Assessing the Potential Replacement of Laurel Forest by a Novel Ecosystem in the Steep Terrain of an Oceanic Island
Biological invasions are a major global threat to biodiversity and often affect ecosystem services negatively. They are particularly problematic on oceanic islands where there are many narrow-ranged endemic species, and the biota may be very susceptible to invasion. Quantifying and mapping invasion...
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doaj-0f937aecfce04dcab2ff0b94c37b37112020-12-09T00:02:03ZengMDPI AGRemote Sensing2072-42922020-12-01124013401310.3390/rs12244013Assessing the Potential Replacement of Laurel Forest by a Novel Ecosystem in the Steep Terrain of an Oceanic IslandRam Sharan Devkota0Richard Field1Samuel Hoffmann2Anna Walentowitz3Félix Manuel Medina4Ole Reidar Vetaas5Alessandro Chiarucci6Frank Weiser7Anke Jentsch8Carl Beierkuhnlein9Department of Biogeography, University of Bayreuth, D-95440 Bayreuth, GermanySchool of Geography, University of Nottingham, Nottingham NG7 2RD, UKDepartment of Biogeography, University of Bayreuth, D-95440 Bayreuth, GermanyDepartment of Biogeography, University of Bayreuth, D-95440 Bayreuth, GermanyServicio de Medio Ambiente. Cabildo de La Palma, 38700 Santa Cruz de La Palma, SpainDepartment of Geography, University of Bergen, P.O. Box 7802, 5020 Bergen, NorwayBiodiversity and Macroecology Group, Department of Biological, Geological & Environmental Sciences, Alma Mater Studiorum-University of Bologna, Via Irnerio 33, 40126 Bologna, ItalyDepartment of Biogeography, University of Bayreuth, D-95440 Bayreuth, GermanyDisturbance Ecology, University of Bayreuth, D-95440 Bayreuth, GermanyDepartment of Biogeography, University of Bayreuth, D-95440 Bayreuth, GermanyBiological invasions are a major global threat to biodiversity and often affect ecosystem services negatively. They are particularly problematic on oceanic islands where there are many narrow-ranged endemic species, and the biota may be very susceptible to invasion. Quantifying and mapping invasion processes are important steps for management and control but are challenging with the limited resources typically available and particularly difficult to implement on oceanic islands with very steep terrain. Remote sensing may provide an excellent solution in circumstances where the invading species can be reliably detected from imagery. We here develop a method to map the distribution of the alien chestnut (<i>Castanea sativa</i> Mill.) on the island of La Palma (Canary Islands, Spain), using freely available satellite images. On La Palma, the chestnut invasion threatens the iconic laurel forest, which has survived since the Tertiary period in the favourable climatic conditions of mountainous islands in the trade wind zone. We detect chestnut presence by taking advantage of the distinctive phenology of this alien tree, which retains its deciduousness while the native vegetation is evergreen. Using both Landsat 8 and Sentinel-2 (parallel analyses), we obtained images in two seasons (chestnuts leafless and in-leaf, respectively) and performed image regression to detect pixels changing from leafless to in-leaf chestnuts. We then applied supervised classification using Random Forest to map the present-day occurrence of the chestnut. Finally, we performed species distribution modelling to map the habitat suitability for chestnut on La Palma, to estimate which areas are prone to further invasion. Our results indicate that chestnuts occupy 1.2% of the total area of natural ecosystems on La Palma, with a further 12–17% representing suitable habitat that is not yet occupied. This enables targeted control measures with potential to successfully manage the invasion, given the relatively long generation time of the chestnut. Our method also enables research on the spread of the species since the earliest Landsat images.https://www.mdpi.com/2072-4292/12/24/4013invasive speciesisland ecologyassisted migrationlaurel forestplant functional typedeciduous trees |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Ram Sharan Devkota Richard Field Samuel Hoffmann Anna Walentowitz Félix Manuel Medina Ole Reidar Vetaas Alessandro Chiarucci Frank Weiser Anke Jentsch Carl Beierkuhnlein |
spellingShingle |
Ram Sharan Devkota Richard Field Samuel Hoffmann Anna Walentowitz Félix Manuel Medina Ole Reidar Vetaas Alessandro Chiarucci Frank Weiser Anke Jentsch Carl Beierkuhnlein Assessing the Potential Replacement of Laurel Forest by a Novel Ecosystem in the Steep Terrain of an Oceanic Island Remote Sensing invasive species island ecology assisted migration laurel forest plant functional type deciduous trees |
author_facet |
Ram Sharan Devkota Richard Field Samuel Hoffmann Anna Walentowitz Félix Manuel Medina Ole Reidar Vetaas Alessandro Chiarucci Frank Weiser Anke Jentsch Carl Beierkuhnlein |
author_sort |
Ram Sharan Devkota |
title |
Assessing the Potential Replacement of Laurel Forest by a Novel Ecosystem in the Steep Terrain of an Oceanic Island |
title_short |
Assessing the Potential Replacement of Laurel Forest by a Novel Ecosystem in the Steep Terrain of an Oceanic Island |
title_full |
Assessing the Potential Replacement of Laurel Forest by a Novel Ecosystem in the Steep Terrain of an Oceanic Island |
title_fullStr |
Assessing the Potential Replacement of Laurel Forest by a Novel Ecosystem in the Steep Terrain of an Oceanic Island |
title_full_unstemmed |
Assessing the Potential Replacement of Laurel Forest by a Novel Ecosystem in the Steep Terrain of an Oceanic Island |
title_sort |
assessing the potential replacement of laurel forest by a novel ecosystem in the steep terrain of an oceanic island |
publisher |
MDPI AG |
series |
Remote Sensing |
issn |
2072-4292 |
publishDate |
2020-12-01 |
description |
Biological invasions are a major global threat to biodiversity and often affect ecosystem services negatively. They are particularly problematic on oceanic islands where there are many narrow-ranged endemic species, and the biota may be very susceptible to invasion. Quantifying and mapping invasion processes are important steps for management and control but are challenging with the limited resources typically available and particularly difficult to implement on oceanic islands with very steep terrain. Remote sensing may provide an excellent solution in circumstances where the invading species can be reliably detected from imagery. We here develop a method to map the distribution of the alien chestnut (<i>Castanea sativa</i> Mill.) on the island of La Palma (Canary Islands, Spain), using freely available satellite images. On La Palma, the chestnut invasion threatens the iconic laurel forest, which has survived since the Tertiary period in the favourable climatic conditions of mountainous islands in the trade wind zone. We detect chestnut presence by taking advantage of the distinctive phenology of this alien tree, which retains its deciduousness while the native vegetation is evergreen. Using both Landsat 8 and Sentinel-2 (parallel analyses), we obtained images in two seasons (chestnuts leafless and in-leaf, respectively) and performed image regression to detect pixels changing from leafless to in-leaf chestnuts. We then applied supervised classification using Random Forest to map the present-day occurrence of the chestnut. Finally, we performed species distribution modelling to map the habitat suitability for chestnut on La Palma, to estimate which areas are prone to further invasion. Our results indicate that chestnuts occupy 1.2% of the total area of natural ecosystems on La Palma, with a further 12–17% representing suitable habitat that is not yet occupied. This enables targeted control measures with potential to successfully manage the invasion, given the relatively long generation time of the chestnut. Our method also enables research on the spread of the species since the earliest Landsat images. |
topic |
invasive species island ecology assisted migration laurel forest plant functional type deciduous trees |
url |
https://www.mdpi.com/2072-4292/12/24/4013 |
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