Thermal risk of seed germination of <scp>UK's</scp> plant populations and implications for climate‐smart ecological restoration

Abstract Introduction Seed‐based ecological restoration actions are needed to halt biodiversity loss and mitigate climate change effects. However, identifying populations to target for climate‐ready seed sourcing remains a major challenge due to germination and genetic constraints. Objectives This study evaluates thermal tolerance of seed germination in UK populations of species of restoration interest and integrates these findings with existing genetic diversity assessments to guide climate‐smart, seed‐sourcing strategies. Methods Six species ( Achillea millefolium , Centaurea nigra , Daucus carota s.l., Leucanthemum vulgare , Rhinanthus minor , and Scorzoneroides autumnalis ) were identified among those for which assessments of genetic diversity estimates and seed lots banked for long‐term conservation were available. Forty‐five seed lots were incubated at a range of constant temperatures and thermal niches for germination modeling. Thermal risk for germination was then assessed by comparing current and predicted environmental temperatures of each population with the corresponding thermal germination parameters. Results All species except R. minor showed wide thermal windows for germination, suggesting that environmental temperatures are unlikely to limit reproduction from seeds under future UK climates. In D. carota s.l., residual dormancy masked origin effects, while R. minor exhibited narrow germination niches, suggesting higher vulnerability to warming. Combining germination results with genetic‐based restoration assessments allowed species to be classified into four climate‐smart, seed‐sourcing categories: no constraints; genetic constraints; germination constraints; and genetic and germination constraints. Conclusions This study provides a practical framework for evaluating the feasibility and urgency of climate‐smart, seed‐based restoration. This approach is directly applicable to other UK species and to other temperate floras.