## 4 Discussion
For example, the composition and agglomeration degree of the wetland landscape increased in DTLR and its surrounding areas and decreased in the marginal areas (Figure 6), indicating the effectiveness of regional wetland protection measures, especially in the core region. Considering that wetland landscape patterns have a strong relationship with flood regimes in Dongting Lake [64], the results were of significance for regional flood risk analysis. In addition, the degree of forest fragmentation decreased and then increased, the landscape structure tended to be complex, and the overall degree of aggregation was enhanced, indicating the significant benefits of the project of returning farmland to the forest in the study area [65]. The changes in each landscape metric were closely related to the implementation of regional policies [66]. With the economic development, the area of the impervious surface showed a rapid expansion, resulting in the rise of landscape fragmentation, especially for the regions around the Lake. The PLAND of the impervious surface increased rapidly due to urbanization development. In the recent 30 years, driven by economic development and ecological restoration, the aggregation of forest landscape patches showed a decrease, suggesting the transition of forest and farmland. At the same time, the urbanization of DTLR increased rapidly. Although the area of cropland continued to decline, the intensification showed an increasing trend. We also found that carbon storage, GPP, water conservation, and crop yield overall increased (Figure 7). Forest carbon storage increased annually, which was mainly attributed to the increase of reforestation and conversion of cropland to forests, which also led to higher total GPP. However, carbon storage in shrubland, grassland, and croplands declined, which was caused by the decline in the area of these land covers. Water conservation has also improved annually since 2007, also due to the impacts of man-made measures such as returning farmland to forest, vigorous ecological restoration, and protection projects. Crop yields showed an upward trend. An important reason for this increase was the mechanization and intensive management of agriculture in DTLR. Despite the decrease in planted area, the continuous improvement in scientific farming techniques (e.g., variety optimization) and management (e.g., intensive farming and nutrient management) contributed to the continuous increase in crop yield. In general, it can be seen that the ecosystem service capacity of DTLR was increasing, and reasonable anthropogenic regulation and measures were conducive to the sustainable development of DTLR [67]. The trade-offs and synergies between different ecosystem services varied considerably. There was a certain synergistic relationship between crop yield and water conservation, and the overall correlation was positive, but the correlation coefficient (r value) was small, possibly because crop yield was mainly influenced by agricultural measures such as irrigation [68]. Crop yield and GPP/carbon storage showed a clear synergistic relationship, which was mainly determined by the close relationship between C3 and C4 plants and GPP/carbon stock [69; 70]. The correlation between carbon stock and water conservation was weak, but the overall synergistic effect was mainly because water conservation directly benefited vegetation and crops, indirectly affecting the growth of carbon stock. There was a strong synergistic relationship between GPP and water conservation in the surrounding forest regions, while there was a clear trade-off in the center of lake regions. This relationship was due to the synergistic relationship between vegetation and water conservation, as the increase in water conservation capacity indicated that vegetation and water resources were sufficient and conducive to vegetation growth. In the center lake region,the increase in water region was accompanied by a sharp decrease in croplands, which led to a decrease in GPP and thus a trade-off relationship [71; 72].