SELECTING A MODEL TO PREDICT THE ONSET OF GROWTH OF FAGUS-SYLVATICA

1. 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. 2. 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 were fitted to data on leaf unfolding of Fagus sylvatica, collected in the Netherlands over 57 years (1901-68). 3. All models require only temperature as input. For Fagus sylvatica, however, photoperiod may influence the timing of the onset of growth. Therefore, photosensitivity was incorporated in these models. This reduced the predictive power compared to models that do not incorporate photosensitivity. 4. The model proposed by Sarvas (1974), 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.