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1. Recovering wetland biogeomorphic feedbacks to restore the world’s biotic carbon hotspots

   https://doi.org/10.1126/science.abn1479  

   Temmink, Ralph J. ; Lamers, Leon P. ; Angelini, Christine ; Bouma, Tjeerd J. ; Fritz, Christian ; van de Koppel, Johan ; Lexmond, Robin ; Rietkerk, Max ; Silliman, Brian R. ; Joosten, Hans ; et al ( May 2022 , Science)

   BACKGROUND Evaluating effects of global warming from rising atmospheric carbon dioxide (CO 2 ) concentrations requires resolving the processes that drive Earth’s carbon stocks and flows. Although biogeomorphic wetlands (peatlands, mangroves, salt marshes, and seagrass meadows) cover only 1% of Earth’s surface, they store 20% of the global organic ecosystem carbon. This disproportionate share is fueled by high carbon sequestration rates per unit area and effective storage capacity, which greatly exceed those of oceanic and forest ecosystems. We highlight that feedbacks between geomorphology and landscape-building wetland vegetation underlie these critical qualities and that disruption of these biogeomorphic feedbacks can switch these systems from carbon sinks into sources. ADVANCES A key advancement in understanding wetland functioning has been the recognition of the role of reciprocal organism-landform interactions, “biogeomorphic feedbacks.” Biogeomorphic feedbacks entail self-reinforcing interactions between biota and geomorphology, by which organisms—often vegetation—engineer landforms to their own benefit following a positive density-dependent relationship. Vegetation that dominates major carbon-storing wetlands generate self-facilitating feedbacks that shape the landscape and amplify carbon sequestration and storage. As a result, per unit area, wetland carbon stocks and sequestration rates greatly exceed those of terrestrial forests and oceans, ecosystems that worldwide harbor large stocks because of their largemore »areal extent. Worldwide biogeomorphic wetlands experience human-induced average annual loss rates of around 1%. We estimate that associated carbon losses amount to 0.5 Pg C per year, levels that are equivalent to 5% of the estimated overall anthropogenic carbon emissions. Because carbon emissions from degraded wetlands are often sustained for centuries until all organic matter has been decomposed, conserving and restoring biogeomorphic wetlands must be part of global climate solutions. OUTLOOK Our work highlights that biogeomorphic wetlands serve as the world’s biotic carbon hotspots, and that conservation and restoration of these hotspots offer an attractive contribution to mitigate global warming. Recent scientific findings show that restoration methods aimed at reestablishing biogeomorphic feedbacks can greatly increase establishment success and restoration yields, paving the way for large-scale restoration actions. Therefore, we argue that implementing such measures can facilitate humanity in its pursuit of targets set by the Paris Agreement and the United Nations Decade on Ecosystem Restoration. Carbon storage in biogeomorphic wetlands. Organic carbon ( A ) stocks, ( B ) densities, and ( C ) sequestration rates in the world’s major carbon-storing ecosystems. Oceans hold the largest stock, peatlands (boreal, temperate, and tropical aggregated) store the largest amount per unit area, and coastal ecosystems (mangroves, salt marshes, and seagrasses aggregated) support the highest sequestration rates. ( D and E ) Biogeomorphic feedbacks, indicated with arrows, can be classified as productivity stimulating or decomposition limiting. Productivity-stimulating feedbacks increase resource availability and thus stimulate vegetation growth and organic matter production. Although production is lower in wetlands with decomposition-limiting feedbacks, decomposition is more strongly limited, resulting in net accumulation of organic matter. (D) In fens, organic matter accumulation from vascular plants is amplified by productivity-stimulating feedbacks. Once the peat rises above the groundwater and is large enough to remain waterlogged by retaining rainwater, the resulting bog maintains being waterlogged and acidic, resulting in strong decomposition-limiting feedbacks. (E) Vegetated coastal ecosystems generate productivity-stimulating feedbacks that enhance local production and trapping of external organic matter.« less
2. Costs of forest carbon sequestration in the presence of climate change impacts

   https://doi.org/10.1088/1748-9326/ac8ec5  

   Golub, Alla ; Sohngen, Brent ; Cai, Yongyang ; Kim, John ; Hertel, Thomas ( September 2022 , Environmental Research Letters)

   Forests play a critical role in mitigating climate change, and, at the same time, are predicted to experience large-scale impacts of climate change that will affect the efficiency of forests in mitigation efforts. Projections of future carbon sequestration potential typically do not account for the changing economic costs of timber and agricultural production and land use change. We integrated a dynamic forward-looking economic optimization model of global land use with results from a dynamic global vegetation model and meta-analysis of climate impacts on crop yields to project future carbon sequestration in forests. We find that the direct impacts of climate change on forests, represented by changes in dieback and forest growth, and indirect effects due to lost crop productivity, together result in a net gain of 17 Gt C in aboveground forest carbon storage from 2000 to 2100. Increases in climate-driven forest growth rates will result in an 81%–99% reduction in costs of reaching a range of global forest carbon stock targets in 2100, while the increases in dieback rates are projected to raise the costs by 57%–132%. When combined, these two direct impacts are expected to reduce the global costs of climate change mitigation in forests by moremore »than 70%. Inclusion of the third, indirect impact of climate change on forests through reduction in crop yields, and the resulting expansion of cropland, raises the costs by 11%–38% and widens the uncertainty range. While we cannot rule out the possibility of climate change increasing mitigation costs, the central outcomes of the simultaneous impacts of climate change on forests and agriculture are 64%–86% reductions in the mitigation costs. Overall, the results suggest that concerns about climate driven dieback in forests should not inhibit the ambitions of policy makers in expanding forest-based climate solutions.

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3. Global progress in incorporating climate adaptation into land protection for biodiversity since Aichi targets

   https://doi.org/10.1111/gcb.15511  

   Carrasco, Luis ; Papeş, Monica ; Sheldon, Kimberly S. ; Giam, Xingli ( February 2021 , Global Change Biology)

   Climate adaptation strategies are being developed and implemented to protect biodiversity from the impacts of climate change. A well‐established strategy involves the identification and addition of new areas for conservation, and most countries agreed in 2010 to expand the global protected area (PA) network to 17% by 2020 (Aichi Biodiversity Target 11). Although great efforts to expand the global PA network have been made, the potential of newly established PAs to conserve biodiversity under future climate change remains unclear at the global scale. Here, we conducted the first global‐extent, country‐level assessment of the contribution of PA network expansion toward three key land prioritization approaches for biodiversity persistence under climate change: protecting climate refugia, protecting abiotic diversity, and increasing connectivity. These approaches avoid uncertainties of biodiversity predictions under climate change as well as the issue of undescribed species. We found that 51% of the countries created new PAs in locations with lower mean climate velocity (representing better climate refugia) and 58% added PAs in areas with higher mean abiotic diversity compared to the available, non‐human‐dominated lands not chosen for protection. However, connectivity among PAs declined in 53% of the countries, indicating that many new PAs were located far from existingmore »PAs. Lastly, we identified potential improvements for climate adaptation, showing that 94% of the countries have the opportunity to improve in executing one or more approaches to conserve biodiversity. Most countries (60%) were associated with multiple opportunities, highlighting the need for integrative strategies that target multiple land protection approaches. Our results demonstrate that a global improvement in the protection of climate refugia, abiotic diversity, and connectivity of reserves is needed to complement land protection informed by existing and projected species distributions. Our study also provides a framework for countries to prioritize land protection for climate adaptation using publicly available data.

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4. Carbon uptake in Eurasian boreal forests dominates the high‐latitude net ecosystem carbon budget

   https://doi.org/10.1111/gcb.16553  

   Watts, Jennifer D. ; Farina, Mary ; Kimball, John S. ; Schiferl, Luke D. ; Liu, Zhihua ; Arndt, Kyle A. ; Zona, Donatella ; Ballantyne, Ashley ; Euskirchen, Eugénie S. ; Parmentier, Frans‐Jan W. ; et al ( January 2023 , Global Change Biology)

   Arctic‐boreal landscapes are experiencing profound warming, along with changes in ecosystem moisture status and disturbance from fire. This region is of global importance in terms of carbon feedbacks to climate, yet the sign (sink or source) and magnitude of the Arctic‐boreal carbon budget within recent years remains highly uncertain. Here, we provide new estimates of recent (2003–2015) vegetation gross primary productivity (GPP), ecosystem respiration (R_eco), net ecosystem CO₂exchange (NEE;R_eco − GPP), and terrestrial methane (CH₄) emissions for the Arctic‐boreal zone using a satellite data‐driven process‐model for northern ecosystems (TCFM‐Arctic), calibrated and evaluated using measurements from >60 tower eddy covariance (EC) sites. We used TCFM‐Arctic to obtain daily 1‐km²flux estimates and annual carbon budgets for the pan‐Arctic‐boreal region. Across the domain, the model indicated an overall average NEE sink of −850 Tg CO₂‐C year⁻¹. Eurasian boreal zones, especially those in Siberia, contributed to a majority of the net sink. In contrast, the tundra biome was relatively carbon neutral (ranging from small sink to source). Regional CH₄emissions from tundra and boreal wetlands (not accounting for aquatic CH₄) were estimated at 35 Tg CH₄‐C year⁻¹. Accounting for additional emissions from open water aquatic bodies and from fire, using available estimates from the literature, reduced the total regional NEE sink bymore »21% and shifted many far northern tundra landscapes, and some boreal forests, to a net carbon source. This assessment, based on in situ observations and models, improves our understanding of the high‐latitude carbon status and also indicates a continued need for integrated site‐to‐regional assessments to monitor the vulnerability of these ecosystems to climate change.

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5. Restoration Thinning in a Drought‐Prone Idaho Forest Creates a Persistent Carbon Deficit

   https://doi.org/10.1029/2020JG005815  

   Stenzel, J. E. ; Berardi, D. M. ; Walsh, E. S. ; Hudiburg, T. W. ( March 2021 , Journal of Geophysical Research: Biogeosciences)

   Western US forests represent a carbon sink that contributes to meeting regional and global greenhouse gas targets. Forest thinning is being implemented as a strategy for reducing forest vulnerability to disturbance, including mortality from fire, insects, and drought, as well as protecting human communities. However, the terrestrial carbon balance impacts of thinning remain uncertain across regions, spatiotemporal scales, and treatment types. Continuous and in situ long‐term measurements of partial harvest impacts to stand‐scale carbon and water cycle dynamics are nonetheless rare. Here, we examine post‐thinning carbon and water flux impacts in a young ponderosa pine forest in Northern Idaho. We examine in situ stock and flux impacts during the 3 years after treatment as well as simulate the forest sector carbon balance through 2050, including on and off‐site net emissions. During the observation period, increases in tree‐scale net primary production (NPP) and water use persistence through summer drought did not overcome the impacts of density reduction, leading to 45% annual reductions of NPP. Growth duration remained constrained by summer drought in control and thinned stands. Ecosystem model and life cycle assessment estimates demonstrated a net forest sector carbon deficit relative to control stands of 27.0 Mg C ha⁻¹in 2050 due tomore »emissions from dead biomass pools despite increases to net ecosystem production. Our results demonstrate dynamics resulting in carbon losses from forest thinning, providing a baseline with which to inform landscape‐scale modeling and assess tradeoffs between harvest losses and potential gains from management practices.

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