Ecosystem health assessment of Dongshan Island based on its ability to provide ecological services that regulate heavy rainfall

The evaluation of ecosystem health is a hotspot in macro-ecology and ecosystem management. The objective of this paper is to introduce an ecosystem health assessment framework that combines ecosystem service concepts and indicators. We analyzed ecological services on Dongshan Island for regulating heavy rainfall by explicitly addressing the spatial distribution of ecosystem service demand and supply. An index system was then developed for both the areas that provide the ecological service and those that benefit from it. These areas are linked by small watersheds that were extracted using the hydrological analysis function in ArcGIS 10.2. Weights of the indicators were assigned and calculated based on principal component analysis. Finally, at the small watershed scale, the forested area and other land area ratios were weighted to assess the overall health of the areas that provide and benefit from this ecological service. The results revealed that the forest health conditions in the northwestern and northern parts of the island were weak, especially in the vicinity of the county seat. The analysis indicated that forested areas in the regions were relatively small, and the functional ecological service related to the redistribution of rainfall provided by these forested areas was minimal. The health states of areas benefiting from this ecological service generally appeared problematic. Areas benefiting from the service were characterized by dense populations, intense urbanization, and high risk of rain-related disaster. Moreover, only small and scattered forests were observed in the urban areas and towns on Dongshan Island. These urbanized areas rarely support large forest patches, and they fail to provide adequate green corridors or significant green space. This forest condition in urban areas cannot provide commendably protective functionality to mitigate heavy rain disasters. Therefore, to improve the ecological health of Dongshan Island, a system of green areas within urban landscapes must be planned and developed.