THE INFLUENCE OF CLIMATE ON THE FLORISTIC , VEGETATIONAL AND EDAPHIC CHANGES OF OLIVILLO FOREST (AEXTOXICON-PUNCTATUM R-ET-PAV) IN THE COASTAL RANGE OF CHILE - BIOGEOGRAPHICAL IMPLICATIONS

Detrended correspondence analysis of Aextoxicon punctatum forests show s a high floristic and structural similarity between the relict forest s of the Norte Chico and the south temperate rain forests of Chile. Th is result supports the early phytosociological analysis made by Oberdo rfer (1960) who distinguished two floristic associations dominated by Aextoxicon punctatum in Chile: 1) Lapagerio-Aextoxiconetum associated with a southern cold-temperate climate and 2) Peperomio-Aextoxiconetum associated with a mediterranean, semiarid climate, but presenting a h umid local microclimate as a result of frequent cloud-fog precipitatio n. On the contrary in the south-central zone of Chile Aextoxicon punct atum does not form dominant stands but it associates with both sclerop hyllous and deciduous species constituing two subassociations: Boldo-C ryptocaryetum and Nothofago-Peersetum, also defined by Oberdorfer. The major climatic variables which determine this ordination pattern are: the maximum summer average temperature, the average annual temperatur e, and total precipitation. Moreover, the variation of soil chemical v ariables among sites shows concordance with the vegetational ordinatio n. With respect to soil properties, the relict forests of Norte Chico lie close to the relict forests of south Chile, in spite of difference s in the geological substrates. In contrast, in the central zone and s outh central zone of Chile (33-degrees-40-degrees) a decrease of both pH and % of base saturation and an increase of total carbon content ar e observed along with an increase in rainfall from north to south. The se results support the hypothesis of a paleocommunity which was distri buted continously along the coast of Chile during the Pleistocene, and which is presently geographically isolated in the northernmost and so uthernmost sites within the range of Aextoxicon. According to the paly nological and paleoenvironmental evidences the fragmentation would hav e occurred during the Holocene, delaying the floristic and edaphic dif ferentiation of the stand of Norte Chico and southern islands in compa risson to the forests of south-central Chile.