The Effects of Previous Grazing on the Subsequent Nutrient Supply of Ungulates Grazing Late-summer Mixed-Conifer Rangelands

Abstract

Ecological, societal, and political discussions abound regarding intra- and inter-specific competition for nutrients among wild and domestic ungulates grazing shared forested rangelands in summer as cascading effects of prior grazing drive subsequent grazing patterns and nutrient intake. Our objective was to determine diet quality and quantity of cattle (Bos taurus), mule deer (Odocoileus hemionus hemionus; deer), and elk (Cervus elaphus nelsoni) in late-summer in response to early-summer forage utilization by cattle and elk in two consecutive years. Four 2.25 ha enclosures were constructed in previously logged mixed-conifer rangelands dominated by grand fir (Abies grandis [Douglas] Forbes.), and within each enclosure, a 0.75 ha paddock was either: 1) ungrazed, 2) grazed by cattle, or 3) grazed by elk in mid-June and mid-July at a moderate utilization level (31.9 ± 2.7%). After grazing treatments, each paddock was subdivided into three 0.25 ha sub-paddocks and sixteen 20-minute foraging bouts were conducted in each sub-paddock using elk, deer, and cattle (n = 4). Within an animal species CP in diets did not differ (p > 0.05) between ungrazed paddocks and grazed paddocks; however, diet CP and IVDMD of each species was higher (p < 0.05) on cattle grazed paddocks compared to elk grazed. Regardless of treatment, cattle diets contained lower CP, IVDMD (p < 0.05) than did deer or elk diets, and relative to elk, deer consistently selected diets which contained higher CP (p < 0.05). In response to grazing, intake rate of DM, CP, ME did not change (p > 0.05) for any of the ungulates. The study revealed that early-summer grazing by cattle or elk at a moderate utilization level has minimal effect on the subsequent nutrient intake rate of cattle, deer, and elk foraging in mixed-conifer forests.