Naturalization of Sequoiadendron giganteum (Cupressaceae) in Montane Southern California

Abstract

After the August 1974 fire in the upper Hall Canyon area on the southwestern flank of Black Mountain in the northwestern San Jacinto Mountains, Riverside Co., California, the United States Forest Service revegetated the burn in the mixed-conifer forest with the Sierra Nevada endemic Sequoiadendron giganteum (Cupressaceae). On 1 May 2009 a GPS census starting at the head of Hall Canyon revealed both in the canyon and upslope beyond it at least 157 individuals in the vicinity of the Black Mountain Trail, plus an outlier 450 m distant near the summit. This species alien to southern California is regenerating prolifically on Black Mountain, as revealed by multiple age classes, from juveniles (seedlings and saplings) about 20– 60 cm tall to young adult trees over 6 m tall, up to about 40 years old, and reproductively mature. The naturalized population (,7 ha in 2009) also appears to be spreading from its initial ‘‘small area’’ of introduction (,2 ha in 1974). Analysis of published print and Internet literature suggests similar post-fire naturalizations of S. giganteum in the San Gabriel and San Bernardino Mountains of Los Angeles and San Bernardino Counties. State and regional floras and checklists for California should acknowledge the naturalization of this species in montane southern California in the San Jacintos and possibly elsewhere.