Dr. Jack Morgan - Grazinglands and Global Climate Change: What is the Science Telling Us?


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Grazinglands and Global Climate Change: What is the Science Telling Us? - Dr. Jack Morgan, USDA/ARS, from the 2012 Annual Conference of the National Institute for Animal Agriculture, March 26 - 29, Denver, CO, USA.

More presentations at: http://www.trufflemedia.com/agmedia/conference/2012-decreasing-resources-increasing-regulation-advance-animal-agriculture

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Dr. Jack Morgan - Grazinglands and Global Climate Change: What is the Science Telling Us?

  1. 1. Grazinglands & Global Climate Change: What is the Science Telling US? Jack A. Morgan, Fort Collins, Colorado, USA Photos by Sam Cox
  2. 2. Greenhouse Gases Important in Earth’s Energy Balance Estimate of the Earth’s annual and global mean energy balance (Kiehl and Trenberth 1997; Le Treut et al. 2007).
  3. 3. Link Between GHG & Climate Change Increases in concentrations of these gases since 1750 are due to human activities in the industrial era (USGCRP 2009). Increases in annual global surface temperature (over both oceans and land) since 1880. Red bars indicate temperatures above and blue bars represent temperatures below the average temperature period 1901– 2000. The black line is atmospheric CO2 concentration in parts per million (USGCRP 2009).
  4. 4. Projections of future temperature from 16 climate models. The maps feature a higher and lower greenhouse gas scenario. Brackets on the thermometers represent likely ranges of model predictions (USGCRP 2009). The future is predicted to be decidedly warmer, with the actual outcome depending on the particular scenario and region. CLIMATE CHANGE PREDICTIONS
  5. 5. Projected future changes in precipitation as simulated by 15 climate models. Confidence in projected changes is highest in hatched areas (USGCRP 2009). Generally higher precipitation predicted for northern latitudes and less for southern latitudes, depend- ing on time of year. CLIMATE CHANGE PREDICTIONS
  6. 6. Warmer temperatures: Longer growing season, phenology, pests Altered hydrologic cycle (intense rainfall events, timing, more rainfall, more drought) Differential species responses (diverse & individualistic species responses) Photo: Sam Cox
  7. 7. Temperature • Reaction rates • Evaporation Positive • Longer growing season • Increased growth rates • Greater N mineralization Negative • Desiccation • Shorter growing season • water constrained • phenology Climate Zone Humid to sub-humid Temperate to boreal Climate Zone Semi-arid to arid Tropical to temperate Plant Production Often no response to warming (Dukes et al. 2005; Klein et al. 2007; Pendall et al. 2010)
  8. 8. 73.7 gC/m2/y 49.3 gC/m2/y 295 gC/m2/y 233 gC/m2/y Aboveground Biomass Soil Respiration Flux New Soil C ~54 gC/m2/y ~0 gC/m2/y Elevated CO2 Chambers Ambient CO2 Chambers Direct responses of plants to increased atmospheric CO2 Photosynthesis Species effects Functional types C3 vs C4 CO2 Leaf Conductance Water Relations leaf transpiration leaf & soil water dynamics Higher WUE Ehleringer et al. 1997. Oecologia 112:285-299. Wand et al. 1999. Glob. Change Biol. 5:723-741)
  9. 9. Rangeland CO2 Enrichment Experiments Colorado Shortgrass Texas Prairie Kansas Tallgrass Free Air CO2 Enrichment in Mojave Nevada California Annual Grassland
  10. 10. Infra-red Heater Infra-red Radiometer Free Air CO2 Enrichment (FACE) Ring Prairie Heating & CO2 Enrichment Experiment
  11. 11. Variety of Plant Responses to CO2 • California Annual Grassland: Little effect of CO2 enrichment on plant production; reduced diversity due to loss of forb spp. (Dukes et al. 2005. Plos Biology 3:1829-1837; Zavaleta et al. 2003. PNAS 100:7650-54) • Colorado Shortgrass: Up to a doubling of productivity results from doubling ambient CO2...tied to SWC. C3 grasses and sub-shrub NPP increased; C4 grasses did not respond. (Morgan et al. 2007. PNAS 104:14724-14729) • Kansas Tallgrass: Plant Productivity increases in dry years, C4 grasses respond; Forbs (C3) and Cyperaceae spp. (C3) most responsive to CO2 over long term. (Owensby et al. 1999. Global Change Biology 5:497-506) • Wyoming Mixed-grass Prairie: Combined warming and higher CO2 increase expecially C4 grass production over 25%. • Texas Tallgrass: CO2 increased SWC and caused C4 grass spp. shifts as if from mid-grass to tallgrass prairie. Responses varied in different soils. (Polley et al. 2012. Global Change Biology 18:700-710)
  12. 12. Climate Change/CO2 likely leading to plants species shifts. Example: Woody plant encroachment in SW United States Honey locust tree islands in Kansas Tallgrass Prairie. Present-day encroachment? Fire removal, overgrazing CO2? CC? (photograph courtesy of Alan K. Knapp). Mesquite (C3 woody legume) encroachment in southwest United States over past two centuries (photograph courtesy of ARS Jornada).
  13. 13. Invasives: • Thrive in disturbed environments • Evidence that some respond favorably to future conditions Weed Invasions & Climate Change Dalmatian toadflax invasion greatly increased under CO2 enrichment & warming (due to both direct & indirect water-mediated effects of CO2) (Blumenthal et al. in prep.)
  15. 15. In the northern US, increased temperatures will likely improve livestock productivity (Baker et al. 1993, Echkert et al. 1995, Rotter and Van De Geijn 1999)  Increased forage production  Milder winters Derek Bailey, New Mexico State University
  16. 16. In the southwest, livestock producers may need to change management if temperatures increase • Develop more water and shade • Use heat adapted breeds (e.g., Brahmans, Senepol, Tuli) Derek Bailey, New Mexico State University
  17. 17. • Seasonality of production • Species shifts (Morgan et al. 2007. PNAS 104:14724-14729; Polley et al. 2011. Plant Ecology 212:945-957) • Nutrient cycling (Craine et al. 2010; GCB 16:2901-2911. Dijkstra et al. 2010. New Phytologist 187: 426-437; Luo et al. 2004. BioScience 54; 731-739; Rustad et al. 2001. Oecologia 126:543-562.) Forage Availability & Quality
  18. 18. Conclusions • CC/CO2 have likely already affected world rangelands. • Impacts on plant production and species shifts variable; – current climate, plant community, soils and management....complicated! • CC/CO2 likely increasing vulnerability to species shifts, including weed invasions. • Forage quality is vulnerable.
  19. 19. Conclusions • Southern latitude rangelands may be more vulnerable. • Variability in weather patterns, including more extreme weather is likely to lead to increased uncertainty.