mixed results for weeds

Weeds from warm climates are poised to claim new turf as temperatures increase. But other invasives may lose ground.

Princeton researchers Bethany Bradley, Michael Oppenheimer and David Wilcove used computer models of global climate change to predict the future ranges of weeds that are widespread in the West.

Just as native species are expected to shift in range and relative competitiveness with climate change, they wrote in a study published in the journal Global Change Biology, “the same should be expected of invasive species.”

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.

SFGate, 16 Aug 2009