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• The nexus between forest-based climate mitigation and health is poorly researched. • This scoping review identified exposure pathways and health co-benefits from forests. • There is potential for synergies between forest management and health benefits. • Interdisciplinary efforts are required for advancement of research and understanding. Climate change is a pressing global challenge with profound implications for human health. Forest-based climate change mitigation strategies, such as afforestation, reforestation, and sustainable forest management, offer promising solutions to mitigate climate change and simultaneously yield substantial co-benefits for human health. The objective of this scoping review was to examine research trends related to the interdisciplinary nexus between forests as carbon sinks and human health co-benefits. We developed a conceptual framework model, supporting the inclusion of exposure pathways, such as recreational opportunities or aesthetic experiences, in the co-benefit context. We used a scoping review methodology to identify the proportion of European research on forest-based mitigation strategies that acknowledge the interconnection between mitigation strategies and human impacts. We also aimed to assess whether synergies and trade-offs between forest-based carbon sink capacity and human co-benefits has been analysed and quantified. From the initial 4,062 records retrieved, 349 reports analysed European forest management principles and factors related to climate change mitigation capacity. Of those, 97 studies acknowledged human co-benefits and 13 studies quantified the impacts on exposure pathways or health co-benefits and were included for full review. Our analysis demonstrates that there is potential for synergies related to optimising carbon sink capacity together with human co-benefits, but there is currently a lack of holistic research approaches assessing these interrelationships. We suggest enhanced interdisciplinary efforts, using for example multideterminant modelling approaches, to advance evidence and understanding of the forest and health nexus in the context of climate change mitigation. [ABSTRACT FROM AUTHOR]

Hundreds of millions of unstable croplands have been underutilized in the time series by repeated cultivation and abandonment, leading to threats to food security and loss of ecological benefits due to frequent disturbance on ecosystem restoration. Understanding unstable cropland and its connections to Sustainable Development Goals (SDGs) is required in the context of increasing food demand and natural conservation. Here, we first investigate the global cropland instability and influencing factors, then simulate the stable utilization of unstable cropland and its ecological effects under different scenarios of maintaining crop production. 395 million hectares of croplands in 173 countries are found under unstable utilization, accounting for 22% of global croplands. Over three-quarters of unstable croplands are distributed in areas with unfavorable agricultural conditions or high conservation value, and countries experiencing high cropland instability share a common characteristic of climatic or terrain constraints on agriculture. According to the simulation results, 141 million hectares or 36% of the unstable croplands could be released for ecological restoration with 3.8 more billion tons of carbon sequestration, while the rest of the unstable croplands could be stably used to increase 3% of global total crop production. This study highlights the importance of managing unstable croplands in climate mitigation and natural conservation as well as reconciling crop production and other SDGs, with guiding significance for land-use management, climate action, and biodiversity conservation. • 395 million hectares of croplands in 173 countries are under unstable utilization. • Three quarters of unstable croplands are constrained by natural and socio-economic factors. • 36% of the unstable croplands could be released for durable ecosystem recovery by simulation. • Projected increase of 3.8 billion tons of carbon sinks with a 3% increase in crop production. • Stabilizing unstable croplands can benefit the SDG win-win by lasting ecosystem recovery. [ABSTRACT FROM AUTHOR]

Abstract Assessing the status of important carbon sinks such as seagrass meadows is of primary importance when dealing with potential climate change mitigation strategies. This study examined plant and sediment properties in seagrass meadows (Cymodocea nodosa (Ucria) Asch.) from two high p CO 2 –low pH Mediterranean vent systems, located at Milos (Greece) and Vulcano (Italy) Islands, providing insights on carbon storage potential in future acidified oceans. Contrary to what has been suggested, carbon content (both inorganic and organic) and its surficial accumulation decreased at high p CO 2 –low pH in comparison with controls. The decrease in inorganic carbon may result from the higher solubility of carbonates due to the more acidic conditions. At Vulcano, the seagrass properties (e.g. , leaf area, biomass) appeared negatively affected by environmental conditions at high p CO 2 –low pH conditions and this may have had a detrimental effect on the organic carbon content and accumulation. At Milos, organic carbon decreased at high p CO 2 –low pH conditions, despite the increase in seagrass aboveground biomass, leaf length and area, probably as a consequence of site-specific features, which need further investigation and may include both biotic and abiotic factors (e.g., oligotrophic conditions, decreased sedimentation rate and input of allochthonous material). Results suggest that, in contrast to previous predictions based exclusively on the expected positive response of seagrasses to ocean acidification, carbon storage capacity of the seagrass C. nodosa may not increase at high p CO 2 -low pH conditions. This study emphasizes the need to investigate further the potential alteration in the climate mitigation service delivered by seagrass meadows in acidified oceans. Highlights • Seagrass features differed between control and low pH stations inconsistently in the two vents. • Carbon content and its surficial accumulation decreased at high p CO 2 –low pH conditions. • Carbon storage capacity of the seagrass may not increase at high p CO 2 -low pH conditions. [ABSTRACT FROM AUTHOR]

Studies have suggested that some mangrove soils might contribute to wetland methane (CH 4 ) production and emissions, especially when the mangroves are disturbed. CH 4 emissions were measured seasonally from nine locations on two mangrove creeks on Naples Bay in southwest Florida, USA. One of the tidal creeks has been impacted in the past few decades with alteration of upstream watersheds and freshwater inflows; the other creek was an un-impacted reference tidal creek. Our study sites were established along a longitudinal gradient (distance to the creeḱs mouth) with different plant communities and freshwater influences, which were further evaluated by measurements during the dry and wet seasons. CH 4 emission measurements were also performed during the flood and ebb tides (n = 6) to incorporate the influence of water level fluctuations on CH 4 emissions. Additionally, hydroperiods and soil pore water electrical conductivity (EC) as a measure of salinity were measured along the study creeks. Our study showed very small, if not negligible, CH 4 emissions from mangrove soils in this southwest Florida location at all sampling locations and sampling times. Despite our collecting over 1900 methane samples from methane emission chambers, most analyses of rates of change in the chambers showed no methane emissions. Seasonal averages ranged from 0.24 to 1.68 mg CH 4 -C m −2 d −1 (annual average of 0.32 g CH 4 -C m −2 y −1 ). Ironically, the lowest methane emissions were at the end (December–January) of a typical wet season of daily rainfall and were highest in the dry season (March–April) when freshwater inputs from watersheds and precipitation were negligible. Water level fluctuations, freshwater inputs, and plant species composition did not play a significant role in CH 4 emissions. There appeared to be a slight pattern of methane emissions versus air temperature but the relationship was not linear. Combining our results with carbon sequestration rates in a companion study suggested that mangroves in southwest Florida are clearly net sinks of both carbon and radiative forcing and therefore beneficial for mitigating climate warming. [ABSTRACT FROM AUTHOR]

Among blue carbon ecosystems, seagrass meadows have been highlighted for their contribution to the ocean carbon cycle and climate change mitigation derived from their capacity to store large amounts of carbon over long periods of time in their sediments. Most of the available estimates of carbon stocks beneath seagrass meadows are based on the analysis of short sediment cores in very limited numbers. In this study, high-resolution seismic reflection techniques were applied to obtain an accurate estimate of the potential size of the organic deposit underlying the meadows of the Mediterranean seagrass Posidonia oceanica (known as 'matte'). Seismic profiles were collected over 1380 km of the eastern continental shelf of Corsica (France, Mediterranean Sea) to perform a large-scale inventory of the carbon stock stored in sediments. The seismic data were ground-truthed by sampling sediment cores and using calibrated seismo-acoustic surveys. The data interpolation map highlighted a strong spatial heterogeneity of the matte thickness. The height of the matte at the site was estimated at 251.9 cm, being maximum in shallow waters (10–20 m depth), near river mouths and lagoon outlets, where the thickness reached up to 867 cm. Radiocarbon dates revealed the presence of seagrass meadows since the mid-Holocene (7000–9000 cal yr BP). Through the top meter of soil, the matte age was estimated at 1656 ± 528 cal yr BP. The accretion rate showed a high variability resulting from the interplay of multiple factors. Based on the surface area occupied by the meadows, the average matte thickness underneath them and the carbon content, the matte volume and total C org stock were estimated at 403.5 ± 49.4 million m3 and 15.6 ± 2.2 million t C org , respectively. These results confirm the need for the application of large-scale methods to estimate the size of the carbon sink associated with seagrass meadows worldwide. [Display omitted] • Thickness of P. oceanica carbon sink was estimated over more 20,424 ha in Corsica. • This study is based on the use of an extensive HR seismic reflection dataset. • Matte height and volume were assessed on average at 2.5 m and 404 ± 49 million m3. • Seismic reflection method has proved valuable for large-scale carbon sink estimates. [ABSTRACT FROM AUTHOR]

• i-Tree planting tool was used for a life cycle analysis on current and potential CSS. • The CSS potential of green yards is limited, but the impact increases with upscaling. • Soil with added biochar can significantly contribute to the CSS capacity. • CSS needs more attention in the planning of urban green. Cities have been identified as key actors in climate change mitigation. Nature based carbon sinks have been suggested as a means of mitigating the greenhouse gas emissions of cities. Although there are several studies on the carbon storage and sequestration (CSS) of urban green, the role of residential sites is not fully understood. In addition, the carbon storage of soils is often excluded. Also the implications for planning require more attention. This study estimates the CSS potential of trees and biochar in urban residential yards and identifies effective means to enhance it. Moreover, the study discusses the results at the city scale. The research is based on a case study in Helsinki, Finland, and applies i-Tree planting tool to assess the current and potential life cycle CSS of the case area. The results reveal that trees and the mixing of biochar into growing medium can increase the CSS considerably. The CSS potential of the case area is 520 kg CO 2 per resident during 50 years. The added biochar accounts for 65 % of the capacity and the biomass of trees accounts for 35 %. At the city scale, it would lead to 330 000 t CO 2 being stored during 50 years. The findings suggest that green planning could contribute more strongly to climate change mitigation by encouraging the use of biochar and the planting of trees, in addition to ensuring favourable growing conditions. [ABSTRACT FROM AUTHOR]