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

Abstract

Background and AimsOlearia 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.MethodsPopulation 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 evaluate sensitivities in vital rates.Key ResultsMost 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 plant were produced annually in most populations, sensitivity analysis showed that the transition to the seed bank and the transition from the seed bank to seedlings are key vulnerabilities in the life-cycle.ConclusionsSeedling establishment is promoted by recent disturbance. Increasing the number of disturbance events in populations, even severe disturbances that almost extirpate populations, significantly increases longer-term 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.

Seed provenance for changing climates: early growth traits of nonlocal seed are better adapted to future climatic scenarios, but not to current field conditions

“…The reasons why uncommon species fail to thrive in restoration sites (e.g. Olearia flocktoniae ; Gross & Mackay ) may not be that different from the reasons that common species sometimes fail to thrive—comparative approaches have yet to explain substantial variation among rare and common species (Bevill & Louda ; Scott & Gross ; Kolb et al ) in establishment success. However, although many researchers stress the importance of microclimate matching for restoration success (e.g.…”

“…Using a combination of genetic screening, climate‐house stress experiments, and field trials, we evaluated the performance of local and nonlocal seed sources for Hardenbergia violacea , a desirable species for restoration (see below). We focused on the regeneration phase, which although short, can have a long‐lasting effect on species (Poorter ) and population persistence (Gross & Mackay ).…”

“…violacea, a desirable species for restoration (see below). We focused on the regeneration phase, which although short, can have a long-lasting effect on species (Poorter 2007) and population persistence (Gross & Mackay 2014).…”

Time to cut: population models reveal how to mow invasive common ragweed cost-effectively

“…Although the pattern of the r-cost curves is independent of seed survival, mowing will bring r to lower values when seed survival is lower. It is known in other systems, especially annuals with a seed bank, that demographic models can be strongly influenced by seed survival rates (Gross and Mackay 2014), but long-term data on spatial variation in soil seed banks are scarce for many invasive species (Gioria et al 2012). Secondly, we do not, unfortunately, have field data on how mowing affects recruitment, sizes of new plants and plant survival of our species and hence, we did not include such effects in our models.…”

Arrested recovery in a sandy woodland correlates with a lack of heavy and long seeds in the seed bank

“…Although we have presented extensive information on dormancy, these data are not a surrogate for persistency as there is no simple relationship between the two (Baskin andBaskin 1998, Thompson et al 2003)-seeds with a physiological dormancy mechanism germinated within 7 days in our study and sporadically through to the end of the trial (e.g., Aristida ramosa, data not shown). Non-dormant seeds can be quiescent and persist in the seed bank, just as they can in a packet of seeds (Gross and Mackay 2014). For these reasons we urge caution in equating persistence with a dormancy mechanism; using this approach to determine the placement of seeds with persistence against seed shape and mass will be meaningless.…”