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The morphology and properties of the post−arable soils that influence the trophic status of forest habitats on the Barycz river terraces (south−western Poland) were analyzed. The fieldwork included the characterization of the soil, tree layer, and the vegetation of the forest floor, as required for the forest habitat evaluation. In the collected soil samples, a set of physico−chemical analysis was carried out, that included: soil texture, bulk density, pH in KCl and water, total organic carbon, total nitrogen, hydrolytic acidity, base cations, and the content of plant−available phosphorus, potassium, and magnesium. Sandy post−arable soils in the Barycz valley have a thick, double− or triple−layered ploughed humus horizon, and the high stock of humified organic matter, nitrogen, and phosphorus, that emphasizes anthropogenic transformation of soils and differentiates them from the natural soils of river valleys. The diagnosis based on the soil trophic index (SIG) indicates generally lower trophic status (mesotrophic) as compared to the diagnoses based on forest floor vegetation and tree−stand (eutrophic status). The SIG model for the post−agrar moist valley habitats should be supplemented with the factors, which improve the apparent trophic status of sandy soils, including the thick humus horizon (post−ploughing) and shallow table of eutrophic ground water.
The objective of the study was to determine the impact of selected soil properties on site index of oak (Quercus sp.) stands in the Międzyrzec Forest District (eastern Poland). We utilised data rom the soil−habitat survey, which provided information about physical and chemical properties of soils and stand descriptions for 21 oak stands (tab. 1). The collected data served to determine site index (SI), defined as the stand top−height at the age of 100, and soil trophic index (SIG) that is a synthetic measure of the soil fertility. For SI and SIG distributions met the criteria of the normal distribution (Shapiro−Wilk test p−values equalled 0.118 and 0.297, respectively), we applied one−way analysis of variance, t−test and correlation analysis to determine the influence of the forest habitat type and moisture as well as soil properties and fertility measures on the site index of analysed oaks. The SI of investigated oaks ranged from 23.2 to 29.3 m, 26.5 m on average (tab. 2). It was significantly dependent on the site type (F=6.913, p=0.006) with the lowest values on oligotrophic habitat and the highest – on eutrophic one. No effect of habitat moisture content and soil type was found (t=–0.408, p=0.688 and F=2.599, p=0.076, respectively). The SIG values ranged from 20 to 36, with the average of 29.5 (tab. 2). Similarly to the site index, we found significant impact of the forest habitat type (F=5.384, p=0.015) on SIG values. Soil fertility and physical properties significantly influenced site index of the analysed oaks (fig.). We found positive correlation between SI and SIG values (r=0.566, p=0.007) as well as between SI and clay content (r=0.454, p=0.037). Chemical properties of the soils under studied stands seem to have less profound effect on site index of oak. The highest, but insignificant, correlations were found for recalculated acidity (r=–0.420, p=0.056) and magnesium content (r=0.400, p=0.071).
Chemical properties and fertility of soils were compared under spruce, mixed and beech stands in four types of forest habitat (mountain broadleaf forest, mountain mixed broadleaf forest, mountain mixed coniferous forest and mountain coniferous forest) in 373 sites of forest monitoring in the Stołowe Mountains National Park, SW Poland. Soils under the spruce stands had higher organic carbon pools in their upper horizons, but lower pH, increased activity of exchangeable aluminum, lower contents of exchangeable base cations, available potassium and magnesium, resulting finally in lower values of the soil trophic index (SIG). The negative impact of spruce monocultures on the physicochemical soil properties was much stronger in the eutrophic habitats (dedicated to broadleaf forest) than in dystrophic ones. Weak positive effect of the beech introduction on soils in the dystrophic habitats indicated that the conversion of the coniferous into mixed or deciduous stands would not cause a rapid improvement in the physicochemical properties deformed previously under spruce monocultures.
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