Conservation translocation – an increasingly viable option for managing threatened plant species

Abstract

Translocation is the establishment and augmentation of plant populations using ex situ material, and can reduce extinction risk. Historically, translocation has been considered to be high cost and high risk, but today, translocation is increasingly recognised as a necessary option for managing many threatened plant species. To examine the viability of translocation as a management action, we analysed the frequency of it being a recommended management action, its estimated cost over time, and its perceived likelihood of success as compared with other management actions. We did this using the 368 threatened plant species in the New South Wales state register of threatened species management strategies (the Saving our Species (SOS) database). Translocation was recommended as a management action for 30% of threatened plants (112 species), mostly in response to demographic threats (i.e. threats affecting species with small population sizes/restricted distributions, for example, environmental and demographic stochasticity or low genetic diversity). The estimated cost of translocation per species was similar to other common management actions. However, expert elicitation data (in the SoS database) indicated that translocation was less certain of a beneficial outcome, compared with almost all other management actions. Based on these findings, we create a decision framework, which uses the principles of extinction risk assessment to assist conservation managers in determining when translocation is most likely to be beneficial. We suggest that the use of translocation to mitigate the risk of extinction associated with small population sizes/restricted ranges is supported by the principles of extinction risk assessment. With a growing knowledge base, and costs comparable to other management actions, translocation is becoming an increasingly viable option for the conservation management of threatened plants, provided best practice guidelines are followed.

Mixing gene pools to prevent inbreeding issues in translocated populations of clonal species

“…The choice of seed source populations for translocations is still usually determined based on demographic criteria (large census sizes, high reproductive success) (e.g., Fenu et al, 2019; Zimmer et al, 2019). When the genetic status of the source populations could be assessed, it has often been conducted on the adults (e.g., Orsenigo et al, 2017; Van Rossum & Raspé, 2018; Van Rossum, Destombes, et al, 2021; but see Gentili et al, 2019; St. Clair et al, 2020).…”

“…However, some specialized habitats are too isolated in inhospitable landscape matrices, with geographic distances exceeding pollen and seed dispersal abilities of the target species, and many declining species do not form such a persistent seed bank or the seed bank is already impoverished (Godefroid et al, 2018; Török et al, 2018). In such case, the strategy is to implement assisted gene flow by intentionally introducing new genetically diverse material by plant translocations (seed sowing or plug planting), to reinforce (augment) existing populations, to replace extinct populations (reintroduction) or to establish populations in new locations (introduction) (Ottewell et al, 2016; Weeks et al, 2011; Zimmer et al, 2019).…”

“…The design of the translocation, such as the choice and number of populations used as sources for material (seeds, cuttings), the number of seeds or cuttings collected, the number of translocated founders (plug plants or sown seeds), planting design and pre‐ and post‐translocation management interventions in the field are important determinants of translocation success (e.g., Maschinski & Albrecht, 2017; Silcock et al, 2019; Van Rossum et al, 2020). The source populations are usually selected using demographic criteria (populations size, reproductive success) or represent what remains (Fenu et al, 2019; Godefroid et al, 2011; Zimmer et al, 2019). Evaluating the genetic status of the potential source populations, whether they show high genetic variation, and low genetic differentiation and inbreeding levels can also be important (e.g., Commander et al, 2018).…”

“…deltoides , molecular markers were not available yet at the start of the restoration project. Therefore, demographic criteria (see e.g., Commander et al, 2018; ENSCONET, 2009; Zimmer et al, 2019) were used to select the populations as seed sources for propagating the transplants (= founders) of the translocated populations. The last four large local populations in Belgian Lorraine were selected as seed sources (Godefroid et al, 2016b).…”

U.S. conservation translocations: Over a century of intended consequences

“…The geographic distributions of released individuals of the 1,014 conservation translocated taxa and 676 beneficial biological control agents in our dataset revealed that translocated organisms have constructively shaped every ecological community in the contiguous U.S. and Hawaii, as well as many Alaskan ecosystems. Conservation translocations of dozens of taxa are presently in active planning, with hundreds more slated long-term, a trend that appears consistent in other countries (Carter, Foster, & Lock, 2017;Cromarty & Alderson, 2013;Swan et al, 2018;Zimmer, Auld, Cuneo, Offord, & Commander, 2019). Conservationists have avoided damaging unintended consequences because of careful risk assessment and mitigation planning; however, the risks incurred by delaying beneficial translocations fall on the shoulders of regulators and decision-makers.…”