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Remote Sens. 2018, 10(3), 404; https://doi.org/10.3390/rs10030404

A Spectral Mapping Signature for the Rapid Ohia Death (ROD) Pathogen in Hawaiian Forests

1
Department of Global Ecology, Carnegie Institution for Science, 260 Panama St, Stanford, CA 94305, USA
2
USDA Agricultural Research Service, Hilo, HI 96720, USA
3
College of Tropical Agriculture and Human Resources, University of Hawaiʻi at Manoa, Hilo, HI 96720, USA
4
Institute of Pacific Islands Forestry, US Forest Service, Hilo, HI 96720, USA
*
Author to whom correspondence should be addressed.
Received: 2 February 2018 / Revised: 27 February 2018 / Accepted: 4 March 2018 / Published: 6 March 2018
(This article belongs to the Special Issue Remote Sensing of Tropical Forest Biodiversity)
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Abstract

Pathogenic invasions are a major source of change in both agricultural and natural ecosystems. In forests, fungal pathogens can kill habitat-generating plant species such as canopy trees, but methods for remote detection, mapping and monitoring of such outbreaks are poorly developed. Two novel species of the fungal genus Ceratocystis have spread rapidly across humid and mesic forests of Hawaiʻi Island, causing widespread mortality of the keystone endemic canopy tree species, Metrosideros polymorpha (common name: ʻōhiʻa). The process, known as Rapid Ohia Death (ROD), causes browning of canopy leaves in weeks to months following infection by the pathogen. An operational mapping approach is needed to track the spread of the disease. We combined field studies of leaf spectroscopy with laboratory chemical studies and airborne remote sensing to develop a spectral signature for ROD. We found that close to 80% of ROD-infected plants undergo marked decreases in foliar concentrations of chlorophyll, water and non-structural carbohydrates, which collectively result in strong consistent changes in leaf spectral reflectance in the visible (400–700 nm) and shortwave-infrared (1300–2500 nm) wavelength regions. Leaf-level results were replicated at the canopy level using airborne laser-guided imaging spectroscopy, with quantitative spectral separability of normal green-leaf canopies from suspected ROD-infected brown-leaf canopies in the visible and shortwave-infrared spectrum. Our results provide the spectral–chemical basis for detection, mapping and monitoring of the spread of ROD in native Hawaiian forests. View Full-Text
Keywords: Ceratocystis; Hawaiʻi; hyperspectral remote sensing; imaging spectroscopy; invasive species; leaf spectroscopy; Metrosideros polymorpha; ʻōhiʻa; pathogen Ceratocystis; Hawaiʻi; hyperspectral remote sensing; imaging spectroscopy; invasive species; leaf spectroscopy; Metrosideros polymorpha; ʻōhiʻa; pathogen
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Asner, G.P.; Martin, R.E.; Keith, L.M.; Heller, W.P.; Hughes, M.A.; Vaughn, N.R.; Hughes, R.F.; Balzotti, C. A Spectral Mapping Signature for the Rapid Ohia Death (ROD) Pathogen in Hawaiian Forests. Remote Sens. 2018, 10, 404.

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