Abstract:
The vegetation,climate and fire history of high mountain ecosystemsin the southern Ecuadorian Andes are
documented in a continuous pollen and charcoal record,from Lagunas Natosas Forest bog,at 3495 m a.s.l. spanning the late Pleistocene and Holocene periods since 15,930 cal yr BP.The chronology of this record is
based on four radiocarbon dates.Páramo vegetation with abundant Poaceae and Plantago rigida characterized
the Late Glacial(LG)period, implying cold and wet conditions. Slight expansions of mountain forests suggest
warming during the LG. The upper foresl line was lower than today and fire events were rare during the
Pleistocene. During the early and mid-Holocene until 4300 cal yr BP, the area of páramo was markedly smaller and the subpáramo with woody vegetation (Melastomataceae) was larger. The upper mountain forest dominated and the upper forest line shifted to higher elevations. The pollen record provides the first evidence
of the development of Polylepis forests in the southern part of the so-called Andean Depression reflecting
warmer and drier climatic conditions during early and mid-Holocene. The late Holocene after about
4300 cal yr BP is characterized by larger areas of páramo and subpáramo promoted by moister conditions.
These moister conditions and frequent fires may have been the cause of the very rare occurrence or even extinction of Polylepis populations in the Jimbura region. Since ca. 1000 cal yr BP human occupation has altered
the landscape by frequent burning, woodcutting, grazing and cultivation.
