Bison remained out of sight and out of mind for most Americans over the next half-century, but in the 1960s diverse groups began to consider the species’ place on the landscape. Native Americans wanted bison back on their ancestral lands. Conservationists wanted to restore parts of the Plains ecosystems. And ranchers started to view bison as an alternative to cattle production. More ranches began raising bison, and Native American tribes started their own herds. Federal, state, tribal and private organizations established new conservation areas focusing in part on bison restoration, a process that continues today in locations such as the Tallgrass Prairie National Preserve in Kansas and the Fort Peck Reservation in Montana. By the early 2000s, the total North American population had expanded to 500,000, with about 90 percent being raised as livestock – but often in relatively natural conditions – and the rest in public parks and preserves. For scientists, this process has been an opportunity to learn how bison interact with their habitat.
IMPROVING PRAIRIE LANDSCAPES Bison feed almost exclusively on grasses, which, because they grow rapidly, tend to out- compete other plants. Bison’s selective grazing behavior produces higher biodiversity because it helps plants that normally are dominated by grasses to coexist. Because they tend to graze intensively on recently burned zones and leave other areas relatively untouched, bison create a diverse mosaic of habitats. They also like to move, spreading their impacts over large areas. The variety they produce is key to the survival of imperiled species such as the greater prairie chicken (Tympanuchus cupido) that prefer to use different patches for different behaviors, such as mating and nesting. Studies have shown that bison-induced changes in vegetation composition and quality grazing can increase the abundance and diversity of birds and insects in tallgrass prairies. Bison impacts don’t stop there. They often kill woody vegetation by rubbing their bodies and horns on it. And by digesting vegetation and excreting their waste across large areas, they spread nutrients over the landscape. This can produce higher-quality vegetation that benefits other animals. Studies, including my own research, have shown that bison-induced changes in vegetation composition and quality grazing can increase the abundance and diversity of
Grazing by bison on a stretch of prairie has produced an increase in forbs (nongrass flowering plants).
60
July 2019
Made with FlippingBook - professional solution for displaying marketing and sales documents online