ABSTRACT: Plant succession remains a poorly understood process in the Mojave Desert, yet knowledge is needed in this area where increasing human populations may amplify disturbance frequencies and intensities. In a retrospective study, we examined plant communities on two pipeline right-of-ways cleared in 1998 or 1968 to supply water to metropolitan Las Vegas, Nevada. We also evaluated the effectiveness of restoration treatments (raking soil surfaces, spreading artificial desert varnish, and planting four species of native shrubs) applied by the National Park Service on the 1998 right-of-way to enhance recovery of Larrea tridentata communities. Plant cover was sparse (less than 5%) on the untreated 1998 right-of-way eight years after clearing, with a mean shrub density of only 99/ha. On the restoration-treated area, however, L. tridentata established at a density of 300/ha., 36% of the density of an adjacent control area. Restoration treatments also made the right-of-way less visually distinct from surrounding L. tridentata communities. Even 38 years after clearing, the older right-of-way was dominated by species such as Stephanomeria pauciflora and Encelia farinosa, which are classified as early colonizers in the Mojave Desert. Our findings concur with long recovery estimates after vegetation-removing disturbances given in the literature, but suggest that ecological restoration has potential for manipulating the speed and trajectory of plant succession in the Mojave Desert.
ABSTRACT: We report 83 taxa vouchered from Riverside County west of the San Jacinto Mountains not included in our earlier checklist for western Riverside County (Roberts et al. 2004). In addition, four species and a variety are deleted from that checklist based on redetermination of specimens. We also include short discussions of several species reported from western Riverside County by various sources, but to our knowledge not confirmed by specimens, or excluded for other reasons. With these additions and deletions, the known western Riverside County Flora now totals 1,489 taxa (species, subspecies, varieties, and hybrids).