Evaluation of assisted colonization strategies under global change for a rare, fire-dependent plant (Tecate cypress).

Abstract: As a clear consensus is emerging that suitable habitat for many species will dramatically reduce and/or shift with climate change, attention is turning to adaptation strategies to address these impacts. Assisted colonization is one such strategy that has been predominantly discussed in terms of the costs of introducing potential competitors into new communities and the benefits of reducing extinction risk. However, the success or failure of assisted colonization will depend on a range of population-level factors on which the climate change literature has been relatively silent—the quality of the recipient habitat, the number and life stages of translocated individuals, the establishment of translocated individuals in their new habitat and whether the recipient habitat is subject to ongoing threats all will play an important role in population persistence. We link a population model with dynamic bioclimate envelopes to investigate expected changes in populations with climate change, the impact of altered fire regimes on population persistence, and how much assisted colonization is necessary to minimize risk of decline in populations of Tecate cypress, a rare endemic tree in the California Floristic Province, a biodiversity hotspot. We show that when there are large source populations that are expected to decline dramatically due to habitat contractions, multiple nearby sites predicted to contain suitable habitat, minimal natural dispersal, high rates of establishment of translocated populations, and the absence of more serious ongoing threats, assisted colonization may be a risk-minimizing adaptation strategy. However, when serious ongoing threats exist, assisted colonization is ineffective.