Assessment of Western Juniper Encroachment and Removal Using Unmanned Aerial Vehicles and Ground-based Data Collection

Across the western United States, the encroachment of western juniper has been associated with numerous ecological and hydrological impacts. Due to the large scale and remote location of many of the areas of concern, data collection regarding western juniper encroachment can be costly and difficult. By offering a flexible platform and high-spatial resolution, Unmanned Aerial Vehicles (UAVs) may improve the ability to assess these impacts compared to solely using ground-based or satellite-based data collection. While satellite and UAV-based data collection has been used in rangeland monitoring, limited research has addressed the use of UAVs for evaluating western juniper encroachment and removal specifically. This study sought to improve the understanding of the impacts of western juniper in a sagebrush steppe ecosystem in central Oregon with the use of ground-based measurements in conjunction with aerial imagery collected from a UAV. The specific objectives of this study were to 1) assess vegetation characteristics in two watersheds with different western juniper densities and 2) evaluate the potential use of UAV imagery for calculating canopy cover and identifying western juniper. Data regarding canopy cover, stem density, age structure, species richness, and forage production were collected using ground-based techniques. Multispectral and visual imagery was collected using three quadcopter UAVs. Analysis of the UAV imagery was compared to results from the ground-based measurements to assess accuracy. While research is ongoing, preliminary results found differences in stem density and forage production between the two watersheds. Preliminary results also indicate that unsupervised classification techniques using multispectral data may be an effective tool in identifying juniper saplings. Additional analysis and research is necessary to further refine these methods and improve accuracy, but this research suggests that UAV-based data collection can be an effective means of evaluating the impact of western juniper encroachment and treatment.