Abstract: Vegetation carbon use efficiency (CUE) is an important indicator for ecosystem carbon sequestration capacity, and for assessing the regional vegetation carbon sink capacity. Based on remote sensing images and DEM data from 2000 to 2020, we analyzed the spatial and temporal variations and influencing factors of vegetation CUE in Fukang forest region on the north slope of Tianshan Mountains. The results showed that vegetation CUE in Fukang forest region ranged between 0.42 and 0.74, with an average annual value of 0.6. CUE value was the highest in the subalpine meadow zone and the lowest in the mid-mountain forest zone. There was obvious vertical zonal differentiation, with a “parabola” distribution pattern that decreased first and then increased with altitude. The patterns of both net primary productivity (NPP) and gross primary productivity (GPP) were opposite with CUE. The regional vegetation CUE showed limited interannual variation (P>0.05). The area with significantly increased CUE only accounted for 8.72% of the total area, which was mainly distributed in the mid-mountain forest zone, indicating that longterm forest management promoted the increase of vegetation CUE in the mid-mountain forest zone. There were no significant interannual changes in vegetation CUE values between non-grazing area and grazing area (P>0.05), indicating that grazing exclusion had a weak impact on vegetation CUE in forest areas. The distribution of CUE had spatial heterogeneity in slope aspect. CUE valve was the highest in sunny slopes both in the low-mountain grassland zone and mid-mountain forest zone, and in half-sunny slope in the subalpine meadow zone. The increase of precipitation, temperature, and NDVI directly reduced CUE, while the increase of evapotranspiration indirectly reduced CUE. Natural factors had less influence on CUE in the grazing exclusion area than that in the grazing area.

Key words: carbon use efficiency, path analysis, net primary productivity (NPP), gross primary productivity (GPP), grazing exclusion