Identification of unique ecosystem service bundles in farmland - A case study in the Huang-Huai-Hai Plain of China

Ecosystem services (ESs) are essential for human well-being and are relevant to the region's sustainable development. Most studies have emphasized the importance of high ecosystem services areas for entire regions. However, some locations with particular contributions to a region's ecosystem services are still overlooked. Using the InVEST model, this study analyzed three ESs: annual water yield (WY), carbon storage (CS), and soil conservation (SC) in the farmland of the Huang-Huai-Hai Plain of China (HHHP) from 2005 to 2019. Combining climate regulation (NDVI) and food production (FP), this research calculated the city level of the diversity of ecosystem services supply (alpha-multifunctionality) and the unique contribution to the region in each city (betamultifunctionality) from 2005 to 2019. The alpha-multifunctionality combines the number of ecosystem services and their supplies of ecosystem services. At the same time, the beta-multifunctionality assesses the average dissimilarity between the city and all other cities within that region. Furthermore, this study used Spearman correlation and self-organizing map (SOM) to analyze the relationships between these five ecosystem services and identify ecosystem service bundles. Finally, this study used random forests to analyze drivers of ecosystem service multifunctionality. Our results showed that food production in the Huang-Huai-Hai Plain increased significantly by 37.20% over time, annual water yield decreased significantly by 29.59%, and climate regulation decreased significantly by 6.09%. This may be because the Huang-Huai-Hai Plain mainly shifted from monoculture to crop rotation, and the increase in crops required more irrigation, which led to a significant decline in water yield. Furthermore, the area of grain crops in the HHHP was reduced in 2019 compared to 2005, which explains the significant decline in climate regulation. SOM found that cities with a higher beta-multifunctionality were mainly concentrated in the northern and southwest parts of HHHP. Bundles with a high alphamultifunctionality were mainly in the southern and southeast parts of the HHHP. In addition, this research showed that farmers' per capita disposable income was the most important driver of ecosystem service multi- functionality, followed by annual average precipitation and temperature. In conclusion, this study suggests that policymakers should strengthen the protection of some high ecological value but low economic value farmlands, which are crucial for regional ecological security. Meanwhile, policymakers should introduce strict ecological protection policies for farmland to reduce the decline of ecological services caused by farmers' pursuit of economic income.