Two decades of demography reveals that seed and seedling transitions limit population persistence in a translocated shrub

Abstract

Background and Aims: 'Olearia flocktoniae' is an endangered shrub that was passively translocated from its natural ecosystem, where it has since gone extinct. This study aimed to determine sensitivities vital to populations persisting in human-created areas. Methods: Population colonization, longevity and extinction were investigated over 20 years using 133 populations. Seed-bank longevity was determined from germination trials of seeds exhumed from extinct and extant sites via a 10-year glasshouse trial and by 'in situ' sowing experiments. From 27 populations, 98 cohorts were followed and matrix models of transitions from seeds to adults were used to evaluate the intrinsic rate of population growth against disturbance histories. Ten populations (38 cohorts) with different disturbance histories were used to elevate sensitivities in vital rates. Key Results: Most populations had few individuals (~30) and were transient (<5 years above ground). The intrinsic population growth rate was rarely >1 and all but two populations were extinct at year 20. Seeds were short-lived 'in situ'. Although >1000 seeds per plantwere produced annually in most populations, sensitivity analysis showed that the transition to the seed bank and the transition fromthe seed bank to seedlings are key vulnerabilities in the life-cycle. Conclusions: Seedling establishment is promoted by recent disturbance. Increasing the number of disturbance events in populations, even severe disturbances that almost extirpate populations, significantly increases longerterm population persistence. Only populations that were disturbed annually survived the full 20 years of the study. The results show that translocated populations of 'O. flocktoniae' will fail to persist without active management.