Quantitative Assessment and Driving Force Analysis of Mangrove Forest Changes in China from 1985 to 2018 by Integrating Optical and Radar Imagery

Yuhan Zheng,Wataru Takeuchi

doi:10.3390/ijgi9090513

Abstract

Mangrove ecosystems are valuable, yet vulnerable, and therefore they have been an important subject of protection and restoration in China. Reliable information on long-term China mangrove dynamics is lacking but vital to analyze the driving forces and evaluate the efforts of mangrove conversation. This study aims to quantify the conversions among mangroves and other land covers with high accuracy. The updated mangrove base map for 2018 was produced by integrating Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar 2 (PALSAR-2) yearly mosaics and Landsat imagery with an overall accuracy of 95.23 ± 6.02%. Then, a novel approach combining map-to-image and image-to-image methods was proposed to detect the changed pixels in mangrove forests from 1985 to 2018. The mangrove base map was adopted to mask the images from other years. To determine the changed pixels, the differencing values in the masked area between two images were calculated and compared with the corresponding thresholds. Based on the changed pixels, the possible driving forces were analyzed and associated with socioeconomic development. The resultant mangrove dynamics demonstrated that mangrove forests in China experienced a tendency of loss first and recovery later during the past 30 years. Most mangrove gains came from aquaculture and mudflat, whilst losses were due to the built-up construction and aquaculture reclamation. These conversions indicated that mangrove deforestations were mainly due to human-induced destruction, while the recoveries were strongly associated with conservation and restoration actions.

Highlights

Mangrove ecosystems are amongst the most productive ecosystems on the earth and provide a wide range of essential ecosystem services [1,2], such as coastal protection and nurseries for juvenile coral reef fishes
Instead of analyzing the spectral characteristics in the whole mangrove forest [25], we focused on the image differencing at the pixel level, which could detect the changes in detail
This study provides the first quantitative assessment of mangrove dynamics in China for the past 30 years by integrating Advanced Land Observing Satellite (ALOS) PALSAR/PALSAR-2 and Landsat imagery

Summary

Introduction

Mangrove ecosystems are amongst the most productive ecosystems on the earth and provide a wide range of essential ecosystem services [1,2], such as coastal protection and nurseries for juvenile coral reef fishes. The mangrove ecosystem is one of the most vulnerable and threatened ecosystems in the world and has experienced a dramatic loss due to human activities like urban development, reclamation for aquaculture, and coastal landfill. Mangroves in China experienced a 50% loss from 40,000 ha in 1957 down to 18,800 ha in the mid-1980s [9]. Mangrove conservation and restoration started from the early 1980s and were widely conducted after 1995 with the announcement of China’s Biodiversity Conservation Action Plan. It is important to understand long-term China’s mangrove dynamics and evaluate the achievements of conservation efforts between the 1980s and the 2010s

Objectives

Methods

Results

Discussion

Conclusion