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Rates and patterns of revegetation were studied during and after construction of the 500 kV Navajo Project Southern Transmission Line at two sites in the Arizona Sonoran Desert from 1972 through 1977. Herbs were reduced temporarily during the construction phase of the study. Perennial herbs did not return in the 5-year post-construction period. Annual herbs invaded immediately after disturbance. In one case annual herb density and diversity was higher after disturbance due to removal of larger woody plants. The tree and shrub community exhibited dynamic changes in cover, diversity, and richness, presumably in response to the climate. However, colonization by new species was not observed during the 5 years of study. Colonization by previously existing species seemed to be limited to Ambrosia deltoidea, probably due to its ability to reproduce vegetatively and to annual herbs. Annuals which were also on two control plots were probably a colonizing sere of plants. Patterns of revegetation and plant succession in arid areas have been documented by only a few researchers. Wells (1961) described a specialized community, with more species than the climax, that established itself on the deserted streets of a Nevada ghost town. The specialized community persisted in marginal areas such as arroyo bottoms where the neighboring climax was prevented from becoming established, probably because of natural disturbances there. Its presence on the streets was thought to be due to the removal of the more competitive climax shrubs. The results obtained by Vasek, et al. (1975) were similar, especially that washes served as refugia for pioneering species. However, they also emphasized that the early successional species composed a significant proportion of the undisturbed vegetation. The ability of the original plants to regrow, either from seeds or rhizomes may also be a crucial factor in patterns of revegetation. Egler (1954) and Connell and Slatyer (1977) have discussed this concept and Niering and Goodwin (1974) have shown its importance under a powerline in Connecticut. We studied revegetation and colonization of plants before, during, and after construction of the 500 kV Navajo Project Southern Transmission Line (NPSTL), which connects the Navajo Power Plant in Page, Arizona, with Phoenix, Arizona. Construction was initiated in 1972 when a survey strip varying from 7 m to over 20 m wide was cleared by bulldozers. The middle of the survey strip received additional use as an access road while pylons and powerlines were erected in 1973. We chose two areas along the powerline which had received different degrees of disturbance. At Site 1, vegetation and the top Authors are with the Department of Biological Sciences, Northern Arizona University, Flagstaff 8601 1. Authors thank Arizona Public Service Company. Tucson Gas and Electric Company, and Salt River Project for funds to conduct this research. Manuscript received September 18, 1980. several inches of soil were removed on a hillside. At Site 2 large trees, cacti, and shrubs were removed, but removal of small shrubs such as bur-sage (Ambrosia deltoidea (Torr.)) and prickly pear cactus (Opuntia probably phaeacantha Engelm.) was not

Disturbance and Revegetation of Sonoran Desert Vegetation in an Arizona Powerline Corridor