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Journal of Experimental Botany (1)
Proceedings of the Royal Society B: Biological Sciences (1)
Anfodillo, Tommaso (2)
Banavar, Jayanth R. (1)
Carrer, Marco (1)
Deslauriers, Annie (1)
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An allometry-based approach for understanding forest structure, predicting tree-size distribution and assessing the degree of disturbance
Banavar, Jayanth R.
Proceedings of the Royal Society B: Biological Sciences
Tree-size distribution is one of the most investigated subjects in plant population biology. The forestry literature reports that tree-size distribution trajectories vary across different stands and/or species, whereas the metabolic scaling theory suggests that the tree number scales universally as −2 power of diameter. Here, we propose a simple functional scaling model in which these two opposing results are reconciled. Basic principles related to crown shape, energy optimization and the finite-size scaling approach were used to define a set of relationships based on a single parameter that allows us to predict the slope of the tree-size distributions in a steady-state condition. We tested the model predictions on four temperate mountain forests. Plots (4 ha each, fully mapped) were selected with different degrees of human disturbance (semi-natural stands versus formerly managed). Results showed that the size distribution range successfully fitted by the model is related to the degree of forest disturbance: in semi-natural forests the range is wide, whereas in formerly managed forests, the agreement with the model is confined to a very restricted range. We argue that simple allometric relationships, at an individual level, shape the structure of the whole forest community.
self-thinning; old-growth forests; allometry; finite-size scaling
Widening of xylem conduits in a conifer tree depends on the longer time of cell expansion downwards along the stem
Journal of Experimental Botany
The diameter of vascular conduits increases towards the stem base. It has been suggested that this profile is an efficient anatomical feature for reducing the hydraulic resistance when trees grow taller. However, the mechanism that controls the cell diameter along the plant is not fully understood. The timing of cell differentiation along the stem was investigated. Cambial activity and cell differentiation were investigated in a Picea abies tree (11.5 m in height) collecting microsamples at nine different heights (from 1 to 9 m) along the stem with a 4 d time interval. Wood sections (8–12 μm thick) were stained and observed under a light microscope with polarized light to differentiate the developing xylem cells. Cell wall lignification was detected using cresyl violet acetate. The first enlarging cells appeared almost simultaneously along the tree axis indicating that cambium activation is not height-dependent. A significant increase in the duration of the cell expansion phase was observed towards the tree base: at 9 m from the ground, xylem cells expanded for 7 d, at 6 m for 14 d, and at 3 m for 19 d. The duration of the expansion phase is positively correlated with the lumen area of the tracheids (r2=0.68, P < 0.01) at the same height. By contrast, thickness of the cell wall of the earlywood did not show any trend with height. The lumen area of the conduits down the stem appeared linearly dependent on time during which differentiating cells remained in the expansion phase. However, the inductive signal of such long-distance patterned differentiation remains to be identified.
Auxin; cambium; cell differentiation; conduit tapering; Picea abies polar pattern growth
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