Uncharted Territory: Drone Applications in Plant Conservation

Plants make life on earth possible. They clean the air, capture energy from the sun, and provide habitat for other organisms. Over the past 500 million years, plants have evolved into an estimated 400,000 different species across the globe. The distribution of this diversity is uneven, with tropical regions identified as hot spots where botanical diversity is concentrated. Tropical islands are recognized for their high levels of localized endemism, and nowhere is this more apparent than in the Hawaiian Islands, where 90% of plant species are endemic.

Human activities are causing increased pressure on natural ecosystems through land development, extraction, and greenhouse gas emissions. These factors have led to plant extinction rates that are estimated to be 500 times the background rate. To identify which species are most threatened and address their conservation needs, the International Union for the Conservation of Nature (IUCN) has provided a framework for assessing the conservation status on a species-by-species basis. Understanding the distribution and abundance of each taxa is a critical first step in their conservation. Evaluation of the threat category for a range of plants based on geographic location (Chapter I), and taxonomic group (Chapter II) estimate that 70% of the vascular flora of Hawaii is threatened, but that endangerment is not consistent across geographies or plant groups.

The assessment process helps identify locations of specific conservation importance and also determine areas that may require further investigation. These dark spots are especially critical as an estimated 15% of plant species are yet to be described. We have focused the bulk of this research on a dark spot that has long evaded complete botanical exploration; cliff habitats. The natural protection provided by this terrain makes cliff areas refugia for rare plants. Due to the inherent difficulty and danger of working in these vertical environments, they have been historically understudied. Baseline data was extracted from the IUCN Red List to provide a global overview of the conservation status of cliff flora (Chapter III). This study suggests that cliff floras may be at higher threat of extinction, however, these areas require additional research to augment the IUCN Red List assessment process and to strengthen conservation actions.

Another approach to gathering botanical data in cliff environments is the deployment of Uncrewed Aerial Systems (UAS, aka drones). The development of an in-depth survey methodology has allowed for efficient floristic investigation of cliff habitats and other hard-to-reach areas (Chapter IV). Across a range of island locales, the application of this technology has uncovered many unknown populations of rare taxa (Chapter V) showing the effectiveness of this approach. The imagery collected contains a wealth of information on plant distributions, microhabitats, and species associations, all of which establish baseline knowledge of these habitats and provide a clearer view of necessary conservation efforts (Chapter VI).

While the knowledge gained from this survey method has changed our fundamental understanding of species distribution and abundance, on-the-ground conservation efforts face challenges as many areas are still completely inaccessible to humans on foot. This barrier has given rise to a new drone-based tool for collecting plants remotely (Chapter VII). The iterative development process has led to a refined mechanism that has collected 55 samples from 12 endangered species to date and now has an interchangeable head system allowing for customized sampling based on the target species. The remote collection mechanism has been utilized to locate and collect what may be the first new plant species described from a drone collection (Chapter VIII), highlighting the functionality of this technology to expedite taxonomy, especially in hard-to-reach areas.

As we face unprecedented challenges with environmental degradation, there is a critical need for efficient and effective conservation planning and action. Drone-based methodologies and new technologies are improving data and propagule collection in cliff habitats, which will support informed decision-making, conservation action, and ultimately help prevent plant extinction. These new drone-based conservation solutions are opening a new era for the exploration and conservation of cliff environments.