A pollen record of a complete glacial cycle from lowland Panama

Abstract. A long pollen record from lowland Panama describes the vegetation during glacial times and probably includes a history of the last 150 000 yr, thus representing a complete glacial cycle. The record is from sediments of an extinct caldera lake under the town of El Valle. Throughout most of the last glacial period oaks and other plants of the modern montane forest maintained significant populations about 700 m lower than present. Immediately before the 14000 B.P. start ofthe late glacial period oaks had reached to 1000 m below present limits. These data require significant temperature depressions, perhaps in the order of 4 ‐ 6 °C at some seasons ofthe year. Lowland forest taxa persisted in the neighbourhood of El Valle throughout the glacial period, however, suggesting reassortment of plant populations into communities without modern analog. Although our reconstruction of levels ofthe El Valle lake in the period 30 000 to 12 000 B.P. suggests less precipitation than in modern times, the lowland climate appears to have been moist enough for taxa of tropical forests to persist. The montane floras of the western and eastern Panama highlands did not merge at any time in the glacial cycle and an hypothesis of dispersal between enlarged areas of montane forest is put forward to explain modern disjunctions in Quer cus distributions. The wet highlands of Panama were never refugia for tropical rain forest taxa at any time during the Quaternary, rather rain forest species existed in unfamiliar communities in the Panamanian lowlands.