Geobotanical and Geomorphological Reconnaissance in West Greenland, 1961

Abstract

Lichen growth rates are used to determine glacier behavior in West Greenland in modern times where no documents are available. The vegetation and flora of the areas visited by the authors in 1961 and the plant succession on glacier forelands are described. The earliest pioneers are vascular plants and bryophytes, initially in silty pockets. Rock surfaces are invaded by algae and fungus spores which succeed after about 10 years. The first lichen to appear on loose ground is commonly Stereocaulon alpinum. When foliose or nearly fruticose species reach about 2 cm diameter, crust lichens, including Rhizocarpon spp. and Lecidea spp., can be identified. During the first seven decades the growth of Rhizocarpon spp. is slow; maximum size is attained only on moraines exceeding 1,000 years. Direct comparison of lichens appearing in photographs taken on Disko Island in 1896 and 1961 show that the majority have not increased measurably in size in the following 63 years. Comparison with photographs taken in 1958 show increases of only 1 to 4 mm for the fastest growing lichens. Datable substrates, e.g., cairns and graves, were also used to establish lichen growth rates. Photographic records of glacier outlets confirm an advance maximum around 1880–1890. Rapid retreat appears to have commenced shortly before 1961. The maximum diameters of lichens on the outermost moraines are recorded. The lichen factor defined as the diameter attained by Rhizocarpon tinei in 100 years of growth varies considerably, and correlates with the oceanic or continental character of the vegetation and is least in continental areas. By extrapolating growth rates, a number of older moraines have been dated and from this the history of moraine deposition reconstructed. Growth rates of lichens do not appear to be affected by rock types; differences are more likely to be explained by climate.