Abstract
A strip of 20th-century landscape woodland planted alongside a 17th to mid-18th century ancient and semi-natural woodland (ASNW) was investigated by applied aerial spectroscopy using an unmanned aerial vehicle (UAV) with a multispectral image camera (MSI). A simple classification approach of normalized difference spectral index (NDSI), derived using principal component analysis (PCA), enabled the identification of the non-native trees within the 20th-century boundary. The tree species within this boundary, classified by NDSI, were further segmented by the machine learning segmentation method of k-means clustering. This combined innovative approach has enabled the identification of multiple tree species in the 20th-century boundary. Phenotyping of trees at canopy level using the UAV with MSI, across 8052 m2, identified black pine (23%), Norway maple (19%), Scots pine (12%), and sycamore (19%) as well as native trees (oak and silver birch, 27%). This derived data was corroborated by field identification at ground-level, over an area of 6785 m2, that confirmed the presence of black pine (26%), Norway maple (30%), Scots pine (10%), and sycamore (14%) as well as other trees (oak and silver birch, 20%). The benefits of using a UAV, with an MSI camera, for monitoring tree boundaries next to a new housing development are demonstrated.
Highlights
One of the major challenges in conserving designated woodlands is controlling the spread of invasive plant species that are non-native to the location [2]
The principal component analysis (PCA) results were used to derive an normalized difference spectral index (NDSI) using the eigenvectors in PC1 and PC2 (Figure 5a), which showed a pronounced spectral response in the green, red, red edge, and NIR spectral bands between PC1 and PC2
The PCA derived NDSI algorithm allows the different tree species to be clustered into groups (Figure 6b)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Designated woodlands are protected places for native species of trees and shrubs that provide habitats for numerous species of fungi, invertebrates, birds, mammals, and reptiles that all contribute to providing a balanced ecosystem [1]. One of the major challenges in conserving designated woodlands is controlling the spread of invasive plant species that are non-native to the location [2]. Invasive plant species in woodland are trees and shrubs introduced by humans, negatively impacting native plant and animal communities [3]
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