Lichenometric dating (lichenometry) and the biology of the lichen genus rhizocarpon:challenges and future directions

Lichenometric dating (lichenometry) involves the use of lichen measurements to estimate the age of exposure of various substrata. Because of low radial growth rates and considerable longevity, species of the crustose lichen genus Rhizocarpon have been the most useful in lichenometry. The primary assumption of lichenometry is that colonization, growth and mortality of Rhizocarpon are similar on surfaces of known and unknown age so that the largest thalli present on the respective faces are of comparable age. This review describes the current state of knowledge regarding the biology of Rhizocarpon and considers two main questions: (1) to what extent does existing knowledge support this assumption; and (2) what further biological observations would be useful both to test its validity and to improve the accuracy of lichenometric dates? A review of the Rhizocarpon literature identified gaps in knowledge regarding early development, the growth rate/size curve, mortality, regeneration, competitive effects, colonization, and succession on rock surfaces. The data suggest that these processes may not be comparable on different rock surfaces, especially in regions where growth rates and thallus turnover are high. In addition, several variables could differ between rock surfaces and influence maximum thallus size, including rate and timing of colonization, radial growth rates, environmental differences, thallus fusion, allelopathy, thallus mortality, colonization and competition. Comparative measurements of these variables on surfaces of known and unknown age may help to determine whether the basic assumptions of lichenometry are valid. Ultimately, it may be possible to take these differences into account when interpreting estimated dates

Plateau and valley glaciers in north Norway: responses to climate over the last 100 years

No abstract available

Oksfjordjokelen - Norway

No abstract available

Glacier Fluctuations in Nufsfjord, Finnmark

No abstract available

Recent glacial history and climatic change, Bergsfjord, Troms-Finnmark, Norway

Systematic documentation of climatic change using historical records of glacier fluctuations in North Norway is complicated by the strong topographic control exerted on glacier and ice-cap development in plateau regions. Ice avalanches from high plateaux maintain valley glaciers up to 600 m below in the surrounding valleys. Ice-marginal recession due to changing mass balance on the plateau ice caps has reduced ice avalanching and contributed to the subsequent decline of outlet and valley glaciers. The plateau ice caps on the Bergsfjord Peninsula occupy a critical altitudinal threshold between 900 and 1200 m which is particularly sensitive to recent climatic change. Patterns of glacier response are recorded with the aid of historical records and field mapping. The changes in ice distribution are linked to both fluctuations in mass balance and to important topographic controls on summit ice caps