Late Holocene vegetation, fire, climate and upper forest line dynamics in the Podocarpus National Park, southeastern Ecuador

Fernando Rodrguez 0 Hermann Behling 0 0 F. Rodrguez (&) H. Behling Department of Palynology and Climate Dynamics, Albrecht- von-Haller Institute for Plant Sciences, University of Gottingen , Untere Karspule 2, 37073 Gottingen, Germany Late Holocene vegetation, fire, climate and upper forest line dynamics were studied based on detailed pollen and charcoal analyses. Two sediment cores, from the Rabadilla de Vaca mire (RVM) and the Valle Pequeno bog (VP), with an age of about 2100 and 1630 cal yrs B.P., respectively, were taken at the modern upper forest line in the Parque Nacional Podocarpus (Podocarpus National Park) in southeastern Ecuador. The two pollen records reflect relatively stable vegetation with slight changes in floral composition during the recorded period. Changes of the proportion between subparamo and paramo vegetation are related to lower and higher frequency of fires. The RVM records show that the upper forest line moved to a higher elevation between 1630 and 880 cal yrs B.P., stabilising after 310 cal yrs B.P. Human impact is suggested by a high fire frequency, mainly between 1800-1600 and 880310 cal yrs B.P. The VP records indicate no marked changes in the upper forest line. The charcoal records suggest an increased human impact from 230 cal yrs B.P. to the present. The results indicate that high fire frequency is an important factor in reducing the expansion of subparamo vegetation and upper montane rainforest and in favouring the distribution of grass paramo. Since there is a clear correlation between fire and vegetation dynamics, it is difficult to detect how far climate change also played a significant role in upper forest line changes during the late Holocene. - The current altitudinal position of the Andean upper forest line (UFL) indicated by the uppermost forest patches is, to a large extent, the result of past ecological processes influenced by environmental changes including climate, fire and land use. These forest patches are interpreted as remnants of high altitude forests now destroyed by anthropogenic fires and forest clearance (Ellenberg 1958; Laegaard 1992; Sarmiento and Frolich 2002). Reconstruction of vegetation history is therefore an essential tool for understanding the dynamics of the UFL positions. The limit between montane rainforest and paramo grassland has important ecological and socioeconomic relevance. Studies on deforestation in Ecuador have estimated that only 4% of the forests on the western Andean slope are left. In the central valley, almost no natural forests are left because of the long occupation history and, in particular, increasing human impact during recent decades (Dodson and Gentry 1991). The potential position of the UFL is still not known due to a lack of both ecological and historical information about tropical ecosystems. According to some authors, the uppermost forest patches found above the actual tree line indicate the potential UFL. However, there is no evidence that these highest forest patches have ever been connected (Islebe and Hooghiemstra 1997; Wille et al. 2002), and present patches are mostly restricted to special micro-sites such as ravines and boulder slopes (Troll 1959; Walter and Medina 1969). The situation of forest patches at lower altitudes, close to the actual UFL, is not well known. These may also rely on unique local conditions or they may be remnants of formerly more extensive forest (Miehe and Miehe 1994; Kessler 2002; Bakker et al. 2008). A few palaeoenvironmental records are available from southern Ecuador and neighbouring countries (Fig. 1). Studies from southwestern Ecuador in the Cajas National Park on the Western Cordillera at 3,700 m indicate that there was a herb paramo there in the Late-glacial period (1700011000 cal yrs B.P.), reflecting climatic conditions colder and moister than those of today (Hansen et al. 2003). During the Holocene, Polylepis became more frequent and reached its maximum during the mid Holocene period. The climate was warmer with a more moderate seasonality during the early Holocene than it is nowadays. Fires were much more frequent during the early and mid Holocene than during the Late-glacial period. However, after 4000 cal yrs B.P., the vegetation changed and the decrease of charcoal particles suggests a change towards moister conditions (Hansen et al. 2003). The results of the 17000 yrs B.P. old record of the Paso El Tiro, which is today covered by subparamo vegetation, provide important insights on past vegetation, climate and fire history (Niemann and Behling 2008a). Fig. 1 Map of South America showing the study sites mentioned in the text. 1, Laguna Zurita; 2, Paso El Tiro; 3, Cocha Caranga; 4, Laguna Rabadilla de Vaca; 5, Cerro Toledo; 6, Guandera; 7, Pantano de Pecho; 8, Ro Napo; 9, Laguna Yambo; 10, Lago Surucucho; 11, Laguna Chochos; 12, Huascaran; 13, Laguna Loma Linda The Holocene history of UFL dynamics in the northern Andes has been addressed by an increasing number of palynological studies since the 1960s (van der Hammen and Gonzalez 1960; van Geel and van der Hammen 1973; Hooghiemstra 1984; Colinvaux 1997; Hansen et al. 2003). However, there is no consensus about what happened there during the Holocene, as different pollen studies and their interpretations are often contradictory, and the timing of events is somewhat uncertain (Markgraf 1989; van t Veer et al. 2000; Marchant et al. 2001). Velez et al. (2003) studied areas situated between the western and central Andean Cordilleras in Colombia, showing the dynamics of forest expansion/reduction with a clear increase in wetness during the mid Holocene. On the eastern Andean Cordillera, pollen records also show dry and cold conditions during the Late Pleistocene, very wet conditions for the early to mid Holocene, and dry conditions during the mid to late Holocene, while on the eastern savannas, records suggest dry conditions during the early Holocene and generally wet conditions for the mid and late Holocene (Behling and Hooghiemstra 1998, 2000). Predictions of future global change suggest that changes in biodiversity composition and distribution are likely to occur in these ecosystems (IPCC 2007). Higher temperatures together with human influence will allow fires to occur more frequently and will increasingly transform the landscape. Two sediment cores were collected at the modern upper forest limit (UFL) and studied by pollen and charcoal analysis, in order to obtain long-term records of vegetation dynamics in the study area. Four main questions will be addressed: (1) What was the nature of vegetation, fire and climate dynamics in the Parque Nacional Podocarpus (Podocarpus National Park, PNP) during the late Holocene? (2) How dynamic or stable were the vegetation and UFL during the late Holocene in the upper region of the PNP? (3) Which environmental factors have driven possible changes in vegetation and UFL dynamics? (4) Has fire, natural or anthropogenic, played a role i (...truncated)