Thermal germination niche: implications for seed‐based restoration in climate‐sensitive alpine environments

Understanding the germination requirements of native plant species is crucial for restoration practitioners to ensure successful outcomes, especially as restoration efforts expand and global initiatives aim to restore millions of hectares. However, fundamental research on the germination niche of native species, particularly those from climate‐sensitive ecosystems such as alpine environments, remains limited. This study quantifies the thermal germination requirements of 20 common co‐occurring Australian alpine species that are key to restoration efforts. Seeds of each species were collected and subjected to germination tests over a temperature gradient (5–35°C). We analyzed species‐specific germination responses to temperature, described thermal germination niches, and modeled cardinal temperatures (Tb: base temperature, To: optimum temperature, Tc: ceiling temperature) for 50% germination. In situ soil temperatures were used to assess the thermal risk for germination under current and future climates. Species generally exhibited unimodal responses to temperature with some species‐specific exceptions. Germination niche breadth varied between species, with some germinating a little at even extreme temperatures and others restricted to warmer or colder temperatures. Optimum temperatures (To) ranged from 15 to 20°C, ceiling temperatures (Tc) from 25 to 30°C, and base temperatures (Tb) from 10 to <5°C. For most species, current alpine soil temperatures meet the Tb − Tc threshold for 140–180 days per year (~45%). Future climate will increase the number of days that soil temperatures reach this threshold. Restoration practitioners can improve the success of seed‐based restoration efforts by considering the thermal preferences described in this study and increasing their focus on direct seeding revegetation efforts.