• Livestock grazing and topographic site effects on grassland plant communities after long-term grazing cessation

      Gornish, Elise S.; Eastburn, D. J.; Oneto, Scott; Roche, Leslie M.; Univ Arizona, Sch Nat Resources (CSIRO PUBLISHING, 2018)
      Ranchers are increasingly expected to manage grasslands for forage production and native biodiversity enhancement goals. However, longstanding relationships between grazing and plant species are often understudied because elucidating effects of grazing absence and presence often requires experimental opportunities that are difficult to establish, such as the introduction of grazing to long-term ungrazed pastures. Addressing this knowledge gap is critical for heterogeneous landscapes where site-specific properties might interact with grazing effects to ultimately structure plant communities. We conducted vegetation surveys for 3 years after grazing was reintroduced to an annual California grassland that was not grazed for more than 60 years. We investigated how grazing affected plant communities in terms of cover and richness of native and invasive species and how topographic sites of summit, backslope and toeslope altered these relationships. The plant communities were affected by the independent effects of grazing, site and year. Across years, native cover was 39% greater in grazed plots compared with ungrazed plots. Native species richness was slightly lower in ungrazed compared with grazed plots for toeslope sites relative to the other topographic positions. Invasive species cover was 17% lower in grazed plots compared with ungrazed plots and no predictors were found to contribute to significant differences across plots. Although we generally did not find expected relationships between site and plant response to grazing, this work demonstrates how managers can use livestock to quickly modify plant communities in areas with a long history of grazing absence.
    • Outcomes of fire research: is science used?

      Hunter, Molly E.; Univ Arizona, Sch Nat Resources & Environm (CSIRO PUBLISHING, 2016)
      An assessment of outcomes from research projects funded by the Joint Fire Science Program was conducted to determine whether or not science has been used to inform management and policy decisions and to explore factors that facilitate use of fire science. In a web survey and follow-up phone interviews, I asked boundary spanners and scientists about how findings from a random sample of 48 projects had been applied and factors that acted as barriers or facilitators to science application. In addition, I conducted an investigation of recent planning documents to determine whether products from the sampled projects were cited. All lines of evidence suggest that information from most (44 of 48) of these projects have been used by fire and fuels managers in some capacity. Science has mostly been used during planning efforts, to develop treatment prescriptions, and to evaluate current practices. Lack of manager awareness was commonly identified as a barrier to application of science. Conversely, activities and organisations that foster interaction between scientists and managers were identified as facilitating the application of science. The efforts of the Joint Fire Science Program to communicate science findings and engage managers has likely contributed to the application of fire science.
    • Widespread fire years in the US–Mexico Sky Islands are contingent on both winter and monsoon precipitation

      Arizpe, Alexis H.; Falk, Donald A.; Woodhouse, Connie A.; Swetnam, Thomas W.; Univ Arizona, Lab Tree Ring Res; Univ Arizona, Sch Nat Resources & Environm; Univ Arizona, Sch Geog Dev & Environm (CSIRO PUBLISHING, 2020)
      The climate of the south-western United States and northern Mexico borderlands is marked by a bimodal precipitation regime with the majority of moisture arriving during the cool season via Pacific frontal storm systems, and intense convective storms during the North American Monsoon (NAM). The fire season occurs primarily during the arid foresummer in May and June, before the development of the NAM. Most tree-ring studies of fire climatology in the region have evaluated only the role of winter precipitation. We used tree-ring-width-based reconstructions of both winter and monsoon precipitation, coupled with fire scar reconstructions of fire history from mountain ranges in the US and Mexico, to quantify the historical role and interactions of both seasons of precipitation in modulating widespread fire years. Winter precipitation was the primary driver of widespread fire years in the region, but years with drought in both seasons had the highest fire frequency and most widespread fires. These relationships define a unique monsoon fire regime, in which the timing and amount of monsoon precipitation are important factors in limiting the length of fire season and regulating widespread fire years.