A Low Temperature and Photoperiod Multiplicative Model for Predicting Autumn Plant Phenology

From the viewpoint of plant physiology, there is a general consensus that leaf senescence is controlled by photoperiod and temperature. How the control of leaf senescence is split between photoperiod and temperature, however, is not known for many species. In light of this, we developed a new process-based autumn phenology modelautumn phenology model to represent coupling controls of photoperiod and temperature on leaf senescence and calibrated the model using 67 leaf coloration and brown-down time series for 27 woody and herbaceous species at 18 stations on the Qinghai-Tibetan Plateau from 1981 to 2012. Results show that leaf senescence processes were triggered by photoperiod shortening in 61.2% of time series and by daily minimum temperature decrease in 38.8% of time series. Photoperiod control of the leaf senescence start occurs predominantly at stations with shorter annual maximum daylength (88.9%), while daily minimum temperature control of the leaf senescence start appears mainly at stations with longer annual maximum daylength (71.0%), especially for the native species. This model reveals coupling effects of shortened photoperiod and decreased daily minimum temperature on leaf senescence processes. Compared to the representative existing process-based autumn phenology models, the new model is a more general model and more robust in accurately fitting and predicting leaf coloration and brown-down dates.