This thesis investigates wind flow and wind turbine performance in forested complex terrains, with emphasis on the combined influence of topography and forest canopies on velocity distribution, turbulence intensity and extracted power. Large-Eddy Simulation (LES) was employed within the WiRE-LES code, integrating an explicitly resolved canopy model to represent vegetation effects. The model was validated against field data and applied to both idealized hill configurations and the real-case study of the Juvent wind farm in Switzerland. Results highlight that explicit canopy modeling improves the accuracy of flow predictions and power estimation compared to a simpler roughness-length approach, while also capturing enhanced turbulence and altered wake recovery induced by forests.