Tree species distribution on mafic and felsic fells in Finnish Lapland

摘要

Physical-chemical properties of glacial tills, derived from felsic or mafic lithologies, were studied in the forest, treeline, and on tundra in western Finnish Lapland. Scots pine [Pinus sylvestris L.] dominated on felsic fells, but excess soil water content was found edaphically constraining for pine. Low soil electrical conductivity (ECa) and low Ca to Al ratios was found to constrain Norway spruce [Picea abies (L.) Karst.]. The soil ECa positively correlated with soil Mg, Na, and Ca, but negatively with Al signifying the distribution of spruce to be associated with mafic lithologies. The limit of mountain birch [Betula pubescens ssp. Czerepanovi Hamet-Ahti] was below the conifer krummholz-zone. In winter, the treeline soil was unfrozen beneath the snowpack, whereas subzero temperatures applied to forest and tundra. In spring, soil water became available weeks before final melting of snowpack, while soil temperature (ST) increased notably above 0oC three weeks after the disappearance of snow. Early season ST was not attributed to elevation or aspect. Mid-season ST was highest on tundra. We contend that, instead of ST, water or N availability, winter winds, and spatial distribution of snow are crucial with regard to spreading of tree species on the studied fells.