# Monitoring Land Cover Change on a Rapidly Urbanizing Island Using Google Earth Engine
## 4 Discussion
### Drivers of LULC Change  
Reforestation and built-up expansion were accompanied by a decrease in cultivated land on Haitan Island. Results from this study showed that built-up expansion and cultivated land reduction were concentrated in the middle of the island. The reason for this phenomenon is related to government development policy [39]. According to the national development strategy, the layout planning of 'Comprehensive Pilot Zone' focused on the central and western plain regions' development [29]. Under the guideline of strategy, the cross-strait bridge was built in 2010 [39], which connects Pingtan Island and mainland China and boosts its development. Pingtan cross-strait, highway-railway bridge nears completion, and the high-speed rail will be open to traffic in the coming years. The station is located in Tancheng town, in the middle of the island. Those measures accelerate urban development of Pingtan Island. Likewise, the 'Grain for Green Project' contributed to cultivated land transfer to forest land. Similar projects have also greatly contributed to forest increase in other parts of China due to government policy making, for instance, Three North Protection Forest Project [25,40]. This program is successful in protecting the ecosystem and environment by afforestation based on the guideline of national strategy. [PERSON] et al. (2013) [41] discussed reforestation efforts and payments for ecosystem services' programs on tropical Hainan Island, where the Sloping Land Conversion Program (SLCP) increased tree cover on the island while losing diverse natural forests. [PERSON] et al. (2013) [41] discussed the limitations of using \"forests\" as a classification category in forest restoration programs because it includes both natural, native, and non-native forests. According to [PERSON] (2011) [42], continued use of general category \"forest\" would further risk tropical natural forests and associated biodiversity. Economic subsidies to plant non-native monoculture-type forests (e.g., rubber plantations, etc.) would further place conversion pressure on natural forests [41]. [PERSON] et al. (2000) [43] conducted an econometric analysis of the causes of forest land use changes on Hainan Island and concluded that population growth was behind the decrease in natural forests. In addition, higher timber prices led to rain forest loss while increasing the area of plantation forests [43].  
Besides the policy factor for land use transition, population and economic activity also have contributed to land cover change. According to the Fuzhou Statistical Yearbook [44], the urban population of Pingtan County was 94,500 people in 1990, which increased to 230,900 people in 2019. The population increased considerably in the town of Tancheng (County government location). The growing population results in the expansion of built-up land, such as road construction, industry, residential houses, and other changes. The GDP of Pingtan County was 46.03, 455.59, 772.94, and 4159.56 million USD in 1990, 2000, 2007, and 2019, respectively, which indicated rapid economic growth. In addition, another threat to sustainable development in Pingtan County is physical factors, particularly strong wind [23]. With further uncertainty factors arising in recent years, the balance between nature conservation and socio-economic development is necessary.