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Understanding the ecological constraints of limiting the magnitude and the allocation of carbon density is critical for executing adaptive forest management programs and upgrading the size of carbon sinks. Taking a typical karst mountainous region Guiyang City as a case study area, this study computed the biomass of different forest types using the volume–biomass equations and mapped the carbon density distribution of forests. Furthermore, the random forest algorithm and spatial autoregression model were adopted to reveal the effects of site conditions on carbon density in karst forests. The results indicate that the forest ecosystems of Guiyang City had a high carbon sequestration potential, and there was a significant difference in the carbon density of forests in terms of space dimensions. Road density, 0 cm cation exchange capacity, and soil parent materials were the dominant factors determining the spatial distribution of homogeneous units with different levels of carbon density. This study underlines the urgency adapting to the growing conditions of forests in terms of complex site conditions, and provides a scientific basis for optimizing forest management practices, to maintain their carbon sequestration capacity under urbanization pressure and fragile habitats.

Rapid urban expansion has significantly altered the regional landscape pattern, posing a serious threat to the sustainable development of natural and social ecosystems. By using landscape patterns indices and an area transfer matrix, this study analyzed the spatial-temporal changes of landscape patterns in the karst mountainous cities of southwest China from 2000 to 2020, by taking the central urban area of Guiyang City (CUAG) as the study area. This study explored the spatial and temporal driving factors of landscape pattern changes by using stepwise multiple linear regression and geographic detector methods. The results show: (1) CUAG’s landscape types altered changed drastically, with the area of forestland and construction land rapid increment and cultivated land decrement significantly. (2) The patches of construction land and forestland tended to be aggregated, the degree of fragmentation was reduced, and the shape was complex; cultivated land fragmentation was intensified. The connectivity of the landscape was improved, while the level of landscape diversity declined, the trend of landscape homogenization was obvious. (3) Socioeconomic and geographical endowment drivers have determined landscape pattern changes. The findings of this study may be used to interpret other similar landscapes worldwide and may imply the protection of urban ecosystem and sustainable development.