POSTGLACIAL VEGETATION HISTORY OF THE MARIANA LAKE REGION, ALBERTA

A fossil pollen record extending from 11 300 BP to the present was rec overed from Mariana Lake, Alberta (55-degrees-57'N, 112-degrees-01'W). Initially, the region had a sparse vegetation dominated by forbs arid graminoids, which at approximately 10 500 BP succeeded to Picea glauc a forest. Picea mariana - Sphagnum peatlands began to develop between 10 000 and 9500 BP. After 9000 BP Sphagnum-dominated sites decreased; P. glauca declined while Betula increased. From 7500 to 5500 BP Populu s reached its maximum Holocene representation in the vegetation. Sphag num-dominated peatlands almost disappeared. The changes following 9000 BP were likely caused by increased aridity. However, the presence of P. mariana, Abies, and Larix in the pollen record suggests that mesic sites remained. Beginning at 6500-6000 BP the extent of Sphagnum peatl ands began to increase. Abies declined in importance following 5000 BP , possibly due to paludification of mesic sites. The expansion of park land into central Alberta during the mid-Holocene did not extend to Ma riana Lake. However, Mariana Lake records changes in vegetation result ing from increased aridity in the early to mid-Holocene which are not apparent at more northerly sites in Alberta.