Selecting a model to predict the onset of growth of Fagus sylvatica.
To evaluate the impacts of climate change on the primary production of temperate deciduous tree species, the onset and cessation of the growth must be accurately described. The aim of this study is to find a model which predicts the onset of growth of Fagus sylvatica (European beech) accurately. Several models have been proposed for the prediction of the timing of budburst of woody plants. Most of these models have been evaluated for species other than Fagus sylvatica, and in some cases for flower buds. Six models (brief descriptions are given of each) were fitted to data on leaf unfolding of Fagus sylvatica, collected in the Netherlands during 1901-68. All models require only temperature (chilling induces budburst) as input. For Fagus sylvatica, however, photoperiod may also influence the timing of the onset of growth. Therefore, photosensitivity was incorporated into these models. The predictive power of the models was tested using German data. Incorporation of photosensitivity reduced the predictive power of models compared with models those that do not incorporate this parameter. The model proposed by Sarvas, R. [Communicationes Instituti Forestalis Fenniae (1974) 84, 1-101], in which the development of rest and quiescence is strictly separated in time, resulted in the best predictions of the average date of leaf unfolding in Fagus sylvatica.