Climate change is having impacts on rangelands worldwide. The science shows that increasing greenhouse gases are trapping more heat in the lower atmosphere and warming the planet. Models project continued warming in the future under different climate scenarios. Rangeland plant responses to higher temperatures and carbon dioxide levels vary depending on location, plant community, and soil factors. Some areas may see increased forage production while others face water constraints. Species shifts are also occurring, such as woody plant encroachment in some regions. Invasive species and weeds may thrive under altered conditions. Forage quality is also vulnerable to changes. Overall, rangelands are becoming more vulnerable to impacts, with southern latitudes facing greater risks and more weather variability

1. Grazinglands & Global Climate Change:
What is the Science Telling US?
Jack A. Morgan, Fort Collins, Colorado, USA
Photos by Sam Cox

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. 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. 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. 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. 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. 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. 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. Rangeland CO2 Enrichment Experiments
Colorado Shortgrass
Texas Prairie
Kansas Tallgrass
Free Air CO2 Enrichment in Mojave
Nevada
California Annual Grassland

10. Infra-red Heater
Infra-red Radiometer
Free Air CO2 Enrichment (FACE) Ring
Prairie Heating & CO2 Enrichment Experiment

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. 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. 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.)

14. LIVESTOCK ISSUES/OPTIONS

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. 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. • 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. 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. Conclusions
• Southern latitude rangelands
may be more vulnerable.
• Variability in weather patterns,
including more extreme weather
is likely to lead to increased
uncertainty.