Multivariate statistical estimates of Holocene vegetation and climate change,forest-tundra transition zone,NWT, Canada

Newly derived fossil pollen data were obtained from four sites along a transect from the boreal forest limit into tundra in the eastern Northwest Territories. Multivariate statistical analyses were employed to interpret the pollen assemblages. Transfer functions were constructed between the pollen data and climatic data, and paleoclimatic estimates were derived. The objective nature of the reconstructions provides an independent verification of the general outlines of the chronology of tree-line movements during the mid- and late-Holocene as established in previous paleosol and pollen studies. Boreal forest extended to approximately 62°N, associated with mean July temperatures 1 to 3°C above modern means, from at least 5500 to 3700 yr B.P. Although a major episode of southward displacement of tree line at about 3700 yr B.P. is recorded, later events are not clearly represented. Considerations of the statistics, the time scales, and the nature of the pollen rain suggest only conservative interpretations of the results are possible. It is suggested that the pollen sites may have been sensitive recorders of regional vegetation change only when they were near the ecotone, corresponding to a climatic threshold.