• Climatic influences on recruitment of 3 subspecies of Artemisia tridentata

      Maier, A. M.; Perryman, B. L.; Olson, R. A.; Hild, A. L. (Society for Range Management, 2001-11-01)
      Previous research suggested that big sagebrush (Artemisia tridentata Nutt.) recruitment occurs in pulses consistent with favorable climatic conditions. In 1997, 75 stem sections were collected from 9 stands of each of the 3 subspecies of big sagebrush in Wyoming along elevation and climatic gradients. Annual growth rings were used to identify the year plants were established. Large cohorts of Wyoming big sagebrush (A. tridentata ssp. wyomingensis Beetle and Young) appeared in 1982, 1981, 1964, 1961, and 1955. Basin big sagebrush (A. tridentata ssp. tridentata Beetle and Johnson) cohorts flourished in 1991, 1986, 1985, 1982, and 1977. Mountain big sagebrush (A. tridentata ssp. vaseyana [Rydb.] Beetle) cohorts prospered in 1985, 1982, 1981, 1979, and 1974. Mean monthly precipitation and temperature records were compared to years with high and low recruitment using logistic regression models at 3 geographic scales (single-stand, regional, statewide). Wyoming big sagebrush recruitment was greatest in years with above-average December and January precipitation occurring after the first growing season (r2 = 0.10, 0.04, P < 0.05). Basin big sagebrush recruitment was most successful in years with above-average March, May, and June precipitation during the first growing season (r2 = 0.06, 0.09, 0.18, P < 0.05). Mountain big sagebrush recruitment was greatest in years with below-average February, April, and May precipitation after the first growing season (r2 = 0.03, 0.04, 0.04, P < 0.05). While variable precipitation patterns appear to contribute significantly to recruitment of big sagebrush, responses among the 3 major subspecies were quite variable. More complex models need to be developed to foster our understanding of the mechanisms affecting big sagebrush establishment.
    • Long-term plant community development as influenced by revegetation techniques

      Newman, G. J.; Redente, E. F. (Society for Range Management, 2001-11-01)
      A revegetation techniques study was initiated during the fall of 1976 in northwestern Colorado in a disturbed sagebrush (Artemisia tridentata Nutt.) community. The study included 2 irrigation treatments, three seed mixtures, 2 seeding techniques, and 2 fertilization treatments. Short-term results were published and conclusions were made regarding the initial success of each treatment. The objective of the current study was to determine the effects of each treatment on plant community production, species composition, and species diversity after 20 years of plant community development. Among irrigated plots, the native seed mixture produced greater aboveground biomass compared to an introduced mixture and a mixture of both native and introduced species (combination seed mixture). The native seed mixture also resulted in greater total species richness than the introduced mixture when averaging over all other treatments. Altered seeding rate ratios among life forms as well as altered seeding methods (drill versus broadcast seeding) did not significantly alter plant community development after 20 years. However, a single application of nitrogen and phosphorus significantly increased grass production on plots seeded to the combination seed mixture. All revegetation plots have remained grass-dominated. However, shrub biomass was greater in the native and combination mixtures than in the introduced mixture under initial irrigated conditions in part due to successful establishment and growth of four-wing saltbush (Atriplex canescens Pursh Nutt.). Thus, the seed mixtures evaluated in this study have resulted in distinctly different plant communities and demonstrate that such initial treatments can influence long-term plant community development on severely disturbed rangelands. Broadcast seeding a native seed mixture that has been irrigated for 2 growing seasons without fertilization appears to be an effective long-term combination of cultural revegetation practices.