Modeling productivity of silver birch (Betula pendula Roth.) combining phytocentric and geocentric approaches in Northwestern Europe

The current climate emergency and its associated impacts on forest ecosystems are leading forest owners and managers to consider a broader diversity of species to enhance forest resilience. In this context, there is a growing interest in lesser-used timber species, such as silver birch, a promising candidate for forest diversification in Western Europe. Estimates of site productivity are essential to guide forest management decisions, but have not yet been accurately determined for silver birch in northwestern Europe. This study pursuits two main goals: (a) providing dominant height growth curves for birch in southern Belgium; (b) identifying the key biophysical factors affecting the productivity of silver birch within the study area. In this study, we tested and compared 16 growth models on a stem analysis dataset gathering the past height growth of 68 birch trees from 40 stands. The Duplat and Tran-Ha I model best predicted the dominant height growth. Using this model, the site index (SI) was estimated for 103 stands distributed throughout the study area and its variation was modeled in response to biophysical variables (climatic, edaphic and topographic). The best selected model (R² adj=0.50) revealed a positive effect of mean annual temperature on the SI, although limited when maximal soil water content was low. This model was ultimately used to map the spatial variation in birch yield potential in the study area, highlighting the ecological conditions under which birch silviculture could be promoted.