Planted Forests Greened 7% Slower Than Natural Forests in Southern China Over the Past Forty Years

Forests have seen a strong greening trend worldwide, and previous studies have attributed this mainly to land-use conversions such as afforestation. However, for the greening of existing forests, the role of human interventions is unclear. Here we paired neighboring natural and planted forests in Southern China to minimize the differences between the forest types and analyzed the vegetation index EVI2 from Landsat over 1987 to 2021. The EVI2 trends observed in natural forests can be seen as mainly responses to large-scale environmental changes, whereas the difference between the forest types represents the impact caused by human interventions. We found that though the mean EVI2 of planted forests was comparable to that of natural forests, the greening trends were overall 7.0% lower in planted forests. Our results suggest that human interventions associated with planted forests did not accelerate their greening, indicating the necessity for refined policies to enhance future forest greening. General greening of forests has been reported worldwide. While previous studies have tended to attribute forest greening to land-use conversions such as re- and afforestation, the role of human interventions for existing forests is still unclear. The greening trend of natural forests are mainly impacted by environmental changes, whereas those in planted forests are also influenced by human interventions. Therefore, the comparison of greening trends between the two forest types can help quantitatively distinguish the role of human interventions. Here, we paired spatially adjacent natural forests with planted forests in Southern China, and performed a pairwise comparisons of greenness and its trend between the forest types over 1987 to 2021 based on Landsat satellite series. It was found that although their mean greenness was similar, the greening trends of planted forests were 7.0% lower than the natural forests. Thus, human interventions may lead to a weakened greening trend while environmental changes were likely the main driver of greening of existing forests in Southern China. Such distinction of drivers is key for our understanding of the impact of environmental changes, land use and land use change, and for designing policies that put us on a pathway to a more sustainable future. Planted forests showed slightly lower greenness than paired natural forests in Southern China from 1987 to 2021 Over the past 40 years, the greening trends of planted forests were overall 7.0% lower than natural forests in Southern China Environmental change, and not human interventions, was likely the dominant cause of observed greening in Southern China