There is an urgent need to explore a novel field to enhance the comprehensive research of cultivated land use transition. Simultaneously, few studies on the coupling research of cultivated land use pattern and function transition have been done so far. Based on these considerations, we aim at presenting a novel field of cultivated land use transition research from the perspective of cultivated land use vulnerability to biological disasters (CLUVBD). First, this study integrates the motivations of profit-seeking and loss-avoiding and induced substitution in agricultural production from the perspective of agricultural biological disasters, thus establishing a theoretical framework of the transition in CLUVBD based on the socio-ecological interaction logic of "socio-economic environment - cultivated land use - feedback of biological disasters - disaster prevention and control". Then, CLUVBD transition was diagnosed and analyzed at the national, regional, and provincial levels between 1988 and 2017 using the logic growth model, single-factor simulation, and panel data regression model. Results show that CLUVBD transition is remarkable at both national and provincial levels. The value of CLUVBD at the national level firstly increased from 15.33% to 22.45% in 1988-2009 and then decreased from 22.40% to 19.49% in 2010-2017. The transition at the provincial level shows two typical pathways. Decrease of CLUVBD is mainly derived from the decline in exposure due to the narrowing of urban-rural income ratio and the increase in cultivated land area per capita of agricultural employee, followed by the increase of adaptive capacity due to the increase of retrieved grain loss ratio and the failure ratio of biological disaster prevention. Meanwhile, as CLUVBD value turns to decrease, the sensitivity increases, which is mainly due to the decline in crop diversity and the increase of fertilizer use intensity in cultivated land. The study demonstrates that CLUVBD is expected to become a novel field of comprehensive study on cultivated land use transition. In addition, the policy proposals on CLUVBD control are also discussed.

Based on the panel data of China's inter-provincial grain production from 1996 to 2018, the modified gravity model was used to accurately calculate the spatial correlation of grain production and build a spatial correlation matrix. Firstly, the structural characteristics of grain production spatial correlation network were investigated from three aspects: overall characteristics, individual characteristics and block model through the social network analysis method (SNA) and then, the quadratic assignment procedure (QAP) method was used to explore its formation mechanism. The study found that: (1) The level of inter-provincial spatial correlation of grain production increases in fluctuation, but there is still room for improvement. The network structure shows better stability and accessibility, and the spillover effect has multiple superposition. (2) The inter-provincial spatial correlation network of grain production presents a significant core-edge distribution pattern of major grain-producing areas, main-sales areas and grain balance areas, and the major grain-producing areas are at the core position in the network, and the grain main-sales areas and the balance areas are at the edge. (3) The spatial correlation network of grain production can be divided into four functional blocks, namely, net spillover block, main beneficial block, broker block and bidirectional spillover block, and the spillover effect between blocks are featured by obvious gradient transmission. (4) The combined effect of natural endowment conditions and socio-economic factors promote the formation of spatial correlation network of grain production. The geographical proximity, differences in economic development, rural labor scale, mechanical service scale and cultivated land resources, and the similarity of precipitation and sunshine hours have significant impacts on the formation of spatial correlation network of grain production. The conclusions are of great significance for us to grasp the spatial transmission mechanism, realize the cross-regional coordination and formulate differentiated grain policies in China.

Being a key ecological security barrier and production base for grassland animal husbandry in China, the balance between grassland forage supply and livestock-carrying pressure in China's pasture regions directly affects grassland degradation and restoration, thereby impacting grassland ecosystem services. This paper analyzes the spatiotemporal variation in grassland vegetation coverage, forage supply, and the balance between grassland forage supply and livestock-carrying pressure in China's pasture regions from 2000 to 2015. We then discuss the spatial pattern of grassland ecological conservation under the impacts of grassland degradation and restoration, and livestock-carrying pressure. Over the last 16 years, the total grassland area in China's pasture regions decreased by 16,000 km², with vegetation coverage degraded in 6.7% of grasslands but significantly restored in 5.4% of grasslands. The provisioning of forage by natural grassland mainly increased over time, with an annual growth rate of approximately 0.3 kg/hm², but livestock-carrying pressure also increased continuously. The livestock-carrying pressure index (without any supplementary feeding) reached as high as 3.8. Apart from the potential livestock carrying capacity in northeastern Inner Mongolia and the central Tibetan Plateau, that in most parts of China's pasture regions is currently overburdened. Considering the actual supplementary feeding during the cold season, the livestock-carrying pressure index is about 3.1, with the livestock-carrying pressure mitigated in central and eastern Inner Mongolia. Assuming full supplemental feeding in the cold season, livestock-carrying pressure index will fall to 1.9, thus significantly alleviating pressure in Inner Mongolia and the Tibetan Plateau. Based on these data, we propose different conservation and development strategies to balance grassland ecological conservation and animal husbandry production in different regions, namely nature reserves, pastoral areas, semi-farming and semi-pastoral areas, and farming areas, according to prevailing patterns of grassland ecological protection.