Populations included in the database can be populations that have been reinforced with individuals from abroad (reinforcement) or created in a site where the species had gone extinct before (reintroduction) or in a site where it has never occurred to our knowledge (introduction or assisted migration), with the objective of improving or obtaining the viability (see box) of the population thereby reinforced or newly created. These translocations thus include conservation-driven translocations and certain mitigation-driven translocations where the viability of the translocated population is a clear objective of the translocation.

The necessary objective of viability can be one objective among others. For example, we include in the database populations that have been translocated with the double objective of obtaining both a viable population and data to improve further translocations (e.g. Colas et al. 1997, 2008, Noël et al. 2011), or with the double objective of obtaining a viable population as well as a so-called ecosystem service (Millenium Ecosystem Assessment 2005). We also include in the database translocated populations which viability is a particular goal included in a broader objective of, e.g., restoring a given community (e.g. Donath et al. 2007).

On the contrary, we do not include populations that were translocated for experimental purpose only, such as reciprocal transplant experiments to test for local adaptation with no aim of improving population viability (e.g., Raabová et al. 2007), or survival experiments in artificial ecosystems like aquaculture tanks (e.g. Balestri et al. 2011). We neither include the translocation of game species with no population viability consideration like, e.g., the massive release of captive born birds for recreative shooting. We neither include in the database translocation cases where individuals were just displaced from their original site to close vicinity, allowing these individuals to be saved from, e.g., civil engineering, but where no reinforcement and no new population could be considered (e.g. Bruelheide and Flintrop 2000).

We consider translocations in the Western Palearctic, i.e., in European territories up to Ural and Caucasus, and countries bordering the Mediterranean.

We consider all taxa from Animalia, Fungi, and Plantae kingdoms.

We use a definition of the population from population biology theory, i.e., a group of organisms of the same species that live together in a particular geographic area, with the capability of interbreeding or social interactions. Given what we know about the species biology, the landscape structure and the geographical distance between separated groups of individuals, if we believe that gene flow due to the dispersal of individuals or diaspores (e.g. seeds, fruits) or gametes (e.g. through pollen) between these groups probably occurs only on few occasions per generation, then we consider these groups of individuals as distinct populations. It might be difficult in some cases to decide whether different groups of individuals should be pooled into a single population. In practical terms, patches of plants separated by tens of metres can generally be grouped together into a single population when the barriers to pollen or seed dispersal between patches are weak.

Viability is a concept from population dynamics theory. Given the probabilistic nature of individual survival, growth, reproduction and dispersal, the persistence or extinction of a population in the future must be foreseen with probabilistic analysis. Sophisticated population viability analysis using demographic rates from individual monitoring and matrix models can be conducted to estimate extinction probabilities over a given time period (Beissinger and McCullough 2002). A population is then considered viable if its probability of extinction over a time period in the future is below a given threshold (e.g. less than 5% over 100 years). Practically, relevant demographic data sets allowing such sophisticated population viability analysis are scarce, and viability is often estimated using other indicators, such as those used by IUCN to classify species in Red List categories (A to D criteria in IUCN 2001). See Robert et al. (2015) for the use of red list criteria in the context of translocations.

Translocations are human-induced movements of living organisms into natural or semi-natural ecosystems (IUCN/SSC 2013).

Conservation translocations have the objective to improve the conservation status of a species, locally or globally, or to restore natural ecosystem functions or processes (IUCN/SSC 2013).

Conservation-driven translocations are initiated by conservationists (researchers or practitioners) with the conservation objective as a motivation at the origin of the translocation project. They are therefore necessarily conservation translocations as defined by the IUCN.

Mitigation-driven translocations consist of moving individuals threatened by a change in land use. These translocations have emerged and become widespread in many countries with the application of legal procedures for protected species under the mitigation hierarchy (avoidance, minimization, rehabilitation/restoration, offset; BBOP 2012). The initial motivation for mitigation-driven translocations is to comply with legal procedures, but such translocations may be conservation translocations (sensu IUCN) and be included in the Transloc database if they have incorporated a population viability objective (Julien et al. 2023).

Balestri, E., Vallerini, F., & Lardicci, C. (2011). Storm-generated fragments of the seagrass Posidonia oceanica from beach wrack - A potential source of transplants for restoration. Biological Conservation, 144(5), 1644-1654. https://doi.org/10.1016/j.biocon.2011.02.020

Beissinger, S. R., & McCullough, D. L. (Éds.). (2002). Population Viability Analysis. University of Chicago Press.

Bruelheide, H., & Flintrop, T. (2000). Evaluating the transplantation of a meadow in the Harz Mountains, Germany. Biological Conservation, 92(1), 109-120. https://doi.org/10.1016/S0006-3207(99)00061-0

Colas, B., Kirchner, F., Riba, M., Olivieri, I., Mignot, A., Imbert, E., Beltrame, C., Carbonell, D., & Fréville, H. (2008). Restoration demography : A 10-year demographic comparison between introduced and natural populations of endemic Centaurea corymbosa (Asteraceae). Journal of Applied Ecology, 45(5), 1468-1476. https://doi.org/10.1111/j.1365-2664.2008.01536.x

Colas, B., Olivieri, I., & Riba, M. (1997). Centaurea corymbosa, a cliff-dwelling species tottering on the brink of extinction : A demographic and genetic study. Proceedings of the National Academy of Sciences, 94(7), 3471-3476.

Donath, T. W., Bissels, S., Hölzel, N., & Otte, A. (2007). Large scale application of diaspore transfer with plant material in restoration practice - Impact of seed and microsite limitation. Biological Conservation, 138(1-2), 224-234. https://doi.org/10.1016/j.biocon.2007.04.020

IUCN/SSC. (2013). Guidelines for Reintroductions and Other Conservation Translocations. Version 1.0. IUCN Species Survival Commission.

Julien, M., Schatz, B., Robert, A., & Colas, B. (2023). Monitoring time of conservation-driven and mitigation-driven plant translocations in Europe. Plant Ecology. https://doi.org/10.1007/s11258-023-01311-7

Millennium Ecosystem Assessment (Éd.). (2005). Ecosystems and human well-being : Synthesis. Island Press.

Noël, F., Prati, D., van Kleunen, M., Gygax, A., Moser, D., & Fischer, M. (2011). Establishment success of 25 rare wetland species introduced into restored habitats is best predicted by ecological distance to source habitats. Biological Conservation, 144(1), 602-609.

Raabová, J., Münzbergová, Z., & Fischer, M. (2007). Ecological rather than geographic or genetic distance affects local adaptation of the rare perennial herb, Aster amellus. Biological Conservation, 139(3-4), 348-357. https://doi.org/10.1016/j.biocon.2007.07.007

Robert, A., Colas, B., Guignon, I., Kerbiriou, C., Mihoub, J.-B., Saint-Jalme, M., & Sarrazin, F. (2015). Defining reintroduction success using IUCN criteria for threatened species : A demographic assessment. Animal Conservation, 18, 397-406. https://doi.org/10.1111/acv.12188

UICN. (2001). Catégories et critères de l'UICN pour la liste rouge : Version 3.1. Commission de sauvegarde des espèces de l'UICNUICN.