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Globally, carbon-rich mangrove forests are deforested and degraded due to land-use and land-cover change (LULCC). The impact of mangrove deforestation on carbon emissions has been reported on a global scale; however, uncertainty remains at subnational scales due to geographical variability and field data limitations. We present an assessment of blue carbon storage at five mangrove sites across West Papua Province, Indonesia, a region that supports 10% of the world's mangrove area. The Additional supporting information may be found online in the Supporting Information section. How to cite this article: Sasmito SD, Sillanpää M, Hayes MA, et al. Mangrove blue carbon stocks and dynamics are controlled by hydrogeomorphic settings and land-use change. Glob

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Aim Mangrove wetlands span broad geographical gradients, resulting in functionally diverse tree communities. We asked whether latitudinal variation, allometric scaling relationships and species composition influence mangrove forest structure and biomass allocation across biogeographical regions and distinct coastal morphologies. Location Global. Time period Present. Major taxa studied Mangrove ecosystems. Methods We built the largest field‐based dataset on mangrove forest structure and biomass to date (c. 2,800 plots from 67 countries) to address macroecological questions pertaining to structural and functional diversity of mangroves spanning biogeographical and coastal morphology gradients. We used frequentist inference statistics and machine learning models to determine environmental drivers that control biomass allocation within and across mangrove communities globally. Results Allometric scaling relationships and forest structural complexity were consistent across biogeographical and coastal morphology gradients, suggesting that mangrove biomass is controlled by regional forcings rather than by latitude or species composition. For instance, nearly 40% of the global variation in biomass was explained by regional climate and hydroperiod, revealing nonlinear thresholds that control biomass accumulation across broad geographical gradients. Furthermore, we found that ecosystem‐level carbon stocks (average 401 ± 48 MgC/ha, covering biomass and the top 1 m of soil) varied little across diverse coastal morphologies, reflecting regional bottom‐up geomorphic controls that shape global patterns in mangrove biomass apportioning. Main conclusions Our findings reconcile views of wetland and terrestrial forest macroecology. Similarities in stand structural complexity and cross‐site size–density relationships across multiscale environmental gradients show that resource allocation in mangrove ecosystems is independent of tree size and invariant to species composition or latitude. Mangroves follow a universal fractal‐based scaling relationship that describes biomass allocation for several other terrestrial tree‐dominated communities. Understanding how mangroves adhere to these universal allometric rules can improve our ability to account for biomass apportioning and carbon stocks in response to broad geographical gradients.

Coastal wetlands have disproportionately high carbon densities, known as blue carbon, compared to most terrestrial ecosystems. Mangroves and their blue carbon stocks are at risk globally from Land Use and Land Cover Change (LULCC) activities such as aquaculture, alongside biophysical disturbances such as sea-level rise and cyclones. Global estimates of carbon emissions from mangrove loss have been previously unable to differentiate between the variable impacts of different drivers of loss. This Review discusses the impacts that different LULCC activities and biophysical disturbances have on carbon stocks (biomass and soil) and carbon fluxes (CO 2 and CH 4 ). The dynamics of carbon stocks and fluxes depends on the type of LULCC; aquaculture often results in biomass and soil carbon removal, and some forms of agriculture can substantially increase methane emissions. Natural disturbances

West Papua’s Bintuni Bay is Indonesia’s largest contiguous mangrove block, only second to the world’s largest mangrove in the Sundarbans, Bangladesh. As almost 40% of these mangroves are designated production forest, we assessed the effects of commercial logging on forest structure, biomass recovery, and soil carbon stocks and burial in five-year intervals, up to 25 years post-harvest. Through remote sensing and field surveys, we found that canopy structure and species diversity were gradually enhanced following biomass recovery. Carbon pools preserved in soil were supported by similar rates of carbon burial before and after logging. Our results show that mangrove forest management maintained between 70 and 75% of the total ecosystem carbon stocks, and 15–20% returned to the ecosystem after 15–25 years. This analysis suggests that mangroves managed through selective logging provide an opportunity for coastal nature-based climate solutions, while provisioning other ecosystem services, including wood and wood products.

Mangrove forests in Bintuni Bay, West Papua, Indonesia, have been managed for timber extraction since 1988 to produce wood chips using a 30-year rotation cycle. The first rotation cycle was completed, resulting in secondary mangrove forests with various stand ages (1–30 years). A large-scale forest inventory was conducted for all harvested blocks to recognize actual standing stock for the 2021–2030 management plan. A total of 434 quadrat plots (20 m x 20 m) covering 17.36 ha each were used to observe forest standing stock. The results present the dynamics of secondary mangrove forests after the initial rotation cycle. At the end of the first cycle (30-year-old stand), secondary mangrove forests provided a volume of 290.12 m3 ha-1 and potential extractable biomass of 203.03 ton ha-1 with mean diameter, basal area, and stem density of 16.91 cm, 29.18 m2 ha-1, and 1,370 stem ha-1, respectively. Annual increment of volume, biomass, and diameter were estimated to be 9.67 m3 ha-1 year-1, 6.77 ton ha-1 year-1, and 0.56 cm year-1, consecutively. The dynamics of secondary mangrove forests could provide significant information in the context of the management plan and implementation of the silviculture system to ensure the sustainability of utilization in managed mangrove forests. Keywords: Forest regeneration, Silviculture, Standing stock, Sustainable management, Timber utilization

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