Définition et présentation

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URI: http://hdl.handle.net/2042/33568
Title: Définition et présentation
Author: Ayral, Pierre
Abstract: SUMMARY. Method of volume calculation fur stands within experimentalplots of sylvicultureStudies about forest production and more particularly the onesabout treatment methods should be based on the most accurate data.They should he qualitative and quantitative. Therefore, in orderto build the tariff tables necessary to volume estimation of stands,P. _AyRAL, Leader of the first Section of the Research Station,worked on a method of « stratified sample » whose applicationhas already given excellent results. The most important charactersare1) Place of the trees in stories of vegetation (t, 2, 3) ;2) Crown dev elopinent (:\, B, C) ;3) Quality of the stem (D, T, r, etc...).The stratified sample should include sample tree of each class ofsuch characters in every girth class, proportionally with the correspondingnumber of steins in the stand in order to avoid a systematicdistortion. Volume measurements of standing trees. necessaryto that system, are realized with the « Fcole Forestière » entrainminladder.One must then prepare, with this representative sample, a tarifftable, suitable to the stand after its thinning. The practical basis ofstudies was constitued of seven clear felled stands, most accuratelymeasured, tree by tree, after numeration.Instead of the graphical method, improper by many ways,A1;Ani E has worked on a mathematical method, less subjective andallovfing calculation of the standard-error of volume estimation.Several mathematical laws (as V = f (c)) have ben tested(V = volume; c girth at b. h.).The following formula has been adopted:V=a+bc2whose normal equations are easy to solve and which keeps the standard-error, between 1 and 2 %.The constants a and b are calculated according to the method ofleast squares. The constants once known. the volume of a stand of N steinsis given with the formula:V Na + b ,^ n ;It is practical and even cheaper to have these calculations madeby an electronic machine. It will be noted that,, if a scale of squaresis used for abscissae. the law should he graphically represented bya straight line.Some conclusions, though less general, but very interesting, areto remember :i ) in each considered stand, within the same class of characters.the volume distribution for a given girth is the usual distributionof LAPLACE-GAUSS.2) for a given girth, there is a very significant difference betweenthe volumes of{ trees of class I and trees of class 2 for instance.Every thing equal besides, there are no differences between thevolumes of a tree « A » and a tree « B »...\t last, the quabtative study of stands, considered as necessaryfor specifying the influence due to methods of treatment, has beenundertaken, the methods of investigation, made clear.\ graphic study (diagram) will be started, which will permit toknow what simple curve should he calculated. in order to take intoaccount the distribution of the different qualities of products accordingto the b. 11. girth.
Publisher: ENEF, Ecole nationale des eaux et forêts, Nancy (FRA)
Date: 1956

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