No abstract

ABSTRACT. The pollen record from Lagunas de Mojanda, located at 3748 m a.s.l. (northern Ecuadorian Andes) reflects the vegetation and climate dynamics for the last ca 3400 cal yr BP. Páramo vegetation has been the main vegetation type since the beginning of the record. At Lagunas de Mojanda, from the last ca 3400 to 2200 cal yr BP, grass páramo was well represented mainly by Poaceae (40%) and the occurrence of Valeriana (5%), while montane forest taxa were poorly represented and subpáramo taxa were rare. The vegetation composition suggests cool and humid conditions. Between ca 2200 and ca 1300 cal yr BP, montane rainforest and subpáramo taxa had a higher presence but páramo taxa remained the main vegetation type in the study area, suggesting cool climatic conditions. From ca 1300 to ca 500 cal yr BP, páramo vegetation remained stable, with higher presence of Phlegmariurus and Isoetes, suggesting cool and humid conditions. The last ca 500 cal yr BP generally show lower frequency of montane rainforest and subpáramo taxa. Páramo vegetation reached the highest share, with the presence of Poaceae, Plantago and Ranunculus suggesting a trend of peat bog drying. Fires were present during the whole record, perhaps human-caused, but the study area does not show great disturbance except from ca 1300 to 500 cal yr BP, a period of an evident higher influx of charcoal particles coincidentally with nearby ancient human occupation.

To reconstruct the environmental history including vegetation, fire and climate dynamics, from the Cajanuma valley area (3285 m elevation) in the Podocarpus National Park, southern Ecuador, we address the following major research question: (1) How did the mountain vegetation developed during the late Glacial and Holocene? (2) Did fire played an important control on the vegetation change and was it natural or of anthropogenic origin?. Palaeoenvironmental changes were investigated using multiple proxies such as pollen, spores, charcoal analyses and radiocarbon dating. Pollen data indicated that during the late Glacial and transition to the early Holocene (ca. 16 000-10 500 cal yr BP) herb páramo was the main vegetation type around the study area, while subpáramo and mountain rainforest were scarcely represented. The early and mid-Holocene (ca. 10 500 to 5600 cal yr BP) is marked by high abundance of páramo during the early Holocene followed by a slight expansion of mountain forest during the mid-Holocene. During the mid-to late Holocene (ca. 5600-1200 cal yr BP) there is a significant presence of páramo and subpáramo while Lower Mountain Forest decreased substantially, although, Upper Mountain Forest remained relatively stable during this period. The late Holocene, from ca. 1200 cal yr BP to present, was characterized by páramo; however, mountain forest and subpáramo presented significantly abundance compared to the previous periods. Fires became frequent since the late Holocene. The marked increased local and regional fire intensity during the wetter late Holocene strongly suggests that were of anthropogenic origin. During the late Glacial and early Holocene, the upper forest line was located at low elevations; but shifted slightly upslope to higher elevations during the mid-Holocene.

The last ca. 4100 cal yr BP of palaeoenviromental conditions in the Llanganates National Park, central Ecuadorian Andes has been reconstructed from the pollen record "Anteojos Valley" (3984 m elevation). The pollen record, dated by 4 radiocarbon dates, indicates that the local páramo vegetation was a relatively stable with only minor fluctuations since the mid-Holocene. The páramo vegetation was characterized mainly by Poaceae, Cyperaceae and Asteraceae. The regional Lower Mountain Rainforest vegetation is mainly represented by Moraceae/Urticaceae and the Upper Mountain Rainforest by Melastomataceae, Polylepis and Weinmannia. Between ca. 4100 to 2100 cal yr BP, páramo was the main vegetation type with low presence of mountain rainforest; probably reflecting cool conditions. Between ca. 2100 cal yr BP to the present, the proportion of páramo vegetation increased with a decreased occurrence of mountain rainforest suggesting cooler and moister conditions. Low frequencies of fires were evidenced since the mid-Holocene. However, there is a slight increase of regional fire between ca. 4100 to 3100 cal yr BP. The low abundance of larger carbonized particles since the beginning of the record, suggests low occurrence of local fire in the study area.