Lichens are the best terrestrial bioindicators for radioactive fallout and also the most important link in foodchain lichen - reindeer - man. Generally, Fenced permanent sampling plots are used to study the biological half-life of 137Cs in lichen. However, some of the STUKs sampling plots are unfenced which are subjected to grazing by reindeer. Start year: early 60's as a project of the Radiochemistry Department of University in Helsinki. Stuk's participation since 1975. Data are collected from 1961, 1980, 1982 or 1986, continuously every 3-5 years. Data processing/work-up and data archiving/reporting work are conducted from 1961, 1980, 1982. Continous data sets from 1986 to 2010.