This paper presents a vision-based localization approach for Unmanned Aerial Vehicles (UAVs) flying at low altitude over forested areas. We address the task as a point cloud registration problem using local 3D features with the intention to exploit the shape and relative arrangement of the trees. We propose a 3D descriptor called SHOT-N which is an adaptation of the state-of-the-art SHOT 3D descriptor. SHOT-N leverages constraints in the extrinsic parameters of a gimballed, nadir-looking camera. Extensive experiments were performed with semi-simulated point cloud data based on real aerial images over four forested areas. SHOT-N is shown to outperform two state-of-the-art 3D descriptors in terms of the rate of successful registrations. The results suggest a high potential of the approach for aerial localization over forested areas.