Predicting the seed germination response of four rare Grevillea species (Proteaceae) to current and future temperatures

Context Grevillea is one of Australia’s largest plant genera, with 15% of species being federally listed as threatened. Although seed germination studies have largely focused on common species, knowledge of germination in threatened species remains limited. This gap is critical to address effective conservation actions, including translocations. Aims This study used a bi-directional thermogradient plate (TGP) to examine the germination responses of four threatened Grevillea species from New South Wales to varying temperatures. Methods Generalised additive models were used to predict monthly final germination proportions and time to 50% germination (t50) across 36 TGP temperature regimes, representing current and two future climate scenarios (SSP2-4.5 and SSP5-8.5). Results Three species exhibited high germination across most temperatures, whereas G. iaspicula had a narrow range, preferring cooler conditions (≤15–20°C). For G. masonii and G. rivularis, t50 was under 5 days at all but the most extreme temperatures. G. wilkinsonii and G. iaspicula showed longer germination periods, with t50 exceeding 15 days for most temperatures. All species except G. iaspicula were predicted to maintain consistent germination across current and future climates, whereas G. iaspicula and G. wilkinsonii showed stable t50, and G. masonii and G. rivularis predicted longer t50 in winter. Conclusions Modelling seed germination under current and future temperatures highlights potential climate change risks and helps predict impacts on regeneration. Implications Germination in G. masonii, G. rivularis, and G. wilkinsonii may be resilient to temperature rises, whereas a cooler temperature preference for G. iaspicula may indicate a sensitivity to future temperature changes.