Effects of life history and reproduction on recruitment time lags in reintroductions of rare plants

Abstract

Reintroductions are important components of conservation and recovery programs for rare plant species, but their long‐term success rates are poorly understood. Previous reviews of plant reintroductions focused on short‐term (e.g., ≤3 years) survival and flowering of founder individuals rather than on benchmarks of intergenerational persistence, such as seedling recruitment. However, short‐term metrics may obscure outcomes because the unique demographic properties of reintroductions, including small size and unstable stage structure, could create lags in population growth. We used time‐to‐event analysis on a database of unusually well‐monitored and long‐term (4–28 years) reintroductions of 27 rare plant species to test whether life‐history traits and population characteristics of reintroductions create time‐lagged responses in seedling recruitment (i.e., recruitment time lags [RTLs]), an important benchmark of success and indicator of persistence in reintroduced populations. Recruitment time lags were highly variable among reintroductions, ranging from <1 to 17 years after installation. Recruitment patterns matched predictions from life‐history theory with short‐lived species (fast species) exhibiting consistently shorter and less variable RTLs than long‐lived species (slow species). Long RTLs occurred in long‐lived herbs, especially in grasslands, whereas short RTLs occurred in short‐lived subtropical woody plants and annual herbs. Across plant life histories, as reproductive adult abundance increased, RTLs decreased. Highly variable RTLs were observed in species with multiple reintroduction events, suggesting local processes are just as important as life‐history strategy in determining reintroduction outcomes. Time lags in restoration outcomes highlight the need to scale success benchmarks in reintroduction monitoring programs with plant life‐history strategies and the unique demographic properties of restored populations. Drawing conclusions on the long‐term success of plant reintroduction programs is premature given that demographic processes in species with slow life‐histories take decades to unfold.

Genetic monitoring of translocated plant populations in practice

“…As most of the newly established individuals had distinct multilocus genotypes, and given the low values for the clonality rate, we can assume that clonality played a marginal role in the establishment of the rosettes identified as new individuals in the field. Recruitment was therefore mainly based on sexual reproduction, indicating the success of the translocation design in initiating population demographic growth and in increasing the effective population size (Albrecht et al., 2019; Menges, 2008).…”

“…The success of a translocation (and its design: the choice of source populations, seed collection, number of translocated individuals and planting design) in restoring genetically viable and self‐sustaining populations is usually evaluated by demographic monitoring (Albrecht et al., 2019; Godefroid et al., 2011). Demographic monitoring assesses population processes such as recruitment, survival and reproductive success.…”

An early evaluation of translocation actions for endangered plant species on Mediterranean islands

“…The success of such projects can rarely be evaluated in the short-term, because seeds may enter the soil seed bank and persist there for years. As noted by Albrecht et al. (2018), little is understood about translocating annuals, for which there is no alternative to sowing.…”

Guidelines for genetic monitoring of translocated plant populations

“…Demographic monitoring is very useful to assess population growth by recruitment, plant survival and reproductive success (Godefroid et al 2011;Commander et al 2018;Albrecht et al 2019;Fenu et al 2019). However, it cannot give insights into the evolutionary potential of translocated populations nor into the detailed reproductive processes occurring after translocation, which are key determinants of the success or failure of the translocation (Schwartz et al 2007;Van Rossum et al 2020).…”