Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

Abstract

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland ( Pinus contorta ) with alder ( Alnus ), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce ( Picea sitchensis ) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock ( Tsuga mertensiana ) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock ( Tsuga heterophylla ) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars ( Chamaecyparis nootkatensis , Thuja plicata ) appeared on Mitkof Island during the late Holocene.