14. The Holocene vegetation history of Iceland, state-of-the-art and future research

Abstract

In the Late Preboreal and Early Boreal Chronozones dwarf-shrub heath and shrub heath, followed by juniper and mountain birch copses, replaced snow beds and fellfield vegetation characteristic of the Lateglacial/Early Preboreal newly deglaciated landscape of Iceland. During the Late Boreal and Early Atlantic Chronozones birch woodland established itself in the more favourable places, especially fjord lowlands and inland valleys. The development of birch woodland suffered a setback due to a transient climatic oscillation some 7500 14 C years ago, but recovered again relatively quickly and more than 6000 14 C years ago birch woodland covered the lowland areas both in northern and southern Iceland. At that time it reached its highest altitude, at least in northern Iceland. During the Late Atlantic and Subboreal Chronozones the birch woodland showed a retrogressive succession towards a more open landscape with expanding mires and heaths. There is some conflict between the evidence from pollen percentages, which indicate that the woodland regenerated several times during the latter half of the Holocene, and pollen influx values which reflect no such regeneration of the woodland. New habitats were created for birch after a period of cool climate and instability during the Early Subatlantic Chronozone as fresh screes and sandur plains became vegetated, at least partly, by woodland. This development was halted at the beginning of the Norse settlement, which resulted in further opening of the woodland. The birch woodland closest to the farms in the lowland of Iceland was cut and utilized for timber and fuel. Grazing of domestic animals opened the landscape still further and the previous woodland never re-established itself. This happened within only half a century from the arrival of the first settlers. During the ensuing 1100 years of human influence the sub-alpine birch woodland has been so intensively utilized that only in fenced, protected areas and at the most inaccessible and remote places has birch survived. The shrub and dwarf-shrub heaths, widespread mires, fell fields, and hay fields so characteristic for the Icelandic landscape at present thus developed as a relatively recent phenomenon in the form in which they appear today. A number of areas are identified for future research: elucidating the origins of the Icelandic flora, deriving palaeoclimatic data from the vegetation record, correlating terrestrial with marine and ice core records and expanding our understanding of the human impact on vegetation.