Abstract
This paper aims to assess the effectiveness of ASTER imagery to support the mapping of Pittosporum undulatum, an invasive woody species, in Pico da Vara Natural Reserve (S. Miguel Island, Archipelago of the Azores, Portugal). This assessment was done by applying K-Nearest Neighbor (KNN), Support Vector Machine (SVM) and Maximum Likelihood (MLC) pixel-based supervised classifications to 4 different geographic and remote sensing datasets constituted by the Visible, Near-Infrared (VNIR) and Short Wave Infrared (SWIR) of the ASTER sensor and by digital cartography associated to orography (altitude and "distance to water streams") of which the spatial distribution of Pittosporum undulatum directly depends. Overall, most performed classifications showed a strong agreement and high accuracy. At targeted species level, the two higher classification accuracies were obtained when applying MLC and KNN to the VNIR bands coupled with auxiliary geographic information use. Results improved significantly by including ecology and occurrence information of species (altitude and distance to water streams) in the classification scheme. These results show that the use of ASTER sensor VNIR spectral bands, when coupled to relevant ancillary GIS data, can constitute an effective and low cost approach for the evaluation and continuous assessment of Pittosporum undulatum woodland propagation and distribution within Protected Areas of the Azores Islands.
Highlights
Invasive Alien Species (IAS) is a large, if not the largest, threat to conservation
The lower separation between these two classes using just 3 VNIR bands can be explained by the fact that Pittosporum woodland is usually dense, homogeneous and mostly composed of evergreen trees and large shrubs
The results have shown that using ASTER multispectral imagery for Pittosporum woodland mapping in Pico da Vara Natural Reserve can constitute an effective and low-cost solution for continuous monitoring of the species’ spread in this protected area
Summary
Invasive Alien Species (IAS) is a large, if not the largest, threat to conservation. It is generally accepted that IAS management is a significant issue for Protected Areas management in such ecosystems (MEYERSON; REASER, 2003; REASER et al, 2007; GUTIERRES et al, 2011). Introduced in the Azores in the 19th century as a hedgerow species for the protection of orange tree plantations, Pittosporum undulatum has spread during the last 100 years to a wide range of habitats throughout the Azores islands, disturbing plant communities at elevations of 100 to 600 m. It overgrows native vegetation, forming pure stands (SJOGREN, 1973). Distance to water streams, as a specific and relevant disturbance factor in the vegetation’s spatial distribution at Pico da Vara Natural Reserve (due mostly to hydrological regime and slope) (GIL, 2005) shall be considered as a relevant landform factor for Pittosporum undulatum occurrence in this Protected Area
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