Utviklingen av sen-glasial og holocen vegetasjon på Sørøstlandet, presentert i et 14C-datert standard pollendiagram

Abstract

A new Standard Pollen Diagram for southeastern Norway (c.f. Hafsten 1956) is compiled from 60 local pollen diagrams supplied with 229 14C-dates. Eight regional pollen assemblage zones describe the vegetation history for the last 12 300 years (all dates in calibrated years b2ka). The Younger Dryas vegetation was an arctic tundra with pioneer herbs and low bushes. At the onset of the Preboreal summer thermal maximum ca. 11 400 years ago, a birch Betula spp. woodland was established together with pioneers such as sea buckthorn Hippophäe rhamnoides. About thousand years later pine Pinus sylvestris and hazel Corylus avellana expanded. At the start of the Holcene ecological optimum ca. 9 200 years ago, alder Alnus spp. and elm Ulmus glabra expanded, followed by the expansion of oak Quercus robur and later lime Tilia cordata and ash Fraxinus excelsior ca. 7 600 years ago. Together they formed the thermophilous mixed oak forests of mid-Holocene, where the occurrence of mistletoe Viscum album, ivy Hedera helix, and holly Ilex aquifolium indicate a longer growing season with favorable summer and winter temperatures. Approximately 6 000 years ago the first traces of agriculture are recorded in the southern part of the region. Indicators of grazing / introduction of livestock occur first, followed by cereal-growing (barley Hordeum spp., oats Avena sativa, and wheat Triticum spp.) at the transition Mesolithicum – Neolithicum. Some other agricultural indicators such as weeds, hemp/hops Cannabis/Humulus, and linen Linum are mentioned. Rye Secale was introduced ca. 3 200 years ago. Agriculture increased during Bronze Age, and expanded at the beginning of the Iron Age. This had an increasing influence on the forest ecosystems. The last trees to expand were Norway spruce Picea abies and beach Fagus sylvatica. The latter has mainly been established in Vestfold county, but occur sporadic further south along the coast. Spruce expanded a little earlier on the eastern side of the Oslofjord compared to the western side, Vestfold and southeastern Telemark, were the expansion occurred ca. 1 200 years ago. http://nhm2.uio.no/botanisk/nbf/blyttia/