Background Under the double influence of ecological construction and energy development, the ecological environment in northern Shaanxi is facing great pressure. Quantitative study on the human impact on net primary productivity (NPP) of vegetation, which is the basis of quantitative study on human impact on regional ecosystem, can lay a foundation for trade-off analysis between regional soil and water conservation services and socio-economic development. Therefore, it is necessary to quantitatively study the impact of human activities on NPP of vegetation in northern Shaanxi.

Methods Based on the normalized differenced vegetation index (NDVI) data which was validated, the vegetation coverage data and the climate data which was resampled to 250 m resolution, the NPP of vegetation and its human impact value were calculated using CASA model and the human impact assessment model respectively. Then the spatio-temporal variation of human impact on NPP was analyzed using the Theil-Sen trend degree. Finally, the specific human factors were made an empirical analysis based on the statistics data and land use degree data.

Results 1) The impact of human activities on vegetation NPP in northern Shaanxi showed an annual trend of increasing positive impact and decreasing negative impact from 2001 to 2014. The negative impact decreased by 3.40 g/(m²·a) and the positive impact increased by 0.91 g/(m²·a). Especially in 2013, the positive impact of human activities on vegetation NPP was the strongest. 2) The positive and negative effects of human activities on vegetation NPP were mainly increasing trend. The positive trend of human impact was obvious in the central and eastern regions, the highest positive trend value was 40.39 g/(m²·a), and the positive effects of significant and significant changes were mainly located in the hilly and gully region along the Kuye River in Fugu county and Shenmu county, as well as the Yuxi River Wetland at the junction of Yuyang district and Mizhi county. While the negative trend of human impact was obvious in the northwest and southern regions, the highest negative trend value was -37.17 g/(m²·a), and the negative effects of significant and significant changes were mainly distributed in the northern energy area and the farming and pastoral areas in the middle east. 3) The "Grain for Green Project" was the main reason for the positive influence of vegetation NPP. The increase of the proportion of energy industry and the urban expansion were the main reasons for the gradual increase of human negative influence. And there was not a simple linear relationship between the human impact of vegetation NPP and land use degree.

Conculsions The human positive impact of vegetation NPP shows an increasing trend, while the negative impact decreasing. The effect of ecological governance has been obvious, but the human negative impact is still stronger in the northern energy area and the southern tableland agricultural area, thus the ecological governance should be further strengthened.