Browsing by Subject "fennoscandia"

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  • Kulha, Niko Aleksi; Pasanen, Leena; Holmström, Lasse; Grandpre, Louis de; Kuuluvainen, Timo Tapio; Aakala, Tuomas (2019)
    Identifying the scales of variation in forest structures and the underlying processes are fundamental for understanding forest dynamics. Here, we studied these scale-dependencies in forest structure in naturally dynamic boreal forests on two continents. We identified the spatial scales at which forest structures varied, and analyzed how the scales of variation and the underlying drivers differed among the regions and at particular scales. We studied three 2kmx2km landscapes in northeastern Finland and two in eastern Canada. We estimated canopy cover in contiguous 0.1-ha cells from aerial photographs and used scale-derivative analysis to identify characteristic scales of variation in the canopy cover data. We analyzed the patterns of variation at these scales using Bayesian scale space analysis. We identified structural variation at three spatial scales in each landscape. Among landscapes, the largest scale of variation showed the greatest variability (20.1-321.4ha), related to topography, soil variability, and long-term disturbance history. Superimposed on this large-scale variation, forest structure varied at similar scales (1.3-2.8ha) in all landscapes. This variation correlated with recent disturbances, soil variability, and topographic position. We also detected intense variation at the smallest scale analyzed (0.1ha, grain of our data), partly driven by recent disturbances. The distinct scales of variation indicated hierarchical structure in the landscapes studied. Except for the large-scale variation, these scales were remarkably similar among the landscapes. This suggests that boreal forests may display characteristic scales of variation that occur somewhat independent of the tree species characteristics or the disturbance regime.
  • Lindholm, Tanja (Helsingin yliopisto, 2010)
    Object of this reseach is geochemical characterization of Häme diabase dyke swarm. The analysed dyke (n=42) samples were collected using a hammer. The chemical analysis were performed at Helsinki University for major and some trace elements using XRF analyser and at GeoLab, Washington University for lanthanides and trace elements using ICPMS analyser. The reseach area is situated in the east 35 km north from Tampere and in the west the area of Heinola city. The age of Häme dike swarm is ~1.6 Ga, which is also the age of nearby rapakivi inturions in the area. The Häme dike swarm cuts sharply 1.9 Ga svecofennian bedrock. The Häme swarm has been divided into two sets of dykes based on different strikes, compositional features and in age. One of the sets strikes WNW and the other one NW. Häme dyke swarm resembles continental flood basalts. They are relatively alkaline ironrich continental quartz and olivine tholeiites. Main minerals are olivine, pyroxenes and plagioclase. Their TiO2 (1,4–3,3 p. %), P2O5 (0,4–1,1 p. %), Fe2O3 (12,3–16,6 p. %) and Al2O3 (12,9–18,6 p. %) contents are relatively high and MgO (3,4–5,9 p. %) and CaO (6,2–8,7 p. %) contents are relatively low. The abundances of incompatible trace elements are high and they show LREEenriched REEpatterns, also their Ni and Cr contents are relatively low. In Spider diagram you can see negative Eu, Nb and Ti anomalies in and positive Pb anomaly. Geochemical data doesn’t correlate with two different strike sets and dykes have no correlation with their geographical settings.