<p>The use of chainsaws and heavy machinery in forest harvesting is increasing, resulting in elevated contamination of the environment with the fuel and lubricating oils they require. Little is known about how different chainsaw lubricating oils used during forest harvesting influence soil contamination and biological responses in forest soils. This study aimed to evaluate these effects under both operational and controlled conditions. Two experiments were conducted: a field based trial at a timber harvesting site to assess operational contamination, and a nursery trial to simulate extreme contamination. Three lubricating oil types (biodegradable, mineral, and recycled oils) along with an uncontaminated control were tested. One week after harvesting, soil total petroleum hydrocarbon (TPH) concentrations increased by 71.4%, 49.5%, and 90.6% in the biodegradable, mineral, and recycled oil treatments, respectively, compared with that of the control. In the nursery site, the initial TPH levels were 1.5–12.5 times higher than those at the harvesting site. After one year, the TPH concentrations in the biodegradable oil treatment declined, reaching those in the control at both sites, whereas the TPH concentrations in the mineral and recycled oils remained more than two times higher than the control concentrations. Across all treatments, bacterial diversity, soil CO₂ and CH₄ fluxes, and seedling growth and sprout regeneration showed no significant differences, indicating that the observed contamination did not impair short-term soil biological activity. These findings highlight the inherent resilience of forest soils to hydrocarbon contamination while suggesting that the long-term persistence of some lubricating oils should be considered in future management and oil selection.</p>