A review of research on hybrid unmanned vehicles in complex forest and grassland terrains

The sustainable management ofEuropean forest ecosystems necessitates innovative mechanisation solutions toaddress operational challenges inhilly, mountainous, and ecologically sensitive terrains. Hybrid-drive unmanned vehicles (HDUVs) present atransformative potential byintegrating fuel-electric powertrains with autonomous navigation systems, enabling energy-efficient operations with minimal environmental impact. This review synthesises and critically analyses advancements inthree critical domains: (<i>i</i>) dynamic modelling and chassis design for enhanced terrain adaptability, (<i>ii</i>) hybrid powertrain optimisation for reduced emissions and extended operational range, and (<i>iii</i>) the integration of unmanned systems for precision forestry tasks. By examining multi-body dynamics, power management strategies, and AI-driven navigation algorithms, we elucidate the role of HDUVs in improving operational efficiency while mitigating soil disturbance and carbon footprint. The review identifies prevailing research gaps and suggests that future work should prioritise the development of standardised testing protocols and foster cross-disciplinary collaboration to align HDUV development with EU biodiversity and climate objectives.