Climatic and photoperiodic effects on flowering phenology of select eucalypts from south-eastern Australia

Abstract

Flowering phenology plays an important role in the plant life cycle as it is sensitive to climate. The timing and intensity of flowering is important for the reproductive success, fitness, survival and diversity of plants. Its study in relation to the environment can therefore aid in understanding the response of species to climate change. Long-term studies examining the relationship between flowering phenology and climate are limited in Australia. This study explores the effect of photoperiod length, temperature and rainfall on flowering duration and intensity of Eucalyptus tricarpa, Eucalyptus microcarpa and Eucalyptus polyanthemos using long term data sets from two locations and the statistical model: generalised additive model for location, scale and shape (GAMLSS). The study further incorporates the phenological response to calibrate the flowering sub-module of the mechanistic model TACA-GEM to investigate the effect of predicted climate change on flowering phenology. Flowering intensity of E. microcarpa increased as temperatures warmed in the months prior to flowering but declined when warmer temperatures occurred in the early stages of bud development. For E. polyanthemos flowering decreased with increases in temperature combined with decreased rainfall and shorter days. Increased rainfall, cooler temperatures and shorter days increased flowering in E. tricarpa. Modelling of species response to climate change showed that decreases in flowering intensity and duration for all three species are likely. The temperature thresholds required for flowering of E. polyanthemos were exceeded under climate change while the requirement for longer days prevented flowering phenology shifting to cooler months. E. tricarpa exhibited a decline in flowering intensity and duration under climate change; however, its requirements for shorter days allowed the species to continue to flower during winter. E. microcarpa displayed no consistent relationship to photoperiod and a decline in flowering intensity and duration under climate change was modelled. The species’ specific responses to photoperiod suggests that flowering asynchrony between the coexisting species may be linked to day length and that the asynchrony will be strengthened under climate change as flowering duration and intensity contract under a warmer and drier climate.