Predicting, preventing, and minimizing machinery-induced soil compaction are of paramount importance in forest ecosystems. Understanding the soil’s susceptibility to compaction is crucial in achieving these goals. This meta-analysis assessed the relevance of climatic and soil conditions for the susceptibility of forest soils to wood-harvesting-associated compaction across global climatic zones. We utilized soil bulk density change data (effect sizes; compacted versus uncompacted) from 81 forest sites worldwide, and mapped global patterns of the susceptibility of forest soils to compaction using climate and soil data. Wood-harvesting operations by harvester-forwarder technologies disturb the soil less as compared to skidders and cable yarders. It has been shown that a high number of vehicle passages (> 20 times) lead to maximum soil damage, although this contradicts the general belief that major soil disturbance occurs within the first few vehicle passages. Despite these important findings, a global compilation of local information on forest soil compaction induced by mechanized wood harvesting is currently lacking. A map that illustrates the global pattern of soil susceptibility to compaction is also required to identify particularly susceptible forest regions. Forest soils in tropical and temperate zones were most susceptible to compaction (48% and 30% bulk density increase, respectively), while forest soils in arid and cold zones were less susceptible (15% and 18% bulk density increase, respectively). Soils in tropical and temperate forests receive high annual precipitation amounts, are characterized by high soil organic carbon content and low bulk density, and are often wet, resulting in high susceptibility to compaction. Since tropical and temperate forests are biodiversity hotspots, forest managers and policymakers should pay particular attention to mechanized wood-harvesting operations in these zones, as the recovery of compacted forest soils requires decades.
