Removal of kiawe brush sparks native recovery at Mo’omomi Preserve
The Nature Conservancy News Release
Fragile sand dunes of Mo’omomi on Molokai, once overrun with alien kiawe thickets, are blooming with new native growth.
A 14-year passive restoration program by The Nature Conservancy and the Molokai Land Trust is letting the blue blossoms of pa’u o Hi’iaka and the yellow flowers of ‘ilima bloom amid the spiky native ‘aki ‘aki and shimmering hinahina.
That’s on dunes that once held single-species thickets of the introduced legume, kiawe (Prosopis pallida), which was brought to Hawaii to support cattle ranching.
“Kiawe transforms the ecosystem. It forms dense thickets. If there’s a fire, it burns hot and hard. Since it’s a legume and fixes nitrogen, it changes the soil,” said Russell Kallstrom, graphical information system coordinator for the Conservancy’s Molokai Program.
Kiawe removal combined with predator and weed control benefits not only native plants, some of them rare, but also the ua’u kani or wedge-tailed shearwater. The number of wedge-tailed shearwater burrows has increased from three nests in 1999 to 704 nests in 2012.
“It seems like the shearwaters were trying to recolonize before 1999, but feral cats used the safety of kiawe thickets as staging areas for raids on the nests,” said Wailana Moses, the Conservancy’s Molokai weed coordinator. “When we removed some of the kiawe clumps near the bird colony, we would find piles of shearwater wings.”
The shearwaters face a three-pronged mammal threat: mongooses would prey primarily on eggs, cats would take birds one at a time, and dogs would occasionally wipe out dozens at a time. In 2009, a single dog killed 60 shearwaters in one night.
The Nature Conservancy began kiawe control at its 921-acre Mo’omomi Preserve in 1998, under the direction of Molokai Program manager Ed Misaki.
“The idea of passive restoration was to focus on removing invasive species and let the natives naturally regenerate — removing the threats and allowing the native system to heal itself, basically,” Misaki said.
The conservation crews learned as they went along. One key strategy was to remove kiawe next to intact native sand dune habitat so the natives could reclaim the open area naturally.
Another technique was to quickly paint a small amount of herbicide on the cut kiawe stump to prevent it from re-sprouting. Still another was to use a chipper to grind up kiawe branches, creating mulch that helped the native crawling plants and inhibited weeds.
“We learned that if we took out too much kiawe we would have a hard time keeping up with removing weeds coming into the area — primarily buffel grass, foxtail, golden crownbeard, Australian saltbush and a non-native goosefoot,” Moses said.
The ‘aki’aki grass was generally the first species to move in after kiawe removal. “The chips slowed the weeds down a little and helped the ‘aki’aki grow into the area,” she said.
“Little by little, the other species came in like ‘ena’ena, kaunaoa and ‘akoko, even the rare Solanum nelsonii (popolo),” Moses said.
Kallstrom said the native plants do better on some of the land you’d think was the worst habitat for them — the northeast sides of dunes, which are blasted by the trade winds and regularly doused with salt spray. Most of the weeds can’t handle the salt; the coastal natives, by contrast, are adapted to it.
“It’s really an amazing thing to see. After the kiawe is removed and the chips cover the open area, the natives just crawl in from the outside. The ‘aki’aki turns fluorescent green when it hits the nitrogen left by the kiawe chips,” Kallstrom said.
The kiawe occurs in patches across the Mo’omomi dunes, and the removal process, since increments must be small, has cleared a little over nine acres in the program’s 14 years. For most of that period, it was done by Conservancy staff and volunteers, but since 2010, some of the work has been contracted to the Molokai Land Trust, which also does weed control.
The results are remarkable. Some of the cleared areas, originally bare sand, now support dense mats of Hawaiian coastal species.