Monitoring loss and recovery of mangrove forests during 42 years: The achievements of mangrove conservation in China

Mangroves are valuable ecosystems that have been protected and restored for decades in China. However, little is known about achievements of China's mangrove conservation efforts, This study aims to analyze the effectiveness of these efforts by presenting long-term dynamics of mangrove forests areal extent at the national scale. To achieve this goal, 123 Landsat images, covering all the mangrove forests in China from 1973 to 2015, were interpreted. For the first time, we built a new dataset of China's mangrove forest changes during past 42 years called Chinese Academy of Sciences Mangroves (CAS_Mangroves). Based on this dataset, we conducted case studies in seven mangrove national nature reserves to show dramatic changes of mangrove forests before and after the establishment of the reserves. Results showed that: 1) on the national scale, mangrove forests declined from 48,801 ha to 18,702 ha between 1973 and 2000, then partially recovered to 22,419 ha in 2015; 2) in each reserve, the areal extent of mangrove forests increased immediately after the reserve was established. Depending on our analysis, in the early time, agricultural reclamation caused the loss of mangrove forests; in contrast, recently, protection and reforestation actions prompt to mangrove forest restoration greatly. Because of China's conservation efforts, since 2000, direct destruction by human beings has rarely happened, and natural disasters and the existing artificial seawalls have become major threats to mangrove forest in China. This study is an application of remote sensing technologies in evaluating effectiveness of conserving natural resources. And the experiences and achievements of China's mangrove conservation efforts presented in this study will facilitate the development of applicable coastal management strategies globally, especially in developing countries.