## 3 Results
### Influence of Different Cropland Use Transitions on GPP
#### 3.2.2 Loss of GPP Due to the Cropland Abandonment  
During the study period, the area of abandoned cropland in Guangdong Province remained relatively stable, totaling 92.7 thousand km\({}^{2}\), with an abandonment rate of 13.75% (Figure 7). The most severe abandonment occurred in the WG, particularly in cities like Zhanjiang and Maoming, accounting for a total area of 35.1 thousand km\({}^{2}\). By contrast, cities such as Shenzhen, Zhongshan, and Zhuhai had the least abandoned cropland, with Zhongshan accounting for only 301.87 km\({}^{2}\). It's worth noting that the spatial pattern of cropland abandonment in the PRD exhibited lower abandonment rates in the core area and high rates in the surrounding areas. This pattern may be due to the rapid economic development in the PRD, which created a significant \"siphoning effect\", attracting  
Figure 6: Non-agriculturalization of cropland on GPP in Guangdong province from 1991 to 2020. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Districts**} & \multicolumn{3}{c}{**Area (km\({}^{2}\))**} & \multicolumn{3}{c}{**GPP (10\({}^{4}\))**} & \multicolumn{3}{c}{**Area (km\({}^{2}\))**} & \multicolumn{3}{c}{**GPP (10\({}^{4}\))**} \\ \cline{2-10} \multicolumn{1}{c}{} & **1991–2000** & **2001–2010** & **2011–2020** & **1991–2000** & **2001–2010** & **2011–2020** & **1991–2020** & **1991–2020** \\ \hline \multirow{10}{*}{PRD} & Dongguan & 1158.99 & 469.63 & 361.06 & 57.20 & 22.59 & 19.87 & \multirow{10}{*}{PRD} & \multirow{10}{*}{Stan} & \multirow{10}{*}{Stan} \\  & Foshan & 1361.72 & 757.19 & 635.23 & 75.66 & 43.78 & 42.33 & & \\  & Guangzhou & 2420.80 & 1233.28 & 1015.31 & 104.70 & 56.55 & 52.50 & & \\  & Shenzhen & 627.67 & 334.45 & 285.74 & 25.35 & 12.54 & 11.83 & & \\  & Zhongshan & 687.18 & 383.91 & 324.66 & 30.55 & 17.40 & 16.26 & 28,745.96 & 1240.26 \\  & Zhuhai & 481.80 & 267.52 & 268.34 & 7.00 & 3.67 & 4.10 & & \\  & Huizhou & 2486.67 & 1459.87 & 1288.00 & 99.05 & 63.73 & 67.82 & & \\  & Jiangmen & 2104.44 & 1868.60 & 1531.27 & 79.22 & 71.34 & 75.69 & & \\  & Zhaoqing & 2242.41 & 1505.76 & 1184.45 & 76.23 & 51.53 & 51.75 & & \\ \hline \multirow{10}{*}{EG} & Shantou & 712.80 & 431.87 & 396.04 & 28.08 & 17.67 & 18.96 & \multirow{10}{*}{Stan} & \multirow{10}{*}{Stan} \\  & Shanwei & 1077.09 & 623.03 & 753.06 & 36.94 & 23.22 & 33.22 & \\  & Jieyang & 1592.06 & 991.40 & 863.10 & 65.88 & 40.97 & 45.34 & \\  & Chaozhou & 944.57 & 470.23 & 333.74 & 31.83 & 17.03 & 15.64 & & \\ \hline \multirow{10}{*}{WG} & Zhanjiang & 2970.04 & 3381.26 & 2721.06 & 186.57 & 212.95 & 205.66 & \multirow{10}{*}{Stan} & \multirow{10}{*}{Stan} \\  & Yangjiang & 1773.93 & 1524.91 & 928.59 & 61.19 & 59.63 & 43.54 & 19,787.06 & 1056.41 \\ \cline{1-1}  & Maoming & 2636.22 & 2334.55 & 1516.52 & 103.76 & 100.50 & 82.61 & & \\ \hline \multirow{10}{*}{NG} & Meizhou & 2693.25 & 1149.06 & 1270.54 & 73.08 & 33.74 & 51.18 & \multirow{10}{*}{Stan} & \multirow{10}{*}{Stan} \\  & Yunfu & 1675.31 & 1187.77 & 706.88 & 41.43 & 31.00 & 28.23 & & \\ \cline{1-1}  & Shaoguan & 2371.74 & 1210.99 & 1158.23 & 106.58 & 49.14 & 60.63 & 24,987.57 & 891.54 \\ \cline{1-1}  & Qingyuan & 3308.60 & 2057.36 & 1563.65 & 117.00 & 72.53 & 72.69 & & \\ \cline{1-1}  & Heyuan & 2447.41 & 1006.60 & 1180.17 & 72.91 & 32.89 & 48.50 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistics on the area and GPP of cropland non-agriculturalization. many people from surrounding areas to migrate to the core region for non-agricultural activities. This population movement significantly reduced the agricultural labor force in surrounding areas, leading to gradual cropland abandonment and exacerbating the abandonment phenomenon. Throughout the study period, cropland abandonment in Guangdong Province resulted in a decrease in GPP of 21.45 million tons, averaging an annual loss of 0.71 million tons (Table 4). Among them, cropland abandonment in the WG had a significant impact on grain production, directly causing a loss of 10.53 million tons of GPP.