Using drones to monitor sensitive species

Denver Botanic Gardens has been conducting demographic studies of rare plants in Colorado since 1994 to inform extinction risk from demographic and environmental stochasticity. These studies are typically “low-tech” jobs that involve tracking survival, growth, and reproductive rates of individuals in the population. However, not all species are suitable for the traditional methods of annual demographic monitoring. In 2023, Denver Botanic Gardens piloted a study to use drones as a method of monitoring for an ESA Threatened species, Phacelia submutica. This is an annual species found in small patches in western Colorado and persists in a specific type of sensitive, undisturbed soil. Traditional annual monitoring would cause a great deal of disturbance and trampling of these soils, thereby harming the populations both in the short term and long term. Drones provide a promising remote solution to annually monitor the populations without disrupting the sensitive soils. We will present results from this pilot study, specifically addressing how optimal flight height and timing were determined and how to process the images for analyses. In this first year of the study, we learned about the potential, as well as the limitations of using drones to monitor rare annual species. Future adjustments will be made based on what was learned and we hope to propose recommendations for long-term monitoring of other species that would benefit from drone imaging.