Abstract
Aim of the study: Acacia dealbata is an alien invasive species that is widely spread in Portugal. The main goal of this study was to produce an accurate and detailed map for this invasive species using ASTER multispectral imagery.Area of study: The central-eastern zone of Portugal was used as study area. This whole area is represented in an ASTER scene covering about 321.1 x 103 ha.Material and methods: ASTER imagery of two dates (flowering season and dry season) were classified by applying three supervised classifiers (Maximum Likelihood, Support Vector Machine and Artificial Neural Networks) to five different land cover classifications (from most generic to most detailed land cover categories). The spectral separability of the land cover categories was analyzed and the accuracy of the 30 produced maps compared.Main results: The highest classification accuracy for acacia mapping was obtained using the flowering season imagery, the Maximum Likelihood classifier and the most detailed land cover classification (overall accuracy of 86%; Kappa statistics of 85%; acacia class Kappa statistics of 100%). As a result, the area occupied by acacia was estimated to be approximated 24,770 ha (i.e. 8% of the study area).Research highlights: The methodology explored proved to be a cost-effective solution for acacia mapping in central-eastern of Portugal. The obtained map enables a more accurate and detailed identification of this species’ invaded areas due to its spatial resolution (minimum mapping unit of 0.02 ha) providing a substantial improvement comparably to the existent national land cover maps to support monitoring and control activities.Keywords: remote sensing; invasive alien species; land cover mapping; vegetation mapping.
Highlights
Fire and invasive species are becoming two of the most important global problems in natural and anthropogenic ecosystems (Pimentel et al, 2005; Keeley, 2006; Arán et al, 2013)
Overall separability assessments performed for more generic land cover classifications
Spectral confusion was only found between the categories “acacia” and both “agricultural areas” and “coniferous” when using the imagery of March 2007
Summary
Fire and invasive species are becoming two of the most important global problems in natural and anthropogenic ecosystems (Pimentel et al, 2005; Keeley, 2006; Arán et al, 2013). Invasive species constitute a major environmental problem, as they have profound consequences on biodiversity conservation and on ecosystem processes and functioning (Parker et al, 1999; González-Muñoz et al, 2012). In the past few centuries, thousands of woody plant species have been moved out of their natural ranges around the world. In recent decades many species of trees and shrubs have become naturalized or invasive. Many have spread from planting sites and some are among the most widespread and damaging of invasive organisms (Richardson & Rejmánek, 2011).
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