Introduction

Over the past millennium, 75 × 106 km2 representing 59 % of primary natural vegetation has been altered by humans to support agriculture, forestry, and other land uses globally1. These activities continue to alter the Earth’s energy balance through changes to terrestrial greenhouse gas fluxes and land surface albedo2. From 2007 to 2016, for example, agriculture, forestry, and other land uses contributed 12.0 Pg of carbon dioxide (CO2) equivalent per year of greenhouse gas emissions, including their associated nitrous oxide (N2O) and methane (CH4) emissions, representing 23 % of all anthropogenic greenhouse gas induced radiative forcing during this period3. From 1700 to 2005, agriculture, forestry, and other land use-induced surface albedo changes resulted in global cooling, with a radiative forcing impact of –0.15 W m–2, offsetting 22 % of the agriculture, forestry, and other land use’s greenhouse gas-induced radiative forcing4. With land use exerting this degree of control on the global climate, many have proposed the adoption of sustainable land use practices as nature-based climate solutions5,6,7,8. In particular, the potential to deliver carbon dioxide removal could make nature-based climate solutions a crucial tool for reversing the effects of climate change and ameliorating those impacts that extend well beyond the 21st century, such as sea level rise. However, our understanding of the net climate impacts of nature-based climate solutions is hampered by the lack of long-term, replicated land use change experiments that measure each of the major radiative forcing budget components.

Here we compile long-term radiative forcing budgets for ten different land uses in the U.S. Upper Midwest to quantify the climate impact of historical deforestation and the adoption of eight nature-based climate solutions, ranging from natural forest regeneration to conservation agriculture. Our continuous measurements of ecosystem carbon (C) stock components, soil nitrous oxide fluxes, and soil methane fluxes span 35 years from 1989 to 2023, with our land surface albedo measurements extending back further from 1984 to 2024. These measurements include soil and root carbon stocks based on 510 large diameter soil cores taken to a depth of 100 cm; soil nitrous oxide and methane fluxes based on 14,568 manual static chamber measurements, which were collected bi-weekly to monthly for over three decades; and land surface albedo measurements based on 47,075 observations from six different high resolution satellite platforms. Using the replicated land use change experiment at the Kellogg Biological Station Long Term Ecological Research site (KBS LTER) we estimate the climate impact of both historical land use change in the region and the future adoption of proposed nature-based climate solutions9.

We scale our results to the ecological region our study site is representative of, U.S. E.P.A. Level III Ecoregion 56, which covers 51.7 × 103 km2 in Michigan and Indiana10 (Fig. 1a; Supplemental Methods). For understanding historical land use change, we supplement the data collected at our site with 113,643 original witness trees that were identified to species, measured for their diameter at breast height, and mapped to exact coordinates in the study area by the U.S. Public Land Survey from 1828 to 1839. These witness trees provide the aboveground biomass data for our historical ecosystem carbon stock budget11. Similarly, for the reforestation scenarios, we supplement the data collected at our site with aboveground biomass data from the U.S. Forest Inventory and Analysis program for a total of 468 plots spread across the study area that met our inclusion criteria12.

The eight nature-based climate solutions studied here (Table S1) include three conservation agriculture land uses, three perennial agriculture/forestry land uses, and two types of ecosystem restoration. The predominant land use in the region, which is row crop agriculture, is represented here by a conventional (CON) corn-soybean-winter wheat rotation (Zea mays, Glycine max, Triticum aestivum). This land use serves as the reference baseline for the nature-based climate solution scenarios, which each play out over a 100-year time frame. The three conservation agriculture land uses include a no-till (NT) system managed with conventional fertilizer and pesticide inputs, a reduced input (RI) system that receives one-third the fertilizer and pesticide inputs, and an organic (ORG) system that receives no external synthetic inputs. The RI and ORG systems also include a winter cover crop and do not have their winter wheat straw harvested, as is done in the CON and NT systems. Three perennial agriculture/forestry land uses have different rotation lengths which include alfalfa (ALF; Medicago sativa), rotated every six years, a poplar plantation (POP; Populus nigra x Populus deltoids and Populus nigra x Populus maximowiczii), harvested every 10 years, and an eastern white pine plantation (PIN; Pinus strobus) harvested every 50 years. Lastly, we studied two types of ecosystem restoration, denoted here as early (ES) and mid- (MS) succession. The ES system is managed with annual prescribed fire each spring while the MS system has been unmanaged and naturally regenerating into second growth temperature deciduous broadleaf forest for approximately 50 years. For the MS scenario’s timeline from 50 to 100 years, as well as for the historical land use change scenario, the late succession (LS) land use serves as a reference for what undisturbed forests transition into, and how the pre-deforestation ecosystems of the study region functioned, respectively. The LS old growth forest studied here is some of the last remaining intact temperature deciduous broadleaf forest in the U.S. Upper Midwest.

Results

Widespread conversion of native vegetation in the region occurred in a brief boom-bust fashion in the latter half of the 19th century, resulting in lasting net positive radiative forcing11,13 (1626 ± 44 µW m–2; Figs. 1 and S1; Table S2). The loss of the region’s woody biomass (730 Tg C) as well as the 31 % reduction in soil carbon to a depth of 100 cm contributed most to the carbon dioxide-induced radiative forcing of 2029 ± 44 µW m–2 (Fig. 1, Table 1 and S2). Furthermore, the 84 % reduction in soil methane oxidation rates and the 115 % increase in soil nitrous oxide emissions contributed to warming of 35 ± 2 and 63 ± 7 µW m–2, respectively. Counteracting this warming was a cooling effect of land surface albedo change (–502 ± 10 µW m–2) due to the more reflective agricultural vegetation and the absence of tree cover that formerly obscured underlying snow during winter months.

Fig. 1: Historical deforestation and it’s climate impacts.
figure 1

A Original witness tree aboveground biomass data from the U.S. Public Land Survey for the study region, U.S. EPA Level III Ecoregion 56, that occurred from 1828 to 1839, smoothed for visualization. B Following the historical deforestation of this region, we show here the resulting climate impacts caused by each radiative forcing budget component. The encircled point represents the net effect of all components (mean ± s.e). Positive values indicate a warming effect and negative values indicate a cooling effect.

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Table 1 Ecosystem carbon stock components
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The nature-based climate solution scenarios similarly owed much of their 100-year radiative forcing differences to ecosystem carbon stock changes (Fig. 2). For the NT, RI, and ORG conservation agriculture scenarios, the 4.5, 3.6, and 7.1 ± 2.3 Mg C ha–1 of soil carbon sequestration that occurred over the first ~25 years following their adoption were the predominant cause of the observed radiative forcing changes, respectively (Fig. 2; Tables 1 and S2). For the ALF, POP, and PIN perennial agriculture scenarios, both soil carbon sequestration (9.3, 10.6, and 8.1 ± 3.1 Mg C ha–1, respectively) and woody biomass carbon accumulation (0.0, 10.5, and 48.7 ± 1.6 Mg C ha–1, respectively) made important contributions to negative radiative forcing. The ES and MS ecosystem restoration scenarios similarly relied on soil and woody biomass carbon gains for negative radiative forcing. The ES scenario sequestered the most soil carbon (13.5 ± 2.8 Mg C ha–1) of the scenarios with herbaceous vegetation despite the annual prescribed fires removing its aboveground biomass. In the absence of prescribed fire, the MS natural forest regeneration scenario was able to store 70.4 ± 1.6 Mg C ha–1 in woody biomass. This jump in magnitude highlights the ability of woody biomass to sequester carbon well after soil carbon stocks saturate.

Fig. 2: Radiative forcing from adopting nature-based climate solutions.
figure 2

Mean radiative forcing of each land use and component over the 100-year time period for the nature-based climate solution scenarios. Encircled points show the net radiative forcing of each land use change scenario (mean ± s.e.). Positive values indicate a warming effect and negative values indicate a cooling effect. CON conventional, NT no-till, RI reduced input, and ORG organic row crops; ALF alfalfa, POP poplar, and PIN pine perennial crops, ES early succession and MS mid-succession ecosystems.

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The next largest component of the nature-based climate solution scenarios’ radiative forcing budgets was land surface albedo (Fig. 2; Tables 2 and S2). Outgoing shortwave radiation at the top of the atmosphere (\({{{{\rm{SW}}}}}_{{{{\rm{out}}}}}^{{{{\rm{toa}}}}}\)) responded most to the inherent reflectivity of the different vegetation types during the growing season, as well as the canopy’s ability to obstruct solar radiation from reflecting off of the underlying snow cover during winter months. The conventional and conservation agriculture scenarios, as well as the ALF scenario, had the highest outgoing shortwave radiation at the top of the atmosphere, with a range of 17.7 to 18.3 ± 0.1 W m–2. The short and medium length forest rotations, POP and PIN, each had lower outgoing shortwave radiation at the top of the atmosphere of 16.1 and 10.5 ± 0.1 W m–2, respectively, owing to their darker vegetation and taller stature. Similarly, the ES and MS scenarios had lower outgoing shortwave radiation at the top of the atmosphere (15.7 and 14.0 ± 0.1 W m–2, respectively), caused by their less reflective vegetation and protruding stems during periods of snow cover.

Table 2 Nitrous oxide, methane, and albedo fluxes with revenue and plant species diversity
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Following carbon stock and albedo changes, the next largest component of the radiative forcing budget was soil nitrous oxide emissions, with the exception of methane emissions from biomass burning in ES, described below (Fig. 2; Tables 2 and S2). Surprisingly, the conservation agriculture scenarios had equal or higher soil nitrous oxide emissions in comparison to the conventional agriculture scenario despite reduced or eliminated synthetic nitrogen fertilizer inputs. The NT, RI, and ORG scenarios produced 1.5, 1.4, and 1.7 ± 0.1 kg N2O ha–1 y–1, compared to the CON scenario of 1.3 ± 0.1 kg N2O ha–1 y–1. This 10 to 30 % increase in soil nitrous oxide emissions could result from multiple factors that alter the cycling of nitrogen from plant residues (NT, RI, and ORG) and from nitrogen-fixing cover crop inputs (RI and ORG), including hydrologic changes that alter the magnitude and timing of nitrogen leaching, plant uptake, and soil microbial activity. The highest nitrous oxide emissions came from the ALF scenario (2.0 ± 0.1 kg N2O ha–1 y–1), which is a perennial nitrogen fixing crop. The PIN forest scenario had intermediate nitrous oxide emissions (1.3 ± 0.1 kg N2O ha–1 y–1) when compared to the lowest emitting scenarios, POP, ES, and MS, whose emissions were 0.7, 0.5, and 0.8 ± 0.1 kg N2O ha–1 y–1, respectively. Notably, the direct nitrous oxide emissions from the prescribed fire in the ES system more than doubled the ecosystem’s soil emissions from 0.5 ± 0.1 kg N2O ha–1 y–1 to a total ecosystem emission rate of 1.1 ± 0.1 kg N2O ha–1 y–1.

Finally, the soil methane oxidation sink had the smallest impact on the total radiative forcing budgets (Fig. 2; Tables 2 and S2). The strong methane sink in the intact LS forest of –3.7 kg ± 0.1 CH4 ha–1 y–1 was greatly diminished upon conversion to agricultural land uses. The scenarios with herbaceous vegetation were largely unable to recover that original sink strength (–0.5 to –0.8 kg ± 0.1 CH4 ha–1 y–1). Only the PIN and MS forest scenarios recovered much (~80 %) of the soil methane sink with rates of –3.0 and –2.9 ± 0.4 kg CH4 ha–1 y–1, respectively. Methane fluxes from the prescribed fire in the ES system took the ecosystem from a net sink of –0.7 kg CH4 ha–1 y–1, to a net source of 9.4 kg CH4 ha–1 y–1 when combining both the soil methane oxidation sink and the direct fire emissions.

Summing each component of the radiative forcing budgets, we found that the net climate impact of the different nature-based climate solutions presented clear tradeoffs for climate, nature, and society. Conservation agriculture provided the smallest amount of climate mitigation with the NT, RI, and ORG scenarios contributing net radiative forcings of –76, –40, and –39 ± 31 µW m–2, over a 100-year time period, respectively (Fig. 2; Table S2). The perennial crops ALF, POP, and PIN each provided more climate mitigation (–147, –296, and –881 ± 44 µW m–2, respectively). In the ES scenario, the albedo induced forcing of 241 ± 7 µW m–2 as well as the fire-related methane emission forcing of 95 ± 2 µW m–2 completely offset the carbon sequestration forcing, making this scenario induce a net global warming of 69 ± 31 µW m–2. Finally, the largest amount of climate mitigation was provided by the MS natural forest regeneration scenario at –1555 ± 44 µW m–2.

Discussion

Our pairing of 35+ years of in situ and remote sensing data from a long-term replicated land use change experiment with the best available historical and contemporary forest inventory data provides the most comprehensive bottom-up assessment to date of net radiative forcing caused by land use change in the study region. The carbon dioxide fluxes from the loss or gain of the woody biomass measured throughout the study region by these two forest inventory datasets form the bulk of the greenhouse gas-induced radiative forcing from the historical deforestation, MS mid-succession, and PIN pine plantation scenarios11,12 (mean 86 %, Figs. 1, 2; Tables 1 and S2). As a result, these spatially distributed measurements provide confidence in the global warming impact of regional deforestation and the global cooling impact of regional reforestation presented here.

For the other scenarios that rely on upscaling in situ measurements from our long-term experimental site to the wider study region, we recognize the limitations associated with such an extrapolation. However, a comparison with previous bottom-up studies in the area that focused on select components of the radiative forcing budget and/or select land uses shows that our  carbon dioxide, nitrous oxide, and methane fluxes, as well as our land surface albedo estimates, are well within the range of other sites in the region14,15,16,17,18,19,20,21,22,23 (Supplemental Methods). Furthermore, a spatial representativeness analysis we conducted shows that the climate, plant, soil, and historical/contemporary land management characteristics of our site are sufficiently similar to those of the study region for our site to serve as an excellent basis for upscaling those in situ measurements that were too intensive to be measured at a large spatial scale (Supplementary Methods). Notably, the length of time that our study’s land management practices were consistently maintained and the large volume of data from our intensive measurement campaigns allowed us to definitively demarcate the end of the transient response of variables to these common land use transitions that can be slow to change such as soil carbon stocks, land surface albedo, and soil methane fluxes24,25,26,27.

As reported in this study, land use change, even at the scale of individual fields, can alter the global climate through changes to greenhouse gas concentrations and land surface albedo. But at a sufficiently large scale, regional land use change also has the potential to alter cloud dynamics, an additional source of radiative forcing28. Deforestation, for example, reduces the total amount of solar energy absorbed by the land surface (through increased albedo, as shown here), and the proportion of it used for turbulent energy exchange (through reduced surface roughness), reducing the amount of energy that can be used for convection of the atmospheric boundary layer29,30. This reduction in convection of the atmospheric boundary layer, along with potential reductions in evapotranspiration (which can impact water vapor supplies) and biogenic volatile organic compound production (which can impact cloud condensation nuclei), can result in reduced formation of low altitude clouds31,32. Low altitude clouds cause net cooling of the Earth as their reflection of incoming solar radiation to space predominates. This potential source of additional radiative forcing from land use change is difficult to quantify and attribute to specific land cover changes with observational data alone, however, it could be an important component of the planetary radiative forcing budget if the anthropogenic contribution can be constrained by future studies.

Apart from the climate impacts presented here, land touches a wide range of natural and human domains that are important to consider when evaluating the implications of our findings. Land is property, habitat, territory; it is integral to livelihoods, food security, and many other aspects of natural and human life. It therefore is worthwhile to consider that the conservation agriculture scenarios studied here (NT, RI, and ORG) provide little habitat for native plants and animals33,34,35,36,37,38 (Table 2) However, they do provide food and economic returns that are readily scalable, making conservation agriculture’s relatively small climate mitigation per unit land area potentially impactful if applied extensively5,6,8,39 (Table 2). The perennial agriculture/forestry land uses in this study (ALF, POP, and PIN) that had moderate levels of climate mitigation also provide food or fiber returns and some limited habitat for plants and animals33,38,40 (Table 2). The ES scenario supports a diverse community of herbaceous plants that attract insects and other wildlife33,38,41,42 (Table 2), but it does not provide food, fiber, or (when burned) climate mitigation.

The natural forest regeneration scenario (MS) provided the most climate mitigation of any nature-based climate solution studied here. During its ecological succession, the ecosystem slowly but steadily recruited trees that attracted insects and other wildlife33,38,41,43 (Table 2). Persisting well after these changes for perhaps 150 years post-disturbance, the trees at the stand level continue to sequester carbon, including in downed woody materials and roots44. The U.S. Forest Inventory and Analysis data from our study region, which the MS scenario relies on, has very few plots with a stand age greater than 100 years, but other studies from the small number of well documented old-growth forests in the region with more than 100 years since their last major disturbance suggest a whole ecosystem carbon sequestration potential upwards of 243–359 Mg C ha–1 12,19,44. At a 100-year stand age, the MS natural forest regeneration scenario from this study has a whole ecosystem carbon stock of 199 Mg C ha-1, suggesting that if undisturbed, carbon sequestration could continue. On the other hand, the preindustrial witness tree data of the study region (sampled from 1828 to 1839) shows a wide range of total ecosystem carbon stocks with the 5th and 95th percentiles’ having 109 and 325 Mg C ha–1. This wide range suggests that disturbances like wind, snow and ice damage, insect and fungal diseases, fire, and human exploitation created a mosaic of stand ages from young to old11. As the study region’s already widespread second growth forests continue to mature, stakeholders can take the climate mitigation potentials our study provides into account when deciding how to manage these disturbances.

Stakeholders can also factor in the climate mitigation potentials we provide for the agricultural and forestry nature-based climate solutions when evaluating the tradeoffs involved in placing them on the landscape. Expanding these nature-based climate solutions with food, fiber, and economic returns onto the already maturing second growth forests would sacrifice the substantial climate mitigation these forests are currently providing and come at significant costs to plant and animal habitat. In contrast, integrating these nature-based climate solutions into existing agricultural landscapes would make significant, if modest, steps towards repaying the climate debt of past deforestation in the region. Reconfiguring land for climate benefits is not a simple task, but the pressures of a changing climate, a growing human population, and an increasingly precarious natural world motivate the effort to chart a sustainable trajectory for the Earth system with resolve and determination.

Methods

Study site

Analyses here are based on data from the W.K. Kellogg Biological Station Long Term Ecological Research site established by Michigan State University in 1989 (42.4 N, 85.4 W, 288 m elevation)9. The site has a mean annual temperature of 9.3 °C and a total annual precipitation of 1067 mm. The soil texture over the 0–100 cm depth is 66 % sand, 20 % silt, and 14 % clay (Supplemental Methods). Following the most recent deglaciation and the northward advance of tundra then boreal ecosystems, the site was covered by mid to late successional temperate deciduous broadleaf forests for the past ~10,000 years until the mid-19th century when industrial logging cut over the entire study region11,13 (Fig. S1). Subsequently, agriculture, including row crops and pasture, has been the predominant land use in the study region (currently 49 %), though a substantial proportion of the study region has been naturally regenerating as second growth forest for upwards of 150 years (currently 32 %). The main experimental site follows a randomized complete block design with six replicates of each non-forested land use and a plot size of 1 ha. The three forested land uses in this study (PIN, MS, and LS) are replicated on the same soil series with three sites each, all within ~1 km of the main site.

Nitrous oxide and methane fluxes

Soil nitrous oxide and methane flux measurements occurred bi-weekly to monthly from 1991 to 2023 at a consistent time of day following the static chamber method14. Briefly, 28 cm diameter chambers were inserted into the soil and fitted with a lid for 1.5 h, during which time four headspace gas samples were taken and stored in vials (Labco Limited, Lampeter, UK). Samples were then analyzed for nitrous oxide and methane on a gas chromatograph (Hewlett-Packard 5890 series, CA, USA, until 2008 and 7890 A Agilent Technologies Inc., CA, USA, thereafter) equipped with a 63Ni electron capture detector (350 °C), a Poropak Q column (1.8 m, 80/100 mesh) at 80 °C, and a carrier gas of argon/methane (90/10). Areal fluxes were calculated from changes in the headspace gas concentration over time with the ideal gas law and assumed to represent the daily mean flux. Each flux was visually inspected for outlier points (e.g. from a leaky vial) and discarded when necessary. While the diurnal variability of soil nitrous oxide and methane fluxes is quantifiable, the objective of this study was to estimate differences in fluxes due to land use change. Accordingly, our limited time and resources were spent on sampling the largest sources of variation, namely spatial and intra-annual variability. Positive fluxes indicate emission to the atmosphere whereas negative fluxes indicate uptake. Between 681 and 1779 fluxes were available for each land use, for a total of 14,568 fluxes measured from 1991 to 2023, making this one of the longest running datasets of its kind.

Biomass burning nitrous oxide and methane emissions were estimated separately for the ES scenario that is burned each Spring. Biomass was clipped at five stations within each of the six replicate plots in the dormant season post-senescence and pre-burn from 1 m–2 quadrats, dried in an oven at 60 °C, and weighed. When this post-senescence data was missing, pre-senescence data collected in the same manner was used and adjusted by the observed post-senescence aboveground biomass loss rate, which was 39 % at our site. Emission factors for g of N2O and g of CH4 per kg of biomass burned (0.17 and 2.70, respectively) were then applied to these weights by considering the plant functional type as ‘Savanna and Grassland’45. A total of 879 observations were available from 1991 to 2022.

Ecosystem carbon stocks

Soil and fine root carbon and nitrogen stocks were measured after the growing season and before the first soil freeze event in the fall of 2022 with a hydraulic probe (Geoprobe 540MT, Salinas, KS USA) in a similar fashion to Cordova et al.46. After clearing away the surface litter, two intact cores 7.6 cm in diameter were taken to a depth of 120 cm at each of the five stations in each of the 6 replicate plots (3 replicate plots in the forest land uses) for a total of 510 cores. Each core was then split into four sections by depth at 0–10 cm, 10–25 cm, 25–50 cm, and 50-end cm, where the end depth was between 90 and 115 cm. Each section was sieved to 4 mm to remove gravel, which was weighed and recorded as the coarse fraction. Roots were taken from the top of the 4 mm sieve as well as from the soil passed through the sieve. Roots were then washed with water over a 0.25 mm sieve, dried at 60 °C, and weighed. Similarly, soil passed through the 4 mm sieve was dried at 60 °C and weighed. The coarse fraction-free dry weight of the soil and the section’s volume were used to determine the bulk density of the sample. A total of 510 cores split into four depths gave 2040 paired observations of gravel content, bulk density, root biomass, carbon concentrations, and nitrogen concentrations.

Surface litter carbon and nitrogen stocks were sampled in the three forested sites at the same five stations within a 75 by 115 cm quadrat by collecting leaves, stems, and branches smaller than 5 cm diameter. Coarse woody debris, defined as non-living woody material having a diameter of > 5 cm, was sampled along five 50 m transects using the method of the U.S. Forest Inventory Analysis program, from which areal standing carbon stocks were then calculated according to Eq. (3.2) in ref. 47. Soil, fine root, non-woody surface litter, and fine woody surface litter samples were pulverized to less than 0.25 mm in a shatterbox in preparation for carbon and nitrogen concentration measurements (SPEX SamplePrep Shatterbox 8530, Metuchen, New Jersey USA). Elemental analysis by dry combustion was conducted with three analytical replicates (Costech ECS 4010 CHNSO Analyzer, Valencia, California, USA).

Land surface albedo

Land surface albedo was measured at each experimental unit from 1984 to 2023 with the Landsat 5, 7, 8, and 9 satellites as well as the Sentinel 2 A and 2B satellites48. Surface reflectance observations with cloud, shadow, excessive aerosol, and radiometric saturation quality flags raised were filtered out and the bands were then combined into total shortwave reflectance using narrow to broadband coefficients49,50. Shortwave broadband albedo was calculated using the albedo:reflectance ratio, also known as the concurrent MODIS technique48,51,52. The bidirectional reflectance distribution function (BRDF) was solved to correct for surface anisotropy effects using MODIS BRDF/albedo product parameters (MCD43A1 V6.1) from adjacent representative pixels. Diffuse and direct surface downwelling shortwave radiation components during satellite overpass times were taken from the ERA5 data product53. Further details can be found in the Supplemental Methods. Between 2817 and 5546 albedo observations that passed all quality screening criteria were available for each land use, resulting in a total of 47,075 albedo observations measured from 1984 to 2023.

Woody biomass carbon stocks

Aboveground live woody biomass data for the nature-based climate solution and historical scenarios were extracted for the U.S. E.P.A. Level III Ecoregion 5610. The PIN and MS scenarios leveraged aboveground live woody biomass data from the U.S. Forest Inventory and Analysis program12. For the MS natural forest regeneration scenario, publicly protected areas with no documented disturbance or artificial planting were stratified by stand age from 0 to 100 years to obtain the natural regeneration growth curve for the study region. A total of 439 plots and 717 plot years in the study region met these criteria and were used for the MS scenario. Similarly, for PIN, areas classified as northern pine plantations were stratified by stand age from 0 to 50 years. A total of 29 plots and 51 plot years in the study region met these criteria and were used for the PIN scenario. Belowground live woody biomass and coarse woody debris estimates from these plots were extracted in parallel.

For the historical scenario, the original witness tree data from the U.S. Public Land Survey was collected for the region from 1828 to 183911. We used the aggregated 8 km resolution Level 1 data that estimates total aboveground biomass on an areal basis from a total of 113,643 trees in the study region. Belowground live woody biomass was calculated using the average belowground:aboveground ratio from the contemporary data described above (0.18 for MS and 0.22 for PIN) and a carbon concentration of 48 % was assumed.

Radiative forcing calculations and statistical analysis

Radiative forcing calculations for each scenario used the annual outgoing shortwave radiation fluxes at the top of the atmosphere, as well as the carbon dioxide, nitrous oxide, and methane fluxes from the measurements described above with their corresponding gas-specific atmospheric lifetimes and radiative efficiencies54,55. The atmospheric lifetime of nitrous oxide and methane was modeled according to Eq. (1)

$${{{{\rm{C}}}}}_{{{{\rm{i}}}}+1}={{{{\rm{F}}}}}_{{{{\rm{i}}}}}+{{{{\rm{C}}}}}_{{{{\rm{i}}}}}* {{{{\rm{e}}}}}^{(-\frac{1}{{{{\rm{L}}}}})}$$
(1)

Where Ci is the atmospheric concentration in the ith year, Fi is the annual flux in the ith year, and L is the atmospheric lifetime of the gas. The atmospheric lifetime of carbon dioxide was modeled according to Eq. (2).

$${{{{\rm{C}}}}}_{{{{\rm{i}}}}+1}={\sum }_{{{{\rm{p}}}}=1}^{4}\left({{{{\rm{f}}}}}_{{{{\rm{p}}}}}* {{{{\rm{F}}}}}_{{{{\rm{i}}}}}\right)+{{{{\rm{C}}}}}_{{{{\rm{i}}}},{{{\rm{p}}}}}* {{{{\rm{e}}}}}^{(-\frac{1}{{{{{\rm{L}}}}}_{{{{\rm{p}}}}}})}$$
(2)

Where Ci is the atmospheric concentration in the ith year, fp is the fraction of emissions associated with each pool, Fi is the annual flux in the ith year, Ci,p is the atmospheric concentration of the pth pool in the ith year, and Lp is the atmospheric lifetime of carbon dioxide in the pth pool. Radiative forcings for each gas were calculated as the product of the atmospheric concentration and the radiative efficiency. Constants for atmospheric lifetimes and pool fractions for Eqs. (1) and (2) can be found in refs. 56,57, as can the constants for the radiative efficiencies of each gas.

Annual fluxes (Fi) used in Eq. (1) were estimated with a separate statistical model for each component. For soil nitrous oxide and methane fluxes, as well as land surface albedo, a generalized additive mixed effect model was fit with land use as a fixed effect, land use nested within block as a random intercept, and a continuous smooth function of month and year. Repeated measures were accounted for by fitting an autocorrelation structure of order 1, with a continuous time covariate for each land use nested within block.

For CO2, annual fluxes (Fi) used in Eq. (2) were calculated for each experimental unit as the sum of annual changes in each ecosystem carbon stock component, including soil, live biomass, and surface litter pools. A time series of carbon stocks was constructed for each scenario using our measured data and assumptions about the transition timeline. For soil carbon stock changes, we assumed the measured changes occurred over a 25-year time period. A reasonable range of 15–30 years could change our radiative forcing estimates for soil carbon stock changes by –15 to 5%, using the extremes of that range; that said, over longer timescales (e.g. past 2100) this effect diminishes. Once each carbon stock time series was constructed for each scenario, the total change in ecosystem carbon stocks each year was taken as the annual CO2 flux (Fi in Eq. 2) to be used in the radiative forcing calculations. Both the historical and nature-based climate solution scenarios were assumed to take place on the vegetated area of U.S. E.P.A. Level III Ecoregion 56, which was 51.7 × 109 m–2. The final radiative forcing budget components as well as their net climate impacts were extracted for each experimental unit as the mean value during the 100-year time period. These radiative forcings represent the global (i.e. planetary) impact of each land use change scenario applied to the vegetated area of this study region as a whole. Further methodological details, including those for regional upscaling, revenue, and species diversity, are provided in the Supplemental Methods.

Reporting summary

Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article.