Rare Habitat Threatened By Imported Weeds

February, 2010

 Yellowtuft grows to about one meter tall.  Because most of the leaves drop when the plants bloom during early summer, the two species look nearly identical in flower.  Both are fast growing perennials which become reproductive within a year or two. Photo by Ken French, Oregon Department of Agriculture.

Local botanists urge northwestern Californians to be on the lookout for two newly-introduced European species, commonly known as yellowtuft (Alyssum corsicum and Alyssum murale), which were planted in southwest Oregon with the intent of mining nickel from native serpentine soils.

The botanically unique serpentine areas in southwestern Oregon and northern California are the largest in North America.  This area is now at risk of invasion by these two plants; they recently escaped cultivation and have spread onto public lands, where they threaten native plant species.

Serpentine soils have natural concentrations of metals such as copper, chromium, and nickel at levels toxic to most plant species.  Interestingly, that very toxicity has resulted in high concentrations of certain rare plant species.  

More than 12 percent of California’s plant species are only found on these heavy metal-laden soils, even though only 1.5 percent of the state’s soils are serpentine.

“Nearly all of Oregon’s serpentine soils occur within Josephine, Jackson and Curry Counties, which make up only six percent of Oregon’s land area, said Kelly Amsberry, Conservation Botanist for Oregon Department of Agriculture, in an e-mail. “However, 28 percent of the rare plant collections in the Oregon State University Herbarium (the repository of the state’s floral diversity since the 1880’s) were collected in these three counties.  These collections represent not only the high concentration of rare species that inhabit southwest Oregon’s serpentine, but also the public’s long-standing interest in these unique plants.”

Yellowtuft was originally examined by the USDA for use in removing metals from polluted soils. These species showed promise because of their unique ability to extract metal and accumulate it into their tissues. A Texas-based company, Viridian Resources, then proceeded to use yellowtuft in an attempt to commercially mine naturally occurring nickel from serpentine soils near Cave Junction, Oregon.

Despite inadequate information about potential invasiveness, the Oregon State Extension Service promoted yellowtuft as a new farm crop. In 2002 Viridian Resources planted dozens of acres of yellowtuft throughout Josephine County’s Illinois Valley, including a 50-acre field at the county airport immediately adjacent to the floristically diverse Rough and Ready Botanical Area.

In 2006, two long-time Illinois Valley residents independently discovered yellowtuft growing on National Forest land near a popular swimming hole. This discovery led to increased vigilance and careful documentation of the plants’ expansion into wildlands.  By 2008, it became clear that yellowtuft was invading rare plant habitat well beyond the cultivated fields.

In August of 2009, after reviewing a formal Pest Risk Assessment and hearing public and private testimony, the Oregon State Weed Board voted unanimously to list both Alyssum species as Noxious Weeds.  Viridian Resources agreed to eliminate the fields that had been planted in Oregon – but invasion into wildlands had already begun.  

Widespread Impact

While mining serpentine soils with heavy equipment would impact plant communities and water quality, nickel mining with yellowtuft presents environmental problems of its own.

”Because both species of yellowtuft are restricted to nickel-containing soils in their natural ranges in southern Europe, these two species represent a unique threat to our flora,” said Amsberry.

 Ken French, Noxious Weed Specialist for Oregon Department of Agriculture agreed, adding, “Plants on serpentine soils have historically been less susceptible to invasion because of the high metal soils with low fertility. Now, along comes a plant that is specifically adapted to serpentine. Unless yellowtuft is stopped, the future of these serpentine plant communities are at a higher risk of invasion which could alter plant community composition, structure and function.”

“If yellowtuft invades, it has the potential to crowd out and displace rare plants,” said Amsberry.  “Rare plants receiving legal protection on Oregon’s publicly-managed serpentine areas include McDonald’s rockcress, Cook’s desert parsley, Howell’s mariposa lily, and Howell’s microseris.  Twelve additional rare serpentine plants could also be impacted.”

One of the most difficult aspects of managing invasive species is their ability to reproduce by seed.  Once seeds enter the landscape, controlling them becomes an unpredictable and expensive affair. It is unknown how long yellowtuft seeds remain viable in the soil, but it is likely that the more seeds that are produced, the longer and more expensive it will be to eradicate. 

Early Detection Is Key

When an invasion is at the beginning phases like this one, early detection makes a big difference. Yellowtuft is most likely to be spotted near California along the Wimer Road (Forest Road 4402), along Highway 199.

In Oregon, detecting spread along the forks of the Illinois River downstream of the Rough and Ready mill will be critical.

If you learn of any plantings or you discover yellowtuft spreading into nature, please contact  the Humboldt-Del Norte Weed Management Area Coordinator, or the Invasive Plants Coordinator of the North Coast Chapter, California Native Plant Society.

For more information on the plant diversity and natural history of serpentine habitats in the Klamath-Siskiyou Mountains, click here.

Alyssum corsicum, seen here in the foreground, has grayish white oval shaped leaves about 0.5-1.5 cm long  and covered by dense silvery hairs.  Alyssum murale, seen in the background, has gray-green leaves 0.5-1.0 cm long that are wider near the tip than at the base.

Photo by Maureen Jules.

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