Seed germination, hydrothermal time models and the effects of global warming on a threatened high Andean tree species

Seed germination is a crucial event in a plant’s life cycle. Because temperature and water availability are important regulators of seed germination, this process will likely be influenced by global warming. Insight into the germination process under global warming is thus crucial, and requires the study of a wide range of water availability and temperature conditions. As hydrothermal time (HTT) models evaluate seed germination for any combination of water potential and temperature, they can be suitable to predict global warming effects on seed germination. We studied the germination characteristics of the high Andean endemic tree species Polylepis besseri (Rosaceae), using HTT models. We were especially interested in the potential effects of global warming on seed germination. Assembly of HTT models for P. besseri was fairly straightforward due to the lack of a seed dormancy mechanism. The models allowed prediction of Polylepis germination under constant and alternating temperatures. Initially, a global warming induced increase in the field minimum and mean temperature will increase P. besseri germination, but as maximum temperatures rise above the optimum temperature for the species, seed germination will become jeopardized. Effects of global warming on seed germination are currently considerably underexplored. HTT models prove to be useful tools to study a plant species’ general germination characteristics, and how they may become affected under global warming. For the endemic mountain tree species P. besseri, we predict an increase, followed by a decrease of seed germination under global warming.