Contributions of climate change to the boundary shifts in the farming-pastoral ecotone in northern China since 1970

Critical transitions of farming-pastoral ecotone (FPE) boundaries can be affected by climate change and human activities, yet current studies have not adequately analyzed the spatially explicit contributions of climate change to FPE boundary shifts, particularly those in different regions and periods. In this study, we present a series of analyses at the point (gravity center analysis), line (boundary shifts detected using two methods) and area (spatial analysis) levels to quantify climate contributions. This was done at a 1-km scale in each ecological functional region during three study periods from the 1970s to the 2000s using climate and land use data. Both gravity center analysis and boundary shift detection revealed similar spatial patterns with more extensive boundary shifts in the northeastern and southeastern parts of the FPE in northern China, especially during the 1970s-1980s and 1990s-2000s. Climate contributions in the X- and Y-coordinate directions and in the directions of transects along boundaries showed that significant differences in climate contributions to FPE boundary shifts existed in different ecological functional regions during the three periods. Additionally, the results in different directions exhibited good agreement in most of the ecological functional regions during most of the periods. However, the values of contributions in the directions of transects along the boundaries (1-17%) were always smaller than those in the X-and Y-coordinate directions (4-56%), which suggests that the analysis in the transect directions is more stable and reliable. Thus, this is an alternative method for detecting the climate contributions to boundary shifts associated with land use changes. Spatial analysis of the relationship between climate change and land use change in the context of FPE boundary shifts in northern China provides further evidence for explanation of the driving forces of climate change. Our findings provide an improved understanding of the quantitative contributions of climate change to the formation and transition of FPE in northern China, which will be essential for addressing current and future adaptation and mitigation measures and regional land use management.