Invasive species are so pervasive in Hawaii’s low-lying areas that the U.S. Forest Service says it’s not cost-effective or practical to eradicate them all. Instead, it’s launching new research into developing “hybrid ecosystems” that will incorporate some nonnative plants but allow native plants to thrive.

The service has received a $1.6 million grant from the Defense Department’s strategic environmental research program to study the possibility.

“Invasive species are so prevalent. You’re hand weeding, trying to eliminate them and aren’t able to keep up with them. It feels like you’re fighting a losing battle,” said Susan Cordell, research ecologist with the Forest Service. “Restoring these lowland tropical forests to a historic native state is not financially or physically feasible.”

Hawaii’s low-lying native trees and plants were wiped out by cattle, goats and other nonnative mammals that were set free to graze after the arrival of the first Europeans in the islands in the late 1700s. The animals trampled on ferns and undergrowth, drying the soil and tree roots. Later reforestation efforts resulted in the planting of fast-growing nonnative trees like eucalyptus instead of native trees.

To see intact native ecosystems, you have to climb high into the mountains.

Cordell said the grant will allow researchers to find ways for native species to “coexist” with some nonnative species.

The study, to be carried out at Keaukaha Military Reservation, a 200-acre site on the Big Island run by the Army National Guard, is due to begin in April and last for five years.

The first phase is a 14-month analysis of existing native and nonnative species. The second phase will involve test plantings of several species combinations.

Rebecca Ostertag, a University of Hawaii-Hilo biology associate professor, and Peter Vitousek, a biology professor at Stanford University, are due to be part of the research team along with Cordell.

Sam Gon, a senior scientist and cultural adviser with the Nature Conservancy of Hawaii, said the idea of hybrid ecosystems is not entirely new, and reflects some realism.

While Gon would like to see ecosystem efforts assert native species as much as possible and see native plants re-established in areas where they’re not longer found, he also recognizes this is difficult and time consuming.

“Sometimes you find that they actually hold their own pretty well as long as you don’t have things like fire or other major disturbances,” Gon said. “And other times you find the moment you stop caring for them and actively removing their competitors, within the course of five years or so, you barely know that the place had native plants at all.”

Gon said hybrid ecosystems could be part of a spectrum that would also include purely native ecosystems.

“It’s just maybe the realization that even though we would like to see nothing but natives, we might have to settle for being happy to see a percentage of natives,” Gon said.

He said this would still be an improvement compared with the 1950s or even 1970s in Hawaii, when there weren’t any native plants in the lowland parts of the islands.