Decoupling and partitioning the effect of climate and afforestation on long‐term vegetation greening in China since the 1990s

AbstractVegetation is an essential component of the Earth's surface system, and is a clear indicator to global climate changes. Understanding the long‐term characteristics of vegetation variations and their relationship to climate and human activities is important for regional sustainable development and ecological construction. In this study the ensemble empirical mode decomposition, the breaks for additive seasonal and trend algorithm and trend analysis were applied to obtain the spatiotemporal characteristics of the long‐term interannual normalized difference vegetation index in China. Partial least squares‐structural equation modeling and geographically weighted regression were used to separate the effects of climate and human activities on vegetation greening and achieve the partitioning of these driving forces. The results suggested that vegetation growth in China experienced an abrupt change in 1995, there was obvious vegetation ‘browning’ during 1990–1995, and noticeable vegetation recovery from 1996 to 2018 (slope = 0.129/yr, p = 0.009). Spatially, vegetation ‘greening’ was occurred in central and southern China, reflecting the positive effect of ecological restoration projects on vegetation growth. Climate was a directly main driving force for vegetation greening in China. It played a positive role in South China, but had a negative effect in Northwest China. Improving socio‐economic conditions had a slightly negative impact on vegetation greening, while afforestation played a direct and obvious role in promoting vegetation growth, especially in Northwest China. Furthermore, afforestation and socio‐economic conditions would also indirectly affect vegetation growth by directly influencing the local microclimate, and the indirect effect of them on vegetation growth was far greater than its direct impact in some cases; therefore, research attention should be paid to the indirect effects of these driving forces on vegetation growth. There was obvious spatial heterogeneity in the effects of different forces on vegetation greening in China, and the dominant driving force of vegetation change in each geographical region also differed.