Vegetation, climate and fire in the eastern Andes (Bolivia) during the last 18,000 years Joseph J. Williams a, ⁎, William D. Gosling a , Stephen J. Brooks b , Angela L. Coe a , Sheng Xu c a Department of Environment, Earth & Ecosystems, Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR), The Open University, Walton Hall, Milton Keynes. MK7 6AA, UK b Department of Entomology, Natural History Museum, Cromwell Road, London. SW7 5BD, UK c NERC Radiocarbon Laboratory, Scottish Enterprise Technology Park, East, Kilbride, Glasgow. G75 0QF, UK abstract article info Article history: Received 20 April 2011 Received in revised form 3 October 2011 Accepted 5 October 2011 Available online 12 October 2011 Keywords: Fossil pollen Fossil charcoal Deglaciation Holocene dry event (HDE) Polylepis woodland Temperature Precipitation A c. 18 ka cal BP long sediment record from Laguna Khomer Kocha Upper (4153 m asl), Bolivia, shows that fire regime, governed by climatic variation, has long been a transformative agent in the eastern Andes. Before c. 14.5 ka cal BP, warming and relatively moist conditions free from fire, facilitated the expansion of high An- dean Polylepis woodland. Fire onset at c. 14.5.ka cal BP, quickly transformed the local vegetation and the woodlands became restricted to areas protected from fire. A major increase in burning, c. 10.1–6.4 ka cal BP removed Polylepis woodland locally and this coincided with a region-wide Holocene dry event (HDE) which caused falling lake levels and allowed fire intensification. A decline in burning at c. 6.4 ka cal BP and an increase in marsh–woodland (Alnus) marked the termination of the HDE and a return to wetter condi- tions. As well as recording the environmental history of local vegetation dynamics, long-distance pollen transport provides evidence of changes in the Yungas montane forests, highlighting their sensitivity to cli- mate and burning regimes. Simultaneous adjustments in both Andean and Yungas montane taxa suggest that vegetation dynamics in the two environments are linked to a common climatic driver. There is no evi- dence to indicate that human activity had any impact on the local landscape. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Worldwide, mountainous regions have been observed to provide early warning for adjustments in environmental processes driven by climate change (Ørbæk et al., 2004). The northern and central Tropical Andes, is one of the most biologically diverse regions on Earth (Myers et al., 2000), which is partly attributable to the complex topography and large elevational range (2500–4500 m above sea level [m asl]) which supports many microclimates. However, predicted future climate changes are considered a serious threat to this biodiversity (Malcolm et al., 2006). The extreme altitudinal and climatic variation, and the close relationship between species and climate, means that continuous montane forests can be found within just a few tens of kilometres of grassland and bare rocky peaks (Young et al., 2002). The narrow vertical species ranges mean that even small variations in temperature or precipitation can result in considerable changes in species distribution. This sensitivity of Andean ecosystems to climate can however be useful to scientists because it facilitates the monitor- ing of change in modern floras (e.g. Sarmiento et al., 2003; Feeley et al., 2011) and examination of longer-term shifts in the fossil record (e.g. Bush et al., 2004; Cárdenas et al., 2011). The pattern of environmental change in the Andes in response to global climate change since the Last Glacial Maximum (LGM; 21 ± 2 ka cal BP) is complex. During the LGM high northern and central Andean regions were ~7–8 °C cooler than today and moisture availability varied regionally (Cook, 2009; Sylvestre, 2009). The sub- sequent deglaciation does not seem to have been a synchronous event across the Andes and mechanisms driving this environmental change are still debated (Bush et al., 2011). However, some tempera- ture and precipitation changes during the last deglaciation have been identified as broadly coincident with key global events, including the warm Bølling–Allerød chronozone (c. 15–14.0 ka cal BP) and the colder Younger Dryas chronozone (c. 12.9–11.6 ka cal BP; Thompson et al., 1998; Baker et al., 2001a; Rasmussen et al., 2006; Zech et al., 2010) but the overall picture is not spatially consistent. Following de- glaciation and throughout the Holocene (11.7 ka cal BP to present) moisture balance fluctuated and there were small-scale variations in temperature (Bush et al., 2005). A middle Holocene dry event (HDE) was the most pronounced reduction in precipitation in the northern to central Andes (c.8–5 ka cal BP; Sandweiss et al., 1996; Urrego et al., 2009). However, as more records of past environmental change become available it is becoming apparent that it would be better to describe this period as one of increased drought frequency punctuated with episodic wet events, rather than as a single dry Palaeogeography, Palaeoclimatology, Palaeoecology 312 (2011) 115–126 ⁎ Corresponding author at: Department of Geography, Kansas State University, 118 Seaton Hall, Manhattan. KS 66506-2904, USA. E-mail addresses: josephjw@k-state.edu, joe.j.williams84@googlemail.com (J.J. Williams). 0031-0182/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2011.10.001 Contents lists available at SciVerse ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo