A Holocene pollen record of vegetation change and human impact from Pantano de Vargas, an intra-Andean basin of Duitama, Colombia

Abstract

Holocene environments in the intra-Andean basin of Duitama (Eastern Cordillera of Colombia, 2510 m altitude) are presented based on the 620 cm long Vargas pollen and sediment record. Seven AMS radiocarbon dates show these lake and swamp sediments represent the period from 8800 to 2610 14C yr BP. We identified seven distinct periods of environmental conditions in the basin. From ca. 8800 to 7700 14C yr BP (9450–8300 cal yr BP) Alnus and Myrica swamp forest grew on wet soils. On the surrounding slopes Andean forest was present with Hedyosmum, Melastomataceae and Quercus. Between 7700 and 6090 14C yr BP (8300–6750 cal yr BP) open water with aquatics alternated with peat-forming Plantago meadows reflecting repeated lake levels changes. From 6090 to 5220 14C yr BP (6750–5680 cal yr BP) open water and grassy vegetation around the lake was replaced by Alnus-dominated swamp forest, suggesting lower lake levels and drier climatic conditions. Between 5220 and 4500 14C yr BP (5680–4810 cal yr BP) an alternation between Alnus-dominated swamp forest and open grassy vegetation continued, reflecting fluctuating water levels. At that time Hedyosmum, Miconia, Quercus, Solanaceae, Relbunium and Rubiaceae were common elements in the Andean forest. From about 4500 to 3680 14C yr BP (4810–3800 cal yr BP) Alnus-dominated swamp forest alternated with Myrica shrub and much organic material accumulated in the basin. Evidence of deforestation (reduction of Quercus in particular), lowering of water tables and increasing disturbance, probably by erosion (presence of Amaranthaceae/Chenopodiaceae, Borreria and Dodonaea) point to the settlement of pre-Hispanic populations. Between 3680 and 2610 14C yr BP (3800–2470 cal yr BP) there is clear evidence of crop cultivation (presence of Zea mays) and frequent fires (high amounts of charcoal in the sediments). Erosion all over the basin led to significant sediment supply and the lake gradually changed into a swamp. By this time pre-Hispanic populations had used nearly all alder wood in the catchment area. The uppermost sediments are oxidised and the last 2610 radiocarbon years of the Holocene are not represented, possibly due to agricultural activities.