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VRANOVA, V., HOLIK, L., ROHLIK, T., REJSEK, K., FORMANEK, P.: Carbon, nitrogen, C/N ratio and their stand heterogeneity in the soil of Norway spruce stands. Acta univ. agric. et silvic. Mendel. Brun., 2010, LVIII, No. 5, pp. 413–416 This work is aimed to determine the eff ect of thinning of young spruce stands in Moravian-Silesian Beskids Mts. on concentrations and relative stand heterogeneity of Cox, Nt and C/N in soil. Concentrations of Cox and Nt were signifi cantly higher in individual horizons of forest humus fl oor. The thinning did not infl uence signifi cantly (P > 0.05) concentrations of Cox, Nt and C/N ratio in particular soil horizons, with the exception of C/N ration in E horizon. Relative stand heterogeneity of the studied soil properties was mostly higher in soil of dense forest stand. The values of relative stand heterogeneity for individual horizons ranged from 3.1 to 61.9 % in case of Cox, from 4.9 to 55.2 % for Nt and from 5.3 to 42.5 % for C/N ratio. Results of this work are useful to predict stand heterogeneity of soil biochemical properties which are known to correlate with especially Cox in soil on studied plots, especially soil respiration and enzymatic activities. soil, thinning, forest, heterogeneity, carbon, nitrogen Norway spruce (Picea abies [L.] Karst.) is one of the most important commercial tree species in European forests. Norway spruce is o en grown in even-aged, single-species stands and managed using a clear-cutting system. Thinning is a regular component of the management program if this species is to reach the dimensions needed for the timber trade (Slodicak et al., 2005). The thinning process is accompanied by a decrease in stand density and leaf area and an increase in light and nutrient avai la bi li ty. This leads to changes in soil temperature, soil water, regime root density, respiration of roots, leaching of dissolved organic matter from canopy, and changes in soil microorganisms (Tang et al., 2005; Bird et al., 2002). Thinning may reduce possible competition between plant roots and saprophytic mi cro or ganisms for water and nutrients and, in turn, enhance decomposition and nutrient cycling in these ecosystems (Slodicak et al., 2005). As thinning aff ects inputs of aboveand belowground biomass, its decomposition and distribution in soil, it is necessary to determine its eff ect on change in heterogeneity of organic compounds in soil. For this reason, we have performed an experiment to determine the eff ect of young spruce stands thinning on stand heterogeneity of soil carbon oxidable (Cox), nitrogen total (Nt) and carbon / nitrogen ratio (C/N) content in particular horizons of Typic Haplohumod. MATERIAL AND METHODS The “Bilý Křiž” (“White Cross”) Experimental Ecological Research Site, where the experiments took place, is located in the Moravian-Silesian Beskids Mts. in the northeastern part of the Czech Republic at 908 meters a. s. l. (N 49°30’10”, E 18°32’20”). The region has a subcontinental climate with a typical mean annual air temperature of 4.9°C and mean annual precipitation of 1.100 mm. The number of days with snow cover is 160 per year (Formanek et al., 2008). The experimental 23-years-old Norway spruce stand is located on slightly descending slope. The stand comprises approximately 99 % Norway spruce and 1 % fi r (Abies alba Mill.). Within the experimental stand, two 0.25 ha study plots were established, each diff ering in intensity of thinning: 414 V. Vranova, L. Holik, T. Rohlik, K. Rejsek, P. Formanek the forest dense (FD) and the forest sparse (FS) plots. The thinning of the plots was performed according to Table I. The plots are located side by side and a fence surrounds each of them. The experimental Norway spruce stand was originally established as the 2nd generative stand on an area created by clearcutting the previous 120-years-old Norway spruce forest. Before thinning in 1995, the experimental stand was of the same initial density of 2,830 trees/ ha throughout. Thinning of the FD and FS plots was then performed on a number of separate occasions as shown in Table I. Both plots were limed on three occasions (in 1983, 1985 and 1987), using dolomite limestone with a total application rate of 9 t / ha (3 × 3 t / ha) (Formanek et al., 2008). In comparison with the FD plot, the FS plot has a relatively rich herb layer with grasses, shrubs, rowan seedlings, etc. Both plots maintain Typic Haplohumod (sequence horizons: Oi-Oa-Oe-A-E-Bhs-Bs-BC-C) and Entic Haplorthod (sequence horizons: Oi-Oa-Oe-A-Bsw-BCC) soil types and subtypes (USDA-NRCS, 1999). Experiments were restricted to only one of the two soil types on both stands: Typic Haplohumod. On each of the forest stands, fi ve holes (15 × 15 × 70 cm) were randomly dug in period of October 6–7, 2005. Soil samples were taken from horizons Oi-OaOe-A-E-Bhs-Bs, and placed into plastic bags. A er transportation to the laboratory, the samples were air-dried at room temperature and consequently, except Oi and Oa horizons, sieved through 2 mm mesh size. The samples were milled using Mixer Mill MM 200 (Retsch, Germany). The content of carbon and nitrogen was measured using NC 2100 Soil Analyzer ThermoQuest (Italia S.p.A., Italy). Soil was completely oxidized by combustion, and organic nitrogen was converted into ele men tal nitrogen and carbon into carbon dioxide. The gas mixture was then separated on a gas chromatographic column and measured using a thermoconductivity detector (TCD). As preconditions for parametric statistical testing were not fulfi lled, the nonparametric Kruskal-Wallis ANOVA and Dannet’s t-test were used. All statistical analyses were undertaken using the Statistica 9.0 program (StatSo , Inc. Tulsa, USA). Coeffi cients of Variation (CV) for particular soil properties and particular horizons of each of the studied plots were calculated. RESULTS AND DISCUSSION From the results obtained in this study it is evident that young thinned forest stands did not infl uence signifi cantly (P > 0.05) soil contents of Cox, Nt and C/N ratio in particular horizons of Typic Haplohumod (Figure 1). C/N ratio only was signifi cantly (P < 0.05) higher in FD compared to FS stand in the E horizon. Relative stand heterogeneity of the studied soil properties was mostly higher in FD than in FS plot (Table II). The reason of higher he te ro ge nei ty of measured soil properties in FD stand may be higher heterogeneity of root systems; on the other hand, diff erences in C/N may indicate diff erent decomposition rate of soil organic matter, diff erent stand nutrition (N content in needles), and diff erent leaching of organic compounds from fo rest humus fl oor into mineral soil which is connected with diff erent intensity of throughfall between stu died stands. Different intensity of leaching from forest humus fl oor into mineral soil and its stand heterogeneity could also aff ect fi nal heterogeneity of studied properties in particular horizons. Further research is necessary to better understand these processes. The results obtained in this work are consistent with those determined for diff erently managed meadows of the same locality. As reported by Vranova et al. (2007), about 12 years abandonment of I: Stand density (trees/ha) in experimental Norway spruce stands (FD-dense plot and FS-sparse plot), before and a er thinning (* human – induced, in other cases stand density was reduced by natural thinning) (Formanek et al., 2008). Stand density was formed for the experimental purposes. year plot 1997 1998 1999 200