干旱区生态环境知识资源中心

This study was conducted to determine what changes have occurred in an arid alluvial riparian shrub habitat in the upper Santa Ana River basin over a 20+-yr period beginning prior to the completion of the Seven Oaks Dam in San Bernardino County, California and continuing until 8 yr after the completion of the dam in 2000 to assess the implications any changes may have on the persistence of the short-lived Santa Ana River Woolly Star (Eriastrum densifolium ssp. sanctorum, Polemoniaceae). Small-scale habitat changes were determined by comparing non-native annual plant data from 1989 to 2008. Large-scale habitat changes were determined by comparing perennial plant data from 1987 to 2008. The results of this study suggest that annual species, lichen crust, and dead shrubs are increasing, and that bare ground and live shrubs are decreasing. The older sites are also increasing in annual grass cover. Successional changes have occurred since the last significant flood event in 1969 although these changes are gradual and on a continuum, precluding a sharp distinction between different age stages. The data support previously predicted rates of succession indicating ultimate maturity within at least 100 yr. The continuation of these habitat changes will likely contribute to the decline of the Woolly Star population, particularly during future drought periods.