[Spatial-temporal Evolution and Quantitative Attribution of Habitat Quality in Typical Karst Counties of Guizhou Plateau].

The purpose of this study was to reveal the spatial and temporal evolution patterns of habitat quality in karst counties of Guizhou plateau and its driving factors and to provide scientific basis for balanced ecological conservation and sustainable development of karst regions. Using DEM data, meteorological data, socio-economic data, and four periods of land use data in 1989, 2003, 2010, and 2020, the InVEST model was used to analyze the spatial and temporal evolution characteristics of habitat quality in Puding County from 1989 to 2020 and to quantitatively detect the driving forces of its spatial divergence. The results were as follows:① Arable land and forest land were the main land use types in Puding County, which constituted the surface cover landscape matrix. Land use changes from 2003-2010 were the most significant, among which forest land had the largest increase of 86.42%; arable land was the most severely lost land use type, with an area decrease of 157.57 km2, mainly flowing to forest land and construction land. ② From 1989 to 2020, the average value of habitat quality index in Puding County increased from 0.60 to 0.73. Spatially, the distribution pattern of "high-low-high" was generally from northeast to southwest, with the high value areas of habitat quality mainly distributed in the woodland and grassland areas in the northeast and the low value areas concentrated in the construction land in the central and south areas. ③ Land use type was the primary factor affecting the spatial and temporal distribution of habitat quality, with an explanation of 91.00%. In the interaction detection, the interaction of any two influencing factors was greater than that of individual factors alone, and the interaction between land use type and average annual precipitation was the strongest, reaching 96.00%; the interaction with lithological factors reached 94.00%, with natural and human factors jointly dominating the spatial and temporal changes in habitat quality. From the results of this study, we concluded that the habitat quality of Puding County was generally good from 1989 to 2020, and the relationship between land use type changes and habitat quality was close. Optimizing the land use structure and reducing the influence of human activities are important to improve the habitat quality of Puding County.

Unexpected response of terrestrial carbon sink to rural depopulation in China.

China is experiencing large-scale rural-urban migration and rapid urbanization, which have had significant impact on terrestrial carbon sink. However, the impact of rural-urban migration and its accompanying urban expansion on the carbon sink is unclear. Based on multisource remote sensing product data for 2000-2020, the soil microbial respiration equation, relative contribution rate, and threshold analysis, we explored the impact of rural depopulation on the carbon sink and its threshold. The results revealed that the proportion of the rural population in China decreased from 63.91 % in 2000 to 36.11 % in 2020. Human pressure decreased by 1.82% in rural depopulation areas, which promoted vegetation restoration in rural areas (+8.45 %) and increased the carbon sink capacity. The net primary productivity (NPP) and net ecosystem productivity (NEP) of the vegetation in the rural areas increased at rates of 2.95 g C m-2 yr-1 and 2.44 g C m-2 yr-1. Strong rural depopulation enhanced the carbon sequestration potential, and the NEP was 1.5 times higher in areas with sharp rural depopulation than in areas with mild rural depopulation. In addition, the rural depopulation was accompanied by urban expansion, and there was a positive correlation between the comprehensive urbanization level (CUL) and NEP in 75.29 % of urban areas. In the urban areas, the vegetation index increased by 88.42 %, and the urban green space partially compensated for the loss of carbon sink caused by urban expansion, with a growth rate of 4.96 g C m-2 yr-1. Changes in rural population have a nonlinear impact on the NEP. When the rural population exceeds 545.686 people/km2, an increase in the rural population will have a positive impact on the NEP. Our research shows that rural depopulation offers a potential opportunity to restore natural ecosystems and thus increase the carbon sequestration capacity.