Nikos Alexandris

Remote Sensing Scientist, Dr

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Monitoring The Restoration of Mangrove Ecosystems from Space

Alexandris, N., Chatenoux, B., Lopez Torres, L., and Peduzzi, P. (2013): Monitoring mangrove restoration from space, UNEP/GRID-Geneva.

Executive Summary

Link to Monitoring The Restoration of Mangrove Ecosystems from Space [PDF]

Mangrove establishment and rehabilitation projects have had varying level of success at different locations around the world. Given the money that has been invested in restoring mangrove coverage, it is useful to map, monitor and compare results and experiences in different parts of the globe to compare the success of such projects. This study conducted temporal analyses for 24 mangrove sites from 10 different projects in six different countries (Senegal, the United Arab Emirates, Madagascar, Kenya, Solomon Island and Indonesia) using satellite imagery and GIS technology to map and monitor their status. Given that many of the sites were small, very high-resolution satellite imagery (0.45, 0.6 and 1 metre resolution from Worldview, Quickbird and Ikonos, respectively) was used.

Compared with ground surveys, remote sensing provides a synoptic view and, using ancillary data, makes it possible to look at historical data. However, it may preclude gaining a clear understanding of reasons for failure and successes of projects.

Given the time and financial resources for this project, it was not possible to conduct ground surveys. However, the results were sent to the mangrove recovery project managers. As it turned out, results were mostly unchallenged. The results provided include a quantitative evaluation of the mangroves restoration (in both absolute number of ha and in percentage of the total). An analysis of the change in other vegetation coverage was also included where relevant. Additionally, the results show a range of various degrees of success. Half of the projects were very successful, 20 per cent were successful, 20 per cent show limited or no change, and in one project a decline of mangroves was observed.

Several limitations for detecting mangrove recovery from space have been highlighted, the main one being that the satellite images should be taken at least three to four years after the complexion of the mangrove recovery, as the size of the mangrove canopy would otherwise not be large enough to be detected. It also has to be noted that mangroves and tropical vegetation can be easily confused, and such distinction from space therefore remains challenging. Overall, the study showed that remote sensing is a good tool for monitoring mangrove recovery.