Spectral discrimination of giant reed (Arundo donax L.): A seasonal study in riparian areas Maria Rosário Fernandes ⇑ , Francisca C. Aguiar, João M.N. Silva, Maria Teresa Ferreira, José M.C. Pereira Universidade Técnica de Lisboa, Instituto Superior de Agronomia, Centro de Estudos Florestais, Tapada da Ajuda, 1349-017 Lisboa, Portugal article info Article history: Received 15 May 2012 Received in revised form 6 November 2012 Accepted 21 March 2013 Available online 19 April 2013 Keywords: Giant reed Common reed Phenological period Riparian vegetation Invasive plant species Field spectroradiometry abstract The giant reed (Arundo donax L.) is amongst the one hundred worst invasive alien species of the world, and it is responsible for biodiversity loss and failure of ecosystem functions in riparian habitats. In this work, field spectroradiometry was used to assess the spectral separability of the giant reed from the adja- cent vegetation and from the common reed, a native similar species. The study was conducted at different phenological periods and also for the giant reed stands regener- ated after mechanical cutting (giant reed_RAC). A hierarchical procedure using Kruskal–Wallis test fol- lowed by Classification and Regression Trees (CART) was used to select the minimum number of optimal bands that discriminate the giant reed from the adjacent vegetation. A new approach was used to identify sets of wavelengths – wavezones – that maximize the spectral separability beyond the min- imum number of optimal bands. Jeffries Matusita and Bhattacharya distance were used to evaluate the spectral separability using the minimum optimal bands and in three simulated satellite images, namely Landsat, IKONOS and SPOT. Giant reed was spectrally separable from the adjacent vegetation, both at the vegetative and the senes- cent period, exception made to the common reed at the vegetative period. The red edge region was repeatedly selected, although the visible region was also important to separate the giant reed from the herbaceous vegetation and the mid infrared region to the discrimination from the woody vegetation. The highest separability was obtained for the giant reed_RAC stands, due to its highly homogeneous, dense and dark-green stands. Results are discussed by relating the phenological, morphological and structural features of the giant reed stands and the adjacent vegetation with their optical traits. Weak- nesses and strengths of the giant reed spectral discrimination are highlighted and implications of imagery selection for mapping purposes are argued based on present results. Ó 2013 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS) Published by Elsevier B.V. All rights reserved. 1. Introduction The giant reed or cane (Arundo donax L.), is an alien invasive riparian species that significantly threatens global biodiversity and riparian ecosystem functions in many regions of the world (Cushman and Gaffney, 2010; Everitt et al., 2008; Ge et al., 2008; Herrera and Dudley, 2003) causing numerous management, eco- logical and economic problems in the southwestern US, especially in California, and in many sub-tropical and warm-temperate re- gions of the world (Everitt et al., 2004; Ge et al., 2008). The giant reed is a tall-growing perennial grass, belonging to the Poaceae family. Flowering occurs in later summer and dries completely if the roots are not connected with groundwater. Giant reed inva- sions form large, monotypic and impenetrable stands that contrib- ute to the degradation of the riparian habitat for native fauna, deplete water resources and trap sediments (Everitt et al., 2004; Quinn and Holt, 2008). Moreover, heavy infestations of giant reed frequently obstruct river flow and damage adjoining lands (Dudley, 2000). In Portugal, the giant reed is largely widespread in western and southern coastal rivers where it was introduced for erosion control, as windbreaks, to confine properties and as a tutor for creeper-cul- tivated plants (Aguiar et al., 2007). There are some doubts on its geographic origin, and some authors consider this species as natu- ralized in Iberia, however it is included in the Annex I of Executive Law of 565/99 (Ministério do Ambiente, 1999), which legislate the introduction, use and commercialization of alien species. There is a lack of knowledge about its spatial distribution and abundance and about the effectiveness of control measures, usu- ally mechanical or combined with herbicides. Many water resource managers point giant reed as one of the major invasive plants in 0924-2716/$ - see front matter Ó 2013 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS) Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.isprsjprs.2013.03.007 ⇑ Corresponding author. Tel.: +351 213653380; fax: +351 213653338. E-mail addresses: mrfernandes@isa.utl.pt (M.R. Fernandes), fraguiar@isa.utl.pt (F.C. Aguiar), joaosilva@isa.utl.pt (J.M.N. Silva), terferreira@isa.utl.pt (M.T. Ferreira), jmcpereira@isa.utl.pt (J.M.C. Pereira). ISPRS Journal of Photogrammetry and Remote Sensing 80 (2013) 80–90 Contents lists available at SciVerse ScienceDirect ISPRS Journal of Photogrammetry and Remote Sensing journal homepage: www.elsevier.com/locate/isprsjprs