Re-introduction and translocation are conservation strategies often employed to circumvent declining wild orchid populations but their efficacy as conservation strategies is widely debated. The aim of this study was to investigate the long-term efficacy of re-introduction and translocation strategies for an endangered orchid as its climate changed. Vital rates of the wild, re-introduced and translocated populations of an endangered terrestrial orchid Caladenia amoena were compared from 2008 to 2019. Emergence and flowering declined at significantly faster rates in the translocated and re-introduced populations than in the wild population. Emergence and flowering declined as mean maximum temperatures rose, whereas flowering increased with rainfall. Both emergence and flowering were positively correlated with the length of the growing period, which decreased by >33% during the study. The relevant orchid mycorrhizal fungi (OMF) (Serendipita sp.) were more abundant in soil at the wild population than at the translocated or re-introduced populations. However, the limited soil sampling used to minimise disturbance may not have detected true fungal heterogeneity. This study suggests that translocation and re-introduction may not be effective long-term solutions for C. amoena. Reduction in above-ground growing period length was probably the over-riding influence in the decline of all populations. Greater OMF abundance in the soil may be the critical factor that renders the wild population more able to withstand the influences of climate change. Future research should consider methods to reduce the impacts of increased temperature and reduced rainfall on threatened orchid taxa.
Dormancy is common in many terrestrial orchids in southern Australia and other temperate environments. The difficulty for conservation and management when considering dormancy is ascertaining whether non-emergent plants are dormant or dead. Here we use a multi-state capture–recapture method, undertaken over several seasons, to determine the likelihood of a plant becoming dormant or dying following its annual emergent period and evaluate the frequency of the length of dormancy. We assess the transition probabilities from time series of varying lengths for the following nine terrestrial orchids in the genus Caladenia: C. amoena, C. argocalla, C. clavigera, C. elegans, C. graniticola, C. macroclavia, C. oenochila, C. rosella and C. valida from Victoria, South Australia and Western Australia. We used a Bayesian approach for estimating survivorship, dormancy and the likelihood of death from capture–recapture data. Considering all species together, the probability of surviving from one year to the next was ~86%, whereas the likelihood of observing an individual above ground in two consecutive years was ~74%. All species showed dormancy of predominantly 1 year, whereas dormancy of three or more years was extremely rare (<2%). The results have practical implications for conservation, in that (1) population sizes of Caladenia species are more easily estimated by being able to distinguish the likelihood of an unseen individual being dormant or dead, (2) population dynamics of individuals can be evaluated by using a 1–3-year dormancy period and (3) survey effort is not wasted on monitoring individuals that have not emerged for many years.
A disproportionate number of threatened plant species in Australia are found in the genus Caladenia, although little has been published on their life history. Here we examine data from nine species to evaluate some of the basic life-history strategies in Caladenia, specifically the transitions between life-history stages. We constructed life-history transition models of the orchids by using a Bayesian approach, we evaluated the growth rate of populations, compared transition values among species and determined which stage influenced the population growth most. We assessed extinction likelihood and considered the effect of variation in transitions among states on the probability of extinction. Bayesian model selection showed differences between species regarding their life cycle. The probability of individuals flowering in two consecutive years is extremely rare and was found to be common in only one species, C. amoena. All other species had a high likelihood of returning to a vegetative state, and some were likely to enter dormancy after flowering. High elasticities in the transition from the dormant to dormant stage suggest that dormancy has a large impact on population persistence. The quasi-extinction rate suggests that C. rosella, C. clavigera, C. graniticola and C. macroclavia are most at risk when all species have an equal initial population size. Conservation management should focus on studies to identify cues that influence flowering in consecutive years, emergence from dormancy and increasing recruitment.
The genus Caladenia contains the largest number of threatened orchid species in Australia and improv- ing the success of re-introductions would allow exist- ing populations to be strengthened and new popula- tions to be established. Batty et al. (2006) showed that direct seeding of C. arenicola Hopper & A.P. Br. into habitat soil inoculated with mycorrhizal fungus resulted in a good in situ germination rates.
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