Wood formation under varying environmental conditions

The timing and rate of xylem formation during the growing season are key processes in determining the amount and properties of wood produced. Wood formation depends on genetic signalling, availability of resources for growth, temperature, tree water and n utrient status, and the stage of ontogenetic development. The European climate is expected to change rapidly during the 21st century. In northern Europe, the elevation in temperature is likely to increase annual growth of trees because of longer growing p eriod, whilst in Central and Southern Europe, expected changes in rainfall are likely to affect the growth rate more than temperature. Our present knowledge concerning the timing and rate of xylem formation is surprisingly fragmentary. We will study, wi th the help of empirical observations and mechanistic models, the production and the allocation of carbohydrates, and the dynamic interplay between environmental and genetic factors as they affect cambial activity. To accomplish these objectives, we will (1) analyse the effects of weather variables on wood formation, fibre characteristics, and chemistry, (2) analyse the effects of genetic origin on wood formation, (3) study the factors controlling the seasonality in carbon assimilation and availability of current and stored photosynthates during the growing season, and their relationship to nitrogen availability, (4) analyse the effects of water relations and nutrient status on xylem and phloem transport and wood formation, and (5) formulate a dynamic pro cess-based model describing wood formation in terms of whole-tree physiology. Thus, the applicability of growth models for predicting the effects the environmental factors - such as climate change and forest management - will improve. The Norwegian parti cipants will be responsible for WP2 and take part in WP1, WP4 and WP6.