Development of strategies for joint allocation of cultivated land and ecological land in Tianjin based on system dynamics

Tianjin was prioritized as a functional development region in China, but its cultivated land is seriously polluted and exhausted. This study adopted complex systems modeling to develop a land allocation strategy that allows food production to be secured and land recuperated in Tianjin, where is an optimum development area in the National Main Functional Areas Planning with seriously polluted cultivated land and scarcely reserved land resources. Upon analyzing the subsystems of population, economy, and cultivated land and ecological land, a restoration model, named Tianjin System Dynamics (TSD), was developed to optimize joint allocation of cultivated land and ecological land. Validity test showed that the model had a good stability and the prediction error was < 5%. The model was then used to simulate land allocation between cultivated land and ecological land from 2016 to 2025 for Tianjin under the following strategies:inertial, in-provincial allocation, and inter-provincial allocation of cultivated land resources. The analysis showed that, with the current practice, damaged cultivated land could still be repaired, but only by 2025. Cultivated land could then still be maintained above the red line minimum, and the land ecology could still be preserved. However, food production might not be secured, as the productivity of cultivated land would be pressed to drop to the threshold. The in-provincial allocation of cultivated land resources would alleviate the pressure on cultivated land while still maintaining production above the threshold, but the ecological security of the land would be impaired, the output pressure of cultivated land still be higher than the warning threshold. In contrast, the scenario of the inter-provincial allocation of cultivated land resources could minimize land pressure to below the warning value, and improve land ecological security as a result of its flexibility. The TSD model developed optimized allocation between cultivated land and ecological land for Tianjin, and could be used for land restoration planning for other regions that are lacking in land reserve.