Relative roles of founder population size, propagule stage, and life-history in the persistence of reintroduced plant populations

Background/Question/Methods The reintroduction of rare and endangered plant species to unoccupied habitat is now widely practiced to conserve biodiversity. Yet very little is known about the ecological determinants of successful and failed plant reintroductions. We compiled a global dataset, consisting of 60 plant taxa and over 150 reintroduction events, via literature review and by extracting information from the Center for Plant Conservation’s (CPC) International Reintroduction Registry. For each reintroduction event, the following predictor variables were recorded: 1) founder propagule stage, 2) initial population size, 3) life-history, 4) project onset date and duration, and 5) whether the reintroduced population persisted or not. We used generalized linear mixed models to answer the following questions: How do initial population size and propagule stage influence the persistence of reintroduced plant populations? Does the persistence of reintroduced populations vary across life histories? How does reintroduction success vary within and among taxa?

Results/Conclusions Population persistence varied across life histories (P < 0.05). Overall, perennials were easier to establish a persistent population than with annuals, but there was considerable variation within life histories. Separating perennials into herbaceous and woody plants revealed that the odds of establishing a persistent population with the latter was 2.7 times greater than with the former, although this was only marginally significant (P = 0.08). Compared to annuals, the odds of population survival was 5.2 and 14.3 times greater for perennial herbs (P = 0.09) and woody plants (P < 0.05), respectively. The odds of a population founded with plants were 7.0 times (P < 0.05) more likely to persist than a population founded with seed, but only 2.3 times more likely than those founded with seedlings (P = 0.18). Effects of founder size on population persistence also varied across life histories (P < 0.05). There was no relationship between initial population size and persistence in annual species founded with seed (P = 0.78). In contrast, increasing founder population size of non-seed transplants enhanced persistence in perennials, but not consistently among herbaceous and woody plants. Species accounted for more variation in a full model that all other parameters, indicating that persistence of reintroduced plant populations is highly idiosyncratic among species and sites. Our results offer guidance for improving success in future reintroductions, but also demonstrate that reintroduction is a risky and highly unpredictable endeavor.