Drone Imagery Enables Fine-Scale Detection of Sagebrush Dieback During a Summer Heatwave

Sagebrush species are an essential part of the western desert ecosystem and influence local recreation and employment. These shrubs help prevent erosion, capture water, sustain wild animal populations, and more. Climate change imposes a significant threat to these populations as we see an increasing number of wildfires, less precipitation, and more high heat summer days.

This project focuses on the latter issue by comparing imagery taken at Castle Rocks State Park, in southern Idaho, over the summer of 2021 during an unprecedented heatwave. We used drones to gather aerial imagery in June and September, and then I stitched together the multiple overlapping images to create one large image with high resolution. By outlining individual shrubs, I extracted the green band of the color images and calculated the average Green Leaf Index (GLI) values as an indicator of greenness for each shrub. Greenness directly corresponds to the photosynthetic activity and health of a plant. After comparing the images from June and September, I found that 72% lost values, and of these shrubs, there was an average loss of 10.8%. The other 28% of shrubs gained an average of 5%. This location is one site out of four along an elevation gradient with several sagebrush subspecies. The next step is to find the change of GLI at all four Castle Rocks sites from June and September to get a broader range of data analysis over the 2021 heatwave.

These methods allow us to identify resilient shrubs that have retained their greenness during this heatwave, and we can target those shrubs to collect seeds for restoration efforts. The advantage of drone data is to create a map that spans hundreds or thousands of individual shrubs, which is more data than we could collect on the ground. This research brings vital information to the conversation of where and how to allocate tight budget funds to conserve the sagebrush steppe that so many of us depend on. It also shows the impact one hot and dry summer can have on this slow-growing plant.