Quantification of Woody Biomass Available for Wood Harvesting and Sequestration in the Continental United States – a Top-Down Approach

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Quantification of Woody Biomass Available for Wood Harvesting and Sequestration in the Continental United States – a Top-Down Approach

https://doi.org/10.21203/rs.3.rs-2493262/v1

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Background: Wood Harvesting and Sequestration is a form of Carbon Removal and Storage (CRS) that utilizes a combined natural and engineered process to harvest woody biomass and put it into long term sequestration, most frequently in the form of subterranean burial. This paper aims to quantify the availability of woody biomass for the purposes of wood harvesting and sequestration in the continental United States using a top-down approach. Using a regional version of the VEGAS terrestrial carbon cycle model, this paper calculates the annual woody net primary production in the continental United States. It then applies a series of constraints to exclude woody biomass that is unavailable for wood harvesting and sequestration. These constraints include fine woody biomass, current land use, current wood utilization, land conservation, and topographical limitations. These results were then split into state by state and regional totals

Results: In total, the model projects the continental United States could produce 1,274 MtCO₂e (CO2 equivalent of woody biomass) worth of coarse woody biomass annually in a scenario with no anthropogenic land use or constraints. In a scenario with anthropogenic land use and constraints on wood availability, the model projects that 415 MtCO₂e of coarse woody biomass is available for wood harvesting and sequestration annually. This is enough to offset 8.5% of the United States’ 2020 greenhouse gas emissions. Of this potential, 20 MtCO₂e is from the Pacific region, 77 MtCO₂e is from the Western Interior, 91 MtCO₂e is from the Northeast region, and 228 MtCO₂e is from the Southeast region.

Conclusion: There is enough coarse woody biomass available in the continental United States to make wood harvesting and sequestration a viable form of carbon removal and storage in the country. There is coarse woody biomass available all across the continental United States, All four primary regions analyzed have enough coarse woody biomass available to justify investment in wood harvesting and sequestration projects.

Carbon removal

Carbon sequestration

Forestry

Wood harvesting and sequestration

United States

Carbon cycle modeling

According to the United Nations’ Intergovernmental Panel on Climate Change¹ the planet has warmed by approximately 1 degree Celsius since the early 1800s as a direct result of anthropogenic emissions of greenhouse gasses, most notably carbon dioxide. A direct reduction in these emissions will likely not be enough to stave off potential catastrophe, so other solutions are required as part of a complete response¹. One potential avenue for climate change prevention is Carbon Removal and Storage (CRS), sometimes referred to as Carbon Capture and Sequestration (CCS) or Carbon Dioxide Removal (CDR). CRS refers to any technology or technique where carbon dioxide is taken directly out of the atmosphere and placed into long term storage or sequestration². While current applications of CRS are relatively limited, various techniques have the potential to offset significant portions of anthropogenic carbon dioxide emissions and sequester the carbon for a permanent duration².

In this paper we will focus one a specific CRS technique, Wood Harvesting and Sequestration (WHS), attempting to quantify the sequestration potential of WHS in the continental United States. WHS is a mixed natural and engineered form of CRS³. It is designed to take advantage of the natural CRS processes inherent in photosynthesis. In photosynthesis a plant intakes water, sunlight, and CO₂ to create energy, release O₂, and store carbon in the plant’s biomass³. In WHS, plant material (specifically woody biomass (WB)) is harvested and placed into long term sequestration in an environment specially engineered to prevent decomposition⁴.

Although there are several sequestration techniques that can be deployed for WHS the most common and well researched is WB burial in a specifically engineered Wood Vault⁴. This means WB is buried in an anaerobic environment below the active soil layer where decomposition is minimized. Archeological evidence has shown examples of buried WB surviving relatively intact on a century or even millenia time scale when entombed in the correct conditions⁴.

There are several methods of harvesting WB for WHS. First one can create plantations specifically for the purposes of WHS: plant trees, harvest and sequester the grown WB, then reseed the original plot of land and wait for trees to regrow in order to repeat the process⁴. The second method is to harvest dead and waste WB that would otherwise decompose and place it directly into long term sequestration. This WB can come from natural forest mortality or urban waste generation and requires minimal intervention⁴. In both cases, only coarse woody biomass (CWB), which refers to trunks, main branches, and other large pieces of wood⁵, is collected for sequestration. Fine wood, such as twigs, bark, roots, and other small woody material, has too high a ratio of surface area to volume to guarantee long term sequestration⁴.

This analysis will quantify the total CWB available for WHS in the entirety of the continental United States. It will look at the nation as a whole, four broad geographic regions, and all 48 states in the continental United States.

This paper is based on work done in Zeng et al (2013)⁶. However, several key differences and advances justify this new endeavor. The 2013 paper was a global assessment of WHS availability, using grid points of 250 km by 250 km while this paper uses much more precise 10 km by 10 km grid points. Additionally, improvements in the VEgetation Global Atmosphere Soil (VEGAS) carbon cycle model used by both papers have occurred between 2013 and 2022^7.9. These improvements include the addition of anthropogenic land use constraints, wood utilization data, and general performance upgrades. In addition, this paper makes use of more current and accurate land conservation estimates and includes topographical constraints that the 2013 paper⁶ ignored.

This paper is a top-down analysis of the CWB (and thus carbon) available for WHS in the continental United States. It also quantifies the total unconstrained annual Net Primary Production (NPP) of CWB for the same region. This analysis uses a carbon cycle model to estimate the excess CWB generated in the region. In order to assess the potential availability of CWB for WHS and the unconstrained NPP of CWB, this analysis used two runs of the VEGAS Carbon Cycle Model Version 2.6^7,8. This analysis used a regional run of the model with daily timesteps and a spatial resolution of 0.1 degree latitude by 0.1 degree longitude (about 10 km by 10 km). Every value analyzed was an average of quantities between the years 2010 and 2019. The first simulation was a spin up scenario with no constraints for human activities. The spin up run also lacked the carbon fertilization effect⁷. The second model run is a full run with considerations for anthropogenic land use (both agriculture and urbanization) as well as the impacts of anthropogenic climate change⁷. Both model runs use wood death rates (from fire, stress, and background mortality) in forested areas as a proxy for WB NPP (see Equation 1). This proxy assumes a steady state equilibrium in the forests of the United States. While this may not be accurate for an individual plot of forest, it holds true on the spatial scales of the top-down analysis employed by this paper.

Where NPP_Wood is Net Primary Production of Woody Biomass, D is death rate, F is fire, STR is stress, BRM is background mortality, and k is VEGAS vegetation type with k=1 corresponding to evergreen forests, k=2 corresponding to deciduous forests, and k > 2 corresponding to grassland, cropland, and urban areas.

Going from woody NPP to CWB available for WHS is a matter of applying 5 constraints to available WB (see Figure 1). These constraints are as follows:

Exclude fine wood
Add current land Use constraints to the model run
Exclude urrent wood utilization
Exclude land set aside for conservation
Exclude difficult to access regions

Once all of these constraints were applied, we were left with CWB that is usable for the purposes of WHS (see Figure 2).

2.1 Fine Woody Biomass

The first constraint is that only CWB is suitable for burial in WHS. Fine woody biomass is a part of the total wood growth/death rate calculated by the VEGAS carbon cycle model and needs to be excluded. While a tree is mostly coarse wood by mass (trunk, main branch structures) the fine wood dies and regrows at a much faster rate. As such, we assumed that 59% of all WB produced is CWB^6,0. We applied this factor to both the Spin Up run and the full anthropological forced run. This factor is all that is needed to calculate the unconstrained CWB NPP that is used as a baseline for further analysis. As such, it was the only constraint placed upon the spin up run of the VEGAS model. In total, there is 1,274 Mt of carbon dioxide equivalent (CO₂e) worth of CWB NPP in the continental United States annually.

2.2 Land Use

The next constraint is anthropogenic land use. No WB can be harvested from land that is already being used for agriculture, human habitation, or some other anthropogenic use case. The VEGAS model already has built in parameters for land use and they were utilized for this analysis. As such, at this point we switch from the spin up model run which lacked anthropogenic forcing to the full model run with complete anthropogenic forcing. In total, once land already used by humans is taken out of consideration, there are 724 MtCO₂e available for sequestration in the continental United States.

2.3 Wood Utilization

The next constraint is CWB already utilized by human activities. Hurtt et al¹⁰ provides an analysis of wood harvested across the country for human utilization and consumption. This is simply excluded from the CWB at every grid point. This leaves a total of 659 MtCO₂e available.

2.4 Conservation

Next, we exclude all CWB already set aside for conservation purposes. The Biden Administration has set a long-term goal of placing 30% of America’s forestland under some form of conservation or protection¹¹. As such, we assume that 30% of remaining available CWB will be part of this conserved land and thus unavailable for utilization in WHS. This approach is relatively crude, as not all regions of the country will be conserved equally. As more details of future conservation plans become available, it may become possible to mask out protected grid points instead of applying a 30% reduction to the yield of every grid point. In total, this conservation constraint leaves us with 461 MtCO₂e of CWB for WHS.

2.5 Topographic Gradient

Finally we set aside all CWB grown on land that is difficult to reach and harvest from due to geographical limitations. For this, we assume that any grid point with a topographical gradient of greater than 0.1 m/m is too difficult to harvest from and has a CWB production of 0. This mask is applied based on the EROS¹² HYDRO1K dataset. This leaves us with a final WHS potential for the continental United States of 415 MtCO₂e. See Figure 3 for a detailed spatial distribution of the WB excluded by all of these constraints.

In total, under the harvest assumptions made in this paper’s methodology,the model predicts that the US can generate 415 MtCO₂e worth of sequestration via WHS annually. Without any constraints (land use, conservation, existing utilization, and ease of access), the continental US could theoretically generate 1,274 MtCO₂ worth of sequestration annually. This means that only 32.5% of the CWB the continental United States could theoretically generate annually is actually available for the purposes of sequestration.

We also split up the WHS potential by state to determine several geographic trends (see Fig. 4). The highest potential for WHS comes from the gulf coast states (Alabama, Florida, Georgia, Louisiana, Mississippi Puerto Rico, and the East coast of Texas). All have WHS potentials well above 1.0 tCO₂/ha. The Gulf Coast region has warm temperatures, plentiful rainfall, plentiful sunlight, flat terrain, and a limited footprint of cropland. All of these factors combine for rapid and consistent wood growth, ideal for the production of available CWB necessary for WHS.

On the other hand, there are several categories of states that have very low potential for WHS. A few categories of states have geographical/climatological factors that severely limit the viability of WHS. Desert states with low rainfall (Arizona, New Mexico, Nevada, Utah) simply lack the capacity to produce the quantity of CWB required for WHS. Mountainous states (Colorado, Wyoming) are simply too difficult to effectively harvest CWB from, though future innovations and cost reductions could help make their CWB more easily available. Finally, there are agricultural states (California, Ohio, Illinois, Iowa, Kansas). These states have geographical/climatic conditions that could lead to high levels of CWB production, as shown in their CWB NPP totals and intensities. However, most of the productive land in these states is already claimed by agriculture. As such, any attempt to utilize these states for WHS will produce only limited sequestration without disrupting food production.

This analysis also split the continental United States into 4 regions, based on the regions set out by the US Forest Service¹³. While the Forest Service had 9 regions, this analysis consolidated the smaller ones, creating four regions with similar properties in terms of forest type and geographic conditions (See Fig. 5 for detailed spatial plots of the CWB production of each of the regions and Fig. 6 and Tables 1 and 2 for a detailed breakdown of the constrained CWB avaliability). The four regions are as follows:

Pacific Coast: CA, OR, WA

Interior: AZ, CO, ID, KS, MT, NE ND, NM, NV, SD UT, WY

Southeast: AL, AR, FL, GE, KY, LA, MS, NC, OK, SC, TN TX, VA

Northeast: CT, DE, IA, IL, IN, MA, MD, ME, MI, MN, MO, NH, NJ, NY, OH, PA, RI, VT, WI, WV

In general, the Southeast has the highest potential for WHS, with warm temperatures and plentiful rainfall spurring on significant productivity. It also lacks significant constraints, meaning a relatively high proportion of the region’s CWB (45.2%) is actually available for WHS.

The Northeast has moderate production throughout, with some outliers in either direction. A few unbroken forests near the Canadian border (Maine, Northern Minnesota, and Michigan’s Upper Peninsula) have CWB production values that rival the productive Gulf Coast. Combined with limited constraints and these regions are some of the most productive in the nation. The region is also heavily constrained by both agriculture and human habitation, meaning much land with high theoretical CWB production is actually unavailable.

The Pacific region is constrained by large mountain ranges as well as a high propotion of land utilized for agriculture and human habitation. The Paciffic Northwest (Washington, Oregon) also has a lower CWB production than what would be expected given the region’s climate. This error persits throughout VEGAS’s global and regional runs and should potentially be addressed in future versions of the model.

The Interior region is categorized by two primary constraints: desert and mountains. Desert regions simply lack any CWB production to begin with. And mountainous regions are excluded by the topographic constraints. As such, any potential WHS projects in the interior region must carefully select where to harvest CWB.

The closer look provided by Figs. 5 and 6 can also provide a clearer picture of overall national trends. Fertile and prosperous river banks (for example, the Mississippi River) are often entirely claimed by human activity, be it agriculture or dense settlement. This creates significant areas of limited to no potential for WHS. And it’s not as simple as the further south a grid point is, the higher its WHS potential. While that trend holds mostly true for the Southeast, it is reversed for the Northeast. It’s a more complicated calculus than how much sun and rain is available.

Table 1

Regional WHS Potential Totals (MtCO₂e)
	Pacific	Interior	South East	North East
NPP Wood	113.992	637.913	855.434	553.058
NPP Coarse Wood	67.255	376.368	504.706	326.304
Constrained by Land Use	49.009	150.768	372.834	152.841
Constrained by Current Utilization	44.427	149.714	331.135	133.784
Constrained by Conservation	31.099	104.8	231.794	93.649
Constrained by Geography	19.841	76.549	228.112	90.505

Table 2

Regional WHS Potential Intensities (tCO₂e/ha)
	Pacific	Interior	South East	North East
NPP Wood	1.016	1.589	3.234	2.458
NPP Coarse Wood	0.6	0.938	1.908	1.45
Constrained by Land Use	0.437	0.376	1.409	0.679
Constrained by Current Utilization	0.396	0.373	1.252	0.595
Constrained by Conservation	0.277	0.261	0.876	0.416
Constrained by Geography	0.177	0.191	0.862	0.402
Coarse Wood Availability (%)	29.5	20.4	45.2	27.7

Here we present more detailed analysis of a few representative states. For similarly detailed plots of any other state in the continental United States, contact this paper’s corresponding author. The selected states are:

Arizona

California

Florida

Illinois

Michigan

Texas

Arizona is a fairly low intensity state for the purposes of CWB production. Across the entire state, there is only 0.159 tCO₂e/ha worth of CWB NPP available for WHS. Given that much of the state is dominated by an arid climate, this is unsurprising. Although there is some mountainous terrain, Arizona has a relatively high ratio of available CWB to unconstrained CWB (45%). There is simply a low baseline CWB production in the state. Overall, there are very few regions of Arizona appropriate for WHS.

While California has high productivity of CWB in an unconstrained model run, several constraints severely limit the state’s WHS potential. Anthropogenic land use, both agricultural and urban, take up much of the state’s land area. And many undisturbed grid points are too mountainous for effective CWB harvesting. So, California’s climate shows potential for CWB production, but in reality can only output 0.223 tCO₂e/ha worth of sequestration, only 30% of the state’s unconstrained CWB production and not even double the intensity of desert states like Arizona and Utah.

With a potential WHS intensity of 1.922 tCO₂e/ha Florida is the single most productive state in the continental United States. Florida has very limited constraints on its CWB production, with 67% of its unconstrained CWB NPP available for WHS. Florida is the epitome of the high productivity characteristic of the warm and wet Gulf Coast Climate. However, a more granular and detailed analysis of land conservation may limit Florida’s WHS potential. Its highest productivity region is the Everglades in the Souther portion of the state. As this is a popular National Park and a unique ecosystem, it is unlikely that this region will be accessible for intense CWB harvesting.

Illinois is a good example of the characteristics of many of the Midwestern states. It has relatively high unconstrained CWB NPP. Illinois’ intensity of 1.614 tCO₂e/ha is about 70%-80% of the unconstrained total for most of the high productivity Gulf Coast states. But the vast majority of Illinois’s land area is occupied by agriculture. As such, Illinois has a constrained WHS potential 0.215 rCO₂e/ha, only 13% of the unconstrained potential. This intensity is less than the state of California, which has less than half of Illinois’ unconstrained CWB NPP. Illinois has only a few scattered grid points available for WHS projects.

Michigan is divided into two regions. The main Southern region of the state is relatively standard for states in the Northeast region. A mixture of relatively productive forests with heavy land use produces a statewide WHS potential of 0.515 tCO₂e/ha, about average for the nation. But the Upper Penninsula is dominated by dense, unbroken forest. The peninsula, along with Northern Minnesota and Maine have WHS potentials above 1 tCO₂e/ha, the highest of any region outside of the Southeast region.

Texas, the largest state by area in the continental United States is a mix of a high NPP Gulf Coast climate and a less productive arid interior, much of which is set aside for ranching and other land use constraints. Texas has the single largest total WHS potential of any state, accounting for 13% of the WHS potential in the continental United States. This is a combination of the state’s superlative size and above average WHS potential intensity of 0.681 tCO₂e/ha. Overall, Texas has ample opportunities for potential WHS projects.

Overall, the continental United States has a large potential for WHS. The US emitted about 5,200 MtCO₂e in the year 2020¹⁴. This means that WHS in the continental United States can offset about 8.0% of the nation’s annual emissions. This total can be increased by converting agricultural land, developing more cost efficient ways to log mountainous terrain, discovering a way to permanently and cheaply sequester fine woody biomass, or harvesting at a higher (potentially unsustainable) intensity.

The results of this analysis are also relatively similar to a similar (if coarser) analysis conducted in Zeng et al (2013). That analysis estimated the United States had a WHS potential of 513 MtCO₂, 98 MtCO₂ more than this analysis. The 2013 analysis used much coarser resolution (2.5 degree grid points), made less conservative estimates about land conservation (only 10% of land conserved) and ignored the reductions imposed by steep slopes. As such the difference in WHS totals makes sense.

The next step could be to repeat this analysis for other regions of the world. Many nations including Brazil, China, Canada, India, and Russia have large and productive forested regions. Analysis similar to that found in this paper could determine where WHS projects have the most potential to offset industrial emissions. Scaling WHS up to the Megatonne or Gigatonne scale required to make a significant impact will require many of these analyses. It could also be useful to compare the results of this paper to a study attempting to quantify the same quantities from a bottom up approach. While doing this on the national scale may be prohibitively time consuming, a bottom up analysis of the WHS potential of a few key states may prove enlightening.

CCS: Carbon Capture and Sequestration

CDR: Carbon Dioxide Removal

CO₂e: Carbon Dioxide Equivalent

CRS: Carbon Removal and Storage

CWB: Coarse Woody Biomass

IPCC: Intergovernmental Panel on Climate Change

NPP: Net Primary Production

VEGAS: VEgetation Global Atmosphere Soil

WB: Woody Biomass

WHS: Wood Harvesting and Sequestration

Ethics Approval and Consent to Participate

Not Applicable

Consent for Publication

Not Applicable

Availability of Data and Materials

All data utilized for the purposes of this paper can be made available upon request by contacting the corresponding author.

Competing Interests

Not applicable.

Funding

We acknowledge support from NOAA Climate Program Office (NA18OAR4310266), and NIST Greenhouse Gas Measurement Program (70NANB14H333).

Author’s Contributions

HH performed the primary analysis, generated all figures, and wrote the manuscript. NZ conceived the idea, developed the VEGAS model, and helped to write the paper. Both authors read and approved the final manuscript.

CQ set up the VEGAS model run, created boundary conditions and datasets

Acknowledgements

The authors of this paper would like to thank the following people:

Dylan Vrana, for coding assistance in regards to utilizing shapefiles and other coding tasks.

Al Steele and Dave Hollinger for advice and insights.

Abby Sebel, Ben Woods, Sarah Loughran, and the rest of the AOSC Graduate Students for moral support and advice throughout.

Intergovernmental Panel on Climate Change (IPCC), Special Report Global Warming of 1.5 degree. (2018).
National Academies of Sciences Engineering and Medicine (NASEM). Negative emissions technologies and reliable sequestration: a research agenda. Washington. The National Academies Press, (2019).
Zeng, N. Carbon sequestration via wood burial. Carbon Balance Manage 3, 1 (2008).
Zeng, N., Hausmann, H. Wood Vault: remove atmospheric CO2 with trees, store wood for carbon sequestration for now and as biomass, bioenergy and carbon reserve for the future. Carbon Balance Manage 17, 2 (2022).
Keddy, P.A.; Drummond, C.G. Ecological properties for the evaluation, management, and restoration of temperate deciduous forest ecosystems. Ecological Applications. 6 (3): 748–762. (1996).
Zeng, N., King, A.W., Zaitchik, B. et al. Carbon sequestration via wood harvest and storage: An assessment of its harvest potential. Climatic Change 118, 245–257 (2013).
Zeng, N., Zhao, F., Collatz, G. et al. Agricultural Green Revolution as a driver of increasing atmospheric CO2 seasonal amplitude. Nature 515, 394–397 (2014).
Zeng N, Mariotti A, Wetzel P. Terrestrial mechanisms of interannual CO2 variability. Glob Biogeochem Cycles 19. (2005).
Bechtold, W., Patterson, P. The Enhanced Forest Inventory and Analysis Program - National Sampling Design and Estimation Procedure. USDA Forest Service Southern Research Station. (2022).
Hurtt, G., et al. Harmonization of land-use scenarios for the period 1500-2100: 600 years of global gridded annual land-use transitions, wood harvest, and resulting secondary lands. Climatic Change. (2011).
White House Briefing Room. FACT SHEET: Biden-⁠Harris Administration Celebrates Expansion of Locally-Led Conservation Efforts in First Year of “America the Beautiful” Initiative. (2021).
Earth Resources Observation and Science (EROS) Center. USGS EROS Archive - Digital Elevation - HYDRO1K. United States Geological Survey. (2018). https://www.usgs.gov/centers/eros/science/usgs-eros-archive-digital-elevation-hydro1k
Forest Service. Regions. United States Department of Agriculture. (2022). https://www.fs.usda.gov/wildflowers/regions/index.shtml
Environmental Protection Agency (EPA). Overview of Greenhouse Gases and Sources of Emissions. (2022).

No competing interests reported.

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You are reading this latest preprint version

Quantification of Woody Biomass Available for Wood Harvesting and Sequestration in the Continental United States – a Top-Down Approach

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Version 1

Abstract

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1. Introduction

2. Methodology

2.1 Fine Woody Biomass

2.2 Land Use

2.3 Wood Utilization

2.4 Conservation

2.5 Topographic Gradient

3. Results

4. Conclusions

Abbreviations

Declarations

Ethics Approval and Consent to Participate

Consent for Publication

Availability of Data and Materials

Competing Interests

Funding

Author’s Contributions

Acknowledgements

References

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