Discussion

By integrating life-history traits and distribution data into the frameworks developed by Neaves (2019) and Ottewell et al. (2016) and including Genetic EBVs (Hoban et al. 2022), we have given informed recommendations and risk evaluations for conservation management and ecological restoration activities for 52 UK plant species. LC species were the least likely category to be recommended for conservation management; while all threatened species (VU, EN or CR) were instead recommended conservation action aiming to increase genetic diversity at population level. Regarding recommendations for ecological restoration, all plant species classified as NT, VU, EN or CR were predicted to have risks associated with sampling limited genetic diversity and selecting donors for mixing populations. While some least concern species also had some risks associated with sampling and donor selection, none of this group was classed as being at high risk for sampling, and only Daucus carota L. was categorised as high risk for donor selection due to taxonomic uncertainties. It is important to recognize that some threatened species may primarily require habitat protection and establishment of new populations rather than interventions to increase genetic diversity. These scenarios should be assessed on a case-by-case basis.
Certain traits were more associated with high sampling or donor selection risks. Species with genetic incompatibilities such as hybridising species and species with multiple ploidy levels were more likely to be high risk for donor selection. Hybridizing species are generally considered high risk for ecological restoration due to concerns like outbreeding depression, which can disrupt locally adapted gene complexes and reduce fitness (Frankham et al. 2011). However, hybridization also offers significant benefits, such as increased genetic diversity and adaptive potential, which are essential for responding to environmental changes like climate shifts or disease outbreaks (Abbott et al. 2013). Recent studies have highlighted how hybridization can result in heterosis (hybrid vigor), enhancing growth, reproduction, or survival in hybrids compared to parental species, and how it facilitates the introgression of advantageous traits, enabling populations to adapt to novel environments (Rieseberg et al. 2007). These benefits are particularly relevant in rapidly changing ecosystems, where adaptive advantages may outweigh potential risks. Careful management, including robust genetic monitoring, is required to balance these risks and ensure hybridization supports restoration goals (Taylor et al. 2015). Management strategies should carefully weigh these risks and benefits. On the other hand, hybridisation has been associated with lower fitness through a variety of mechanisms such as rapid genomic changes and genetic pollution of species integrity (Baack & Rieseberg, 2007; Moran et al. 2021). For example, Silene dioica hybridises with S. latifolia subsp. alba to create the hybrid Silene × hampeana. If a population of S. dioica hybridising with S. latifolia subsp. alba was translocated to a population of S. dioica which does not usually overlap ranges with S. latifolia subsp. alba, alleles from another species may be introduced into a new population with unknown consequences. Furthermore, the risk is higher with threatened species because mixing hybridising populations could also decrease genetic diversity of a species by breaking down reproductive barriers and merging two previously distinct lineages (Todesco et al. 2016).
Species with multiple ploidy levels were also associated with higher risks of donor selection as it can contribute to outbreeding depression. Outbreeding depression has been linked to crossing populations with chromosomal differences (Frankham et al. 2011). For example, Campanula rotundifolia L., despite being classified as a species of least concern by the IUCN was assessed as having some risks of donor selection due to its multiple ploidy levels (Royal Botanic Gardens, Kew 2024a). Throughout the UK, populations of Campanula rotundifolia can be either diploid, tetraploid or hexaploid (Stevens et al. 2012), so mixing individuals from different populations could lead to non-viable or infertile offspring. Outbreeding depression can have an even larger effect on threatened species (Frankham et al. 2011). Threatened species often have lower genetic diversity and fragmented populations so introducing individuals from other populations can disrupt local adaptations leading to lower fitness (Liddell et al. 2021). Hence, all species that were classified as Vulnerable, Endangered or Critically Endangered by the IUCN were either high risk or had some risks associated with donor selection.
A key trait associated with a high risk of sampling limited genetic diversity is population fragmentation. Connected gene flow is the transfer of genetic material from one population to another and is important for maintaining genetic diversity (Gómez-Fernández et al. 2016). Fragmented populations are less likely to have connected gene flow, and can also increase genetic structure between populations and lead to higher inbreeding rates (Wang et al. 2011). As well as population fragmentation, a poor dispersal method also contributes to poor gene flow among populations (Vandewoestijne et al. 2008) and, therefore, species with both a poor dispersal method and evidence of population fragmentation or a scattered distribution were assessed as a higher risk of sampling limited diversity. Moreover, the interaction between fragmented distribution and broad ecological amplitude is crucial in understanding inbreeding risk. In species with a broad ecological amplitude, local adaptation to specific environmental conditions can reduce gene flow between populations, increasing the likelihood of genetic isolation. This isolation, while potentially enhancing local fitness through local adaptation, can also lead to inbreeding depression due to the accumulation of deleterious alleles in small, isolated populations (Lopez et al. 2009; Verhoeven et al. 2010). This link between fragmented distribution, ecological amplitude and inbreeding has been documented in several plant species (e.g., Zhao et al. 2006; Vanden-Broeck et al. 2011).
In conclusion, we conducted species conservation assessments for 52 UK native plant species and gave conservation management recommendations based on their predicted genetic diversity, differentiation, and vulnerability to mixing populations. In general, we found that certain life-history traits were more likely to come with risks for sampling and donor selection such as genetic incompatibilities and population fragmentation. Also, species that are classified by the IUCN as threatened were more likely to be recommended for conservation management. The likely cause for this is that threatened species are rare in the UK, are more likely to have fragmented distributions and therefore are less likely to have connected gene flow, leading to the need for management to increase genetic diversity. Our data reflect conclusions made by Rivers et al. (2014), that IUCN red list classifications seem to broadly represent the genetic diversity of a species. For example, species categorised as Endangered were more likely to have low genetic diversity. However, genetic data are still necessary for effective restoration programmes.
In the absence of genetic data, this framework is useful to recommend conservation management strategies; however, genetic data are needed to make more informed decisions and ensure the conclusions made by each assessment are more robust. We acknowledge that while our framework links life history traits to genetic diversity and differentiation, exceptions to these patterns are common in biology, which highlight the need for caution when implementing our recommendations. Recognizing these possibilities, we advocate for conservation management strategies that adopt our framework as a conservative approach. These strategies act as interim protective measures for plant species until genetic information can be gathered to confirm, refine and optimise conservation actions. Furthermore, the integration of our proposed framework with the approaches of Ottewell et al. and Neaves leverages the complementary strengths of both methodologies. While Neaves’ life-history-based estimates provide a practical solution in data-limited scenarios, Ottewell’s genetic assessments offer precise insights when genetic data are available. Our combined approach benefits from the estimates of EBV genetic variables from Neaves’ approach to provide conservation recommendations for threatened species using Ottewell’s decision-making framework, and enhances the applicability and adaptability of conservation recommendations, ensuring more robust outcomes in ecological restoration and biodiversity preservation.