A Multi-Temporal Object-Based Image Analysis to Detect Long-Lived Shrub Cover Changes in Drylands
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AuthorGuirado, Emilio; Blanco Sacristán, Javier; Rigol Sánchez, Juan Pedro; Alcaraz Segura, Domingo; Cabello, Javier
Arid zonesSeawater intrusionSoil lossTime series classificationCabo de Gata-Níjar Natural ParkSoutheast SpainZiziphus lotus
Guirado, E., Blanco-Sacristán, J., Rigol-Sánchez, J. P., Alcaraz-Segura, D., & Cabello, J. (2019). A Multi-Temporal Object-Based Image Analysis to Detect Long-Lived Shrub Cover Changes in Drylands. Remote Sensing, 11(22), 2649.
SponsorshipE.G. and D.A-S. received support from the European LIFE Project ADAPTAMED LIFE14 CCA/ES/000612, and from ERDF and the Andalusian Government under the project GLOCHARID (Global Change in Arid Zones - 852/2009/M/00). E.G. is supported by the European Research Council grant agreement nº 647038 (BIODESERT). J.B.-S. received funding from the European Union’s Horizon 2020 research and innovation 514 programme under the Marie Sklodowska-Curie grant agreement No. 721995. D.A.-S. received support from the NASA Work Programme on Group on Earth Observations - Biodiversity Observation Network (GEOBON) under grant 80NSSC18K0446, from project ECOPOTENTIAL, funded by the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 641762, and from the Spanish Ministry of Science under project CGL2014-61610-EXP and grant JC2015-00316.
Climate change and human actions condition the spatial distribution and structure of vegetation, especially in drylands. In this context, object-based image analysis (OBIA) has been used to monitor changes in vegetation, but only a few studies have related them to anthropic pressure. In this study, we assessed changes in cover, number, and shape of Ziziphus lotus shrub individuals in a coastal groundwater-dependent ecosystem in SE Spain over a period of 60 years and related them to human actions in the area. In particular, we evaluated how sand mining, groundwater extraction, and the protection of the area affect shrubs. To do this, we developed an object-based methodology that allowed us to create accurate maps (overall accuracy up to 98%) of the vegetation patches and compare the cover changes in the individuals identified in them. These changes in shrub size and shape were related to soil loss, seawater intrusion, and legal protection of the area measured by average minimum distance (AMD) and average random distance (ARD) analysis. It was found that both sand mining and seawater intrusion had a negative effect on individuals; on the contrary, the protection of the area had a positive effect on the size of the individuals’ coverage. Our findings support the use of OBIA as a successful methodology for monitoring scattered vegetation patches in drylands, key to any monitoring program aimed at vegetation preservation.