Forage for Changeby Russell Green OsborneA Summary of Climate Impacts on

Agriculture: Implicationsfor Forage and Rangeland Production

Scope of Article●Meta-Analysis●Broad range of cited works

o International in contextoLess study has been given to the impacts of

climate change on pasture and rangelands

●Work accepts the general consensus, over next 50 years the US will experience:o1.5 - 2 C increase in temperatureo increased [CO2] o increased precipitation

Distribution of Grazing Land

Pasture & Rangeland

Pasture●Intensive mgmt●East Coast

Rangeland●"Wild" spaces●Managed by

grazing practices

Picture credit:Roland Fischer, ZurichUSDA public domain

Define this:

Definitions[CO2] Atmospheric CO2 concentrations

FACE Free Air Carbon Dioxide Enrichment

TNC Total Nonstructured Carbohydrates

C3 Woody and herbaceous broad-leaf species. "cool season" perennial short grasses.

C4 Most dominant perennial and annual rangeland grasses.

Overview of General Science

● General positive response to [CO2] in regards to leaf photosynthesis, biomass, and yield.

● Doubling [CO2] increases the average reproductive yield of C3 species by 30% and C4 by 10% (Hatfield et al.,2011)

Pasture Response

Elevated [CO2], Temperature, and Precipitation● Multiple studies conclude that the increased yield

response is generally limited to C3 species● None or little response by C4

Even grazing can affect results● Newton et al. observed significant difference in

response to increased [CO2] between sheep grazed plots and those that were hand defoliated.

Rangeland Response

Plant Phenology and Growing Season Length● Spatial and temporal distribution of precipitation ->soil

water availability -> Rangeland Ecology● Earlier spring green-up

o -> Longer growing seasono -> Changes in reproductive events

● Warming has positive feedback on plant communities

Elevated [CO2] EffectsIncreased Photosynthesis

● C3’s respond favourably● Most C4 grasses nearly CO2 -saturated at current [CO2]

(390umol mol-1)

Other responses● Herbaceous plants partially close stomata● Improved: WUE, plant/soil water relations, under water-

limited.

Rangeland Response to [CO2]

Rangeland Response Cont'dTemperature

● General positive responseo Sensitive biological processeso Stimulated growth at high lat and alt

● Negative response in dry and hot regionso Reduction in available soil moistureo Annual grasslands (south) may be better adapted

Precipitation● Timing of precipitation alone has effect on soil water

content. (10% negative change in aboveground NPP)o Cool-season species NPP primarily depends on soil

moisture in springo Warm-season, C4 and oak savanna species more

sensitive to summer vs winter precip changes.

Management Implications

Pasture● Increases in production come with the risk of

precipitation variability -> Greater livestock production potential for flexible management responses.

● Need long term multifactor studies examining climate change effect on less studied complex systems.

Rangeland Mgmt Implications● Simulation and experimental studies project:

o NPP increase in Great Plains native grasslandso Minimal response NPP in annual grasslands (in

California)● NPP increase in C3 species due to [CO2] may be

surpassed by greater preference of C4 to temperature increases

● Nutrient Cycling often limited by No effect of [CO2] on N is not fully known

Changes in rangeland species evidence of Climate Change effects?Precipitation change favours deep rooted forbs over herbaceous

More Evidence?● Mesquite and Creosote have replaced warm-season

perrenials in SW arid and semi-arid grasslands. Not all change can be accounted for by changes in grazing and fire practices.

● Expanded range of Cheatgrass (B. tectorum)

Summary of Table 3:Carbon dioxide and climate change responses and management options for grazing land factors.

Severity of Impact Impacts Management Options

1. Primary Production2. Plant Community3. Forage Quality

1. Little or no change:[CO2] - Water limitedTemp - Wet or Temperate

2. Shift toward C3

3. Increase when N ample

Stocking rates $Grazing systems $

1. Primary Production2. Plant Community3. Forage Quality

1. Variable change due to water uncertainty

2. (re)productive change; Transition to C4

3. Decrease in N-Limited ([CO2] and Inc. Fibre)

Adapted forage speciesFire management (new rangeland)Enterprise change $$

Interseed legumes $Fertilize where feasible $

1. Primary Production2. Plant Community3. Forage Quality

1. Decreases in arid and semi-arid2. Weeds3. Protein content falls below

acceptable limits

Enhanced weed control $Fire

Diet ammendment $$

Conclusions●Temperature and Precipitation will

potentially alter both Pasture and Rangeland more than increasing [CO2]o+NPP, +/- Communities, +/- Quality

●There will be change in all grazingland ecosystemsopositive or negative impacts on NPP largely due to

precipitation●Interactions between factors need more

studyoSoil-Plant-Water InteractionsoSoil microbiologyoMixed C3 & C4 communities