Drone-Based Assessment of Nonnative Invasive Shrubs in Ramsdell Park, Lenawee County, Michigan

Satellite and aerial photography have been recognized as practical tools for mapping vegetation. However, there have been few attempts to utilize Uncrewed Aerial Vehicles (UAVs) to identify and quantify specific invasive shrubs in grasslands, especially prairies. The present study evaluated whether invasive Honeysuckle (Lonicera spp.) and Autumn Olive (Elaeagnus umbellata) shrubs can be distinguished from native shrubs due to their extended leaf phenologies using orthomaps created from UAV-acquired RGB images in Ramsdell Park, Lenawee County, Michigan. Images were captured using a DJI Phantom 4 Pro drone and processed into orthomaps using Agisoft Metashape Professional. The accuracy of orthomap-based shrub identification was determined in a blinded survey using 40 georeferenced ground-determined shrubs and yielded an accuracy of 92.5%. Our results show that autumn olives can be reliably distinguished in late autumn maps, whereas honeysuckles are better identified in early spring maps. Maps based on UAV-acquired RGB images are a fast and cost-effective tool for determining the identity, degree, and age structure of shrub invasions in grasslands, thereby helping to avoid habitat damage associated with on-site surveys.