The subalpine lake ecosystem, Øvre Heimdalsvatn, and its catchment: local and global changes over the last 50 years

environmental variables are estimated and then applied to fossil assemblages under the assumption Plant and animal remains are often found well that the biota is in equilibrium with concurring preserved and in large quantities as fossils in lake environmental conditions. We have used fossil pollen sedimentary deposits. The composition of the fossil assemblages to reconstruct changes in past mean July assemblages, the biological proxies, can be used to air temperatures and changes in mean annual prec- infer environmental conditions at the time of de- itation (Birks & Birks, 2003). Plant macrofossils were sition. This is based on the uniformitarian assumption used to con?rm and to give more robust interpre- that particular species assemblages of the past have tions about past vegetation and climate than the been shaped by speci?c sets of environmental pollen evidence alone (Birks & Birks, 2000) and has conditions, and that these conditions are re?ected been widely used to con?rm the local presence of tree by the same species assemblages today (Rymer, species in studies of past tree-lines (Barnekow, 2000; 1978; Birks & Birks, 1980). Different proxies used to Bjune, 2005; Eide et al., 2006). Chironomids (n- reconstruct past environmental conditions have in- biting midges) were used to infer past mean July air vidual strengths and weaknesses.