• Simulating Carbon Dioxide Effects on Range Plant Growth and Water Use with GPFARM-Range Model

      Qi, Z.; Morgan, J. A.; McMaster, G. S.; Ahuja, L. R.; Derner, J. D. (Society for Range Management, 2015-09)
      Steadily rising carbon dioxide (CO2) in the Earth's atmosphere has the potential to increase plant biomass production and reduce plant transpiration in semiarid rangelands. Incorporating results from field CO2-enrichment experiments into process-based simulation models enhances our ability to project climate change impacts on these rangelands. In this study, we added algorithms for computing changes in plant biomass growth and stomatal resistance under elevated [CO2] to the GPFARM-Range (Great Plains Framework for Agricultural Resource Management in Rangelands) model, a newly developed stand-alone software package for rangeland management. The GPFARM-Range model was tested against 5 yr (1997-2001) of soil water and plant biomass data from CO2-enrichment (720 ppm) field experiments conducted in shortgrass steppe in northern Colorado. Simulated results for both peak standing crop biomass and soil water for both ambient and elevated [CO2] treatments had a percent bias within ± 10%, Nash-Sutcliffe efficiency ≥ 0.5, and index of agreement > 0.70. The model also captured the observed trend of increased C3 grass biomass and reduced plant transpiration under elevated [CO2]. The model was used to evaluate the separate effectiveness of elevated [CO2] on plant growth rate (C3 grasses only) and stomatal resistance (both C3 and C4 grasses). Two separate simulations showed that increased growth rate and stomatal resistance due to elevated [CO2] enhanced total plant biomass gain (C3 + C4) by 22% and 17%, respectively. The results indicate the algorithms used to simulate the impacts of elevated [CO2] on range plant growth and water use are reliable and can be used to evaluate rangeland production for predicted increases in [CO2], However, further studies are necessary because the reduction in plant transpiration under elevated [CO2] was underestimated, and increase in nitrogen use efficiency due to elevated [CO2] is not included. © 2015 Society for Range Management.
    • Sustaining Working Rangelands: Insights from Rancher Decision Making

      Roche, L. M.; Schohr, T. K.; Derner, J. D.; Lubell, M. N.; Cutts, B. B.; Kachergis, E.; Eviner, V. T.; Tate, K. W. (Society for Range Management, 2015-09)
      Grazed rangeland ecosystems encompass diverse global land resources and are complex social-ecological systems from which society demands both goods (e.g., livestock and forage production) and services (e.g., abundant and high-quality water). Including the ranching community's perceptions, knowledge, and decision-making is essential to advancing the ongoing dialogue to define sustainable working rangelands. We surveyed 507 (33% response rate) California ranchers to gain insight into key factors shaping their decision-making, perspectives on effective management practices and ranching information sources, as well as their concerns. First, we found that variation in ranch structure, management goals, and decision making across California's ranching operations aligns with the call from sustainability science to maintain flexibility at multiple scales to support the suite of economic and ecological services they can provide. The diversity in ranching operations highlights why single-policy and management "panaceas" often fail. Second, the information resources ranchers rely on suggest that sustaining working rangelands will require collaborative, trust-based partnerships focused on achieving both economic and ecological goals. Third, ranchers perceive environmental regulations and government policies-rather than environmental drivers-as the major threats to the future of their operations. © 2015 Society for Range Management.