European Journal of Forest Research vol:131 issue:3 pages:609-622
This study aims at the explanation of internal stem morphology of vital (co)dominant Pedunculate oak (Quercus robur L.) trees in homogeneous even-aged highforests by the factors tree age, forest structure and site quality, using boosted regression trees as a powerful modelling technique. The study area covers the region of Flanders (Northern Belgium), which is characterised by the absence of strong topographic and climatic gradients. For 76 adult sample trees covering the entire productivity range of Pedunculate oak, morphological characteristics were derived from measurements of ring width or heartwood area on wood cores. Forest structure, soil physicochemical properties, humus quality, vegetation indices and litter nutrient contents were quantiﬁed at each sample location.
Model predictive performance and generality are good. Tree
age effects correspond to expected trends in age-related
radial growth and heartwood portion. Even if management
of oak trees in even-aged high-forests is rather similar over Flanders, forest structure is the most important factor
determining ring width, followed by soil fertility. Heartwood portion is determined by soil fertility and crown structure.
Effects of topsoil and humus physicochemical characteristics, litter nutrient contents and water supply mainly conﬁrm autecological knowledge on oak. However, variables related to soil water availability are only occasionally relevant, and always of lower importance than soil fertility. The low importance of water availability in the models contradicts results from other studies, and the potential effect of confounding is discussed. The observed growth reduction at low litter N/P ratios might be indirectly linked to early litterfall.