Noxious Weeds at the Santa Rosa Plateau: the Via Volcano Weed Patch
The following map shows the extent of the Italian thistle, Carduus pycnocephalus, and yellow star thistle, Centaurea solstitialis, invasion along Via Volcano Road between Tenaja Road and the edge of the Mesa de Colorado. There are also a number of Tragopogon dubius plants in this area which are not shown in order to avoid further cluttering up the map.
Individual plants are plotted as individual points where the coverage is not nearly contiguous; areas are shown when there were too many plants to plot individually. Only the outline of each area is shown; in general, the noxious weeds fill at least 80% of each outlined area.
The mapping was done on 29 July 2005. At that time, the yellow star thistle was in full bloom, and could be identified from a hundred feet away. The Italian thistle had finished blooming then, so only plants close to the road could be identified.
The black line underestimates the width of Via Volcano Road. A small segment of the road near the turnout is plotted (in pink) at the actual width of the pavement of the road. The sides of the road have been mowed, and hence no weeds are plotted in that area.
An very rough estimate of the number of yellow star thistle plants is as follows:
- 31 individual plants plotted
- area west of turnout in road: 100 plants
- area west of road, large patch along drainage: 2,000 plants
- area west of road, small patch south of drainage: 50 plants
- area west of road, large southernmost patch: 1,000 plants
- all areas east of road: 400 plants
The total is over 3,500 plants. Judging by my past estimates, this could easily be an underestimate by a factor of 2 or more, since small plants were not included in the estimate.