Revista chilena de historia natural
versión impresa ISSN 0716-078X
VILLAGRAN, CAROLINA. A model for the history of vegetation of the Coastal Range of central-southern Chile: Darwin's glacial hypothesis. Rev. chil. hist. nat. [online]. 2001, vol.74, n.4, pp. 793-803. ISSN 0716-078X. doi: 10.4067/S0716-078X2001000400007.
Isolated communities of conifers and Magellanic moorlands, distributed along Andean and at high latitudes exist in south-central Chile, between 37 and 43° S. According to Darwin (1859), such "islands" are remnants of glacial populations, which were distributed at lower altitudes and latitudes during glacier advances. Also, in Chile there were expansions of the Andean and southernmost flora into the Longitudinal Valley of Los Lagos region during the last glaciation, which reversed during the Late-glacial (14, 600-10,000 14C years BP) and Holocene (after 10,000 14C years BP). Considering this hypothesis, in this study we analyzed two palynological sequences from summits of the Coastal Range of Los Lagos region (Cordillera de Nahuelbuta and Cordillera de Sarao) and both were correlated with published high and low altitude records from the Los Lagos and Los Canales regions. The records from the Coastal Range show the following chronological sequence: (1) at the lower and middle Holocene, after 9,040 14C years BP, the Cordillera de Sarao site documents the colonization of Magellanic moorlands and north-Patagonian forest elements, followed by north-Patagonian-Valdivian forest elements during the upper Holocene; (2) the Cordillera de Nahuelbuta site shows the development of conifer forest and Magellanic moorlands during the middle Holocene, ca. 5,430 14C years BP. Other palynological records from the Coastal Range (Cordillera Pelada and Cordillera de Piuchué) show the development of both communities during the Late-glacial and lower Holocene. In contrast, the low altitude pollen records from the Los Lagos region indicate that conifers and magellanic moorland elements occupied the Longitudinal Valley during the Last Glacial Maximum (LGM), ca. 22,000 14C years BP. Various pollen profiles from Los Lagos and Los Canales regions evidenced for the late-glacial (14,600-10,000 14C years BP) the rapid southern expansion of conifers and other north-Patagonian elements, following the deglaciation of these areas. During the Holocene, Valdivian forest elements invaded the Longitudinal Valley of the Los Lagos region, while conifers and Magellanic moorland elements were displaced to coastal and Andean ranges. Also during the Holocene, Magellanic moorlands were registered south of 46° S, in an area where they have a continuous range today. Based on these results, we propose a model about the historical dynamics of south-central Chilean vegetation during the last glacial-interglacial cycle. This model shows that the most cold resistant elements (Magellanic moorlands, Nothofagus and conifers), survived the last glaciation in low altitude sites, within the Los Lagos region, between 40 and 43° S. During the late-glacial and Holocene, an altitudinal and latitudinal ascent of the glacial vegetation occurred, which culminated with the colonization of southernmost areas, and both Andean and coastal ranges, synchronous with the occupation of lowland sites by north-Patagonian and Valdivian forests. Some inferences of the model to other similar isolated vegetation of north-central Chile, allow us to concluded that Chile is an ideal scenario for such a biogeographical hypothesis
Palabras clave : pollen; historical biogeography; south-central Chile.