Study Predicts Climate Change Impact on Invasive Plants

A new study by researchers at Princeton University's Woodrow Wilson School of Public and International Affairs has found that global climate change may lead to the retreat of some invasive plant species and the spread of other invasive plants in the western United States, according to a Jan. 27 press release.

The study, "Climate Change and Plant Invasions: Restoration Opportunities Ahead?" was co-authored by Bethany Bradley, a biogeographer, Michael Oppenheimer, a geoscientist, and David Wilcove, a conservation biologist, at Princeton's Woodrow Wilson School, and will soon be published in the journal Global Change Biology.

To view the article, visit http://www3.interscience.wiley.com/journal/121521769/abstract.

The researchers assessed the relationship between climate change and the distribution of five prominent invasive plants in the western United States: cheatgrass; spotted knapweed; yellow starthistle; tamarisk; and leafy spurge. Invasive plants are increasingly expensive to control, and it is widely believed that global warming will make the problem worse.

The study authors created "bioclimatic envelope models," wherein the authors identified where the invasive plant species occurred and identified critical climate variables such as precipitation patterns and temperature patterns that are associated with the presence of the invasive plants under investigation. The authors then determined what combined set of climate variables best described the distribution of these weeds, and mapped all of the places where these climate conditions occur.

The researchers employed 10 atmosphere-ocean general circulation models (AOGCMs) that predict what climatic conditions in the West are likely to be in 2100 if emissions are not limited, and matched those predicted conditions to the climate conditions associated with each of the invasive plant species. The projected invasive species distributions for each of the models were added together to create a map of invasion risk under future climate conditions.

The researchers concluded that climate change is likely to expand invasion risk from yellow starthistle in California and Nevada – and lands currently occupied by invasive populations of the weed in California, Oregon, and Washington are unlikely to become unsuitable for the species; hence, they have low potential for restoration. Tamarisk distribution, they found, is unlikely to be affected by climate change.

Cheatgrass, however, is likely to be affected by climate change, potentially moving northwards into parts of Idaho, Montana, and Wyoming, but retreating in southern Nevada and Utah. And, according to Bradley and her co-authors, the impacts of climate change will likely shift spotted knapweed, currently distributed throughout the foothills of the Rocky Mountains and the Colorado Plateau, to higher elevations, leading to both expanded risk and restoration opportunities in part of Montana, Wyoming, Utah, and Colorado.

Leafy spurge, abundant in northern states west of the Mississippi River and some rangeland west of the Rockies, will likely retreat from some places in the face of climate change, creating restoration possibilities in Colorado, Nebraska, Iowa, and Minnesota – but potentially expanding into parts of Canada not included in the researchers' study. In addition, the researchers found that leafy spurge is likely to retreat from Nebraska and parts of Oregon and Iowa, creating strong potential for restoration in these areas.

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