Experimental reintroduction of the federally endangered Santa Cruz Island bush mallow (Malacothamnus fasciculatus var. nestioticus)
Studies of Malacothamnus fasciculatus var. nesioticus were begun in 1995 to understand its distribution, reproductive biology and ecological requirements. After 100+ years of depredation by sheep, two known populations of fewer than 20 plants each survived in 1995. Molecular studies showed that each of the two populations was composed of 1–3 genets. During our study, two additional populations of similar size were discovered. Plants are self-compatible but require insect visitation to augment pollination. Based on seed set, viable embryos, and germination rates, we found no evidence for inbreeding depression. Bush mallow also reproduces vegetatively by rhizomes, the primary means of establishment and persistence in natural populations, and a key feature for maximizing recovery success. Ex situ observations and trial in situ outplantings suggested that supplemental watering was critical to initial survival. We developed a recovery strategy composed of four plots located at varying elevations and aspects. Each plot was enclosed to exclude feral pigs, which posed a continuing threat. Each plot was planted with twelve rooted plants derived from each of three natural populations. Plants were provided supplemental watering for four months. Survivorship after one year ranged from 46% to 91%. Significant differences in survivorship were observed relative to source of plants. After twelve months some plants were flowering and reproducing vegetatively.