Abstract
This study examines the new fossiliferous site Huapilacuy II of Mid-Holocene age (7,344±51-6,865±58 cal years BP.) located in the northwestern coast of the Isla Grande de Chiloé. This area was not affected by the successive Pleistocene glaciations, and therefore it presents a biogeographic relevance as a potential area of refugia and stability for the vegetation. The presence of plant macrofossils contained in a sedimentary sequence of ca. 300 cm thick, confers a special interest to the site, due to the scarce information available on this type of indicator in paleoenvironmental studies of southern Chile. Additionally, several pollen-based reconstructions from the southern Lake District of Chile (40-44˚ S), document the Holocene sequence of recolonization by the different temperate rainforests types that today occupy this region, although there are non-Holocene records for the Pacific coast of the region. The aim of this study is to reconstruct the local environmental conditions and paleoecology based on the stratigraphic context and the analysis of plant macrofossils at the site Huapilacuy II. In addition, based on the pollen analysis of the deposit, we provide new information to reconstruct the regional characteristics of the vegetation during the Middle-Holocene. In particular, the plant macrofossil record of marsh species contained in the sediments of the lower section of the studied sedimentary sequence, together with the pollen analysis of the same sequence, document a first phase of plant colonization at 7,344±51 cal yrs. BP, with predominance of Poaceae, ferns, and trees with regeneration capacity in open areas, such as Embothrium coccineum and Drimys winteri. The analysis of leaf macrofossils and palynomorphs recovered from several intercalated layers, from the middle section of the sedimentary sequence, show the local and regional development of dense and very humid forests dominated by Aextoxicon punctatum, associated with several species of Myrtaceae. The presence of soil moisture indicator species, such as Luma chequen, Myrceugenia sp. and Myrtaceae Blepharocalyx-type is consistent with the sedimentary environment and the local development of swamp or riverine forests. This hygrophile forest environment is also consistent with the assemblage of fossil mosses, dominated by species that grow today in dense closed-canopy forests, such as Weymouthia, Ptychomnium, Rigodium, Porothamnium and Eucamptodon.
 The regional correlation of the pollen spectra from Huapilacuy II and other records from the Lake District allows us to establish latitudinal and longitudinal differences of tree composition in the temperate-rainforests that expanded during the Early to Mid-Holocene. In particular, this study established for the northwestern coast of the Isla Grande de Chiloé the presence of the coastal association of the valdivian forest (As. Lapagerio-Aextoxiconetum), currently distributed along the Chilean coastline between 30˚- 43˚S. In contrast, the Valdivian associations recorded in other areas of the region exhibit the dominance of Eucryphia cordifolia, Caldcluvia paniculata, Weinmannia trichosperma and different species of Nothofagus. Despite the differences in tree composition, the fossil bryophyte species recorded in several of the sites compared are common with those reported for Huapilacuy II, thus showing the wide ecological range of Chilean bryophytes associated with closed-canopy temperate-rainforests.
Highlights
S afectada directamente por las sucesivas glaciaciones del Pleistoceno, otorgándole relevancia biogeográfica como potencial área de refugio y estabilidad para la vegetación
El análisis de los macrofósiles foliares contenidos en varias capas intercaladas en la parte media de la secuencia sedimentaria y el registro polínico del depósito, evidencian el desarrollo local/regional de bosques densos, muy húmedos dominados por Aextoxicon punctatum, asociado a varias especies de Myrtaceae
E coast of the Isla Grande de Chiloé. This area was not affected by the successive Pleistocene glaciations, and it presents a biogeographic relevance as a potential area of refugia and stability for the
Summary
S El sitio fosilífero Huapilacuy II se sitúa en la costa norte de la Isla Grande de Chiloé, al oeste de la ciudad de. P El clima actual de la región es templado-lluvioso y, por su particular situación geográfica, el área está IN favorecida por condiciones oceánicas, como lo indica una comparación del nivel promedio anual y distribución mensual de las precipitaciones de dos registros meteorológicos cercanos al sitio de estudio (Fig. 1A). La estación Punta Corona (41°47’S – 73°52’O), con 2.410,5 mm de precipitación anual promedio, muestra una variación estacional más constante de las lluvias propia de los climas oceánicos, con un leve descenso por bajo 100 mm en el mes de enero (93 mm). La vegetación regional de la costa noroccidental de la Isla Grande de Chiloé corresponde al tipo de bosque valdiviano costero dominado por Aextoxicon punctatum Ruiz & Pav. asociado a distintas especies de mirtáceas como Myrceugenia planipes El área se encuentra parcialmente alterada por actividades de pesca artesanal y turismo
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