Spatio-temporal evolution of vegetation net primary productivity in Qilian Mountain National Park and its driving factors

Qilian Mountain National Park plays an important role in water conservation and ecological balance and is an important ecological security barrier in Hexi and even northwest China. In the present study, the NPP estimation model-CASA model and MODIS NDVI remote sensing product were used to calculate NPP values for the 2000 – 2018 period, and univariate linear regression, correlation analysis, meteorological data, and human activities data, were used to analyze the temporal and spatial variation characteristics of NPP in the study area and to investigate relationships between terrain, climate, and human activities. 1) During 2000 – 2018, the NPP of Qilian National Park exhibited an upward trend of fluctuation, with a multi-year average of 167.35 g·(m²·a)^–1. Meanwhile, monthly changes in NPP exhibited increasing trends, and the growth rate was obviously different. Among them, the growth rate of vegetation NPP from May to September was significantly greater than that of other months. 2) Multi-year mean NPP values decreased from southeast to northwest, and the vegetation NPP exhibited obvious seasonal variation, with NPP being highest during summer, followed by autumn, and lowest during winter. 3) Overall, the NPP of Qilian Mountain National Park first increased and then decreased with increasing elevation and slope, and the vegetation NPP of overcast slopes was greater than that of sunny slopes. Compared with temperature, the correlation between vegetation NPP and precipitation was higher, with a correlation coefficient of 0.632 (P < 0.01). When the intensity of human activity reached > 20%, there was an obvious negative correlation between NPP and human activity intensity. In general, topography and climate factors play a decisive role in the determination of vegetation NPP in the study area. The present study provides a reference for scientific evaluation of the ecological management of Qilian Mountain National Park, as well as for the development of ecological policy and management of the ecological environment, and provides relevant theoretical basis for the further realization of the regional natural-economic-social coordination and sustainable development.