Évolution des forêts résineuses des Pré-alpes de Savoie - Étude Phytosociologique

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English. SUMMARY. This study deals with the conifer forests situated in the S-1Vpart of the Pre-.A1ps, in the Savoy region. They arc growing onseclimentary formations which arc characterized by a more or lesshig11 content in CaCO ;: .The ph^to,cciological study resulted in limiting two definite levels,succeeding to each other and corresponding to a distinctive vegetation.The lower one being situated at an elevation ranging from900 m to 1 300-1 400 in : while the other is limited by an altitudeof 1 700-1 500 iì, with uninterrupted stands. "fhe concerned foreststudy lies between these limits, where the soil is found to he of aLapiaz compact calcareous substratum (Urgoniau), and of mixedcalcareous-loamy- clay alluvions.l'he lower level, are characterized by— a mean annual temperature ranging from 7° to 4,3°C.-- an annual rainfall lying hetween 1 250 and 1 900 mni.snowfall from 2 500 to 3 000 null.The climatic forest is here on represented by a mixed ail selectedI'icr'a-rlbies-Fa¡Jus high forest, with a predominance of fir. Itcan be associated indeed to the Pagetalia-slvatira(' order (Pawl. ;1925) Tx. 1936 ex Tx. et Diem., 1936. Species defining the 1'arcinio-Picec'talia order 13r.-111. are al so found: these plants being machmore important in alnudancc and number when reaching a higherelevation. To charazterize these stands, the A. defines a new Abicti-F%agetttau deattari('tosum j)itutatae stil - assosciation (a. n.) Tab. 1, withDentaria dgitata Lam, as the most characterizing species.The appearance of Calarnintha (Jrandiflora and the presence of aSroup species from the 1'arcinio-Picectalia result in a certain similitudewith the virgin forests of the Dinaric Alps region, whoseassosciation has heen descrilecl by the l\. as the _1lieti-Pagetxrnt dinarictrniticeetosum, 1941. One can find at the same level of vegetationa few rare sub-assosciations, and their occurence can be explainedby the influence of the station. These have already beendetermined in S vitzerlaucl where they are known as the Abicto-Fagetrtrta allietosuttt (Knoch 1954) and gbicti-Paqchoím armtncctosZ+ni(Tab. 2).The following sub-assosciations growing on T^arst calcareousformation can be found: Ibicti-haciatuni festncetosum- (Moor 1952)and Abicti-Fwlcttan z'alerianrtosnnt (\Ioor 1954). Because of heavy tree crops (clear-cutting) made in these forestsduring the last century, the natural distribution of species occurringin these stands has been quite transformed. But, a decrease in thelocal population and the safety regulations prescribed since a centuryby the forest Administration permitted the reconstitution of theforest.On sandy-schistous station, the soil is covered by a vegetationthat is annexed to the Myrtillo-Abietetunn assosciation (Kuoch 1954).Following clear-cutting, the successive stages of reconstitutionbring about Fpilobiuiu, Rubus fruticosos L. and Aspen (Tab. 3,4, 5, 9) ; sometime s Rubus Idaeus L. and Sali.r Capraea. L. Onabandoned pastured lands, Norway spruce is the pioneer specieswithout any transitory stand, while Scotch pine is the first to appearafter avalanche or fallen rocks, being replaced after a while by theNorway spruce forest. Rubus fruticosus grows on lower levels speciallyafter selection cutting (Tab. 7 and 10).In general, a study on the composition of spruce stands, in theSavoy region, sets off an increasing number of fir. And in the futureone can expect mixed forests containing larger quantities of fir.The higher levels (front 1 400 to 1 600 nI) are characterized by :— a mean annual temperature ranging from 4°2 to 2°C.— an annual rainfall lying between 1 800 and 2 500 mm.snowfall from 3 500 to 4 500 nnn.Even if the fir reach a fairly, high altitude growing on calcareousloamyclay soil, this zone is rather a spruce station, where the climaticforest corresponds to:the Piceetuva subalpinuna nav'rtilletosunt sub-assosciation withwarns exposed slopes (Br.-131. 1939) Tab. 12.the Acero-Fagetuni assosciation (Moor 1952), found on calcareousand cool hillsides.On Karst terrace appears a very particular assosciation, mainlycomposed of Picea excelsa and Rubus saxatilis which is describedas a new Rubo-Piceetuna assosciation (a. n.) Tab. 13.When the soil happens to be degrade by forest fire or by grounddisplacement, Laserpitiuin siler L. occurs abundantly compromisingthe forest reconstitution.On the subalpine higher level, Pinus montana Mill. var. itincinata(Ramond) \Villk. (Tab. 15) is found growing on Karst calcareousterraces, mingled with the Rlaodoreto-Vaccinietura rmaglietosum assosciation(Br.-B1. 1939).The exploitation and regeneration of these stands can be consideredin different ways. From 900 to 1 400 nI and with deep soilsfavouring Norway spruce, a small group selection system is desirable.On slight and facing north slopes the above mentioned systemmight have its groups enlarged to favour young spruce growth. On the contrary, if the soil stability is compromised by the presenceof unwooded areas or erosion, which are particularly found at highaltitudes above 1 500 in and on.Karst formation (for example, veryshallow and schistous soil) ; or for fear of wind damages, it isadvisable then to build a hardy stand, as close as possible to theclimatic forest. This type of forest which possesses the best hardycharacters, will bring at the same time the most favourable conditionsfor the soil (soil climax).The best silvicultural treatment to apply for these stands is atree to tree selection system, which is favouring the natural developmentof the vegetation.L. P.