story by Joan Conrow
photo by Monte Costa
The weeds are on the march, and not just in your yard. Until recently the only thing tougher than rooting out the invasive plants endangering Hawai‘i’s native forests was finding them among the jungles of foliage on steep ridges and in narrow valleys. From the air, Hawai‘i’s forests look like an unrelieved carpet of greenery; spotting invaders takes a skilled and patient eye, not to mention a little luck.
But now The Nature Conservancy has a sophisticated new weapon in its arsenal: remote sensing cameras that pinpoint, with remarkable precision, plants that don’t belong. Once identified, it’s easier to get rid of them.
“We cracked the code,” says Trae Menard, TNC’s Kaua‘i program manager, who spent months working with Resource Mapping Hawaii to customize existing imaging technology for conservation use. “We figured it out, and this is going to change everything.”
Introduced plants like the Australian tree fern, miconia, strawberry guava and albizia are smothering native forests crucial to healthy watersheds. But finding these invaders required a visual search from low-flying helicopters, which was tedious, inefficient, expensive—$16 a minute—and dangerous. “We almost crashed a couple of times,” says Menard, who has logged more than eighty hours of such flights.
Instead, a Cessna 182 with three cameras mounted in its belly is doing the dirty work for $3 per acre—half the price of a helicopter—and providing better coverage, too. In September the plane began flying transects over Kaua‘i’s backcountry, photographing thousands of acres. The images, which offer a perspective similar to looking at the ground from the roof of a single-story house, are detailed enough to identify a plant by its leaf structure and can also be viewed three-dimensionally. Ultimately, TNC receives a digital file with GPS coordinates for the troublemakers, which makes aerial application of an herbicide more exact. By regularly updating the images, TNC also can monitor its weed control efforts, track new invasions and document how climate change, feral pigs and plant diseases are affecting Island forests.
“Our ecosystems were a big black box,” Menard says. “This has basically opened the box, and we can shine the light in and see where we need to focus our efforts. Most important, we don’t have to risk our lives anymore.” HH