What leads to rubber leaf senescence in the northern edge of the Asian tropics?

The rubber tree (Hevea brasiliensis) belongs to the evergreen broadleaved species in its native ranges, but it has a concentrated leaf senescence period after it was introduced to the Asian tropics. The mechanism behind the leaf senescence is still unclear. Models for predicting leaf senescence dates of this introduced tree have been rarely explored. This study proposed a series of models to identify the main abiotic drivers for the rubber leaf senescence which include temperature, daylength, and water stress. Model tests using data observed from the rubber plantations over the Xishuangbanna region in China show that: (1) Low temperature or cold stress played more critical roles than water stress and daylength in driving rubber leaf senescence. While models using air temperature and soil temperature showed similar performance, the former was recommended for leaf senescence modelling as it is easy to obtain. (2) The root mean square error of all the proposed models was significantly lower than that of the null model which used the mean date of leaf senescence over the study years, indicating the ability of our proposed models in predicting rubber leaf senescence dates. However, no significant differences were found among the proposed models. The thermal time senescence model was recommended for leaf senescence modelling as it is easy to implement. This study helps to better understand the driving mechanism of rubber leaf senescence.