Abstract
As a large carbon pool, global forest ecosystems are a critical component of the global carbon cycle. Accurate estimations of global forest aboveground biomass (AGB) can improve the understanding of global carbon dynamics and help to quantify anthropogenic carbon emissions. Light detection and ranging (LiDAR) techniques have been proven that can accurately capture both horizontal and vertical forest structures and increase the accuracy of forest AGB estimation. In this study, we mapped the global forest AGB density at a 1-km resolution through the integration of ground inventory data, optical imagery, Geoscience Laser Altimeter System/Ice, Cloud, and Land Elevation Satellite data, climate surfaces, and topographic data. Over 4000 ground inventory records were collected from published literatures to train the forest AGB estimation model and validate the resulting global forest AGB product. Our wall-to-wall global forest AGB map showed that the global forest AGB density was 210.09 Mg/ha on average, with a standard deviation of 109.31 Mg/ha. At the continental level, Africa (333.34 ± 63.80 Mg/ha) and South America (301.68 ± 67.43 Mg/ha) had higher AGB density. The AGB density in Asia, North America and Europe were 172.28 ± 94.75, 166.48 ± 84.97, and 132.97 ± 50.70 Mg/ha, respectively. The wall-to-wall forest AGB map was evaluated at plot level using independent plot measurements. The adjusted coefficient of determination (R2) and root-mean-square error (RMSE) between our predicted results and the validation plots were 0.56 and 87.53 Mg/ha, respectively. At the ecological zone level, the R2 and RMSE between our map and Intergovernmental Panel on Climate Change suggested values were 0.56 and 101.21 Mg/ha, respectively. Moreover, a comprehensive comparison was also conducted between our forest AGB map and other published regional AGB products. Overall, our forest AGB map showed good agreements with these regional AGB products, but some of the regional AGB products tended to underestimate forest AGB density.
Highlights
Global forest ecosystems, which cover 30% of the land surface, play an important role in the global carbon cycle since they sequester atmospheric carbon dioxide and are able to mitigate global warming [1,2]
Since approximately 50% of plant biomass is composed of carbon, accurate estimation of the total Aboveground biomass (AGB) in forest ecosystems is critical for carbon cycle studies from local to global scales [3]
Accurate estimations of the regional to global distribution of forest AGB are of great benefit to improve our understanding of carbon dynamics and quantify anthropogenic emissions caused by deforestation and forest degradation against the background of global climate change [11–13]
Summary
Global forest ecosystems, which cover 30% of the land surface, play an important role in the global carbon cycle since they sequester atmospheric carbon dioxide and are able to mitigate global warming [1,2]. Since approximately 50% of plant biomass is composed of carbon, accurate estimation of the total AGB in forest ecosystems is critical for carbon cycle studies from local to global scales [3]. The amount and distribution of regional to global biomass can provide either initial conditions or validations for ecosystem and biogeochemical models [4–7], which simulate the exchange of carbon and energy between the atmosphere and biosphere. They can provide the baseline of forest carbon stocks for calculating carbon fluxes from deforestation, land cover change, and other disturbances [8,9]. Accurate estimations of the regional to global distribution of forest AGB are of great benefit to improve our understanding of carbon dynamics and quantify anthropogenic emissions caused by deforestation and forest degradation against the background of global climate change [11–13]
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