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.
Highlights
Translocation of plants outside of the geographic region in which they evolved has facilitated the development of highly productive agricultural and plantation forestry systems
Obvious discolouration was evident for plants treated with diquat on the day following treatment and values during weeks 1, 2 and 3 averaged 68, 80 and 84% (Table 3)
This study demonstrates the impact of two herbicide treatments, with contrasting modes of action, on needle discolouration, spectral properties and key physiological parameters
Summary
Translocation of plants outside of the geographic region in which they evolved has facilitated the development of highly productive agricultural and plantation forestry systems. Throughout temperate areas of the southern hemisphere, a small number of introduced conifer species that evolved in the northern hemisphere are the cornerstone of the plantation forest industry These planted forests are frequently fast growing and tolerant of poor growing conditions. They are exempt from damage posed by harmful biotic agents often present in their native range meaning there are fewer risks posed to their productive and reproductive potential. These traits enable these conifer species to provide significant economic, ecological, and social benefits when planted in productive forest systems in southern hemisphere countries such as New Zealand, Australia, and Chile. The same evolutionary traits that make them excellent timber species mean that they can often out-compete indigenous vegetation outside of their natural range (Farjon and Farjon 2008)
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