A Holocene environmental record reflecting vegetation, climate, and fire variability at the Páramo of Quimsacocha, southwestern Ecuadorian Andes

Nele Jantz 0 Hermann Behling 0 0 N. Jantz (&) H. Behling Department of Palynology and Climate Dynamics, Albrecht-von-Haller Institute for Plant Sciences, University of Gottingen , Untere Karspule 2, 37073 Gottingen, Germany We reconstructed the palaeoenvironmental conditions of the last ca. 8,000 years in the Tres Lagunas region of the Quimsacocha volcanic basin (ca. 3,800 m a.s.l.) in the southwestern Ecuadorian Andes. By means of a pollen and charcoal record, we analysed vegetation, fire, and climate history of this area, which is sensitive to climatic changes of both the Pacific as well as of the eastern Andes and Amazon region. Sediment deposits, pronounced increases of pollen and charcoal concentrations, and pollen taxa reflect warmer and drier conditions in the early to midHolocene (*8000 to 3900 cal. B.P.). During the late Holocene (2250 to -57 cal. B.P.), five warm and cold phases occurred at Quimsacocha. The most prominent cold phase possibly corresponds to the globally recognized Little Ice Age (LIA; *600 to 100 cal. B.P.). The cold phase signal at Quimsacocha was characterized by a higher abundance of Poaceae, Isoetes and Gentianella, which are favoured by cold and moist conditions. Frequent charcoal particles can be recorded since the early to mid-Holocene (*7600 B.P.). The high Andean tree species Polylepis underwent several phases of degradation and re-establishment in the basin, which could indicate the use of fire by pre-Columbian settlers to enhance the growth of preferred herb species. The Tres Lagunas record suggests that human populations have been influencing the environment around Quimsacocha since the last ca. 8,000 years. - The Ecuadorian Andes are important: (i) Ecologically because of high diversity (both alpha and beta) and endemism (Balslev and Luteyn 1992; Jrgensen and Leon-Yanez 1999; Luteyn 1999) and (ii) for the provision of ecosystemservices, such as the regulation of Andean hydrology, protection from erosion and the provision of food for a growing population. However, the landscapes of the Ecuadorian Andes suffer a high degradation rate. Ecuador has the highest deforestation rate in South America (Mosandl et al. 2008; Sarmiento 2002), and Paramo areas especially of lower altitudes are subject to overgrazing, fire or cultivation, which lead to reduction of biodiversity and water retention capacity, as well as to soil erosion (Podwojewski et al. 2002). The development of useful and innovative protection strategies in the Ecuadorian Andes is consequently urgently needed. In this context, the knowledge of palaeoecological conditions can be of crucial importance, as the composition of past natural as well as of pre-Columbian anthropogenic landscapes and climate conditions are often not well known. Several palaeoecological studies have been carried out in the eastern tropical Andes (e.g. Brunschon et al. 2010; Hillyer et al. 2009; Niemann and Behling 2008), whereas there are only a few studies that deal with the conditions on the western Cordillera (e.g. Colinvaux et al. 1997; Hansen et al. 2003; Weng et al. 2006). In general, there is a trend of a warm and dry early to mid-Holocene in the west and central Andes region of Ecuador, Peru and Bolivia (Hansen et al. 2003; Paduano et al. 2003; Weng et al. 2006). However, there are still uncertainties concerning the magnitude and time span of this mid-Holocene dry event. A time-transgressive reoccurrence of moister conditions from north to south seems to be evident for the Central Andes region of Peru and Bolivia. A longer and more severe dry phase from 6000 to 2400 cal. B.P. is reported from central Bolivia (Taypi Chaka Kkota, 16 S, Abbott et al. 2003), whereas sediments from Laguna la Compuerta (7 S) in northern Peru show a shorter dry phase from 10000 to 5500 cal. B.P. (Weng et al. 2006). In some parts of the southern tropical Andes region, the midHolocene dry event does not seem to be as pronounced and some palaeorecords show volatile lake levels rather than a complete drying-out, as for example Hillyer et al. 2009 and Valencia et al. 2010 for Laguna Pacucha in Southern Peru (13 S, 3,095 m a.s.l.). To what extend the western cordillera of the Ecuadorian Andes was subjected to the mid-Holocene dry event remains yet to be determined due to an absence of published studies. The late Holocene is marked as a moister period with repeated climatic oscillations for most tropical Andean sites, such as Lake Titicaca and Taypi Chaka Kkota in Bolivia (Abbott et al. 2003). During this period, human influence is reported throughout the Andes. Weng et al. (2006) date human influence back to least 5500 cal. B.P. for Laguna Compuerta in northern Peru and Bush et al. (2005) suggest occasional human influence from 6000 cal. B.P. at Laguna de Chochos, about 200 km northeast of Laguna Compuerta. In the southwestern Ecuadorian Andes, traces of human land use are present in the pollen records of Laguna Pallcacocha and Lagunas Chorreras since *4000 cal. B.P. (Hansen et al. 2003). In this paper, we present results of palaeoecological investigations from the Tres Lagunas region in the Quimsacocha volcanic basin in south Ecuador, which, due to its situation on the eastern ridge of the western Cordillera, is sensitive to climatic changes of both the Pacific as well as of the eastern Andes and Amazon region. Our main objective is to detect climatic patterns of regional to global significance since the early to midHolocene. We will asses the role of the mid-Holocene dry phase, as well as late Holocene climatic patterns for this part of the tropical Andes region. Furthermore, we will integrate our results into a more regional comparison of records. We will also reconstruct regional vegetation and fire dynamics and assess the history of anthropogenic impact of the Quimsacocha volcanic basin. The regional geomorphology was shaped by glacial activity, persisting until the late Pleistocene (*12600011800 B.P.). Characteristic features include U-shaped valleys, numerous small lakes, and moraines (Rodbell 2002; Hansen et al. 2003). Even though a few studies on past vegetation (Colinvaux et al. 1997; Hansen et al. 2003) and soils (Rodbell 2002; Harden 2007) have been carried out in the nearby Cajas National park area and surroundings, no absolute dates for the glacial retreat have been determined so far. However, by the means of pollen and sediment analyses, a glacial retreat has been recorded for the period between 17000 and 15000 cal. B.P. at the lakes Laguna Llaviucu (3,140 m a.s.l.), Laguna Chorreras (3,700 m a.s.l.) and Laguna Pallcacocha (4,060 m a.s.l.) (Hansen et al. 2003; Colinvaux et al. 1997). Potentially natural forest vegetation and land use Three major forest types have been recognised in the Podocarpus National Park today (about 200 km south of the study site) (Homeier et al. 2008). The evergreen lower mountain rainforest is found at altitudes from 1,300 to 2,100 m a.s.l. Here, trees grow up to 40 m in heigh (...truncated)