Modelling seed germination response to temperature in Eucalyptus L'Her. (Myrtaceae) species in the context of global warming

Seed germination is vital for persistence of many plant species, and is linked to local environmental conditions. Small increases in temperature during this critical life history transition may threaten species by altering germination timing and success. Such changes in turn may influence population dynamics, community composition and the geographic distributions of species. In this investigation, a bi-directional temperature gradient plate was used to profile thermal constraints for germination in 26 common, threatened and geographically restricted Eucalyptus species (Myrtaceae) from southern Western Australia. These observed data were used to populate models to predict optimum germination responses (mean time to germination, germination timing and success) under current (1950-2000 averages) and future (2070 high greenhouse gas emission climate scenario) mean monthly minimum and maximum temperatures. Many species demonstrated wide physiological tolerance for high germination temperatures and an ability to germinate outside current and forecast future autumn-winter wet season temperatures, suggesting that climatic distribution is a poor proxy for thermal tolerance for Eucalyptus seed germination. Germination for some species is predicted to decline under forecast conditions, but the majority will maintain or improve germination particularly during the cooler winter months of the year. Although thermal tolerance may benefit persistence of many Eucalyptus species in southern Western Australia as warming becomes more severe, large rainfall declines are also forecast which may prove more detrimental to plant survival. Nonetheless, this framework has the potential to identify seed resilience to heat stress in an early life history phase and hence species vulnerability to one characteristic of forecast environmental change.