Macroecological patterns of forest structure and allometric scaling in mangrove forests

Abstract

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.

Structural Characteristics of the Tallest Mangrove Forests of the American Continent: A Comparison of Ground-Based, Drone and Radar Measurements

“…The mean mangrove AGB values obtained here using the in-situ data are extremely high varying between 862.2 and 626.4 Mg ha −1 (depending on which allometric equation is used). These values are located in the upper range of the recent global synthesis by Rovai et al (2021) and also correspond to the upper range values recently estimated by Trettin et al (2021) for a mangrove forest in Gabon where mangrove trees of up to 60 m can be found. Our estimated mean AGB values are generally higher than those obtained using the AGB values calculated by Simard et al (2019) for the same areas.…”

Predicting mangrove forest dynamics across a soil salinity gradient using an individual-based vegetation model linked with plant hydraulics

“…Such winter depression lowers the production of mangroves in subtropical regions, and may be differentiated from tropical mangroves in terms of productivity. This could be a key factor in explaining and predicting the latitudinal gradients in mangroves' structural variables such as canopy height and AGB with the highest values at the equatorial region (Saenger and Snedaker, 1993;Simard et al, 2019;Rovai et al, 2021).…”

“…Although data and insights on mangrove AGB distributions in relation to environmental variables have recently increased (Simard et al, 2019;Rovai et al, 2015Rovai et al, , 2021, there is still no established way to predict the dynamics of mangrove AGB in the changing environmental conditions. Generally, ecosystem's response to environmental variables is nonlinear, and biomass dynamics is cumulatively affected by nonlinear response.…”

Tropical cyclones cumulatively control regional carbon fluxes in Everglades mangrove wetlands (Florida, USA)

“…It is estimated that mangrove wetlands globally store, in vegetation (above- and belowground) and soil compartments, approximately 4.19–6.17 Pg C 7 , 19 . During the last 10 years, this assessment has improved as more field data are acquired and through remote sensing tools at locations underrepresented in early attempts to produce a global mangrove carbon budget 20 , 21 . However, this value still has large uncertainties at the global scale, as unaccounted carbon budget can range from ~ 104–112 Tg C year −1 22 , 23 .…”