**5. Conclusions**

The combination of very high-resolution historical images and OBIA is a powerful tool for identifying and monitoring communities of sparse vegetation in drylands [62]. Our results sugges<sup>t</sup> that monitoring changes in the number and the cover of a shrub community in a semi-arid ecosystem could help to infer anthropogenic disturbances that affect its health. The vegetation conditions showed that the loss of sandy substrate affected *Z. lotus* negatively, either by reducing its cover or by eliminating individuals by direct sand extraction processes. In addition, seawater intrusion into the aquifer influenced the cover and structure of the shrubs close to the coastline in a period of massive groundwater extraction [35], negatively affecting the smallest shrubs for the most part. However, the legal protection of the area had a positive effect on the health of the remaining individuals, which increased their coverage. The implementation of semi-automatic methods to infer the effects of human activities on shrub populations, such as the one evaluated in this study, could help improve the monitoring programs of existing protected areas. This could reduce the cost of these activities, not only in economic terms but also from a human perspective, which is key to the long-term preservation of any protected area.

**Author Contributions:** E.G. and J.B.-S. designed the experiments, collected the data, implemented the codes, ran the models, analyzed the results, and wrote the first draft. E.G., J.B.-S., D.A.-S., J.P.R.-S., and J.C. provided guidance, and wrote the final manuscript.

**Funding:** E.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 gran<sup>t</sup> agreemen<sup>t</sup> n<sup>º</sup> 647038 (BIODESERT). J.B.-S. received funding from the European Union's Horizon 2020 research and innovation 514 programme under the Marie Sklodowska-Curie gran<sup>t</sup> agreemen<sup>t</sup> No. 721995. D.A.-S. received support from the NASA

Work Programme on Group on Earth Observations - Biodiversity Observation Network (GEOBON) under gran<sup>t</sup> 80NSSC18K0446, from project ECOPOTENTIAL, funded by the European Union's Horizon 2020 Research and Innovation Programme under gran<sup>t</sup> agreemen<sup>t</sup> No. 641762, and from the Spanish Ministry of Science under project CGL2014-61610-EXP and gran<sup>t</sup> JC2015-00316.

**Acknowledgments:** We would like to express our appreciation to the four reviewers for their comments and suggestions which served to substantially improve this research paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
