Temporal and spatial variation characteristics and driving forces of stable grassland net primary productivity in the northern slope of Tianshan Mountains economic zone

Grassland is an important vegetation type on the northern slope of the Tianshan Mountains economic zone and is extremely sensitive to climate change and human activities. The grassland NPP can reflect the carbon sequestration capacity of grassland and is an important indicator for evaluating grassland ecosystems. We evaluated remote sensing NPP data combined with meteorological data, terrain data, and human activities characterized by nighttime light index, using methods such as univariate linear regression analysis, geographic detectors, and spatial correlation. We comprehensively analyzed temporal and spatial changes and driving forces of grassland NPP on the northern slope of the Tianshan Mountains economic zone from 2001－2020. The result showed that: 1) During the study period, the NPP of stable grassland in the study area showed an increasing but fluctuating trend. 2) The temperature tended to increase and precipitation tended to decrease in the stable grassland area. Temperature and precipitation were the main factors influencing grassland NPP changes, with precipitation showing a stronger effect. The relationship between grassland NPP and temperature, or between grassland NPP and precipitation showed a larger area of positive correlation, with that of precipitation showing a more significant value. 3) Topography was an important factor that affected the distribution of stable grassland alongside temperature and precipitation. The stable grassland was concentrated in the middle zone from the foothills to the top of the mountain. 4) Areas less affected by human activities tended to form stable grasslands but still exhibited characteristics of increased intensity of human activities and expanded range. Human activities positively affected the growth of grassland NPP under relevant protection policies. Therefore, studying grassland NPP and changes in its driving force can provide theoretical support for grassland development and utilization, carbon cycle, and sustainable development in the northern Tianshan Mountains economic zone.