Effects of long-term winter-spring grazing on foothill rangeland

Abstract

In the Rocky Mountain foothills of Montana, elk (Cervus elaphus) often occupy the rough fescue/bluebunch wheatgrass (Festuca campestris Rydb./Pseudoroegneria spicata (Pursh) A. Löve ) habitat type in winter and early spring. Previous research has demonstrated that moderate summer herbivory sustains dominant graminoids in this habitat type, but heavy summer grazing does not. This study compared the effects of heavy and light, long-term winter-spring grazing on bluebunch wheatgrass, rough fescue, and Idaho fescue (Festuca idahoensis Elmer), plant yield, ground cover, and soil properties in this habitat type. Eight sites were sampled with similar slope, aspect, soil type, elevation, and precipitation that were grazed nearly exclusively by elk in winterspring for 56 years, with 4 sites each located within heavily and lightly grazed areas. Basal diameter (P=0.04), June and July leaf height (P<0.01 and P=0.01, respectively), number of seedheads per plant (P=0.03), percent filled florets per plant (P<0.01), percent canopy cover (P=0.01), and percent species composition (P=0.02) of rough fescue were less on heavily than lightly grazed sites. June leaf height (P=0.01), and percent filled florets (P<0.01) were less and number of seedheads per plant (P=0.01) of bluebunch wheatgrass was greater on heavily grazed sites. Percent filled florets (P<0.01) and June and July leaf height (P=0.01 and P<0.01, respectively) of Idaho fescue were less on heavily grazed sites. Plant yield did not differ between heavily and lightly grazed sites (P>0.10). Total ground cover was not different between heavily and lightly grazed sites (P>0.10), however, ground cover of graminoids and forbs was less (P=0.04) and ground cover of dense clubmoss (Selaginella densa Rydb.) was greater on heavily grazed sites (P=0.04). Soil bulk density was greater (P=0.02) and the Ah horizon was not as deep (P<0.01) on heavily grazed sites. Comparisons of canopy cover with a near-pristine site in this habitat type indicate that rough fescue did not tolerate many successive years of heavy grazing in winter-spring, but long-term light grazing in winter-spring sustained rough fescue in proportions found within the potential natural community. Heavy or light long-term grazing in winter-spring decreased the abundance of bluebunch wheatgrass but had minimal impact on Idaho fescue.