Sustainable rare plant populations: Factors influencing probability and timing of next generation recruitment
For the 33,000 plant species estimated to be at risk of extinction worldwide, reintroduction is often suggested as a conservation strategy. The design and creation of reintroduced populations that are resilient to environmental change requires understanding the factors that influence population establishment. Using a sample of 102 rare plant reintroductions that were known to be extant in 2012 and have had second generation recruitment, we asked whether life history, maturation rate, founder population size, or life form influenced the probability and timing of second generation establishment. Using logistic regression with time since outplanting as a covariate, we examined the influence of four variables on the probability of second generation establishment. In addition we regressed maturation rate against time to next generation.
Not surprisingly, a significantly higher probability of second generation establishment occurred in short-lived, rapidly maturing taxa than for long-lived taxa. The probability of producing a second generation increased as founder population size increased, suggesting that many reintroductions are prone to founder effects. Species with longer maturation times had significantly greater lag times until next generation establishment than species with short-maturation times. Preliminary findings indicate that even species with 1-4 yr maturation times required up to 4 –8 years to establish next generation. Perennials requiring >10 years to achieve reproductive maturity represented 25% of our sample and are not expected to establish second generation for decades. These results have important implications for improving plant reintroductions. First, to improve the probability of long-term population sustainability, we recommend that practitioners consider as large a founder population size as feasible for the species. Second, expecting reintroduced populations of all taxa to show bench marks of high survival, reproduction, and second generation recruitment within a short time frame is biologically unrealistic. Finally, reintroduction plans should consider monitoring efforts on the scale of decades to measure success rates at time scales relevant to plant life-histories.