This is the latest in a long series of the possible consequences of supposed global warming. The dire scenario is set forth in a San Francisco Chronicle story by Joe Eaton and Ron Sullivan:
For educational purposes, the California Invasive Plants Council will sell you bouquets of plastic weeds, including yellow star thistle, tamarisk, leafy spurge and knapweed. Some recent studies suggest that many gardeners need not invest in these because they can expect more of the real thing to arrive as climate change advances.
Oh goody! I no longer need to shell out big bucks for those all-important plastic weeds. All I need do is wait for global warming to produce them naturally.
A warmer world will have more atmospheric carbon dioxide and nitrous oxide. UC Irvine's Diane Pataki says nitrous oxide has 300 times the global warming potential of carbon dioxide per molecule. It's released when soil bacteria covert ammonium to nitrite.
Weeds from warm climates are poised to claim new turf as temperatures increase.
Using each weed's preferred habitat characteristics and a scenario in which fossil fuel emissions are not reduced, Bradley and her colleagues created an invasion risk map for each weed.
Their results were mixed. The bad news for California: yellow star thistle will keep its current range and probably spread farther here and in Nevada. Tamarisk, an exotic tree that sucks wildland creeks dry, will neither gain nor lose in a warmer West. The largest effects the Princeton group predicted were for cheatgrass and leafy spurge, which will shift their ranges north, and spotted knapweed, which will move to higher elevations.
Climate change is a moving target, and some effects could turn out to be stronger than the models account for. There's also no foolproof way to identify which plants will become invasives. But with weeds moving both in from wildlands and out into them, it's safe to say that weed control will still be on every thoughtful gardener's agenda.
