Large uncertainties in tree and forest carbon estimates weaken national efforts to accurately estimate aboveground biomass (AGB) for their national monitoring, measurement, reporting and verification system. Allometric equations to estimate biomass have improved, but remain limited. They rely on destructive sampling; large trees are under-represented in the data used to create them; and they cannot always be applied to different regions. These factors lead to uncertainties and systematic errors in biomass estimations. We developed allometric models to estimate tree AGB in Guyana. These models were based on tree attributes (diameter, height, crown diameter) obtained from terrestrial laser scanning (TLS) point clouds from 72 tropical trees and wood density. We validated our methods and models with data from 26 additional destructively harvested trees. We found that our best TLS-derived allometric models included crown diameter, provided more accurate AGB estimates (R2 = 0.92-0.93) than traditional pantropical models ( R2 = 0.85-0.89), and were especially accurate for large trees (diameter > 70 cm). The assessed pantropical models underestimated AGB by 4 to 13%. Nevertheless, one pantropical model (Chave et al. 2005 without height) consistently performed best among the pantropical models tested (R2 = 0.89) and predicted AGB accurately across all size classes-which but for this could not be known without destructive or TLS-derived validation data. Our methods also demonstrate that tree height is difficult to measure in situ, and the inclusion of height in allometric models consistently worsened AGB estimates. We determined that TLS-derived AGB estimates were unbiased. Our approach advances methods to be able to develop, test, and choose allometric models without the need to harvest trees.
Tag: allometry
The crab silvofishery system as a conservation strategy in mangrove restoration area: A case study on the coast of Banyuasin, South Sumatra
Anthropogenic activities such as logging and converting mangrove forests into plantations have degraded coastal ecosystems and reduced their ecological stability. Silvofishery is a restoration system that balances the ecological and economic functions of mangroves. In Marga Sungsang Village, South Sumatra, mangrove restoration was integrated with mud crab (Scylla spp.) cultivation through a crab silvofishery system. This study aimed to analyze the contribution of mangrove restoration with a mud crab silvofishery system to mud crab growth. The study was conducted from August 2024 to January 2025. Growth parameters included carapace length, width, and body weight. Analyses covered absolute growth and the correlation between carapace width and body weight. Results showed that in non-mangrove ponds, Scylla tranquebarica males exhibited negative allometry (prominent carapace width), while females showed positive allometry (prominent body weight). Scylla paramamosain showed negative allometry in both sexes. In contrast, in mangrove ponds, both species showed positive allometry for both sexes, indicating higher weight gain. These findings suggest that mangrove vegetation provides optimal habitat conditions by increasing nutrient availability, protecting crabs during molting, and improving substrate quality. The results not only demonstrate the bioecological relationship between mangrove vegetation and mangrove crab growth but also highlight the role of crab silvofishery systems in supporting food security, mitigating climate change, and conserving coastal ecosystems. These results align with the Sustainable Development Goals (SDGs), specifically goal 2 (end hunger, achieve food security and improved nutrition, and promote sustainable agriculture), goal 13 (climate action), and goal 14 (life below water). Although informative, this study was limited by temporal observations conducted only at the start of seed stocking and at harvest. Further research with continuous monitoring and environmental parameter analysis is needed. The findings can support mangrove restoration policies that integrate vegetation recovery with sustainable community-based aquaculture and promote blue economy development.
Allometric estimation of above-ground biomass and leaf area in managed Grevillea robusta agroforestry systems
Non-destructive methods for determining the biomass and leaf area of individual trees throughout their growing cycle are an essential tool in agroforestry research, but must be capable of providing reliable estimates despite the influence that management strategies such as pruning may have on tree form. In the present study, allometric methods involving measurements of the diameter of all branches provided reliable estimates of canopy leaf area and biomass for grevillea trees (Grevillea robusta A. Cunn.; Proteaceae) grown as poles, but proved unsuitable for routine measurements because of their time-consuming nature. An alternative, less laborious method based on measurements of trunk cross-sectional area immediately below the first branch of the canopy provided satisfactory allometric estimates of leaf area and canopy biomass. Trunk biomass was determined from measurements of tree height and diameter at breast height using established methodology based on the assumption that trunk volume may be calculated using a quadratic paraboloid model; biomass was determined as the product of trunk volume and the specific gravity of the wood. The theoretical basis, development and validation of allometric methods for estimating tree growth are discussed and their wider applicability to other agroforestry systems is assessed.
Reducing uncertainty in the use of allometric biomass equations for predicting above-ground tree biomass in mixed secondary forests
Estimates of forest biomass are needed for tracking changes in C stocks, as well as for other purposes. A common method for estimating forest biomass is through use of allometric equations which relate the biomass of individual trees to easily obtainable non-destructive measurements, such as diameter. A common form is B=aDb for biomass B, diameter D and parameters a and b. Field data collected in Sumatra and compared with previously published data show that the values of a and b vary between sites. This variation is likely to be the major source of uncertainty if biomass estimates are produced using equations that are not calibrated for individual sites. However, calibration by collection of B and D data for each site is unrealistic, requiring destructive measures. Methods of choosing values for a and b are, therefore, proposed that do not require destructive measurements. The parameter b can be estimated from the site-specific relationship between height (H) and diameter, H=kDc as b=2+c. The parameter a can be estimated from the average wood density (ρ) at the site as a=rρ, where r is expected to be relatively stable across sites. The allometric equation proposed is therefore B=rρD2+c.
Allometric equations based on a fractal branching model for estimating aboveground biomass of four native tree species in the Philippines
Fractal branching models can provide a non-destructive and generic tool for estimating tree shoot and root length and biomass, but field validation is rarely described in the literature. We compared estimates of above ground tree biomass for four indigenous tree used on farm in the Philippines based on the WanFBA model tree architecture with data from destructive sampling. Allometric equations for the four species varied in the constant (biomass at virtual stem diameter 1) and power of the scaling rule (b in Y = aDb), deviating from the value of 8/3 that is claimed to be universal. Allometric equations for aboveground biomass were 0.035 D2.87 for Shorea contorta, 0.133 D2.36 for Vitex parviflora, 0.063 D2.54 for Pterocarpus indicus and 0.065 D2.28 for Artocarpus heterophyllus, respectively. Allometric equations for branch biomass had a higher b factor than those for total biomass (except in Artocarpus); allometric equations for the leave twig fraction a lower b. The performance of the WanFBA model was significantly improved by introduction of a tapering factor”s” for decrease of branch diameter within a single link. All statistical tests performed on measured biomass versus biomass predicted from the WanFBA results confirm the viability of the WanFBA model as a non-destructive tool for predicting above-ground biomass equations for total biomass, branch biomass and the leaf twig fraction.
Allometric equations for below-ground biomass of four key woody species in West African savanna-woodlands
Accurate estimates of both above-ground biomass (AGB) and below-ground biomass (BGB) are essential for estimating carbon (C) balances at various geographical scales and formulating effective climate change mitigation programs. However, estimating BGB is challenging, particularly for forest ecosystems, so robust allometric equations are needed. To obtain such equations for savanna-woodlands of the West African north sudanian zone, we selected four common native woody species (Anogeissus leiocarpa (DC.) Guill. & Perr., Detarium microcarpum Guill. & Perr., Piliostigma thonningii (Schumach.) Milne-Redh. and Vitellaria paradoxa C.F. Gaertn.). At two sites in Burkina Faso, we determined the BGB of 30 trees of each of these species by excavation, and measured various above-ground dimensional variables. The root:shoot ratio varied widely among the species, from 0.1 to 3.4. Depending on the species, allometric equations based on stem basal area at 20 cm height, basal area at breast height and tree height explained 50–95% of the variation in BGB. The best generic equation we obtained, based on basal area at 20 cm, explained 60% of the variation in BGB across the species. Three previously published generic allometric equations underestimated BGB by 8 to 63%. The presented equations should significantly improve the accuracy of BGB estimates in savanna-woodlands and help avoid costly needs to excavate root systems.
Height-diameter allometric equations of an emergent tree species from the Congo Basin
Reliable tree height-diameter (H-D) allometric equations are a key tool for the estimation of forest productivity and Above Ground Biomass (AGB). Most existing H-D allometric equations developed for the tropical region are based on large-scale multi-species datasets, and their use to derive information on productivity and AGB at the species level is prone to uncertainties. The single-species H-D allometric equations available are mainly focused on monocultures or stands with simple tree species mixtures and did not account for the site effects. Here we measured the height and diameter of 2,288 trees of the emergent tree species Pericopsis elata (Harms) Meeuwen in the Democratic Republic of the Congo (DRC) and in Cameroon. We first examined how accurate multispecies H-D allometric equations are in predicting the total height of P. elata. We then tested whether single-species H-D allometric equations vary between sites. We developed the first H-D allometric equation of P. elata and tested whether and how stand-level and environmental variables induce changes in H-D allometric relationship of P. elata at the regional level. We additionally evaluated whether tree-level variables are important at the local level where climate and stand development stage are expected to be less variable. We found that pantropical, regional and local H-D allometric equations significantly underestimate the total height of P. elata. The local multi-species H-D allometric equation developed for Yangambi showed the highest underestimation in all the studied sites. This result supports the need for an H-D allometric equation specific for P. elata. The species-level H-D allometric equation developed showed significant underestimations for trees from the disturbed and undisturbed forests in DRC, while overestimations were observed for similar sites in Cameroon. Using a mixed-effect H-D allometric equation, we showed that even within a single species, a substantial variation exists between sites. This variation showed to be driven by the differences in the maximum asymptotic height (Hmax) between sites. We found that P. elata trees are taller and attain higher Hmax in DRC than in Cameroon. The basal area showed to be a significant covariate accounting for the site effects at the regional-scale where climate variables showed minor effects. However, at the local-scale, none of climate or stand variables showed to be significant. Local-scale variation showed to be associated with differences in light availability, highlighting the potential of management options that shape the local environment in driving species productivity.
Editorial: Tropical Montane Forests in a Changing Environment
Tropical montane forests (TMFs) are found on most of Earth’s continents along variable elevation ranges, whose potential upper limits are influenced by cloud condensation heights and minimum temperatures. They are most widespread in South America and in (semi-)humid mountain areas.
Macroecological patterns of forest structure and allometric scaling in mangrove forests
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. 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. 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. 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.
Low-emissions and profitable cocoa through moderate-shade agroforestry: Insights from Ghana
Cocoa production is a leading driver of deforestation in the humid-tropics of West Africa. Reconciling climate change mitigation with livelihoods of farmers requires identification of production strategies to concurrently improve yield and profit while curtailing emissions of greenhouse gases (GHG). Using a 2021 plot-survey conducted in Ghana’s Eastern region, we evaluated yields, GHG emissions, and value of production (VOP) (a profit indicator) across a typology representing the diversity of systems at plot-level. The typology was constructed by first stratifying plots according to shade levels and variety (hybrid vs. Amazonia) which resulted in three systems: Hybrid sun, hybrid variety under full-sun (little to no shade); Hybrid shade, hybrid and moderate shade (13–25 shade trees ha−1); and Amazonia, Amazonia under predominantly moderate shade. Next, factor analysis and clustering were used to group plots within each system according to cocoa yield, vegetation, management, and (local) climate conditions. Cluster analysis showed that fertiliser, weeding, pruning, hand pollination, cocoa tree density, and shade tree densities of differing heights were most influential for determination across systems. Hybrid shade had the highest net GHG removal rate at −6.8 ± 1.7 (± 95% CI) Mg CO2eq ha−1 yr−1: 48% and 127% higher (emissions more negative) respectively over Amazonia and Hybrid sun. Hybrid shade additionally had the highest average and least variable VOP among production systems at 669 ± 564 USD ha−1 yr−1, compared to Hybrid sun and Amazonia at 404 ± 442 and 213 ± 280 USD ha−1 yr−1 respectively. These results point to hybrid cocoa grown under moderate shade of 13–25 shade trees ha−1 as optimal for reconciling climate change mitigation with development in West African cocoa.