due to a shared requirement for a complex plant community.2 Pollinators perform such a range of ecological services in natural ecosystems that they are clearly a keystone group in nearly all terrestrial ecosystems and are necessary for plant reproduction and in forming the basis of an energy-rich food web.3 The relationship between pollinators and rangeland goes both ways. Pollinators are important for rangelands but rangelands are important for pollinators because they can provide habitat. Pollinators in North America include hummingbirds and bats, but insects—mainly bees, butterfl ies, moths, wasps, fl ies, and beetles—make up the vast majority of pollinators. Of these, bees are considered the most important pollinators in temperate North America. There are approximately 4,000 species of native bees in North America, many of which will thrive in the varied conditions offered by rangelands. Shrubland and scrub habitat, in particular, can be very valuable habitat. Surveys of pollinators in different California plant communities show that the chaparral community has the largest diversity of bees per unit area of any ecosystem type. Bee habitat requires two basic components: fl owers on which to forage and nest sites. Many pollinators are adapted to forage on particular plants, so a diverse community of pollinators requires a diverse array of fl owers. This can be easily provided by native grassland comprising a variety of grasses and forbs. Most native bees are solitary-nesting. Around 70% of bee species nest in the ground, excavating shallow tunnels in patches of bare soil, with most of the remaining 30% nesting in cavities in old trees or plant stems. Bumble bees require a small cavity such as an abandoned rodent hole. Ground-nesting bees (both solitary bees and bumble bees) are likely the most important pollinators in grasslands, but fl ies, beetles, and butterfl ies will also be prevalent. Rangeland pollinators have benefi ts that go beyond the boundaries of the range. The role that adjacent natural habitat (including grassland, shrubland, and other rangeland types) plays in providing crop pollination services is increasingly well understood: The value of crop pollination by native, wild bees in the United States is estimated at $3 billion. Proximity to natural or seminatural nonagricultural land is often an important predictor of pollinator diversity in cropland. There is evidence of declines in both managed and wild pollinators. Causes of declines are diffi cult to pinpoint, but loss of habitat due to increasing urbanization, expansion of intensive agriculture, invasive plant species, and the widespread use of pesticides all negatively impact pollinator populations, as do disease and parasites affecting the pollinators themselves. Protection of habitat is one way in which rangelands can be of great signifi cance in protecting and conserving pollinators. Natural habitat is integral to maintaining a long-term population of native pollinators in agricultural landscapes. However, it is important that management of rangelands and other nonarable lands takes into account native pollinators.