By Lidong Mo, Constantin M. Zohner et al
Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system. Remote-sensing estimates to quantify carbon losses from global forests are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced and satellite-derived approaches to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151–363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets.
Download full study: (2023) Integrated global assessment of the natural forest carbon potential.pdf
By H. Damon Matthews, Kirsten Zickfeld, Mitchell Dickau, Alexander J. MacIsaac, Sabine Mathesius, Claude-Michel Nzotungicimpaye & Amy Luers
Meeting the Paris Agreement’s climate objectives will require the world to achieve net-zero CO2 emissions around or before mid-century. Nature-based climate solutions, which aim to preserve and enhance carbon storage in terrestrial or aquatic ecosystems, could be a potential contributor to net-zero emissions targets. However, there is a risk that successfully stored land carbon could be subsequently lost back to the atmosphere as a result of disturbances such as wildfire or deforestation. Here we quantify the climate effect of nature-based climate solutions in a scenario where land-based carbon storage is enhanced over the next several decades, and then returned to the atmosphere during the second half of this century. We show that temporary carbon sequestration has the potential to decrease the peak temperature increase, but only if implemented alongside an ambitious mitigation scenario where fossil fuel CO2 emissions were also decreased to net-zero. We also show that non-CO2 effects such as surface albedo decreases associated with reforestation could counter almost half of the climate effect of carbon sequestration. Our results suggest that there is climate benefit associated with temporary nature-based carbon storage, but only if implemented as a complement (and not an alternative) to ambitious fossil fuel CO2 emissions reductions.
(2022) Temporary nature-based carbon removal can lower peak warming in a well-below 2 °C scenario.pdf
A report from the Metcalf Foundation
While the international community has struggled to curtail greenhouse gas emissions, forests around the world have been buying us time to transition to clean, renewable-energy economies. Forests act as giant carbon vaults, storing away in their wood, leaves, and soil more carbon than is found in all currently accessible coal, oil, and gas reserves combined. Forests also continuously add to this carbon vault and in recent decades have absorbed nearly one-third of the greenhouse gases we release each year. The global scientific community has made it clear we must limit warming to no more than 1.5 degrees Celsius (C) in order to avoid the worst impacts of climate change, and that doing so will require not just ending our reliance on fossil fuels, but also protecting intact and primary forests’ ability to store and absorb carbon.
(2020) The Logging Loophole.pdf
By David J. Mildrexler et al
Large-diameter trees store disproportionally massive amounts of carbon and are a major driver of carbon cycle dynamics in forests worldwide. In the temperate forests of the western United States, proposed changes to Forest Plans would significantly weaken protections for a large portion of trees greater than 53 cm (21 inches) in diameter (herein referred to as “large-diameter trees”) across 11.5 million acres (∼4.7 million ha) of National Forest lands. This study is among the first to report how carbon storage in large trees and forest ecosystems would be affected by a proposed policy. We examined the proportion of large-diameter trees on National Forest lands east of the Cascade Mountains crest in Oregon and Washington, their contribution to overall aboveground carbon (AGC) storage, and the potential reduction in carbon stocks resulting from widespread harvest. We analyzed forest inventory data collected on 3,335 plots and found that large trees play a major role in the accumulated carbon stock of these forests. Tree AGC (kg) increases sharply with tree diameter at breast height (DBH; cm) among five dominant tree species. Large trees accounted for 2.0 to 3.7% of all stems (DBH ≥ 1” or 2.54 cm) among five tree species; but held 33 to 46% of the total AGC stored by each species. Pooled across the five dominant species, large trees accounted for 3% of the 636,520 trees occurring on the inventory plots but stored 42% of the total AGC. A recently proposed large-scale vegetation management project that involved widespread harvest of large trees, mostly grand fir, would have removed ∼44% of the AGC stored in these large-diameter trees, and released a large amount of carbon dioxide to the atmosphere. Given the urgency of keeping additional carbon out of the atmosphere and continuing carbon accumulation from the atmosphere to protect the climate system, it would be prudent to continue protecting ecosystems with large trees for their carbon stores, and also for their co-benefits of habitat for biodiversity, resilience to drought and fire, and microclimate buffering under future climate extremes.
(2020) Large Trees Dominate Carbon Storage in Forests East of the Cascade Crest in the United States Pacific Northwest.pdf
By William Moomaw et al
Climate change and loss of biodiversity are widely recognized as the foremost environmental challenges of our time. Forests annually sequester large quantities of atmospheric carbon dioxide (CO2), and store carbon above and below ground for long periods of time. Intact forests—largely free from human intervention except primarily for trails and hazard removals—are the most carbon-dense and biodiverse terrestrial ecosystems, with additional benefits to society and the economy. Internationally, focus has been on preventing loss of tropical forests, yet U.S. temperate and boreal forests remove sufficient atmospheric CO2 to reduce national annual net emissions by 11%. U.S. forests have the potential for much more rapid atmospheric CO2 removal rates and biological carbon sequestration by intact and/or older forests. The recent 1.5 Degree Warming Report by the Intergovernmental Panel on Climate Change identifies reforestation and afforestation as important strategies to increase negative emissions, but they face significant challenges: afforestation requires an enormous amount of additional land, and neither strategy can remove sufficient carbon by growing young trees during the critical next decade(s). In contrast, growing existing forests intact to their ecological potential—termed proforestation—is a more effective, immediate, and low-cost approach that could be mobilized across suitable forests of all types. Proforestation serves the greatest public good by maximizing co-benefits such as nature-based biological carbon sequestration and unparalleled ecosystem services such as biodiversity enhancement, water and air quality, flood and erosion control, public health benefits, low impact recreation, and scenic beauty.
(2019) Intact Forests in the United States- Proforestation Mitigates Climate Change and Serves the Greatest Good.pdf
By Sierra Club BC
Our planet is in the midst of a climate crisis, and the latest science calls for reducing global emissions by half within the next decade to avoid catastrophic climate change. Most of the world’s intact forests, particularly primary (unlogged) forests, help slow climate change by taking carbon out of the atmosphere and storing it in living and dead trees and soil. However, according to provincial data, as a result of destructive logging and climate impacts like beetle outbreaks, forests in B.C. have released more carbon than they absorb for over a decade.
Forest clearcutting is a major contributor to carbon emissions and loss of carbon capture in the Pacific Northwest of North America. Clearcutting causes a rapid and large loss of carbon from decomposing organic matter and soils, particularly when old-growth forests are logged. Additionally, it takes 13 years or more before the replanted young forest begins to absorb more carbon than is still being released from the area cut. For at least 13 years, these areas are “sequestration dead zones”: clearcut lands that emit more carbon than they absorb.
For this report, Sierra Club BC reviewed B.C. government data to identify the total area of old-growth and second-growth forest logged across the province over 13 years (2005-2017), and to estimate the carbon emissions and the loss of carbon capture caused by this logging.
The analysis shows a total area of about 3.6 million hectares of “sequestration dead zones,” an area larger than the size of Vancouver Island. This includes over 1.9 million hectares of old-growth forest and close to 1.7 million hectares of second-growth that were cut. The “sequestration dead zones” make up 9.1% of the total area of relatively productive provincial forests.
(2019) Clearcut-Carbon-report Sierra BC.pdf
By Polly C. Buotte et al
Forest carbon sequestration via forest preservation can be a viable climate change mitigation strategy. Here, we identify forests in the western conterminous United States with high potential carbon sequestration and low vulnerability to future drought and fire, as simulated using the Community Land Model and two high carbon emission scenario (RCP 8.5) climate models. High-productivity, low-vulnerability forests have the potential to sequester up to 5,450 Tg CO2 equivalent (1,485 Tg C) by 2099, which is up to 20% of the global mitigation potential previously identified for all temperate and boreal forests, or up to ~6 yr of current regional fossil fuel emissions. Additionally, these forests currently have high above- and below-ground carbon density, high tree species richness, and a high proportion of critical habitat for endangered vertebrate species, indicating a strong potential to support biodiversity into the future and promote ecosystem resilience to climate change. We stress that some forest lands have low carbon sequestration potential but high biodiversity, underscoring the need to consider multiple criteria when designing a land preservation portfolio. Our work demonstrates how process models and ecological criteria can be used to prioritize landscape preservation for mitigating greenhouse gas emissions and preserving biodiversity in a rapidly changing climate.
(2019) Carbon sequestration and biodiversity co-benefits of preserving forests in the western United States.pdf
By Bronson Griscom et al
Better stewardship of land is needed to achieve the Paris Climate Agreement goal of holding warming to below 2 °C; however, con- fusion persists about the specific set of land stewardship options available and their mitigation potential. To address this, we identify and quantify “natural climate solutions” (NCS): 20 conservation, restoration, and improved land management actions that increase car- bon storage and/or avoid greenhouse gas emissions across global forests, wetlands, grasslands, and agricultural lands. We find that the maximum potential of NCS—when constrained by food security, fibre security, and biodiversity conservation—is 23.8 petagrams of CO2 equivalent (PgCO2e) y−1 (95% CI 20.3–37.4). This is ≥30% higher than prior estimates, which did not include the full range of options and safeguards considered here. About half of this maximum (11.3 PgCO2e y−1) represents cost-effective climate mitigation, assuming the social cost of CO2 pollution is ≥100 USD MgCO2e−1 by 2030. Natural climate solutions can provide 37% of cost-effective CO2 mitigation needed through 2030 for a >66% chance of holding warm- ing to below 2 °C. One-third of this cost-effective NCS mitigation can be delivered at or below 10 USD MgCO2−1. Most NCS actions—if effectively implemented—also offer water filtration, flood buffer- ing, soil health, biodiversity habitat, and enhanced climate resilience. Work remains to better constrain uncertainty of NCS mitigation estimates. Nevertheless, existing knowledge reported here provides a robust basis for immediate global action to improve ecosystem stewardship as a major solution to climate change.
(2017) Natural climate solutions.pdf
By N.L. Stephenson et al
Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest carbon cycle—particularly net primary productivity and carbon storage—increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands.
Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree4–7, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation)decrease, remain constant, or increase as trees increase in size and age.
Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree.
The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree’s total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density.
Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to understand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.
Click to download: (2014) Rate of tree carbon accumulation increases continuously with tree size.pdf
By Heather Keith, David Lindenmayer et al
Management of native forests offers opportunities to store more carbon in the land sector through two main activities. Emissions to the atmosphere can be avoided by ceasing logging. Removals of carbon dioxide from the atmosphere can be increased by allowing forests to continue growing. However, the relative benefits for carbon storage of managing native forests for wood production versus protection are contested. Additionally, the potential for carbon storage is impacted upon by disturbance events, such as wildfire, that alter the amount and longevity of carbon stocks.
Using a case study of montane ash forests in southeastern Australia, we demonstrated that the total biomass carbon stock in logged forest was 55% of the stock in old growth forest. Total biomass included above- and below-ground, living and dead. Biomass carbon stock was calculated spatially as an average across the landscape, accounting for variation in environmental conditions and forest age distribution. Reduction in carbon stock in logged forest was due to 66% of the initial biomass being made into products with short lifetimes (<3 years), and to the lower average age of logged forest (<50 years compared with >100 years in old growth forest). Only 4% of the initial carbon stock in the native forest was converted to sawn timber products with lifetimes of 30–90 years.
Carbon stocks are depleted in a harvested forest system compared with an old growth forest, even when storage in wood products and landfill are included. We estimated that continued logging under current plans represented a loss of 5.56 Tg C over 5 years in the area logged (824 square kilometres), compared with a potential gain of 5.18–6.05 TgC over 5 years by allowing continued growth across the montane ash forest region (2326 square kilometres). Avoiding emissions by not logging native forests and allowing them to continue growing is therefore an important form of carbon sequestration. The mitigation value of forest management options of protection versus logging should be assessed in terms of the amount, longevity and resilience of the carbon stored in the forest, rather than the annual rate of carbon uptake.
(2014) Managing temperate forests for carbon storage (opt).pdf
By Mark E. Harmon, PhD, Richardson Endowed Chair and Professor in Forest Science, Department of Forest Ecosystems and Society, Oregon State University.
Testimony before the Subcommittee on National Parks, Forests, and Public Lands of the Committee of Natural Resources for an oversight hearing on “The Role of Federal Lands in Combating Climate Change”, March 3, 2009.
(2009) Harmon Testimony.pdf
By Cortex Consultants for TimberWest
The project is a forest conservation project that will reduce emissions of GHG to the atmosphere through the avoidance of harvesting activities and post-harvesting debris management. The protection of the old-growth forest will increase the long-term storage of carbon in the project area.
(2008) TimberWest Ecosystem Conservation Project.pdf
By Andrew Black et al for PICS
This White Paper describes the potential of forests in the northern hemisphere in general, and in British Columbia in particular, in sequestering atmospheric carbon dioxide and thus mitigating anthropogenic greenhouse gas emissions, apart from providing environmental and economical benefits. We first describe the extent of forest C stocks and C sequestration rates, and how they are affected by climate change and natural and human-induced disturbances. This is followed by a discussion of management for conservation and efficient utilization of forest C stocks and management options for increasing C sequestration rates. We do not attempt to compare the economics of different management options for maximum C sequestration. Rather, we focus on future research needs required for developing an appropriate adaptive management response framework.
(2008) Carbon sequestration in BC's forests and management options.pdf
Climate change will, and is, having a profound impact on these forest ecosystems. Many impacts, such as increases in average temperature and seasonal shifts, are happening in a more compressed timeframe than originally projected by climate scientists. Insect outbreaks, such as the mountain pine beetle, are occurring at a scale that was unimagined ten years ago and some scientists are beginning to warn that many ecosystems may have a “tipping point” beyond which their resilience will be overcome and completely new ecosystems will replace them. Clearly climate strategies in Canada must include those that address the role of this massive and globally significant forest asset.
In parallel to these changes in the natural world, society is rapidly accelerating its discussions concerning how to mitigate against rising carbon emissions and climate change impacts. As a result governments, business and civil society are accelerating discussions concerning how to develop an effective mechanism to reduce carbon emissions. Strategies under development include an abundance of voluntary, and a few regulatory frameworks. While none are identical, many of them contain carbon trading measures that would enable transfers of money from emitters to entities that could sequester or reduce the net rate of carbon emissions. Most of these systems include forests.
In Canada there is a need to grapple with this emerging market and determine how it can be influenced and directed in a manner that supports the carbon storage and sequestration capacity of forests and conserves forest biodiversity, while helping to reduces our total country-wide carbon emissions (not just those of forests). How to do this involves a strategic discussion among leading advocates for policy reform. It is only in this way that we can arrive at a consensus on the key elements of a carbon reduction strategy that includes forests and a plan to secure the outcomes we seek.
(2007) Forest Carbon sequestration and avoided emissions.pdf