Vues d'ensemble sur l'organisation en France des recherches de sylviculture et d'économie forestière. Les méthodes

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إنجليزي. GENERAL VIEWS UPON THE ORGANISATIONOF SYLVICULTURAL RESEARCHES AND FORESTRY IN FRANCE - Methods - This account is divided into three parts of unequal development: 1. — General views on the way with which the study of forest species is understood by the Research-Station. 2. - Scheme of an organisation of the general disposal of researches for the study of given species in a prescribed region. 3. — Detailed study of the methods of installation and control of the experimental plots. 1) General plan. — In order to secure continuance of views and uniformity of methods, all the sylvicultural researches undertaken by the French forest-service are, as a principle, centralized by the Is' station of the Experiment and Research-Station. As regard to the chief forest species they are studied in their principal localities, in crops regenerated naturally, in various conditions of soil and climate (see table and map). 2) Organisation of an experiment disposal. — One may distinguish between the sylvicultural study, properly speaking which involves installation of several plots in crops of graduate ages, and connected studies: climate, soil, vegetal association. 3) Detailed study of methods of installation and control, — This chapter is extremely difficult to sum up, for it coutains a very large number of details designed to secure a control as exact as possible of vegetation. The area of the experimental plots is 1 hectare, as a principle, sometimes more when it concerns old stands : they are surrounded with zones of shelter and their boundaries are well fixed on the ground. Every three years a painted number and at breast-height aguiding mark. Measures are taken on the circumference with steel rebbons ; exceptionnally in low polewoods when the number of trees is larger than one thousand, they do not wear a number and diameters are mesured (mean length of 2 perpendicular diameters). Wood measurements are calculated by using of proper rates worked for each plot, and periodically rectified. In every plot, about fifty sample trees of each kind of size are felled and measured and a distinction is made between heavy timber which is measured into short logs a meter long, and small wood which is weighted. The rate is made by graphic method by taking in abcissa the circumferences at breast-height, and in ordinate volumes. In a last paragraph we examine briefly the risks of mistakes. Conclusions are as follow : the basal areas are known with a precision from 0,2 to 0,3 % (measurement of circumferences and numbered trees) or of 1 % (measurement of diameters unnumbered trees). Their increments are therefore known at least with a precision of 0,5 % or 2 % according to the methodwhich has been used. The volumes per hectar are know with a precision from 2 to 3 % and their annual increments are exact at least to half cubicmeter, and most often to 2 or 3/10 cubic meter.