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.
Artificial regeneration to Scots pine (Pinus sylvestris L.) has faced substantial economical losses in Finnish Lapland on sites underlain by glacial tills and formerly covered by stands dominated by Norway spruce (Picea abies (L.) Karst.). We studied the survival of pine seedlings and saplings with respect to soil dielectric permittivity (ε), as dependent on soil water content (θv), of ploughed tills. The ε values (θv) were determined beneath 10 500 pines varying in age between 2 and 41 years and growing on 21 sites, 500 per site. Based on the logistic regression models, the survival rate of 2- to 7-year-old seedlings was independent of the soil ε (i.e., θv). In contrast, a significant correlation between the survival rate of 12- to 16-year-old saplings and soil ε was observed. In this age-class, a survival rate of 50% with ε50 = 15.1, with ε50 = 17.0 for planted saplings and ε50 = 12.7 for sowed saplings, were obtained. Of the 2000 pine trees aged between 20 and 41 years, 96.5% were observed to be growing on dry tills with ε < 15 with mean ε = 9.9. The results of this study suggest that artificial regeneration of Scots pine in Lapland is risky on moist and wet tills (ε > 15, θv > 0.27 cm3·cm3).
Low-altitude airborne gamma-ray (AGR) data, obtained with the aircraft-mounted 25-l NaJ(Tl) gamma spectrometer and interpolated into a 50 × 50 m pixel size, over 1200 km2 of glaciated terrain in Finnish Lapland, were applied to classify and interpret site suitability for Scots pine (Pinus sylvestris L.). The selection of the training and validation sets for the classification of AGR data was based on the forest management history and soil moisture content (θv) determined by dielectric (ε) measurements. The ground calibration measurements showed a significant negative correlation between the soil ε (i.e., θv) and terrestrial gamma-ray flux (TGR-γ) from potassium (γK) and thorium decay series (γTh), suggesting that the attenuation of gamma flux is due to soil θv. Both ground and airborne surveys indicated that γK was significantly higher in drift of Scots pine stands than in drift of Norway spruce (Picea abies (L.) Karst.) stands. Out of four tested combinations of the AGR channels, i.e., (i) potassium (K), (ii) K and thorium (Th)/K, (iii) K, Th, and Th/K, and (iv) K and Th, K alone resulted in the best overall accuracy of 80.44% (Kappa coefficient, κ = 0.609) to classify drift materials suitable for Scots pine. The present study demonstrates that the TGR-γK and AGR-γK measurements provide a basis to delineate soil θv patterns within the site and landscape level, thus having a significant implication for the forest management planning to assess sites suitable for Scots pine.
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