Soils with different development stages were found around each subject tree. Cluster analyses of soil properties around each subject tree (based on soil probes and soil profiles descriptions and analyses) suggested the formation of three groups of soil associations with similar properties. Selleckchem Natural Product Library In the first soil association (henceforth SA1), shallow soils with profile O–C (26%) and O–A–C horizons (64%) prevailed, while soils with Bw horizons represented less than 10% (Fig. 3). In the second association (SA2), soils with profile O–A–C (45%) and O–A–Bw–C horizons (45%) prevailed, while soils with only O–C or with O–A–E–Bt–C horizons represented 9% and 1%, respectively.

In the third soil association (SA3), soils with well-developed Bw horizons (45%) and leached soils with O–A–E–Bt–C horizons (23%) prevailed (Fig. 3). Dominant silver firs were between 132 and 209 years old (Table 4). The DBH ranged from 41.0 to 72.0 cm, with a mean value of 59 cm. The average height was 34.0 m, and the mean volume was 4.8 m3. The height increment of silver firs over the last 100 years ranged from 7.4 to 27.7 m. Tree age explained 13% of this variation (M1, Table 5), whereas adding the minimum soil depth around each tree as an additional explanatory variable of height increment did not improve the prediction (M2). The mean check details (M3) or maximum (M4) soil depth, rather than minimum depth, explained more

variability in height increment, but this variable still explained

less than 30% of the variation. Stoniness and competition were not statistically significant variables. The inclusion of individual horizon thickness instead of soil depth as an explanatory variable improved previous models (ΔAIC = 22.1, p < 0.001). The thickness of A horizon had a negative effect on height increment (M5), while other horizons’ influence was positive, in particular a strong positive was the effect of eluvial E and illuvial Bt horizons, FER characterised for well developed, deep soils (M6, M8). Similarly higher share of more developed soils (Cambisol and Luvisol) also influenced positively on height growth (M10). Positive effect on height growth was also confirmed for the amount of available water, which was mainly a function of soil depth (M11). Cambic horizon Bw had positive effect (M7), but did not improve the model (M9). The influence of the sinkhole is considered in the model 12; trees growing at the bottom of sinkholes were higher for 4.28 m in 100 year. The combination of AWC and location of trees in slope position (sinkhole) also had positive influence on height growth (M13). The prediction of the height increment over the last 100 years was further improved (ΔAIC = 9.6, p < 0.001) by considering soil associations in the model (M9). Effect of all available soil variables on height growth are presented in model M14.