Restoring Heterogeneity on Rangelands: Ecosystem Management Based on Evolutionary Grazing Patterns

Abstract

R are the most common form of terrain in both the United States (where it accounts for 61% of all land surface) and the world (70% of all land surface). Rangelands consist primarily of native plant communities managed, typically, for livestock production (Holechek et al. 1998). Because they can embrace extensive native plant communities, rangelands can serve as biodiversity repositories. However, in the Great Plains of the United States, where decisions about land use are made largely at the discretion of the private landowner, many plant and animal species dependent on rangelands are imperiled. For example, according to data from the North American Breeding Bird Survey, 70% of the 29 bird species characteristic of North American prairies experienced a decline in population between 1966 and 1993. Indeed, these grassland species are declining at a faster rate than any other guild of terrestrial birds in North America (Knopf 1994). Excessive herbivory by domestic livestock may have contributed to the decline in some of these species, but many species endemic to North American prairies evolved with large grazing animals. The Mountain Plover (Charadrius montanus), Baird’s Sparrow (Ammodramus bairdii), and Chestnut-collared Longspur (Calcarius ornatus) are examples of birds that occur in highest densities in grazed landscapes (Kantrud 1981, Renken and Dinsmore 1987, Knopf 1996). There are many potential causes for this decline in grassland bird populations, but the fact that it occurred when the condition of rangelands had improved, according to traditional means of evaluation (Holechek et al.1998), suggests that techniques currently used to manage rangelands may be insufficient to maintain biological diversity. Most techniques of rangeland management were developed under the paradigm of increasing and sustaining livestock production by decreasing the inherent variability associated with rangelands and grazing. This rangeland management approach is incapable of providing an ecological framework for alternative management objectives that have become more important over the past quarter-century. For example, the maintenance of biodiversity, as well as the preservation of habitat for many individual species, depends on the interspersion of diverse habitat types throughout a heterogeneous landscape. We contend that traditional rangeland management techniques reduce rangeland heterogeneity by favoring the most productive, most palatable forage species for domestic cattle. In this article, we propose a paradigm that promotes the potential heterogeneity of landscapes through an alternative approach to managing those rangelands with a long evolutionary history of large-ungulate grazing (Milchunas et al. 1988). Hence, for these rangelands we attempt to link the goals