Abstract: Evaluating the effectiveness of forest restoration projects is crucial for designing adaptive restoration strategies. However, existing studies have primarily focused on ecological outcomes while overlooking cost inputs. This gap can lead to increased uncertainties in restoration planning. Here we investigated forest dynamics in China’s Upper Yangtze River Basin (UYRB) using kernel Normalized Difference Vegetation Index (kNDVI), Leaf Area Index (LAI), Gross Primary Productivity (GPP), Ku-band Vegetation Optical Depth (Ku-VOD) time series and climate data from 1982 to 2020. Subsequently, we employed a residual trend analysis integrating temporal effects to determine the relative contributions of climate change and human activities to forest dynamics before and after the implementation of forest restoration engineering in 1998. Additionally, we developed an Afforestation Efficiency Index (AEI) to quantitatively assess the cost efficiency of afforestation projects. Results indicated that forest in the UYRB showed sustained increases during 1982–2020, with most areas experiencing greater growth after 1998 than before. Temporal effects of climatic factors influenced over 42.7% of the forest, and incorporating time-lag and cumulative effects enhanced climate-based explanations of forest variations by 1.61–24.73%. Human activities emerged as the dominant driver of forest dynamics post 1998, whereas climate variables predominated before this period. The cost-effectiveness of forest restoration projects in the UYRB typically ranges from moderate to high, with higher success predominantly observed in the northeastern and eastern counties, while the central, western, and northwestern counties mainly showed relatively low efficiency. These findings stress the need for assessing forest restoration outcomes from both ecological and cost perspectives, and can offer valuable insights for optimizing the layout of forest restoration initiatives in the UYRB.

Key words: Forest restoration, Driving force analysis, Temporal effects, Afforestation efficiency