DOC Manawatū rangers are thinking outside the box when it comes to removing invasive plants from the wetlands of Horowhenua.
Rangers recently used drones to detect purple loosestrife at Lake Papaitonga in Horowhenua. While this worked as a great detection tool, the manual sifting of data proved extremely time-consuming.
Purple loosestrife is a highly invasive plant and environmental weed that outcompetes native vegetation, disrupts and blocks water flow, and can degrade habitats for wildlife. Each plant can produce 2.5 million seeds per year, and are notoriously difficult to control once established, so keeping on top of it is critical to maintaining our wetland ecosystems.
Biodiversity Ranger Stephen Conn, working alongside the rest of the DOC Manawatū team, used open-source tools to develop and test a new process.
Together, they calibrated drone settings and used graphic software to scan hundreds of drone photos for shades of purple. The colour, contrasted within the surrounding vegetation, allowed for the automatic detection of flowering purple loosestrife plants.
“The chosen system hardware can process approximately 70 images per minute,” says Stephen. “This meant we could quickly identify areas that warranted ground inspection and control, letting us work much faster and more efficiently.”
However, finding the plants was only half the battle, as the lake was too shallow for a rowboat to reach an area identified as a significant infestation site.
Tim Gilbertson, also a Biodiversity Ranger, says the team turned to a lower-tech solution for this problem, normally suited for more casual naturing.
“We ended up using an inner tube, inflated and attached to a rope, to transport equipment and rangers across the water to reach the weeds,” says Tim. “Sometimes, modern problems need modern solutions. Other times, an inflatable tyre can save the day.”
In the first season of using this new approach, the team controlled around 950 plants across the reserve. Shifting to ground-based control, as opposed to aerial, has also reduced spray drift, minimising impacts on non-target species, and allowed flowers and seed heads to be removed before treatment, helping prevent further spread.
With plenty of room to further improve the process, the team are hopeful their work will inspire others to think outside the box.
“By combining ranger expertise, drone surveys, image-analysis software, and an old-fashioned inflatable inner tube, we’ve now got a method that makes the goal of eliminating purple loosestrife from Papaitonga Reserve feel far less daunting,” says Tim.
‘It’s no magic bullet, but the future definitely looks a lot less purple from here.”
NATURE LOOKS DIFFERENT FROM HERE
Nature isn’t scenery. Nature is a society that we rely on for everything, every day. It’s behind our identity and our way of life.
