Abstract
Mature forests are often assumed to approach carbon saturation, yet their role in continued carbon accumulation remains uncertain. Here we show that, across the conterminous USA, carbon accumulation in mature forests, covering ~72% of forest area, is systematically underrepresented by current satellite-derived biomass estimates relative to lidar, forest inventories and ecosystem models. Satellite estimates indicate near-neutral biomass changes over recent decades, whereas forest inventories estimate an increase of 102 TgC yr−1. Repeat lidar and forest inventory measurements reveal widespread structural and carbon growth, including in tall forests. By contrast, satellite estimates fail to capture growth beyond canopy closure, showing little biomass increase once canopy height exceeds ~16 m. This asymmetric bias preferentially detects losses over gains yielding a weaker inferred land carbon sink. These findings reveal a critical observational gap in carbon dynamics in mature forests, suggesting that the land carbon sink may be systematically underestimated and highlighting the need for Earth observations sensitive to forest structure and their integration with forest inventories and ecosystem models.
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Subjects
- Carbon cycle
- Forest ecology
Data availability
All datasets used in this study are publicly available. The ESA CCI Biomass product is available at https://catalogue.ceda.ac.uk/uuid/02e1b18071ad45a19b4d3e8adafa2817/; the global AGB products of Xu et al.13, Liu et al.10 and Li et al.55 are available at https://doi.org/10.5281/zenodo.4161694, https://wald.anu.edu.au/global-biomass/ and https://doi.org/10.5281/zenodo.15676177, respectively. NEON airborne lidar data are available at https://www.neonscience.org/data-collection/lidar. Harmonized Landsat–Sentinel (HLS) surface reflectance data are available at https://www.earthdata.nasa.gov/data/projects/hls. National Land Cover Database (NLCD) products are available at https://www.usgs.gov/centers/eros/science/national-land-cover-database. Global Forest Change data are available at https://storage.googleapis.com/earthenginepartners-hansen/GFC-2025-v1.13/download.html. GEDI Level 2A data are available at https://www.earthdata.nasa.gov/data/catalog/lpcloud-gedi02-a-001. FIA inventory and plot data are available at https://research.fs.usda.gov/products/dataandtools/fia-datamart. Source data for Figs. 1–4 are available via Zenodo at https://doi.org/10.5281/zenodo.21192282 (ref. 60).
Code availability
The Python code used to generate Figs. 1–4 is available via Zenodo at https://doi.org/10.5281/zenodo.21192282 (ref. 60). The repository also includes the processed source data used to reproduce each figure and publication-quality exported figures.
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Acknowledgements
The findings and conclusions in this publication are those of the authors and should not be construed to represent any official USDA or US Government determination or policy.
Funding
L.M. and G.H. received support from the NASA Carbon Monitoring System (grant no. 80NSSC25K7221), the NASA GEDI Competed Science Team (grant no. 80NSSC24K0599) and Schmidt Sciences (CLARiTy project, part of the Virtual Institute for the Carbon Cycle). L.M. also received support from the NASA Early Career Investigator Program in Earth Science (grant no. 80NSSC24K1632). H.T. received from Singapore Ministry of Education grant (MOE-T2EP50122-0006). P.C., P.F. and S.S. acknowledge the support from the CALIPSO (Carbon Loss in Plant Soils and Oceans) and CLARiTy projects, both funded by Schmidt Sciences. R.D. and M.H.N. received support from the NASA GEDI contract no. NNL15AA03C. X.W. received support from Maine Space Grant Consortium grant (SG-27-03).
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All authors contributed intellectually to the paper. L.M. and G.H. conceptualized and designed the study, conducted the analyses and drafted the initial paper. H.T. contributed to lidar data processing and interpretation. D.H., P.C., Y.P., S.S., P.F., R.D., M.H.N. and X.W. provided domain expertise, contributed high-level scientific guidance and assisted with data curation. All authors contributed to interpretation of the results and revised the paper.
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Ma, L., Hurtt, G., Tang, H. et al. Widespread carbon accumulation in mature forests remains underestimated by satellite observations.
Nat Ecol Evol (2026). https://doi.org/10.1038/s41559-026-03151-w
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DOI: https://doi.org/10.1038/s41559-026-03151-w
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