Changes in vegetation cover from the time of Iceland's settlement
Iceland has been settled for somewhat over 1100 years – the official date of settlement is 874 AD. The Book of Icelanders, an account of Iceland's settlement written in the early 12th century by priest and scholar Ari Thorgilsson, states that “in those days, Iceland was wooded between the mountains and the shore”. This description of Iceland is certainly in stark contrast with its present landscape. It should be kept in mind however, that these “woods” were not necessarily mighty forests, and scrub and bushes almost certainly covered much of the land that Ari describes as wooded. Birch forests where the trees were actually taller than the settlers who saw them would have grown in sunny, protected valleys and on the lower slopes of hills. These birch trees could reach a height of 10–12 m where growing conditions were best. The woodlands Ari speaks of are long gone: settlers felled the trees and used the land to graze their livestock. These encroachments came at a particularly vulnerable point in Iceland's history, as human pressure was compounded by a cooling climate and worsening growing conditions for birch. The period from around 1600–1900 is often referred to as the Little Ice Age. Indeed, glacier cover in Iceland is believed to have reached a maximum in 1890; not since the end of the last Ice Age (around 10,000 years ago) had outlet glaciers extended so far out.
Erosion and desertification have been serious problems in Iceland for much of its history. After sheltering woods and thickets were lost, the remaining vegetation cover was often unable to withstand the pressure and was gradually eroded away. Large expanses of land were left bare, exposing the soil itself to the forces of erosion. Erosion did not only occur in areas over 400 metres above sea level, where growing conditions were most difficult: it also changed the lowland landscape. Most of what are today barren or sparsely vegetated lowland areas would have been fully vegetated at the time of Iceland's settlement, while traces of soil found in some places in the Icelandic highlands, now virtually devoid of plant life, show that these regions once supported significantly more vegetation and that this vegetation was much more continuous. Although birch forests never extended far up the sides of Iceland's hills and mountains, thickets and scrub once reached up to an average elevation of 300–400 m. In places, thickets grew even higher, as patches of creeping birch at 550–600 m in Þverbrekkur by the Kjölur road demonstrate. Birch strands still grow at 300–400 m in Bleiksmýrardalur, a valley in Northern Iceland; the occasional tree reaches a height of 3–4 m.
Birch thickets and woodlands currently cover only about 1.25% of Iceland. In most places, the upper limits of birch thicket growth have dropped by around 100 m. Exceptions include Bleiksmýrardalur and Hallormsstaðarskógur forest, where birch strands reach an elevation of close to 400 m, and in Bæjarstaðarskógur and other areas of the Morsárdalur valley, where birch grows to an elevation of almost 380 m. Today, proper birch forests do not grow much above 250 metres above sea level.
Sources: Eyþór Einarsson. 2005. Flóra og gróður Íslands. In ÍSLANDSATLAS (pp. 18-23). Reykjavík: Edda.