Habitat changes and successional trends over a 20-year period within the upper Santa Ana River floodplain

Different stages of succession within the floodplain of the upper Santa Ana River have been documented by previous studies, predicting an eventual shift away from the sandy, sparsely vegetated conditions of the younger sites in the absence of future flooding. These habitat conditions are necessary for the endangered subshrub, the Santa Ana River woolly-star (Eriastrum densifolium ssp. sanctorum), as it does not survive on older surfaces due to competition with annual and woody perennial species.;This study was conducted in order to determine the changes that have occurred in this habitat over a 20-year period, and to assess the implications any changes may have on the persistence of the woolly-star. Small-scale habitat changes were determined by comparing annual plant data from 1989 and 2009. Large-scale habitat changes were determined by comparing perennial plant data from 1987 and 2009.;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. It appears that successional changes may have occurred over the past 20 years, although these changes are gradual and on a continuum, precluding a sharp distinction between different stages. The data appear to support previously predicted sucessional rates indicating ultimate maturity within at least 100 years. The continuation of these habitat changes will likely contribute to the decline of the woolly-star population, particularly during future drought periods.