Submitted to: Western Society of Weed Science
Publication Type: Abstract Only
Publication Acceptance Date: February 17, 2012
Publication Date: July 3, 2012
Citation: Blank, R.R., Morgan, T.A. 2012. Lepidium latifolium: monitoring stem density during 18 years of invasion [abstract]. Western Society of Weed Science. 65:50. Technical Abstract: Lepidium latifolium (perennial pepperweed) is a weedy alien crucifer that has invaded wetlands throughout the western United States. We are monitoring the invasion of an Elytrigia elongata (tall wheatgrass) community at the Honey Lake Refuge in northeastern CA. A 40m2 plot was established in 1993 and we have measured L. latifolium stem density yearly. In 1993, two single plants were present. From 1994 through 2000 density of L. latifolium increased to greater than 120 stems m-2, and was most pronounced following flooding in 1997. At its height of stem density and stature in 1999, it appeared that E. elongata had been extirpated. From 2001 through 2006 stem density and plant stature of L. latifolium declined, but there were still areas of the plot where stem density exceeded 60m-2. From 2007 through 2009 stem density decreased considerably and averaged less than 30 m-2 and a healthy recovery of E. elongata occurred. The years 2010, and especially 2011, stem density increased, but individual plants were small in stature. The decline in stem density over time supports our hypothesis that phosphorus is the nutrient “Achilles heel” of L. latifolium. Rooting architecture of L. latifolium dictates phosphorus uptake largely occurs deep in the soil profile where higher water content occurs. Biocycling of phosphorus to the soil surface, over-time, decreases its availability at depth.