New technology may help fight against invasive plants
By Jan TenBruggencate
Advertiser Science Writer
Specific plants invading native Hawaiian forests can now be identified using chemical cues found in high-altitude photographs, scientists have learned.
Image courtesy of Gregory Asner
The new technology will be invaluable in preventing the further spread of miconia and other alien plant pests, researchers at Hawai'i Volcanoes National Park said.
Data from the NASA Airborne Visible and Infrared Imaging Spectrometer let scientists spot different types of plants.
"We can better locate some of our pest weeds, especially in remote areas where they are not easy to get to," said Rhonda Loh, the vegetation program manager at the park's resources management division.
"It will help us identify strategies to deal with the invasions and to discover sites where invasions are just starting."
The breakthrough uses upgraded information from the NASA Airborne Visible and Infrared Imaging Spectrometer to measure leaf nitrogen and water content, allowing scientists to tell one kind of plant from another. The work was conducted by Gregory Asner of Carnegie Institution's Department of Global Ecology and Peter Vitousek of Stanford University's Department of Biological Sciences.
In one case, they were able to distinguish the invading Canary Islands plant Myrica faya, or firetree, from the 'ohi'a, the dominant tree in many native forest areas. As a result, they were able to see where the firetree is in the early stages of moving into the native forest.
The firetree and 'ohi'a have distinctly different signatures for nitrogen, a fertilizer that promotes leafy growth in plants.
The 'ohi'a can grow in areas with poor soil and has comparatively low levels of nitrogen. The firetree is able to convert nitrogen in the atmosphere for its own use, essentially fertilizing itself. The result is that firetree leaves have more than twice the nitrogen of 'ohi'a leaves.
"The high leaf nitrogen associated with the invading tree means that it is basically fertilizing the forest with more nitrogen. The leaves turn over fast and there is more nitrogen in the soil," Asner said. The tree shades out many other plants, and researchers are still working out what all that additional fertilizer will do to the native forest.
In another breakthrough, the scientists were able to detect the presence of the invading kahili ginger plant under the forest canopy, where it has been invisible using normal photography.
"This is the first time in my experience that remote sensing has detected an understory species, kahili ginger, one of the most disruptive weeds in Hawaiian rain forests," said Tim Tunison, chief of resource management at Volcanoes National Park.
Kahili ginger forms dense mats of thick roots that push native plants aside. The scientists spotted the ginger by detecting its high moisture content, and they also found it appears to reduce nitrogen in the leaves of 'ohi'a trees growing around it.
That was new and exciting information, Vitousek said.
"This is the first time where remote sensing showed me something new concerning how an ecosystem works," he said.
" ... These new methods discovered a consequence of biological invasion that had not been detected before and showed how it varies across the landscape," he said.
Officials said it is too early to say when they might begin employing the technique regularly.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
