Un modèle hyperbolique pour l'ajustement de faisceaux de courbes hauteur–diamètre
A hyperbolic model is proposed for the construction of sets of height–diameter curves in even-aged stands. On the basis of 86 samples from pure stands of beech (Fagussilvatica L.) and oak (Quercuspetraea (Matt.) Liebl), this model fitted adequately the geometry of data sets. The qualitative behaviour is correct over the whole range of the independent variable. Each parameter characterizes a significant geometric feature of the curve. The three parameters correspond to the asymptote, the slope at the origin, and the curve shape (curvature). The latter two are fairly stable over a large range of age (30–150 years) and stand density. A fitting procedure is proposed, through step-by-step reductions of the model, to overcome the limitations of poorly conditioned samples; only the asymptote, which is very close to top height, is to be estimated from each data set. The time series of estimates exhibit satisfactory evolutions for a large age interval. We interpret the shape of curve sets as the consequence of dominance on height and diameter growth in hierarchized stands.