Abstract

Ped Pond is a lake lying in a Pleistocene scour channel of the Porcupine valley. The valley is considered to be a possible path of late Quaternary species migrations between interior Alaska and northwest Canada. Pollen in the oldest lake sediments (ca. 13 000 years old) indicates that shrub birch and willow probably occurred locally in a sparsely vegetated, herb-dominated landscape. Populus, Juniperus, and Typha latifolia increased about 10 000 years ago, suggesting particularly warm temperatures during the early Holocene. Picea glauca, which is presently common in the surrounding forests, first arrived near Ped Pond about 8500 years ago. This arrival date, together with existing evidence from other sites, indicates that spruce expanded rapidly across far-eastern Beringia 8000–9000 years ago. Other boreal forest taxa, Picea mariana, Betula papyrifera, and Alnus spp., became established locally between 7000 and 8000 years BP. A date of ca. 7500 years BP at Ped Pond suggests that the Alnus rise in northeast Alaska preceded that in adjacent Canada, possibly reflecting an eastward movement of alder. The vegetation history at Ped Pond suggests the Porcupine valley has been an important transition zone throughout the Holocene; some events are characteristic of northern Alaska and some of northwest Canada.

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