Abstract:
Based on 5 pollen records from locations between ca. 2700 and 3300 masl in the Podocarpus National Park (PNP) area (ca. 4° S and 79° W) within the Andean depression region in southern Ecuador, we reconstructed and visualized upper forest line (UFL) dynamics and past vegetation changes since the last glacial maximum (LGM). Estimates of altitudinal ranges of past UFL shifts in the study area allowed reconstructing past changes of forest and páramo expansion in the study region. During the LGM, the UFL position in the PNP area was at least ca. 700 m lower in the northernmost part and ca. 250 m further south compared to today. Glaciers covered the central PNP at this time, while deglaciation completed with the beginning of the Holocene. Throughout the recorded time UFL shifts and vegetation changes in the study area showed considerable local differences. This can be explained by locally differing vegetation compositions and climatic conditions, but especially during early to late Holocene times also by human disturbances. Only during the earliest Holocene and mid-Holocene the UFL in the central and southern PNP areas reached slightly higher elevations up to 200 m above the present position. The UFL in the PNP area shifted altitudinally over a shorter interval compared to other sites outside the depression. This difference may be caused by the study regions relatively low mountain elevations, wet climatic conditions, different and diverse vegetation pattern as well as by the corresponding vegetation response to climatic changes. The high complexity and heterogeneity of Andean habitats are assumed to be responsible for the variety in altitudinal distribution and compositional changes of vegetation. In the PNP area and the Andean depression region temperature seems to be less important for the UFL and vegetation changes than in other regions of the northern Andes. Instead we assume that other drivers, e.g. precipitation and wind, may be much more important for the developments in our study region.
