## 4 Discussions  
### Optimal Land Management Practices  
Land management practices (LMPs) refer to any administration strategies on lands, including activities related to the benefit of land use and development targeting individual, collective, and economic purposes, which may vary under different ecosystem contexts. In an urban context, LMPs may focus on satisfying commercial or residential needs for the economy while maintaining an ecological benefit for a healthy urban environment [57]. In an agroeocosystem, most LMPs target to promote food or crop production, e.g., by weed removal, fertilizer application, and irrigation [58]. Wood production and soil erosion control are among the targets in a forest ecosystem [59]. Vegetation in urban ecosystems captures atmospheric carbon, indicated by NPP. To maximize the carbon capture, land management strategies need to be adjusted to fit environmental conditions. The effectiveness of LMPs from the perspective of the carbon uptake potential can be computed as the difference between the capacity of carbon uptake with and without the implementation of the LMPs.  
While those environmental factors, e.g., temperature, precipitation, or landform/soil classes may update vegetation productivity and increase carbon capture, they are much more difficult, if not impossible, to be implemented in practice. Transformation of land use and land cover (LULC), for example, from croplands to forests has shown ecological benefit and can potentially capture more atmospheric carbon [60]. However, such practices are not widely acceptable due to food security in an urban context [23]. Reversing impervious land to croplands/forests is also discouraged, given the need for urban expansion to support economic development. This study emphasizes that the strategy to increase vegetation productivity should resort to optimizing LMPs without changes in LULC. Such consideration reflects the goal of sustainable urban development satisfying both ecological and socio-economic needs.  
The LMPs to improve carbon uptake optimize three targets: vegetation proportion, vegetation density, and vegetation complexity [21] (Table 4). Increasing the proportion of vegetation cover can be realized simply by extending vegetated area and urban green space; for example, through planting more trees in barren or discarded lands However, the potential is limited considering unused lands are rare in modern cities. A more promising strategy introduced previously to increase proportion of urban greenspace is to create green walls and roofs in new buildings by applying an ecological urban index called biotope area factor [61]. In addition, the strategies by optimizing vegetation cover density and vegetation landscapes are more welcome and recommended since they promote vegetation growth without altering land use.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Items** & **Forests** & **Croplands** & **Urbanized** & **Rangelands** & **Average \({}^{\#}\)** & **Total** \\ \hline Land area (\(\times 10^{8}\) m\({}^{2}\)) (\%) & 36.7 (52.3) & 6.4 (9.1) & 26.0 (37.1) & 1.1 (1.5) & / & 70.2 (100) \\ NPP flux (gC m\({}^{-2}\)yr\({}^{-1}\)) & 883.3 & 521.5 & 281.5 & 608.7 & 622.2 & / \\ Carbon potential flux (gC m\({}^{-2}\)yr\({}^{-1}\)) & 60.4 & 209.4 & 353.9 & 249.2 & 185.0 & / \\ Total NPP (\(\times 10^{11}\) gC yr\({}^{-1}\)) (\%) & 32.4 (74.1) & 3.4 (7.7) & 7.3 (16.8) & 0.6 (1.5) & / & 43.7 (100) \\ Total potential (\(\times 10^{11}\) gC yr\({}^{-1}\)) (\%) & 2.2 (16.9) & 1.3 (10.3) & 9.2 (70.7) & 0.3 (2.0) & / & 13.0 (100) \\ Ratio (Carbon potential/NPP) & 0.07 & 0.40 & 1.25 & 0.41 & 0.30 & 0.30 \\ \hline \end{tabular} \({}^{\#}\) The averaged NPP column and carbon potential flux is area-weighted from the land cover types.  
\end{table}
Table 3: Contribution of carbon potential in different land (vegetation) cover classes in GGA.