Recherche de la forme de la variation endogène annuelle de l’épaisseur des anneaux ligneux chez Pinus halepensis Mill. )

Abstract

Summary 1. The annual growth rings presented by four sounding directions in the cross-section of twenty-two trunks from a batch of Pinus halepensis Mill., submitted to similar ecological conditions, were dated and their thickness measured according to these four sampling directions; accordingly, this thickness is characterized by four distinct measures. 2. The observation of the cross-sections on the one hand, the checking by analytic-geometry calculations on the other hand, allow the adoption of a circular form for the annual limit of the growth rings; accordingly, the annual ring is the ana comprised between two successive nonconcentric circles, which geometrically explains the differences in thickness that were observed according to the sounding directions. The ineluctable constancy of this circular form enables to characterize the thickness by a single theoretic values, representing in a way the integration of eventual endogenous and exogenous anisotropic influences, with the advantage of constituting a standardization of the data. 3. Starting from the commonplace hypothesis that the standardized thickness of the successive rings figuring in a trunk’s cross-section is the fruit of natural variability, the location of the ring within the section (endogenous variation) and the variation of climatic conditions from one year to another (exogenous variation), a theoretical method is suggested, allowing to minimize the effects of variability, and to extract the variation of endogenous origin in ring-thickness of an imaginary tree, representative of the tree-population, which would be submitted to an exterior influence, rendered non-fluctuating from year to year by the very method itself. 4. Application of this method was made on the batch of Pinus halepensis under consideration. The variation of intrinsical origin of the standardized thickness of the rings, in terms of the tree's age, proceeds through a principal maximum at the 10th year, followed by an oscillating decrease, particularly with two secondary maxima at the 30th and 50th year, and two secondary minima at the 20th and 40th year. The hypothesis of a periodicity in thickness-increase of Pinus halepensis must be considered. 5. The proposed method is applied to another characteristic value of the annual ring, the number of tracheids composing the latter along a radial file, the intrinsic evolution of which as a function of the tree’s age is similar to that of the thickness. The intrinsic variation of this value and of the thickness being known, the intrinsic variation of the value of the average annual radial size of the tracheids has been defined and represented.