Hyperspectral VNIR-spectroscopy and imagery as a tool for monitoring herbicide damage in wilding conifers

Rebecca C. Scholten*, Joachim Hill, Willy Werner, Henning Buddenbaum, Jonathan P. Dash, Mireia Gomez Gallego, Carol A. Rolando, Grant D. Pearse, Robin Hartley, Honey Jane Estarija, Michael S. Watt

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Wilding conifers, the naturally regenerated scions of exotic conifer species, are a major ecological and economic issue in New Zealand. Hyperspectral imagery could provide a useful means of monitoring the efficacy of wilding control measures but little research has examined this possibility. Data were collected from an experiment, that included thirty-nine young Pinus contorta (Douglas) trees allocated to a control and two herbicide treatments (triclopyr butoxyethyl ester and diquat dibromide monohydrate). The objectives of this research were to examine the temporal impacts of herbicide on needle discolouration, spectral properties and tree physiology and to develop models to predict photosynthetic parameters from hyperspectral data. In accordance with obvious discolouration on the first day after treatment, values of net photosynthesis rate (A), electron transport rate (ETR), stomatal conductance (G) and optimal quantum yield of photosystem II (Fv/Fm) declined rapidly for plants treated with diquat. Discolouration following application of triclopyr was not evident before the second week, and values of A, ETR, G and Fv/Fm declined slower than those of diquat. Of the tested narrow-band spectral indices calculated from needle spectra photochemical reflectance index (PRI) exhibited the strongest correlation with the four photosynthetic parameters and R2 values between PRI and A, Fv/Fm, ETR and G were, respectively, 0.53, 0.46, 0.68 and 0.29. Models that used raw spectra as inputs showed that sparse partial least squares (SPLS) outperformed the three other approaches tested (PLS, Support Vector Machines, Elastic Net) and R2 values using this approach for A, Fv/Fm, ETR and G were, respectively, 0.64, 0.62, 0.65 and 0.42.

Original languageEnglish
Pages (from-to)3395-3413
Number of pages19
JournalBiological Invasions
Volume21
Issue number11
DOIs
Publication statusPublished - 1 Jan 2019

Funding

We are very grateful to Liam Wright for the wilding collection. Ben Morrow, Paul Keech, Caro Gous, Stefan Gous, Shideen Nathan assisted greatly with the practical aspects of the trial. The lead author appreciates the assistance of Max Bombrun for proofreading earlier versions of the manuscript and Jane Meiforth for helping organise the exchange, and for providing plenty of practical advice on New Zealand. This research was funded by the German Aerospace Center (DLR) and the German Federal Ministry of Economic Affairs and Energy in the framework of the EnMAP project, Grant Number 50 EE 1530. The research undertaken within New Zealand was funded by the Winning Against Wildings programme (Contract Number C09X1611) which was funded by the New Zealand Ministry for Business, Innovation, and Employment. This funding was supplemented by co-funding from the Forest Growers Levy Trust and Scion’s Strategic Science Investment Fund. We are very grateful to Liam Wright for the wilding collection. Ben Morrow, Paul Keech, Caro Gous, Stefan Gous, Shideen Nathan assisted greatly with the practical aspects of the trial. The lead author appreciates the assistance of Max Bombrun for proofreading earlier versions of the manuscript and Jane Meiforth for helping organise the exchange, and for providing plenty of practical advice on New Zealand. This research was funded by the German Aerospace Center (DLR) and the German Federal Ministry of Economic Affairs and Energy in the framework of the EnMAP project, Grant Number 50 EE 1530. The research undertaken within New Zealand was funded by the Winning Against Wildings programme (Contract Number C09X1611) which was funded by the New Zealand Ministry for Business, Innovation, and Employment. This funding was supplemented by co-funding from the Forest Growers Levy Trust and Scion?s Strategic Science Investment Fund.

FundersFunder number
Forest Growers Levy Trust
German Federal Ministry of Economic Affairs and Energy50 EE 1530, C09X1611
Max Bombrun
New Zealand Ministry for Business, Innovation, and Employment
Deutsches Zentrum für Luft- und Raumfahrt

    Keywords

    • Herbicides
    • Hyperspectral
    • Invasion ecology
    • Lodgepole pine
    • Stress detection
    • Wildings

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