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Morgan: analyze carbon dioxide effects on rangelands, agriculture at local level

by Wyoming Livestock Roundup

Denver, Colo. – “In the last 100 years, temperatures have increased by 1.5 to two degrees Fahrenheit,” says USDA Agricultural Research Service (ARS) research plant physiologist Jack Morgan. “By the middle of the century, a number of models project the temperature to increase from two to three degrees to as high as four to six degrees.”
    Morgan addresses the implications of a changing climate, noting there is concern that changes are becoming more dramatic.
    “People talk about climate change in a very blanket way, but it depends on where you’re at and the plant community,” he says. “North Dakota won’t look like or change like Arizona.”
    Morgan urges producers to talk to a local specialist to determine what climate change might look like in their region.
    “If the climate warms, the consequences are more precipitation worldwide and extreme weather events,” says Morgan.
Growing concerns
    “What concerns me most in terms of rangeland is consistent drying in the southwest and more southern latitudes,” says Morgan. “Through the years, we found a pronounced drying in those areas.”
    Morgan adds that the Mediterranean is consistently predicted to see more drought, as well, but other areas could see increased flooding and production.
    “Warmer temperatures could have a number of effects on rangeland,” he explains, marking a longer growing season, more pests and diseases, as well as altered hydrologic cycles, as potential consequences. “Timing for rainfall is also expected to change.”
    Plants respond differently to these changes, and Morgan notes that some will be favored, while other species will be outcompeted.
    “Increases in temperature can have positive and negative effects,” he explains. “It stimulates the cycling of nutrients in the soil and enhance growth. These types of positive responses are expected to be most important in humid to sub-humid climates.”
    “It can also cause desiccation and independently affect plant phenology,” he continues. “The particular outcome depends on where you are in the country, and we often find that the positive effects offset the negative.”
Increasing CO2
    Morgan says changes in temperature directly relate to increases in the concentration of carbon dioxide (CO2), and CO2 concentration changes also affect plant growth.
    “We know plants directly respond to carbon dioxide,” he explains. “CO2 is a substrate for photosynthesis. If we increase CO2, we see increases in photosynthesis and plant growth.”
    However, different plant species also respond differently, particularly when looking at C3 plants compared to C4 warm season grasses.
    Most plants are classified as C3, meaning they use CO2 to build a three-carbon compound in the leaf during photosynthesis. C4 plants, however, use CO2 to build a four-carbon compound and have been found to be more efficient in higher temperature climates.
    Originally, Morgan says they believed C3 plants would dominate when CO2 levels increased, but that wasn’t the case.
    “CO2 closes pores in C4 plants, and the response is really important – it makes them more water efficient,” Morgan comments. “CO2 has been important in the ability of these plants to move in and become dominant.”
    As a result, woody plants and shrubs seem to perform better in environments with a high CO2 concentration, which should be of concern for ranchers who use rangelands for grazing.
    “Some plants don’t respond much to CO2 because they run out of nitrogen,” explains Morgan. “Woody plants that can fix their own nitrogen really respond, however.”
Effects on livestock
    “The important thing to keep in mind is how climate change unfolds, and how it affects livestock operations will depend on where you are in the U.S.,” says Morgan. “CO2 is going up, we will see higher precipitation, forage production will increase and winters will be milder. It will have positive effects on livestock production.”
    Morgan also encourages producers to think about water and shade, as well as breeds and species more adapted to heat. For producers dependent on grazing, while forage ability may increase, Morgan cautions that species composition will be of concern.
    “Weather patterns are expected to become more variable and important factors for livestock managers to deal with in the future,” he adds.
    “My conclusions are that climate change and CO2 have likely already affected world rangelands,” says Morgan. “It can affect plant production and species shifts, but because plant communities are complex, projecting exactly how species will shift is difficult. Rangeland monitoring will be really important – even more important – in the future.”
    Morgan addressed the Small Ruminants Committee at the National Institute for Animal Agriculture Conference in Denver, Colo. on March 27. Saige Albert is editor of the Wyoming Livestock Roundup and can be reached at

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