Scaling allometric relationships in pure, crowded, even-aged stands: do tree shade-tolerance, repro-ductive mode and wood productivity matter?

Abstract

Tree allometric relationships are likely to be influenced by species tolerance to shade, nutrient availability and plant ontogenetic origin. The aim of this paper was to test to what extent these factors affect the scaling exponents of two allometric relationships in pure, even-aged, canopy-closed forest stands: stem diameter (D) versus stem height (H) and versus stem density (N). Data were collected by tree species (Betula pendula, Fagus sylvatica and Quercus petraea), wood productivity class and reproductive mode (seed origin and sprouting stands) from published forest yield tables. Reduced major axis analysis was used to estimate the slopes of regression lines in the log-log space of H-D and D-N. The scaling exponent of the H-D relationship was significantly larger in birch than in beech stands (0.897 versus 0.745), and in low productivity, beech stands as compared with their high productivity counterparts (0.876 versus 0.745). However, no significant difference was detected between high stands and coppices of durmast oak. The scaling exponent of the D-N relationship was significantly larger in birch than in beech stands (-0.690 versus -0.558), in low than in high productivity beech stands (-0.694 versus -0.558), and in seed origin than in sprouting stands of durmast oak (-0.609 versus -0.580). We explained these results in terms of plant stem growth strategies and resource availability from a biomechanical perspective. Contrary to certain studies that have reported an invariant scaling relation between stem diameter and density across tree species and communities, but in accordance with other recent studies, we have brought new evidence on species-specific allometric scaling under self-thinning. In addition, we have revealed within-species variance of the scaling exponent of stem diameter-density relationship.