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Invasive Species: A Study in Yellow

May 7, 2012

Springtime in Oregon, as seen from a car, reminds us that driving isn’t always about commuting or sobering pump prices: sometimes it’s about seeing as much beauty as possible on a Sunday afternoon.  One shrub in particular presents one of the most stunning displays that can be seen from virtually any highway in Oregon, painting entire hillsides in bold, broad strokes of yellow.

Photo Credit: D.G. Brown, Flickr Creative Commons

The shrub in question is Scotch Broom, Cytisus scoparius, and it is an invasive pest species that costs Oregon an estimated $47 million per year (Oregon Department of Agriculture 2012).

What are invasive species and why are they worth our concern?  There are several ways to define invasive species, but the most common one refers to any non-native species that has an adverse effect on the native ecology, environment, or economy of the bioregion it has invaded.  Some of the “success” stories of invasive species in North America include the European starling, Africanized “killer” bees, Fire ants, Rock pythons, Purple loosestrife, the Zebra mussel, and many others. So how does C. scoparius fit into this rogue’s gallery?

Scotch Broom was introduced to North America as an ornamental plant in the 1800’s (Hoshovsky 1986).  It was prized for its good looks, hardiness, affinity for disturbed or poor soils, and its ability to bind soil and prevent erosion (Hoshovsky 1986).  However, it soon became apparent that those same qualities also made it a serious pest.  Within two years of germination, C. scoparius can grow two meters high and begin producing hundreds of seeds that are hardy and can withstand dormancies lasting decades (Leblanc 2001).  Because it is a legume, it can thrive in nitrogen-poor areas and significantly alters soil chemistry in a way that could make it less hospitable to other species (Caldwell 2006).  Scotch Broom does especially well in disturbed soils, such as those found in recently cleared forestry lands and along highways or construction areas (Leblanc 2001).  These traits combine to make it an aggressive and formidable invasive plant that is detrimental to local ecologies and economies.

Scotch Broom taking over a river flat. Photo Credit: Mollivan Jon, Flickr Creative Commons

This three-part series of blog posts will focus on C. scoparius in Oregon as a case study for the larger topic of invasive species studies.  In the next post, we’ll discuss the impact C. scoparius has had on the ecology and economy of the Pacific Northwest: what it means when entire hillsides are painted yellow.

 

References

Caldwell, B.A., 2006.  Effects of invasive scotch broom on soil properties in a pacific coastal prairie soil.  Applied soil ecology: a section of Agriculture, Ecosystems, & Environment. 32: 149-152.

Hoshovsky, M. 1986. Element Stewardship Abstract for Cytisus scopairus and Genista monspessulanus. The Nature Conservancy. Arlington, VA, USA.

Leblanc, J.W. 2001. Getting a handle on broom: Scotch, French, Spanish, and Portuguese brooms in California. Publication 8049. University of California, Oakland, California, USA.

Oregon Department of Agriculture Plant Division. 2012. Noxious Weed Control: Scotch Broom (Cytisus scoparius).  <http://www.oregon.gov/ODA/PLANT/WEEDS/profile_scotchbroom.shtml.&gt;

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