Impact of Reforestation Programs on Regional Carbon Budget Trajectories
DOI:
https://doi.org/10.5281/zenodo.22812660Keywords:
reforestation, afforestation, carbon sequestration, remote sensing, aboveground biomass, carbon budget, additionality, permanence, land-use change, GEDI lidarAbstract
Large-scale reforestation and afforestation programs are widely promoted as a near-term climate mitigation option,
yet independent, remote-sensing-based accounting of how much carbon such programs actually remove beyond
what would have occurred under continued land degradation remains scarce. We combined a 13-year (2011-2023)
archive of Landsat-derived land-cover change, GEDI spaceborne lidar aboveground biomass density, and 214
permanent forest inventory plots to reconstruct the carbon stock trajectory of a 215,000 ha reforestation program
spanning lowland, mid-elevation and highland strata of an 820,000 ha regional landscape, and compared it against
a matched-pixel synthetic-control counterfactual representing the land-use trajectory the program area would
plausibly have followed in the program's absence. The program's aboveground-plus-belowground carbon stock
increased by 4.55 Tg C over the study period (area-weighted mean accumulation rate 3.2 Mg C ha-1 yr-1), while the
counterfactual stratum continued to lose carbon, declining by 0.86 Tg C over the same interval, yielding a gross
additionality of 5.41 Tg C (19.8 Tg CO2-equivalent) attributable to the program. Accumulation rates differed sharply
by intervention type, from 4.8 Mg C ha-1 yr-1 in fast-growing exotic plantations to 2.0 Mg C ha-1 yr-1 (rising from 1.4
to 2.6 over the period) in assisted natural regeneration on highland exclosures. When realized and projected
permanence losses from fire (affecting 4.1% of the reforested area at least once) and a 2015-2017 regional drought
were discounted, net attributable removal fell by approximately 11% to 4.83 Tg C (17.7 Tg CO2-equivalent), a mean
annual rate of 1.65 Tg CO2-equivalent yr-1. Exotic plantations delivered the fastest early gains but the lowest
disturbance-adjusted retention, while assisted natural regeneration delivered the slowest gains but the highest
retention and the smallest divergence from its confidence interval. These results indicate that reforestation
programs can generate substantial, remotely verifiable additionality relative to a degrading baseline, but that
program-level sequestration estimates that ignore counterfactual land-use trajectories and permanence risk are
likely to overstate net climate benefit, and that intervention type materially changes the trade-off between
accumulation speed and durability.
Keywords: Large-scale reforestation and afforestation programs are widely promoted as a near-term climate mitigation option,
yet independent, remote-sensing-based accounting of how much carbon such programs actually remove beyond
what would have occurred under continued land degradation remains scarce. We combined a 13-year (2011-2023)
archive of Landsat-derived land-cover change, GEDI spaceborne lidar aboveground biomass density, and 214
permanent forest inventory plots to reconstruct the carbon stock trajectory of a 215,000 ha reforestation program
spanning lowland, mid-elevation and highland strata of an 820,000 ha regional landscape, and compared it against
a matched-pixel synthetic-control counterfactual representing the land-use trajectory the program area would
plausibly have followed in the program's absence. The program's aboveground-plus-belowground carbon stock
increased by 4.55 Tg C over the study period (area-weighted mean accumulation rate 3.2 Mg C ha-1 yr-1), while the
counterfactual stratum continued to lose carbon, declining by 0.86 Tg C over the same interval, yielding a gross
additionality of 5.41 Tg C (19.8 Tg CO2-equivalent) attributable to the program. Accumulation rates differed sharply
by intervention type, from 4.8 Mg C ha-1 yr-1 in fast-growing exotic plantations to 2.0 Mg C ha-1 yr-1 (rising from 1.4
to 2.6 over the period) in assisted natural regeneration on highland exclosures. When realized and projected
permanence losses from fire (affecting 4.1% of the reforested area at least once) and a 2015-2017 regional drought
were discounted, net attributable removal fell by approximately 11% to 4.83 Tg C (17.7 Tg CO2-equivalent), a mean
annual rate of 1.65 Tg CO2-equivalent yr-1. Exotic plantations delivered the fastest early gains but the lowest
disturbance-adjusted retention, while assisted natural regeneration delivered the slowest gains but the highest
retention and the smallest divergence from its confidence interval. These results indicate that reforestation
programs can generate substantial, remotely verifiable additionality relative to a degrading baseline, but that
program-level sequestration estimates that ignore counterfactual land-use trajectories and permanence risk are
likely to overstate net climate benefit, and that intervention type materially changes the trade-off between
accumulation speed and durability.
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