ALBERT

Description: Background: Climate change and the environmental impact of food production is a key modernchallenge, becoming part of the wider human nutrition discussion in regard to sustainable diets [...]

Description: The endemic New Zealand kauri trees (Agathis australis) are of major importance for the forests in the northern part of New Zealand. The mapping of kauri locations is required for the monitoring of the deadly kauri dieback disease (Phytophthora agathidicida (PTA)). In this study, we developed a method to identify kauri trees by optical remote sensing that can be applied in an area-wide campaign. Dead and dying trees were separated in one class and the remaining trees with no to medium stress symptoms were defined in the two classes “kauri” and “other”. The reference dataset covers a representative selection of 3165 precisely located crowns of kauri and 21 other canopy species in the Waitakere Ranges west of Auckland. The analysis is based on an airborne hyperspectral AISA Fenix image (437–2337 nm, 1 m2 pixel resolution). The kauri spectra show characteristically steep reflectance and absorption features in the near-infrared (NIR) region with a distinct long descent at 1215 nm, which can be parameterised with a modified Normalised Water Index (mNDWI-Hyp). With a Jeffries–Matusita separability over 1.9, the kauri spectra can be well separated from 21 other canopy vegetation spectra. The Random Forest classifier performed slightly better than Support Vector Machine. A combination of the mNDWI-Hyp index with four additional spectral indices with three red to NIR bands resulted in an overall pixel-based accuracy (OA) of 91.7% for crowns larger 3 m diameter. While the user’s and producer’s accuracies for the class “kauri” with 94.6% and 94.8% are suitable for management purposes, the separation of “dead/dying trees” from “other” canopy vegetation poses the main challenge. The OA can be improved to 93.8% by combining “kauri” and “dead/dying” trees in one class, separate classifications for low and high forest stands and a binning to 10 nm bandwidths. Additional wavelengths and their respective indices only improved the OA up to 0.6%. The method developed in this study allows an accurate location of kauri trees for an area-wide mapping with a five-band multispectral sensor in a representative selection of forest ecosystems.

Description: Resprouting is an important trait that allows plants to persist after fire and is considered a key functional trait in woody plants. While resprouting is well documented in fire-prone biomes, information is scarce in non-fire-prone ecosystems, such as New Zealand (NZ) forests. Our objective was to investigate patterns of post-fire resprouting in NZ by identifying the ability of species to resprout and quantifying the resprouting rates within the local plant community. Fire occurrence is likely to increase in NZ as a consequence of climate change, and this investigation addresses an important knowledge gap needed for planning restoration actions in fire-susceptible regions. The study was conducted in two phases: (1) A detailed review of the resprouting ability of the NZ woody flora, and (2) a field study where the post-fire responses of plants were quantified. The field study was undertaken in the eastern South Island, where woody plants (〉5 cm diameter at 30 cm height) were sampled in 10 plots (10x10 m), five- and 10-months post-fire. The research synthesized the resprouting ability of 73 woody species and is the first to provide extensive quantitative data on resprouting in NZ. Most of the canopy dominant species were non-resprouters, but many smaller trees and shrubs were capable of resprouting, despite their evolution in an environment with low fire frequency. Species composition and abundance were important predictors of resprouting patterns among plots, with similar communities resulting in similar resprouting responses. Resprouting capacity provides species with a competitive advantage in the post-fire recovery. We suggest that it is possible to engineer more fire resilient restoration plantings by planting higher proportions of the resprouters identified in this study. The incorporation of resprouting as a trait in restoration plans is likely to be relevant not just in NZ, but also in other non-fire-prone regions facing increases in fire frequency.