In the case of W. hobdyi, there was thought to be less than 600 individuals growing along the Nā Pali Coast. Many of Kauaʻi's endangered plants sprout only from the steepest cliffs, where goats can't reach. But the foliage now spread out before Nyberg amounted to more than 100 plants. He flew the drone within 5 meters (16 feet) of the greenery, snapping high-resolution photos to confirm his findings back in the lab.
Nyberg and the National Tropical Botanical Garden (NTBG) team, working with the State of Hawaii's Division of Forestry and Wildlife, have rediscovered three species thought to be extinct or locally extinct from Kauaʻi and uncovered larger populations of many other critically endangered species with populations smaller than 100 individuals.
The drone would ultimately turn up 5,500 new individuals in just a few months after years of searching — a more than 900% increase of the plant’s known population.
In the case of such discoveries, “It was just excitement,” Nyberg said. “Even one or two plants would be a great success. Now, we may have a little more time before extinction.”
Today, two in five plant species globally are threatened with extinction. The situation is often even more dire on islands that have a high rate of endemism — species that grow nowhere else in the world — and are cut off from potential refuges.
Kauaʻi has 250 plant species that can be found only on the island.
Invasive species like feral pigs, habitat loss and landslides following heavy rains threaten many of Hawaii’s plants.
About 10% of Kauaʻi’s plants are already extinct or extinct in the wild, and a further 87% are endangered, according to a 2020 assessment for the International Union for Conservation of Nature’s Red List of Threatened Species.
“Things are really special here because we’re so far away from everything,” said Nina Rønsted, director of science and conservation at NTBG who led the assessment. “Each plant plays a very specific role” in the environment.
Species like na`ena`e (Dubautia waialealae) that grow in the island’s boggy forests are critically imperiled. The loss of a single species can throw an entire ecosystem out of balance.
“It’s a bit like a tower of cards,” Rønsted said. “If you take too much out, it will fall.”
Locating rare plants in the wild is only half the battle. To protect species in the long run, botanists need to collect samples — seeds and genetic material — which they can cultivate in greenhouse nurseries. This helps provide an insurance policy against extinction.
In 2020, Nyberg and Canadian researchers from Outreach Robotics began developing a special robotic arm they could attach to a drone to carefully cut off bits of plants growing in perilous locations.
Mamba has so far collected 29 cuttings or seeds from 12 endangered species. These include samples of wahine noho kula, a rare violet thought to be extinct on Kauaʻi and only recently rediscovered by the surveying drone.
Seeds and cuttings are now growing at the NTBG nursery, while some seeds are being stored in the seed bank for future conservation efforts.
The robot “can be the difference between extinction and survival,” Nyberg said.
But species still need to be returned to the wild to make a full comeback. Scientists hope to get them back into their cliffside terrain within the next year or two.
They might even use drones to bomb down collected seeds, packing them into sticky fertilizer balls that can adhere to steep cliffs.
But they might not need to even be dropped in such treacherous terrain. It’s possible “that these plants occurred on flat lands before we had goats here,” Nyberg said.
National Tropical Botanical Garden; Outreach Robotics. La Vigne, H., Charron, G., Rachiele-Tremblay, J. et al. Collecting critically endangered cliff plants using a drone-based sampling manipulator. Sci Rep 12, 14827 (2022).
Courtesy of National Tropical Botanical Garden
Lisa Shumaker and Katy Daigle