A paleobotanical and palynological study of holocene peat from the El Bosque mire, located in a volcanic area of the Cordillera Central of Colombia

Abstract

The influence of volcanic activity and climatic change upon regional and local vegetation developments during the last 5800 years in the area of the El Bosque mire has been traced through examination of a peat section collected from this mire, located ca. 4°45′N, 75°27′W, at an elevation of 3650 m, in the Cordillera Central of Colombia. The 11 m long peat section was examined for all kinds of microfossils and macroscopical plant remains. At approximately 5800 yr B.P. a lava flow of the Nevado Santa Isabel volcano obstructed the El Bosque depression, resulting in the formation of an area of impeded drainage in which a mire vegetation developed. The former vegetation in the surroundings of the depression was seriously affected by the eruptive phase and was mainly replaced by pioneer grasslands. After about 125 years forest vegetation re-appeared. From ca. 5675 to 2160 yr B.P. the vegetation surrounding the mire consisted mainly of a dense high-Andean dwarf forest of Polylepis. The stands of vegetation at the boring site itself developed from an aquatic vegetation in small pools with Azolla and Drepanocladus to relatively drier vegetation types with Carex, Disterigma and Campylopus. During this period regional and local vegetation types were little affected by volcanism, with the exception of an interval between ca. 3900 and 3300 yr B.P. From ca. 2160 yr B.P. onwards the influence of volcanic activity upon the vegetation cover in the El Bosque area increased, Polylepis dwarf forest being replaced by a more open type of high-Andean forest. Disturbances due to volcanic activity also resulted in consecutive vegetational successions in the mire. Although volcanic activity has been the main factor to which changes in the regional vegetation types can be attributed, a more or less gradual lowering of the forest line as a result of a slight deterioration of the climate during the late Holocene can also be deduced from the El Bosque pollen diagrams.