Impacts of human activities on net primary productivity of vegetation in Guizhou Province from 2000 to 2014

Karst rocky desertification, the most significant ecological problem in Guizhou Province, southwestern China, is primarily driven by human activities in recent years. As a main signature of this phenomenon, vegetation degradation can be reflected by Net Primary Productivity (NPP), which is a key indicator of production capacity of the terrestrial ecosystem. However, so far less quantitative analyses have been made on the impact of human activities on vegetative NPP in Guizhou Province, which is of great significance for coordinating the relationship between human activity and karst rocky desertification control, as well as improving the quality of karst eco-environment. In this study, we established the Relative Contribution Index (RCI) by using actual NPP (ANPP) based on MODIS MOD17A3 data and potential NPP (PNPP) based on the Carnegie Ames Stanford Approach (CASA) model. Then, in combination of the classification of karst landform proportion, we analyzed the spatial-temporal variations of human activities and their influence on NPP in Guizhou Province from 2000 to 2014. Finally we discussed the contributions rates of different factors for human activity on RCI values using Correlation Analysis (CA). The results indicate that human activities in Guizhou Province promoted the increase of NPP, and the degree of the influence first increased and then decreased from 2000 to 2014. In the southeastern and northern edges of Guizhou Province where the proportion of karst landform area is less than 51.8%, the RCI value fluctuated violently and was greatly affected by human activities. However, in the areas where the proportion of karst landform is higher than 51.8%, the impact of human activities was relatively weaker and the variation was gentler. Additionally, human activities in the northeast, central and western parts of Guizhou Province generally had negative effects on the ecological environment from 2000 to 2014, while the effects in the southeastern and northern marginal areas were positive. In the past 15 years, the positive impact of human activities on the ecological environment in most areas of central and northern Guizhou Province has increased, while the degree of human intervention in the southwestern marginal area has decreased and the negative interference of human activities in some areas in the southeastern part has increased. Moreover, the CA results show that the total plant coverage area of crops, total agricultural output value, proportion of urban population, gross domestic product per head, disposable income of urban residents and highway mileage had significant positive correlation with RCI values of Guizhou Province during the period from 2000 to 2014, while the population density had a significant negative correlation with RCI values. Among them, agricultural activities played an important role in the negative impact of human activities. On one hand, urbanization and economic development promoted the growth of livable demand and strengthened the positive impact of human activities on the ecological environment; on the other hand, they also expanded the demand for resource development, transportation and public infrastructure. Thus, the destructive interference of human activities on the ecological environment was unavoidable. In addition, compared with other areas, the areas with moderate karst landforms were more likely to be negatively affected by agricultural production, urban development and highway construction.