A mid-holocene vegetational and climatic record from the subalpine zone of the Maligne Valley, Jasper National Park, Alberta (Canada)
Abstract Pollen, macrofossils and isotopic data ( 13 C, 18 O) from gastropod shells are used to reconstruct Holocene vegetational and climatic changes for a lower subalpine forest site (elevation 1690 m) in the Maligne Valley, Jasper National Park, Alberta. Subalpine forest has characterized the site since the inception of the sedimentary record in this small pond ca. 8500 yr B.P. In contrast to the vertical timberline fluctuations recorded at nearby sites above present tree-line, vegetational changes at the site appear to have been mainly horizontal, i.e. forest cover and tree density expanded or contracted laterally in response to climatic warming or cooling. At Maligne Lake forest cover was probably at its maximum extent about 7500 yr B.P., when Pseudotsuga and other montane elements had migrated to this elevation but did not displace the existing vegetation. The modern mosaic of discontinuous subalpine forest and extensive dwarf birch-dominated damp meadows and fens emerged only during the last 1300 years. A warmer Neoglacial episode, dated ca. 2600–3400 yr B.P., is indicated by increases in the temperature-limited gastropod, Lymnaea palustris , and by progressive enrichment in the 18 O and 13 C contents of their shells. Summer temperatures during this period, which has been tentatively identified elsewhere in the Canadian Rockies, may have risen by as much as 1.8°C.