, Department of Geography and Development Studies, University of Chester Lichens are a symbiosis of two organisms, algae and fungi, which colonise exposed surfaces and can be measured to date the approximate age of the surface.
The study of lichens is therefore important to help establish a timescale of events.
The gradient of the proximal and distal slope is also a factor that can affect the size of lichen diameter.
This could be anomalous; however, if the 'Green Zone' does exist there are implications for the reliability of previous studies as they could conclude that substrates are older because the lichen sizes are larger.
This relationship between the size of the lichen thallus and the age of the exposed material is the main principle of lichenometry, which was first introduced by Beschel in the 1950s.
This similar trend suggests that both methods of dating are reliable; however the indirect method to produce dating curves may be more widely adopted as it requires less time measuring lichens in the field.
The environmental influence on lichen growth is complex as differences in variables such as slope, aspect, exposure and moisture availability can affect growth (Worsley, 1990).
If the data collected from Nigardsbreen supports the 'Green Zone' hypothesis, there are implications for using lichens to date surfaces of unknown age.
Keywords: Lichenometry, Nigardsbreen, on proximal, crest and distal (side of the moraine furthest from the glacier) slopes on terminal moraines on a glacial foreland.As a result lichens which colonize the recently exposed rock would not reflect the true age of the moraine.It has been suggested by Armstrong (2002) that the aspect of rock surfaces may affect the growth of the lichen ; his results from Gwynedd, North Wales, showed that the radial growth of the thalli on the north-west facing slopes was 'significantly greater' than that on the south-east facing slopes (Armstrong, 2002: 193).Early colonisers of bare rock surfaces and slow growth rates (Haines-Young, 1983) are the two primary reasons why species from the lichens, by measuring the radial growth directly (Trenbirth and Matthews, 2010; Cook-Talbot, 1991) over a period of time, or indirectly (Matthews, 1994; Bickerton and Matthews, 1993; Haines-Young, 1983) by measuring the thalli of lichens on a surface of known age (Armstrong, 2004).The indirect approach is usually more reliable as it relates to growth over a longer period than that of direct study (Armstrong, 2004); however, it still makes assumptions which may affect the results of a study.In addition to measuring the lichen thalli diameters, 3 other factors were also measured: aspect, gradient and vegetation cover.