Twenty-Third Annual Meeting and Symposium of the
Desert Tortoise Council, April 3-5, 1998
Abstracts

Bromus rubens invaded the Mojave Desert in the early 1900’s and now dominates the winter annual population through much of the middle elevations. On the Nevada Test Site two Bromus removal experiments were performed to see if native species’ populations would rebound. In the first, when Bromus was selectively harvested from small quadrats early in the growing season, the native annual average weight was increased, but not to a statistically significant degree. In the second experiment, 100 m² plots were sprayed with a grass-specific herbicide (fluazifop) where Bromus was dense. Again, results suggested native population densities were increasing where Bromus was reduced, but few results were statistically significant. In three plots the weight of natives per square meter increased significantly in one, the density of natives increased in two, and number of species per quadrat increased significantly in two. The high spatial and temporal variability of native annual populations was a serious impediment to showing that Bromus was reducing native populations. However, observations made on these plots suggested certain species were more severely affected. In shaded conditions under shrubs Caulanthus cooperi and Phacelia vallis-mortae seemed more seriously inhibited. Another group of larger annuals increased on sprayed plots, and may require the more fertile soil under shrubs to mature. Those species included Rafinesquia neomexicana, Chaenactis stevioides and Malacothrix glabrata. Future experiments should be focused on particular species, in particular habitats, and should continue for long time periods.