Читать книгу Biogeography in the Sub-Arctic - Группа авторов - Страница 54

During the last ice age Iceland was covered by an ice cap, the margin of which extended out on to the edge of the shelf (Andrews et al. 2000). Some parts of Iceland were deglaciated during the late glacial, and late glacial raised marine deposits are known from several sites. Late glacial lake deposits have been recovered from the Skagi peninsula in northern Iceland. Studies of late glacial and Early Holocene deposits were conducted in the 1990s (Rundgren 1995, 1998; Rundgren and Ingólfsson 1999).

Sediments from the Allerød chronozone contain a fairly diverse pollen flora with woody plants such as B. nana, Salix, Juniperus and Empetrum that formed a significant part of the vegetation, which also included various herbs, grasses and sedges. Prior to the Allerød and during the Younger Dryas, a vegetation with pioneer plants dominated (Rundgren 1995).

The Early Holocene sediments contain plant macro‐fossils in addition to pollen. Macro‐fossils of B. nana, S. herbacea, Salix cf. phylicifolia, E. nigrum, Vaccinium sp., D. octopetala, C. palustris, Angelica sylvestris and Armeria maritima are recorded. Pollen and plant macrofossil records reflect progressive closing of the vegetation cover, from herb tundra over a dwarf‐shrub phase to a shrub and dwarf‐shrub phase (Rundgren 1998).

Pollen from tree birch are rare in Early Holocene deposits in northern Iceland and it has been suggested that they represent long‐distance transport, either from outside Iceland or from limited areas in Iceland with local tree birch growth (Caseldine 2001). Birch woodland began to develop in Iceland in lowlands along fjords and in valleys ~2000–4000 years after the beginning of the Holocene, and reached their maximum before 7000 years BP. During the Mid‐ and Late Holocene heaths and mires expanded and woodlands became more open (Hallsdóttir and Caseldine 2005).

Rundgren and Ingólfsson (1999) contended that many plant species survived the Younger Dryas in northern Iceland and that these species also could have survived the last glacial maximum in Iceland. In contrast, Buckland et al. (1986), updated in Buckland and Panagiotakopulu (2010), argued that the virtual absence of endemic species supports a model of late glacial or Early Holocene immigration, and maintained that most species of vascular plants and beetles, including heavy flightless beetles, arrived by ice‐rafting from North‐West Europe at the Pleistocene–Holocene transition, an idea first put forward by Coope (1969).