## 3 Results
### Impact of Urban Expansion on Vegetation Distribution Dynamics
For instance, the value of 1115.32 in the fourth column and the third row under \"Grassland\" indicates that a total of 1115.3 km2 of Grassland had transformed into forest by 2021. It should be noted that \"-\" in the table signifies that no transfer occurred from one land category to another. The urban expansion in the Lanxi urban cluster has encroached upon various land types, including cropland, grassland, water bodies, and barren land. Figure 7 illustrates the extent to which urban expansion has affected these land types in different regions. The data reveals significant variability in how different cities have occupied these land cover types during their expansion. Cropland and grassland are the most heavily impacted, indicating that agricultural land and grassland ecosystems have experienced substantial pressure. For instance, urban expansion in Lanzhou and Dingxi has particularly affected cropland, with 45.25 km\({}^{2}\) and 14.94 km\({}^{2}\) being converted, respectively. Similarly, the occupation of grassland in Baiyin and Lanzhou was notable, with 23.69 km\({}^{2}\) and 32.56 km\({}^{2}\) being affected. These figures suggest that agricultural land and grassland resources are under the greatest pressure from urbanization. These are also the main sources of the negative impacts of the Lanxi area. Furthermore, while the occupation of water bodies and barren land is relatively smaller, it is still significant in certain cities. For example, urban expansion in Lanzhou has consumed 4.75 km\({}^{2}\) of water bodies and 4.19 km\({}^{2}\) of barren land, while in Baiyin, 6.56 km\({}^{2}\) of barren land has been occupied. This occupation may be related to urban growth into undeveloped areas or increased utilization of water resources. In summary, urban expansion in the region is primarily focused on the occupation of agricultural and grassland resources, but the impact on water bodies and barren land is also becoming increasingly evident. Figure 7 reveals that the primary source of negative impact on vegetation in the Lanxi urban cluster comes from the loss of grasslands and cropland. In the analysis, we documented the trends in area changes for different land cover types, compared the areas of various types of land surfaces affected by urban expansion, and found that from 2001 to 2021, the urban expansion of the Lanxi urban cluster primarily encroached upon cropland and grassland within the cluster area. The primary land cover type in the Lanzhou urban cluster is grassland, followed by cropland. Although there was an increase in grassland area over the study period, the land types predominantly occupied by the expansion of built-up areas were grassland and cropland. The total area of cropland and grassland occupied by this expansion accounted for more than 90% of the negatively affected vegetation area. This extensive conversion underscores why the negative impact on vegetation has surpassed the positive effects. From 2001 to 2021, the urban expansion of the Lanxi urban cluster occupied an area of 85.72 km\({}^{2}\) of grassland and 87.78 km\({}^{2}\) of cropland. However, due to land type conversion, from 2001 to 2021, 44.43 km\({}^{2}\) and 26.08 km\({}^{2}\) of urban land were converted to grassland and cropland, respectively. Among the main cities experiencing urban expansion, Lanzhou exhibited the largest expansion area, with the greatest area of cropland and grassland being encroached upon. Specifically, 45.25 km\({}^{2}\) of cropland and 32.56 km\({}^{2}\) of grassland were converted to construction land. The next was Baiyin, whose expansion occupied 13.56 km\({}^{2}\) of cropland and 23.69 km\({}^{2}\) of grassland. Dingxi in the Lanxi urban cluster also encroached upon a considerable amount of cropland and grassland, with 14.94 km\({}^{2}\) and 9 km\({}^{2}\), respectively.