A few years back I went to a meeting in Denver sponsored by the Colorado Cattlemen’s Society. I don’t remember the exact title, but it was something about how ranchers could adapt to a changing climate. Scientists explained what their research was telling them about plant responses to increasing CO2 in the atmosphere, and shared computer models of how the weather might change in different parts of the country. As is normal for scientists, their talks were laced with the words, “probable,” “possible,” and “further research is needed.” That’s because, as we all know, the more you learn, the more you realize that there are always a lot of factors affecting what’s happening on a day to day basis, making it difficult to be “sure” of anything. During breaks the cattlemen shook their heads and laughed. It’s hard to make decisions about such long-term potentials when you’re trying to solve today’s very real problems.
I was reminded of that meeting when I came across a 2008 presentation to the Northeastern Weed Science Society, by USDA-ARS scientist Lewis Ziska describing his research on how increasing levels of atmospheric CO2 might affect agriculture and the weeds that so many folks combat. For those who think of pasture weeds as problems, the results of research aren’t good news. Yes, CO2 does increase your pasture weeds, and the weeds seem to do better than our grasses.
In his presentation, Ziska shared results of research showing that:
• Initial evidence indicates that warmer winters are a factor in the northward spread of Kudzu. His work shows that it is likely to spread as far north as the Great Lakes region by 2019. He said that “Data suggest that the link between global warming and the spread of an invasive species is real, not hypothetical.”
• For those of us in the west where cheatgrass is expanding its range, data shows that higher levels of atmospheric CO2 make cheatgrass more combustible. This lowers the point at which cheatgrass becomes a fire fuel and increases fire intensity. Though additional research needs to be done, Ziska said that, overall, the likelihood of fire in cheatgrass has increased as a function of recent increases in CO2. Increased CO2 also reduces the digestibility of many grasses, including cheatgrass. In regions where the spring flush of cheatgrass is the primary forage for cattle, this is not good news.
• Ziska’s work with Canada thistle and CO2 indicates that Canada thistle does quite well as atmospheric CO2 increases. The plant, which can spread by roots (rhizomes) increases root growth as CO2 increases whether nitrogen is present in the soil or not.
He concluded his presentation by saying that we need new management strategies for weeds and that we “Can no longer assume that what worked in the past will work in the future.”
None of that feels like very good news if we keep on thinking of pastures as we’ve always thought of them. But if we change our ideas about pastures and think of “weeds” as forage, the future could still be pretty bright.