Etudes sur le développement et la production de quelques peuplements de douglas (Pseudotsuga douglasii Carr)

International audience

English. SUMMARY. Front the study of sample plots situated in the north-east, theeast ant the center of France; the following provisory conclusionscan be drawn.1° The Douglas is a fast growing species which can reach a highproductivity, greater than the one that can be expected from ourindigenous conifers: the annual increment being as much as 30 or40 cubic meters — total volume — per hectare and per year.2° This high productivity can only be expected in favourable ecologicalconditions.3° From the climatic stand point, the Douglas proves to be anaccomodating tree susceptible of thriving and giving large yieldsunder a wide range of climates, and even in the mountains underalready rather severe conditions. In this respect the question of thewater requirements of the plant is capital.4° Like all the species growing vigorously and quickly, the Douglas is particularly sensible to the edaphic conditions. It prefers arich, deep, porous and cool soil which induces an unusual growthand high yields.5° Its rather shallow rooting; exposes it to wind-storms, chieflyif the ground on which it grows is not deep (rocky bed or layer ofGley forcing it to develop a shallow root system) and if the soilis temporarily softened by rain.6° The Douglas must not be planted too closely — 3 000 plantsper hectare seems quite sufficient. A greater number is not onlyexpensive but detrimental.7° Being a fast-growing species the Douglas requises a sufficientgrowing space. It fears the competition of its associates and in itsyoung, age, that of the other species.It is particularly sensible to repeated thinnings. Too rare or toomoderate thinnings are immediately followed by a considerable. decreasein the yield.8° It would not be reasonable to maintain a dense stand with aview to favour natural pruning. In any way, the Douglas does notprune well naturally.On the contrary a careful artificial pruning is advised. It is profitable,for it corresponds to an important increase in the qualityof the products. 9° The question of productivity being put apart a great densityof the forest does not favour the elongation of the stems. The heightof the mean tree seems to be independent of this density-.Inversely, a moderately 'dense stand brings about an increase ofthe girth and consequently, interesting marketable products may beobtained earlier.10° The question of the races plays centainly a part in the possibilitiesof introducing the species under varied conditions, but perhapsalso from the stand point of mere productivity.11° The use of « slow » volume tables established by L. SCHAEFFER,seems more suitable, for the determination of the volume ofstanding trees, than that of the ALGAN tables.12° If the Douglas is to be introduced in mixture with otherconiferous species growing less quickly (particularly with indigenousconifers), it must be considered than the Douglas outgrowsits competitors rapidly and completely. A mixture in alternate rowsor alternatively in each row is not at all recommended. The secondaryspecies will disappear 'rapidly without any profitable productand its only use will have been to hamper the Douglas in its growth.A mixture in groups will be better or the Doug-las will be scatteredin small groups widely apart from one another (8 to to meters)in the middle of the secondary stand.13°' The proportion of bark in the volume of the standing treesit about 10 per cent.14° The experiments undertaken have shown the importance ofthe « border effect » and the usefulness of an efficient shelter almgthe edge exposed to the wind.(Traduction M. Grosdidier.)