Differences in emergence and flowering in wild, re-introduced and translocated populations of an endangered terrestrial orchid and the influences of climate and orchid mycorrhizal abundance

Abstract

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.

Preventing Extinction of the Critically Endangered Dactylorhiza incarnata subsp. ochroleuca in Britain Using Symbiotic Seedlings for Reintroduction

“…It has been shown that understanding the mycorrhizal diversity and density in the reintroduction site is also key to successful population establishment [ 35 ]. Testing sites suitable for reintroduction/translocation of rare orchids with symbiotic seedlings offer opportunities.…”

“…Putative mycorrhizal fungi from protocorms [ 36 ] or seedlings [ 37 , 38 ] serve as reliable symbionts for seed germination. In some cases, the orchid seeds can only be germinated by a specific lineage of the mycorrhizal fungus from protocorms [ 35 ]. The current study used fungi available from plants at different growth phases and found that Tulsanella OTU from mature phase D. praetermissa was a germination-compatible fungus.…”

“…Greater OMF abundance in the soil is considered as one of the critical factors that render the wild population more able to withstand the influences of climate change [ 35 ]. Additionally, identifying the mycorrhizal fungal diversity and abundance using the qPCR method offers quick and reliable information on the suitability of the proposed reintroduction/translocation site.…”

Optimising conservation translocations of threatened

“…Studies of natural or translocated populations of orchids have often assessed habitat suitability at the population level and for suitability of adult persistence (Janes et al 2010;Duncan and Moloney 2018;Janissen et al 2021), or if comparing microsites, examined the persistence of flowering individuals (Moisan and Pellerin 2013), rather than seedlings. Investigation of microsites suitable for germination of terrestrial orchids (regenerative niche) has been undertaken using seed-burial trials, which is when seed is put in packets and buried near plants or across transects in existing populations (Rasmussen et al 2015).…”

“…Similarly, changes in rainfall patterns between years could see orchids germinate that may not survive (Jersáková and Malinová 2007). In the case of many threatened species, sites may be degraded, within the urban landscape (Duncan and Moloney 2018;Janissen et al 2021) and unrepresentative of the broader habitat requirements of the species. To optimise conservation translocation plantings and funding to the greatest effect, and ensure successful recruitment and sustainable populations, we need to know both the sites that are suitable for adult plants and the sites that are suitable for recruitment, and where these intersect.…”