Recent widespread forest expansion and densification in Southwest China

Abstract

Large-scale afforestation and forest conservation policies have been widely implemented in Southwest China over past decades. These efforts have significantly protected the remaining long-established forests in the region and greatly expanded forested areas. Utilizing nearly 30 years of satellite time-series data, we reveal that the region’s enhanced carbon sequestration (3 × 10¹² g·C annually) is primarily driven by crucial changes in forest structure and age, occurring alongside a nearly 120 % increase in forested land area. We observe that dense forests maintain a rapid growth rate of approximately 2.5 % annually for carbon sequestration in the initial years after establishment. However, this growth rate decelerates with increasing apparent forest age. Meanwhile, the densification (modeled as an increasing forest probability) rate of forests reaches its peak growth during the 10-20 year period, sustaining a high annual growth rate of about 1.8 %. We also find that improvements in forest structure, particularly the increasing of forest canopy density and apparent forest age coupled with a notable reduction in forest fragmentation, are also the main driving factors for the enhanced carbon sequestration capacity. Based on these findings, we conclude that forest restoration policies in Southwest China have been successful not only in facilitating large-scale forest growth in Southwest China but, more critically, in promoting the structural maturation (e.g., densification and reduced fragmentation) that is essential for enhancing the region’s carbon sink capacity and its resilience.

Keywords

Reforestation policy; Forest expansion and densification / Carbon sequestration capacity / Southwest China

Data availability statement

Landsat 5/7/8 is available at https://www.usgs.gov/landsat-missions/. NASADEM is available at https://lpdaac.usgs.gov/products/nasadem_hgtv001/. MOD17A3HGF is available at https://lpdaac.usgs.gov/products/mod17a3hgfv061/. NPP data is available at 10.3974/geodb.2019.03.02.V1/. MCD12Q1 is available at https://lpdaac.usgs.gov/products/mcd12q1v061/. Precipitation, temperature, potential evapotranspiration, net surface solar radiation, soil moisture datasets are all sourced from ERA5 (https://cds.climate.copernicus.eu/datasets/reanalysis-era5-single-levels). China land cover dataset (CLCD) is available at https://zenodo.org/records/4417810/. SPEI data was collected from the global database of the Standardized Precipitation Evapotranspiration Index (SPEI), SPEIbase 2.9 (https://spei.csic.es/). Climate zones and administrative boundaries were collected from https://www.resdc.cn/.

CRediT authorship contribution statement

Daoming Ma: Writing - original draft, Visualization, Investigation. Yang Yu: Writing - review & editing, Writing - original draft, Supervision, Conceptualization. Ming Gong: Investigation, Data curation. Zhiqiang Zhang: Writing - review & editing, Supervision, Methodology, Investigation. Steven A Kannenberg: Writing - review & editing, Visualization, Validation, Supervision.

Declaration of competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This work was funded by the National Natural Science Foundation of China (Grant No. 42377331). SAK was supported by the U.S. National Science Foundation Division of Environmental Biology award #2331162 and U.S. National Science Foundation Dynamics of Integrated Socio-Environmental Systems award #2408954. Special thanks also go to the editor and the anonymous reviewers for their helpful comments and suggestions.

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