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.

Mangroves in the subtropical area of Japan are growing to their northern limits, yet little is known of their phenology. The aim of the present study was to understand both vegetative and reproductive phenology patterns, such as leaf emergence, leaf fall, bud setting, flowering, fruiting and propagule setting, in the mangrove Kandelia obovata. The phenology of this species was assessed using litter-fall data for 5 years. Leaf and stipule litter-falls continued with a clear monthly pattern throughout the years. New leaf production and leaf fall peaked in summer, immediately after the propagules fell. Leaf and stipule litter-falls were linked to monthly sunshine hour, and monthly mean air temperature and monthly mean air relative humidity, respectively. Kandelia obovata had a distinct flowering period, with the flowering phenophase starting in spring and continuing into summer. Fruit initiation started at the end of summer and continued into autumn, whereas propagule production occurred during winter and spring. Flowering of K. obovata was influenced by monthly sunshine hour and monthly mean air temperature, whereas fruit and propagule litter-falls were not linked to any climatic factors. The present results showed that a small portion (4.4%) of flowers developed into propagules. The average development period from flower buds to mature propagules was approximately 11 months. Kendall's consistency coefficient suggested that the monthly trends in vegetative and reproductive litter-fall components, except for branches, did not change significantly among years.

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Despite the potential importance of mangrove forests in carbon cycling and coastal ecology, information on mangrove respiration is scanty. Aboveground nighttime respiration of mangrove Kandelia obovata trees at the northernmost limit of their distribution was measured monthly throughout a year to investigate size-dependence and seasonal variation in respiration. Six sample trees of different sizes were selected from a completely closed canopy stand. Respiration rate (r) of K. obovata trees at a monthly mean temperature increased with increasing mass (m). This tendency was described by means of the power function r = fm h , where f is the multiplying coefficient and h is the scaling exponent. The exponent values ranged from 0.723 to 1.085. In the cool winter (dormant season), the exponent h was close to 1.0, while in the warm summer (growing season) the exponent was closer to 3/4. Respiration varies more between seasons in small-sized trees than in large-sized trees. The relative increase in respiration from the winter dormant season to the summer growing season was large in the small-sized trees compared with that in the large-sized trees. The variation in respiration between the 2 seasons is explained on the basis of theories about resource harvesting and transport. Separation of summer respiration into growth and maintenance components is suggested to better understand the dependence of respiration on size and temperature.

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