###### Abstract  
Local effects of ground-based timber harvesting, such as soil compaction, are often important for forest management and resilience of forests. One way to evaluate the compaction of the forest soils is by the penetration resistance. Most often, however, the control over the weight of the means used to extract the wood is difficult to maintain, influencing therefore the outcomes of the comparison studies. In this study, a controlled experiment was set up to see how the penetration resistance is affected by the number of passes of three wood extraction methods. A first objective of the study was to characterize the undisturbed soils by the mean values of penetration resistance along the profile. The second objective of the study was to compare the changes in penetration resistance induced by the number of passes along the soil profile. The extraction means were selected based on their typical use in flat-land operations, namely horse logging, skidding and forwarding, and the weight of their loads was determined before the experiment; then, each one was tested in a different area by operating in a closed loop on flat land, with 15 passes over the respective testing area. Penetration resistance was sampled up to 80 cm in depth in 10 control points, as well as in 10 sampling points over the wheels' footprints. Ten samples were taken on the latter after the first, second, third, fourth, fifth, tenth and fifteenth passes, and comparisons were set up based on natural changing points in penetration resistance found in the control areas. The comparisons found significant differences by an increase in penetration resistance for all three extraction means, and there was a difference by an order of magnitude and depth; horse logging affected it the least and forwarding the most in magnitude, while skidding seemed to produce more significant changes in depth. However, the magnitude and depth of these changes may have depended on the characteristics of the soils from the test areas, and it cannot be concluded that the found levels of penetration resistance will affect the trees located nearby the experimental trails. The problem of soil compaction should be further examined by dedicated studies, given the variability in soil characteristics and diversity in means used to extract timber. soil layers; effects; controlled weight; horse logging; skidding; forwarding Article  
A Controlled Experiment on Penetration Resistance on Silty-Loamy Soils  
[PERSON], [PERSON], G.  
decisions and actions, which should be tailored to find the balance between the resilience of forests and the benefits that timber harvesting brings to society; this often leads to a high diversity in methods and means used to harvest timber [1]. Environmental performance of timber harvesting systems may be assessed based on local and global effects they produce, and environmental performance of operations has been one of the main concerns in the science and practice [2; 3]; very often, however, it is evaluated based on local effects that machines produce in the forest in which they operate. Ground-based timber extraction such as that using skidders and forwarders requires a direct contact and interaction between the machines and forest soil. Typically, it causes soil compaction to a degree, measured in terms of severity and extent, that depends, among other factors, on the machine's constructive parameters, local soil condition and the decisions on planning and operation [4]. Soil compaction, on the other hand, has serious consequences on other soil-related processes such as increasing the soil's strength and bulk density, decreasing its porosity, infiltration and hydraulic conductivity, impeding the colonization by fauna and increasing the surface water flow, soil loss and sedimentation [5; 6; 7; 8; 9], while soil recovery after mechanical compaction is typically very slow [10; 11; 12].