## 3 Results  
### Penetration Resistance in the Natural Soil  
Figure 2 summarizes the results on the variation in mean penetration resistance along the soils' depth profile up to a depth of 65 cm. Although most of the data were available up to a depth of 80 cm, the choice of limiting the analysis of data in the depth range of 0 to 65 cm was based on the maximum length of available data, which for the forward control (CF) was 65 cm (Table 2). In the CH dataset, there was less variation in the mean penetration resistance for soil depths of 0 to 15, 22 to 27 and 29 to 40 cm (Figure 3a). In CS data, there were data segments with low variation in mean penetration resistance between 8 to 11, 17 to 22 and 33 to 41 cm (Figure 3b), while in the CF data, low variation in the mean penetration resistance was found between 12 to 39 and 45 to 53 cm (Figure 3c). Although the CH dataset did not show an evident changing point at 10 cm, this was the case of CS and CF data. A second changing point can be seen at 20 cm, which was most evident in the CH data, which was similar to the third changing point at 30 cm. In the depth layer of 31 to 50 cm, the mean penetration resistance was relatively constant at about 1.2 MPa in the CH dataset, 2.4 MPa in the CS dataset and 1.9 MPa in the CF dataset, with some variation between 40 and 45 cm in CS and CF datasets. Accordingly, the fourth changing point was set at 50 cm in all datasets. Then, between 51 and 65 cm, the mean penetration resistance started to increase in all control datasets. The data subsets used to estimate the mean values at centimeter-level soil depths were characterized by a large dispersion, particularly beyond the first 5 cm of the topsoil. This can be seen in Figure 3a-c for CH, CS and CF where the standard deviation curves are added along with the coefficient of variation. The latter was uniform along the depth of the soil for the CS dataset (Figure 3b); however, it exceeded 25% for most of the soil depths of this dataset. In terms of uniformity, next in line was the CF dataset, with an increased coefficient of variation in the first 20 cm, followed by a trend similar to CS in the depth layer of 21 to 65 cm. The CH dataset showed the most variability and changing points in the values of the coefficient of variation (Figure 3a). Figure 3d, on the other hand, shows the absolute differences in the mean penetration resistance as a function of the soil's depth. These differences were computed based on the mean soil depth-related values of CH, CS and CF datasets, and they were used to compare the control datasets for each of the three possible data pairs (CH-CS, CH-CF and CS-CF). The data show that the lowest differences were between the CS and CF datasets, with a mean difference of 0.59 MPa (data not explicitly shown herein). Next in line, the lowest differences were between CH and CS datasets, with a mean difference of \(-0.66\) MPa,  
Figure 3: Variation in the mean (x), standard deviation (s) and coefficient of variation (cv) of the penetration resistance along the sampled soil depth, and absolute differences in the mean penetration resistance between the datasets: (**a**) Horse logging control dataset (CH); (**b**) Skidding control dataset (CS); (**c**) Forwarding control dataset (CF); (**d**) Absolute differences between the mean penetration resistance in natural soils between the sites of horse logging and skidding (\(\Delta\)CH-CS), horse logging and forwarding (\(\Delta\)CH-CF) and skidding and forwarding (\(\Delta\)CS-CF). and the largest differences were found between CH and CS datasets (mean difference of \(-\)1.25 MPa). Both the variation in the mean penetration resistance and the variability in the data used to estimate it may be related to the characteristics of the three soil types in H, S and F (Table 1). It is obvious that differences in the mean penetration resistance can be expected between these three soil types, as shown in Figure 3d.