Distinguishing dominant drivers on long-term vegetation dynamics across China considering time-lag and accumulation...

Accurate attribution of vegetation dynamics is essential to ensure the conservation, restoration and sustainability of terrestrial ecosystems. However, due to the time-lag and accumulation effects of vegetation responding climate change and anthropogenic activities, traditional statistical methods often fail to capture the nonlinear impacts, and leading to ongoing debates about the relative contributions. In this paper, we explored the spatiotemporal dynamics of various vegetation types across China from 1982 to 2022 employing the Normalized Difference Vegetation Index (NDVI). Then we integrated machine learning methods with an improved residual trend approach to precisely quantify the contributions of anthropogenic activities and climate change on vegetation dynamics. Our results indicated that (i) the annual increase in NDVI has amounted to 0.012 per decade across all vegetated areas in China, and 57.0 % of the vegetated areas underwent notable greening trends in the past four decades. (ii) Over 92 % of vegetation areas exhibited climatic temporal effects in China, mainly with 1 to 2-month accumulation in response to temperature and precipitation, and 1 to 3-month lag in responses to sunshine duration. Furthermore, forest exhibited the longest time-lag (1.36 months) and accumulation months (0.93 months) to precipitation, whereas grassland responded the shortest time-lag (0.13 months) and accumulation months (0.59 months) to temperature. (iii) Anthropogenic activities predominantly influence 69.7 % of vegetation dynamics in China during 2000-2022. Our improved approaches can diminish quantization uncertainty and show higher accuracy (R² = 0.97 and RMSE = 0.02). Our study provides valuable insights for understanding vegetation dynamics and informs ecological protection and restoration efforts in China.