After its arrival in E Greenland c. 8000 C‐14 years B.P. Betula nana spread rapidly to become a dominant plant. A climatic change c. 5000 B.P. almost exterminated it at more oceanic sites, whereas inland it only lost little ground. Today it is common inland in many kinds of heath and other vegetation types. When it spread to Middle W Greenland around 6500 B.P. it only took two to three centuries to become dominating in the continental inland whereas the spreading to the coastal areas began later and was more gradual. After the Holocene climatic optimum it decreased here but kept its dominating position inland, where today it is a main plant in mossy heaths on N slopes and dry, grassy communities on S slopes.
Betula glandulosa arrived in SW Greenland c. 5 700 B.P., later on in S Greenland. It is a lowarctic, oceanic plant, missing only on the outer skerries, but being common in mossy heaths all through the fjords, where it also occurs in grassland vegetation types and, at the head of the fjords, as undergrowth in the subarctic, usually 4–5 m high birch woodlands formed by B. pubescens, which did not arrive until c. 3500 B.P. The most common plant communities, in which the three Betula species occur in different parts of Greenland are summarized, partly by referring to other publications, partly by presenting six new tables of vegetation analyses, stored in the Botanical Museum or published in “grey literature”. Where the species meet, hybridizing and introgression take place. Distribution maps of the three species and two hybrids are presented, and the taxonomy summarized.
Magnetic measurements have been carried out on four lake sediment successions in interior S. Greenland. The longest record extends back to 7000 C14 years BP. Based on the magnetic susceptibility six units have been distinguished. The results of the magnetic analyses show a close correlation between the four investigated sites, corroborated by pollen stratigraphy and radiocarbon dates. The period after the deglaciation, lasting for some thousand years, was characterized by sparse vegetation on the unstable soils. Erosion rates were high as revealed by the high concentration of magnetic minerals. Along with the spreading of dwarf‐shrub heaths the soils stabilized, reducing the eroding capacity, and are seen as decreasing concentrations of magnetic minerals in the sediments. During the subsequent period there seems to have been an equilibrium between climate and vegetation resulting in minimal erosion. The arrival of the Norsemen in c. AD 1000, introducing cattle and cutting down the ‘forests’, seems to have caused a disturbance in the fragile environment. It destroyed the attained equilibrium and is seen in the sediment records as an increase in magnetic concentrations. Due to the disappearance of the Norsemen in the 15th century, or slightly later, a new phase of soil stabilization began. A new and still ongoing phase of even more severe soil erosion is connected with the reappearance of man, now as a sheep breeder, in the beginning of this century. Magnetic concentrations are again high, being in the same order of magnitude as during early Holocene time.
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