Browsing Rangeland Ecology & Management, Volume 63, Number 4 (July 2010) by Title
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Plant Community and Target Species Affect Responses to Restoration StrategiesIncreases in Kentucky bluegrass and smooth bromegrass on northern Great Plains rangelands have the potential to negatively impact ecosystem function, lower plant diversity, and alter seasonal forage distribution, but control strategies are lacking in the region. A project was initiated on a heavily invaded 16-ha grassland that had not been grazed or hayed for at least 20 yr. Five restoration treatments and a control were initiated in 2003 on communities dominated by 1) smooth bromegrass (Bromus inermis Leyss.), 2) Kentucky bluegrass (Poa pratensis L.), 3) warm-season native grasses, 4) a mix of introduced species, and 5) smooth bromegrass and Kentucky bluegrass. Restoration treatments were 1) late-April burn, 2) late-April burn followed by imazapic at 511.62 mL ai ha-1, 3) imazapic only at the same rate, 4) mowing, 5) mowing followed by litter removal, and 6) control. We found that treatment responses were affected by target species, community category, and year. Generally, burning followed by the herbicide imazapic reduced Kentucky bluegrass in the species composition, but smooth brome was reduced by mowing followed by raking. Burning followed by imazapic reduced live grass biomass in all community categories except the native the year following treatment, but by the third year of the study live grass biomass was maintained across all treatments. In the third year of the study, responses of Kentucky bluegrass, other invasive species, and native grasses to restoration treatment differed depending on community. The use of burning plus imazapic was promising for control of Kentucky bluegrass but its use by producers may be limited by yield reductions in early years. Our data suggest management strategies should vary depending on whether the goal is to reduce one or several invaders, specific invader identity, and community type in which the invader is growing. We also found that the most effective strategy was an adaptive management approach, one where treatments are chosen in response to changes in community composition and depending on resource conditions.
Seedling Interference and Niche Differentiation Between Crested Wheatgrass and Contrasting Native Great Basin SpeciesInterference from crested wheatgrass (Agropyron cristatum [L.] Gaertn.) seedlings is considered a major obstacle to native species establishment in rangeland ecosystems; however, estimates of interference at variable seedling densities have not been defined fully. We conducted greenhouse experiments using an addition-series design to characterize interference between crested wheatgrass and four key native species. Crested wheatgrass strongly interfered with the aboveground growth of Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle Young), rubber rabbitbrush (Ericameria nauseosa [Pall. ex Pursh] G. L. Nesom Baird subsp. consimilis [Greene] G. L. Nesom Baird), and to a lesser extent with bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve). Alternatively, bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey subsp. californicus [J. G. Sm.] Barkworth) and crested wheatgrass had similar effects on each other’s growth, and interference ratios were near 1.0. Results indicate that the native grasses more readily establish in synchrony with crested wheatgrass than these native shrubs, but that once established, the native shrubs are more likely to coexist and persist with crested wheatgrass because of high niche differentiation (e.g., not limited by the same resource). Results also suggest that developing strategies to minimize interference from crested wheatgrass seedlings emerging from seed banks will enhance the establishment of native species seeded into crested wheatgrass-dominated communities.
Vegetation Characteristics of Mountain and Wyoming Big Sagebrush Plant Communities in the Northern Great BasinDominant plant species are often used as indicators of site potential in forest and rangelands. However, subspecies of dominant vegetation often indicate different site characteristics and, therefore, may be more useful indicators of plant community potential and provide more precise information for management. Big sagebrush (Artemisia tridentata Nutt.) occurs across large expanses of the western United States. Common subspecies of big sagebrush have considerable variation in the types of sites they occupy, but information that quantifies differences in their vegetation characteristics is lacking. Consequently, wildlife and land management guidelines frequently do not differentiate between subspecies of big sagebrush. To quantify vegetation characteristics between two common subspecies of big sagebrush, we sampled 106 intact big sagebrush plant communities. Half of the sampled plant communities were Wyoming big sagebrush (A. tridentata subsp. wyomingensis [Beetle A. Young] S. L. Welsh) plant communities, and the other half were mountain big sagebrush (A. tridentata subsp. vaseyana [Rydb.] Beetle) plant communities. In general, mountain big sagebrush plant communities were more diverse and had greater vegetation cover, density, and biomass production than Wyoming big sagebrush plant communities. Sagebrush cover was, on average, 2.4-fold higher in mountain big sagebrush plant communities. Perennial forb density and cover were 3.8- and 5.6-fold greater in mountain compared to Wyoming big sagebrush plant communities. Total herbaceous biomass production was approximately twofold greater in mountain than Wyoming big sagebrush plant communities. The results of this study suggest that management guidelines for grazing, wildlife habitat, and other uses should recognize widespread subspecies as indicators of differences in site potentials.