Soil dielectric permittivity (ε), which is dependent on soil water content (θv), and electrical conductivity (σ), which is dependent on soil solute concentration, were measured in the immediate vicinity of 7596 mature trees naturally established on glacial deposits across granitoid and greenstone assemblages in Finnish Lapland (67°30' N-68°40' N). The proportions of the main timber species Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and downy birch (Betula pubescens Ehrh.) or the diversity of tree species were not affected by the temperature sum (between 750 and 600 degree-days), but the occurrences were strongly influenced by the soil's electrical characteristics. Scots pine and silver birch (Betula pendula Roth) were found to only occupy dry soils (fixed effect estimates ε(p) = 8.5 and ε(sb) = 8.3) with low solute concentration (σ(p) = 0.64 mS·m-1 and σ(sb) = 0.56 mS·m-1), while Norway spruce, downy birch, aspen (Populus tremula L.) and sallow (Salix caprea L.) occupied sites with higher soil moisture (ε(s) = 17.0, ε(db) = 14.7, ε(a) = 16.7, and ε(sa) = 16.7) and solute concentration (σ(s) = 0.96 mS·m-1, σ(db) = 0.90 mS·m-1, σ(a) = 1.07 mS·m-1, and σ(sa) = 0.93 mS·m-1). Species diversity was found to be at its highest with the following soil parameters: 12 < ε < 15 and 0.8 < σ < 1.2 mS·m-1. Scots pine was concentrated on tills derived from granitoid rocks. Norway spruce dominated sites on tills particularly derived from the mafic metavolcanic rocks of the Greenstone Belt but did not occur on tills derived from granulite. The edaphic constraint for pine appeared to be θv > 0.27 cm3·cm-3 (ε > 15) and for spruce σ < 0.5 mS·m-1, respectively.
Upland forest soils affect the atmospheric methane (CH4) balance, not only through the soil sink but also due to episodic high emissions in wet conditions. We measured methane fluxes and found that during a wet fall the forest soil turned from a CH4 sink into a large source for several months, while the CH4 emissions from a nearby wetland did not increase. When upscaled to the whole catchment area the contribution of forests amounted to 60% of the annual CH4 emission from the wetlands, while in a normal year the forest soil consumes 10% of the wetland emission. The period of high upland soil emission was also captured by the nearby atmospheric concentration measurement station. Since the land cover within the catchment is representative of larger regions, our findings imply that upland forests in the boreal zone constitute an important part in the global CH4 cycle not previously accounted for.
The presence of permanent snow cover for 200-220 days of the year has a determining role in the energy, hydrological and ecological processes at the climate-driven spruce (Picea abies) timberline in Lapland. Disturbances, such as forest fires or forest harvesting change the vegetation pattern and influence the spatial variation of snow cover. This variability in altered snow conditions (in subarctic Fennoscandia) is still poorly understood. We studied the influence of vegetation on the small-scale spatial variation of snow cover and wind climate in the Tuntsa area that was disturbed by a widespread forest fire in 1960. Radar was applied to measure snow thickness over two vegetation types, the spruce-dominant fire refuge and post-fire treeless tundra. Wind modelling was used to estimate the spatial variation of wind speed and direction. Due to the altered surface roughness and the increased wind velocity, snow drifting was more vigorous on the open tundra, resulting in a 30-cm thinner snow cover and almost half the water equivalent compared to the forest values. The changes in local climate after the fire, particularly in snow cover, may have played an important role in the poor recovery of vegetation: a substantial area is still unforested 40 years after the fire.
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