• Available water influences field germination and recruitment of seeded grasses

      Abbott, L. B.; Roundy, B. A. (Society for Range Management, 2003-01-01)
      Periodic summer rainstorms in some semi-arid regions result in variable soil moisture and differential establishment of seeded species. A 2-year study investigated soil water effects on germination and survival of 6 native and 2 non-native southwestern U.S. grass species. Bags of seeds were buried and retrieved before and during the summer rainy season. High field germination in seed bags (20-100%) and limited germination in the laboratory of seeds that were ungerminated in seedbags (0-45%) were exhibited by 6 native grasses following initial rainfall events in which the surface soil was saturated for 2 days or water potential (1-3 cm depth) was above -1.5 MPa for more than 9 days. Fewer Lehmann lovegrass (Eragrostis lehmanniana Nees) seeds germinated in response to initial and subsequent rainfall events (0-49%), but this species retained more residual germinable seeds (49-99%) than all other species studied. For 2 sowing dates, the soil drying front exceeded estimated seminal root depth 13 days after germination. Lack of recruitment for some species sown on these dates was probably due to seedling desiccation before adventitious roots had sufficient time to develop. The ability of Lehmann lovegrass to retain a viable seedbank when rainstorms are separated by long dry periods allows it to establish better than some native grasses that germinate quickly and are then subject to seedling desiccation. During a summer with more consistent rainfall, native species recruitment was greatest when seeds were planted during, rather than before the summer rainy season.
    • Targeted Grazing of White Locoweed: Short-Term Effects of Herbivory Regime on Vegetation and Sheep

      Goodman, L. E.; Cibils, A. F.; Lopez, S. C.; Steiner, R. L.; Graham, J. D.; McDaniel, K. C.; Abbott, L. B.; Stegelmeier, B. L.; Hallford, D. M. (Society for Range Management, 2014-11)
      White locoweed (Oxytropis sericea Nuttall) and nontarget vegetation response to 2 yr of targeted grazing by sheep, one treatment of picloram plus 2, 4-D (HER) or no treatment (CON) were compared. Serum of sheep that grazed locoweed intermittently (IGZ, 5 d on locoweed followed by 3 d off locoweed) vs. counterparts that grazed locoweed continuously for 24 d (CGZ) was also examined. Alkaloid toxicity was inferred by serum levels of thyroxine (T4), triiodothyronine (T3), alkaline phosphatase (ALKP), aspartate aminotransferase (AST), and swainsonine, as well as behavior and body weight gains. Three sites were used in a randomized complete block design. IGZ, CGZ, and HER treatments reduced locoweed density (P < 0.01), canopy cover (P < 0.01), number of flower stalks (IGZ: P = 0.02, CGZ and HER: P = 0.01), and plant size (P < 0.01). White locoweed seed density in the soil seed bank was not reduced with grazing, and nontarget vegetation was mostly unaffected by treatments. Grass canopy cover increased in grazed and herbicide plots throughout the study (IGZ: P = 0.03, CGZ and HER: P < 0.01). Percentage bare ground was unchanged (IGZ: P = 0.46, CGZ: P = 0.44) in grazed plots but decreased (P = 0.03) in HER plots. After 24 d, ewes in the IGZ treatment had lower levels of serum ALKP (P < 0.01) and AST (P = 0.02) and marginally lower swainsonine levels (P < 0.07) than CGZ ewes that tended to exhibit lower serum T3 (P < 0.07) and similar serum T4 (P = 0.25) levels. Time spent feeding on locoweed tended to differ (P = 0.06) between treatments. Body weight gain was the same (P = 0.19) regardless of treatment. IGZ of locoweed-infested rangeland with sheep may be a viable short-term means of reducing locoweed density without detrimentally affecting animal health. © 2014 Society for Range Management