Center for Conservation Biology

In 2002, the Center for Conservation Biology (CCB) of the University of California at Riverside initiated a multi-year collaboration with the Coachella Valley Association of Governments to develop a monitoring framework for the Coachella Valley Multiple Species Habitat Conservation Plan (CV MSHCP) (see Allen et al 2005). This final report reflects the findings for the 2005-2006 project period (September 1, 2005 – December 31, 2006), undertaken by the CCB’s Desert Studies Initiative, to initiate an analysis of the impacts of the exotic weed, Saharan mustard (Brassica tournefortii) with regard to the conservation goals of the CV MSHCP. 2005 marked the most severe outbreak of Saharan mustard in more than a decade. Concern over the impacts of this weed not only with regard to the CV MSHCP, but in the entire southwestern desert region was the impetus for initiating this research. In particular, the questions addressed were the following, and are answered in the next section:

• What variables best predict the occurrence and density of this weed species?

• Does anthropogenic nitrogen deposition influence its distribution and density?

• Is the extent of the weed infestations expanding, or is it an oscillation in response to the pattern and amount of precipitation?

• What are the impacts of the exotic plants on the aeolian sand community? Are the impacts different in the different habitat divisions of the aeolian community?

• Does weed density impact CV fringe-toed lizard or flat-tailed horned lizard populations? Are impacts similar for these two species?

• Does weed density impact CV milkvetch populations? Does it impact plant distribution and/or reproduction?