• Combustion of cattle fecal pats ignited by prescribed fire

      Scasta, J. D.; Weir, J. R.; Engle, D. M.; Carlson, J. D. (Society for Range Management, 2014-03)
      Cattle fecal pats readily ignite, are a common source of spot fires, and release extreme amounts of energy when burning. Moreover, dung-dependent livestock parasites can be reduced by combusting fecal pats in prescribed burns. We conducted a study to identify factors that influence combustion of cattle fecal pats. Fifty fecal pats were located in each burn unit before 10 prescribed fires and then rated for combustion after each fire. Combustion of cattle fecal pats was highly variable across fires, with average proportion of combustion of individual pats from the 10 fires ranging from 2-±-2 to 98-±-1% (mean-±-SE). Of 10 fecal pat, fuel, and weather variables assessed, only fecal pat condition, 10-h time-lag dead fuel moisture (DFM), and fuel load entered as variables in a stepwise selection method of constructing a multiple regression model of combustion of fecal pats (R2-=-0.94, P-<-0.01). Condition of fecal pats (a function of elapsed time since deposition, fuel moisture, and decomposition) explained the greatest variation of pat combustion (partial R2-=-0.75), followed by 10-h DFM (partial R2-=-0.12) and fuel load (partial R2-=-0.07). Combustion was <-10% when 10-h DFM exceeded 13% regardless of pat condition. For every 1 Mg-·-ha-1 increase in fuel load, combustion of older and drier fecal pats increased by about 7%, but combustion of fresh fecal pats always averaged <-20% and was unrelated to fuel load. Our results demonstrate that combustion of pats can be managed to meet a variety of ecological and production goals. © 2014 The Society for Range Management.
    • Long-term vegetation change provides evidence for alternate states in silver sagebrush

      Kachergis, E.; Rocca, M. E.; Fernández-Giménez, M. E. (Society for Range Management, 2014-03)
      A key goal in land management is to prevent ecosystem shifts that affect human well-being. Like other types of sagebrush shrublands, large areas dominated by the common but little-studied mountain silver sagebrush may have shifted to a less productive shrub-dominated alternate state under heavy livestock grazing in the 19th century. The goals of this study are to 1) describe long-term vegetation change in a silver sagebrush mountain park and 2) evaluate evidence that these changes constitute alternate states. We examined vegetation change over the last 57 yr in California Park, Colorado, USA, using monitoring data from 15 permanent transects at six sites. We analyzed change in species composition over time and related it to management and climatic drivers using nonmetric multidimensional scaling. We found that management practices influenced species composition. Spraying herbicides resulted in decreases of sagebrush and a dominant, unpalatable forb (Wyethia amplexicaulis), but sagebrush recovered. Spraying also triggered a temporary increase in native palatable grasses and forbs. Native grasses have since decreased again, coinciding with increases in the cattle stocking rate and elk population. The nonnative pasture grass Phleum pratense has increased to become one of the dominant grasses in 2010. Sagebrush and herbaceous understory dynamics were not consistent with a shrub-dominated alternate state: changes were gradual and not persistent. However, historic Wyethia dominance and the widespread increase in the nonnative grass Phleum were persistent and may represent alternate states. We used these findings to update a state-and-transition model of high-elevation silver sagebrush shrubland dynamics for land management decision making. Our analysis differentiated gradual, nonpersistent changes from potentially irreversible changes, as is necessary for identifying alternate states that are important for land management and ecosystem function. The gradual but persistent increase in the nonnative grass Phleum reinforces others' observations that even incremental changes may lead to irreversible shifts. © 2014 The Society for Range Management.