Mires of Finland: Regional and local controls of vegetation, landforms, and long-term dynamics

Abstract

In this review I examine the geographical patterns of the Finnish mires and the role of regional and local factors that lead to their spatial differentiation. Finland can be divided into three roughly latitudinal mire zones (from south to north): the raised bog zone, the aapa mire zone, and the palsa mire zone. The development of the raised bogs is linked to the dominance of Sphagnum, leading to the growth of a thick peat layer that rises above the level of the mineral soil. The gross morphology of an aapa mire is typically inclined and concave. Here, Sphagnum species are less dominant, probably due to spring floods which keep the mire surface minerotrophic. Both raised bogs and aapa
mires have typically regularly-patterned microtopography. Seasonal movements of microtopographical features of the aapa mires reflect the morphological dynamism of the mires. Mires are also important sources of information regarding
past environmental changes. Their growth pattern is affected by environmental conditions and they respond sensitively to the changes in effective humidity and other climatic variables. Most of the present microtopographical patterns have formed during the last 3,000 years as a response to gradual cooling of climate. Research on Finnish peat deposits has shown, however, that not all peat-stratigraphical changes are caused by past climate variations. They can also be due to the natural growth dynamics of the mires, such as the long-term development towards drier conditions on the surface of the raised bogs, the rhythmic growth pattern of the low hummocks, and the local changes in water table resulting from growth of hummocks and hollows.