Hawaii is renowned for its picture-perfect landscapes. But its island ecosystem is also prone to invasive species that can upset the natural balance. One such intruder is the Myrica faya tree that has made its way into the tropical forests of Hawaii Volcanoes National Park. A new aerial monitoring technique is allowing scientists to detect the effects of this invader much earlier than traditional remote sensing approaches can, providing researchers with additional insight to control it.

Using airborne imaging spectroscopy, Gregory Asner of the Carnegie Institution and Peter Vitousek of Stanford University were able to evaluate changes in the chemistry of the rainforest canopy by identifying a chemical fingerprint of the leaves of M. faya. For one, the invading tree species has a high nitrogen concentration compared to the native plants. "The fingerprints showed where the native dominant tree "ohia" (Metrosideros polymorpha) has been taken over by the invading Canary Islands tree, Myrica faya, and more importantly identified areas where Myrica invasion is in its early stages," Asner explains. The aerial survey also uncovered a second intruder: the Kahili ginger plant, which grows under the forest canopy and is invisible to standard satelite detection methods.

The scientists next plan to work with collaborators from the National Park Service, the Nature Conservancy and other groups to generate a chemical and structural map of Hawaii's ecosystems to identify and track invasive species. "Although we don't know exactly what the domino effects of this invasion will be," Asner says, "we are in a good position to predict them as we learn more about the chemical changes the forest is undergoing." The findings are published online this week by the Proceedings of the National Academy.

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