Long‐term impacts of dam construction on plant succession and survival of an endangered species

Abstract

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.

A dam in the drylands: Soil geomorphic treatments facilitate recruitment of the endangered Santa Ana River woolly star

“…A)—altered the natural hydrology and disturbance regime of the Santa Ana River floodplain, thus limiting the normal scouring and deposition processes that confer favorable habitat for woolly star and two other endangered species: the slender‐horned spineflower ( Dodecahema leptoceras ) and the San Bernardino kangaroo rat ( Dipodomys merriami parvus ; Lucas et al. ). Such alterations ultimately preclude natural succession of this alluvial scrub habitat and may result in altered plant communities and species extinction.…”

“…Years (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000) of dam construction and completion (2000) are denoted by the light teal polygon; experimental plots establishment (white) and surveys (purple) are denoted by points along the x-axis. rat (Dipodomys merriami parvus; Lucas et al 2016). Such alterations ultimately preclude natural succession of this alluvial scrub habitat and may result in altered plant communities and species extinction.…”