A new tool to discovering realistic climate-growth relationships

During the last two decades, forest condition in Germany and in some other parts of Europe has stabilized,1 because the emission of harmful pollutants and their deposition in the forests was lowered substantially.2 The still enduring deposition of nitrogen compounds in a typical size between 16 and 20 kg/(ha*a) in German forests exceeds natural levels and must be evaluated as a potential danger for tree vigour.3 Coevally to this change, climate warming occurred and changed the growth conditions of forests once more. The increase of the defoliation values in the forests in France and Spain during the last two decades is closely related to these climatic changes.1 Weather conditions may influence the annual growth rates of trees heavily. Methods of tree ring research are useful to prove the impact of climatic forces and their mid-term and long-term changes. Discovering realistic climate-growth relationships is a central field of dendroecological and dendroclimatological research. The common feature of all existing analysis programs and methods so far (Fritts4 RESPO – response functions; Guiot5 bootstrapped RESPO; Biondi & Waikul,6 Dendroclim; Visser & Molenaar,7 Van Deusen PC:8 Kalman filter technique, state-space models) consists of the use of monthly climatic variables. Additionally, only precipitation and temperature are taken into account in most investigations. Tree growth, however, is a continuous process and therefore independent of temporal borders of monthly climatic variables. The weather, changing shortterm, is not represented realistically only by precipitation and mean temperature. There are a number of additional parameters which are in combination meaningful for the growth processes. On that account, the existing programs and methods, mentioned above, are not suitable for discovering realistic climate-growth relationships. The current situation, however, demands a deeper understanding of the causes and effects of environmental conditions on the growth processes. The development of appropriate methods of detecting and analysing climate-growth relationships is an urgent necessity.