Tree allometry and improved estimation of carbon stocks and balance in tropical forests

Tropical forests hold large stores of carbon, yet uncertainty remains regarding their quantitative contribution to the global carbon cycle. One approach to quantifying carbon biomass stores consists in inferring changes from long-term forest inventory plots. Regression models are used to convert inventory data into an estimate of aboveground biomass (AGB). We provide a critical reassessment of the quality and the robustness of these models across tropical forest types, using a large dataset of 2,410 trees ≥ 5 cm diameter, directly harvested in 27 study sites across the tropics. Proportional relationships between aboveground biomass and the product of wood density, trunk cross-sectional area, and total height are constructed. We also develop a regression model involving wood density and stem diameter only. Our models were tested for secondary and old-growth forests, for dry, moist and wet forests, for lowland and montane forests, and for mangrove forests. The most important predictors of AGB of a tree were, in decreasing order of importance, its trunk diameter, wood specific gravity, total height, and forest type (dry, moist, or wet). Overestimates prevailed, giving a bias of 0.5–6.5% when errors were averaged across all stands. Our regression models can be used reliably to predict aboveground tree biomass across a broad range of tropical forests. Because they are based on an unprecedented dataset, these models should improve the quality of tropical biomass estimates, and bring consensus about the contribution of the tropical forest biome and tropical deforestation to the global carbon cycle. Electronic Supplementary Material Supplementary material is available for this article at     

Allometric equations for integrating remote sensing imagery into forest monitoring programmes

Remote sensing is revolutionizing the way we study forests, and recent technological advances mean we are now able – for the first time – to identify and measure the crown dimensions of individual trees from airborne imagery. Yet to make full use of these data for quantifying forest carbon stocks and dynamics, a new generation of allometric tools which have tree height and crown size at their centre are needed. Here, we compile a global database of 108753 trees for which stem diameter, height and crown diameter have all been measured, including 2395 trees harvested to measure aboveground biomass. Using this database, we develop general allometric models for estimating both the diameter and aboveground biomass of trees from attributes which can be remotely sensed – specifically height and crown diameter. We show that tree height and crown diameter jointly quantify the aboveground biomass of individual trees and find that a single equation predicts stem diameter from these two variables across the world's forests. These new allometric models provide an intuitive way of integrating remote sensing imagery into large‐scale forest monitoring programmes and will be of key importance for parameterizing the next generation of dynamic vegetation models.     

Allometric Models for Tree Volume and Total Aboveground Biomass in a Tropical Humid Forest in Costa Rica1

Allometric equations for the estimation of tree volume and aboveground biomass in a tropical humid forest were developed based on direct measurements of 19 individuals of seven tree species in Northern Costa Rica. The volume and the biomass of the stems represented about two‐thirds of the total volume and total aboveground biomass, respectively. The average stem volume varied between 4 and 11 Mg/tree and the average total aboveground biomass ranged from 4 to 10 mg/tree. The mean specific gravity of the sampled trees was 0.62 ± 0.06 (g/cm³). The average biomass expansion factor was 1.6 ± 0.2. The best‐fit equations for stem and total volume were of logarithmic form, with diameter at breast height (R²= 0.66 ? 0.81) as an independent variable. The best‐fit equations for total aboveground biomass that were based on combinations of diameter at breast height, and total and commercial height as independent variables had R² values between 0.77 and 0.87. Models recommended for estimating total aboveground biomass are based on diameter at breast height, because the simplicity of these models is advantageous. This variable is easy to measure accurately in the field and is the most common variable recorded in forest inventories. Two widely used models in literature tend to underestimate aboveground biomass in large trees. In contrast, the models developed in this study accurately estimate the total aboveground biomass in these trees.     

Testing the generality of above‐ground biomass allometry across plant functional types at the continent scale

Accurate ground‐based estimation of the carbon stored in terrestrial ecosystems is critical to quantifying the global carbon budget. Allometric models provide cost‐effective methods for biomass prediction. But do such models vary with ecoregion or plant functional type? We compiled 15 054 measurements of individual tree or shrub biomass from across Australia to examine the generality of allometric models for above‐ground biomass prediction. This provided a robust case study because Australia includes ecoregions ranging from arid shrublands to tropical rainforests, and has a rich history of biomass research, particularly in planted forests. Regardless of ecoregion, for five broad categories of plant functional type (shrubs; multistemmed trees; trees of the genus Eucalyptus and closely related genera; other trees of high wood density; and other trees of low wood density), relationships between biomass and stem diameter were generic. Simple power‐law models explained 84–95% of the variation in biomass, with little improvement in model performance when other plant variables (height, bole wood density), or site characteristics (climate, age, management) were included. Predictions of stand‐based biomass from allometric models of varying levels of generalization (species‐specific, plant functional type) were validated using whole‐plot harvest data from 17 contrasting stands (range: 9–356 Mg ha^?1). Losses in efficiency of prediction were <1% if generalized models were used in place of species‐specific models. Furthermore, application of generalized multispecies models did not introduce significant bias in biomass prediction in 92% of the 53 species tested. Further, overall efficiency of stand‐level biomass prediction was 99%, with a mean absolute prediction error of only 13%. Hence, for cost‐effective prediction of biomass across a wide range of stands, we recommend use of generic allometric models based on plant functional types. Development of new species‐specific models is only warranted when gains in accuracy of stand‐based predictions are relatively high (e.g. high‐value monocultures).     

Carbon storage,structure and composition of miombo woodlands in Tanzania’s Eastern Arc Mountains

We determine the aboveground biomass and carbon storage (ABGC) of trees and the herbaceous layer in miombo woodland in the Eastern Arc Mountains (EAM) of Tanzania. In four 1‐ha sample plots in Nyanganje and Kitonga Forests, we measured all trees ≥10 cm diameter alongside height and wood mass density. The plots contained an average of 20 tree species ha^?1 (range 11–29) and 344 stems ha^?1 (range 281–382) with Shannon diversity values of 1.05 and 1.25, respectively. We weighted nine previously published woody savannah allometric models based on whether: (i) the model was derived from the same geographical region; (ii) the model included tree height/wood mass density in addition to stem diameter; and (iii) sample size was used to fit the model. The weighted mean ABGC storage from the nine models range from 13.5 ± 2 to 29.8 ± 5 Mg ha^?1. Measured ABGC storage in the herbaceous layer, using the wet combustion method, adds 0.55 ± 0.02 Mg C ha^?1. Estimates suggest that EAM miombo woodlands store a range of 13–30 Mg ha^?1 of carbon. Although the estimates suggest that miombo woodlands store significant quantities of carbon, caution is required as this is the first estimate based on in situ data.     

General allometric equations and biomass allocation of <Emphasis Type="Italic">Pinus massoniana</Emphasis> trees on a regional scale in southern China

Applying allometric equations in combination with forest inventory data is an effective approach to use when qualifying forest biomass and carbon storage on a regional scale. The objectives of this study were to (1) develop general allometric tree component biomass equations and (2) investigate tree biomass allocation patterns for Pinus massoniana, a principal tree species native to southern China, by applying 197 samples across 20 site locations. The additive allometric equations utilized to compute stem, branch, needle, root, aboveground, and total tree biomass were developed by nonlinear seemingly unrelated regression. Results show that the relative proportion of stem biomass to tree biomass increased while the contribution of canopy biomass to tree biomass decreased as trees continued to grow through time. Total root biomass was a large biomass pool in itself, and its relative proportion to tree biomass exhibited a slight increase with tree growth. Although equations employing stem diameter at breast height (dbh) alone as a predictor could accurately predict stem, aboveground, root, and total tree biomass, they were poorly fitted to predict the canopy biomass component. The inclusion of the tree height (H) variable either slightly improved or did not in any way increase model fitness. Validation results demonstrate that these equations are suitable to estimate stem, aboveground, and total tree biomass across a broad range of P. massoniana stands on a regional scale.     

Biomass increases attributed to both faster tree growth and altered allometric relationships under long‐term carbon dioxide enrichment at a temperate forest

Increases in atmospheric carbon dioxide (CO₂) concentrations are expected to lead to increases in the rate of tree biomass accumulation, at least temporarily. On the one hand, trees may simply grow faster under higher CO₂ concentrations, preserving the allometric relations that prevailed under lower CO₂ concentrations. Alternatively, the allometric relations themselves may change. In this study, the effects of elevated CO₂ (eCO₂) on tree biomass and allometric relations were jointly assessed. Over 100 trees, grown at Duke Forest, NC, USA, were harvested from eight plots. Half of the plots had been subjected to CO₂ enrichment from 1996 to 2010. Several subplots had also been subjected to nitrogen fertilization from 2005 to 2010. Allometric equations were developed to predict tree height, stem volume, and aboveground biomass components for loblolly pine (Pinus taeda L.), the dominant tree species, and broad‐leaved species. Using the same diameter‐based allometric equations for biomass, it was estimated that plots with eCO₂ contained 21% more aboveground biomass, consistent with previous studies. However, eCO₂ significantly affected allometry, and these changes had an additional effect on biomass. In particular, P. taeda trees at a given diameter were observed to be taller under eCO₂ than under ambient CO₂ due to changes in both the allometric scaling exponent and intercept. Accounting for allometric change increased the treatment effect of eCO₂ on aboveground biomass from a 21% to a 27% increase. No allometric changes for the nondominant broad‐leaved species were identified, nor were allometric changes associated with nitrogen fertilization. For P. taeda, it is concluded that eCO₂ affects allometries, and that knowledge of allometry changes is necessary to accurately compute biomass under eCO₂. Further observations are needed to determine whether this assessment holds for other taxa.     

Allometric Models for Predicting Aboveground Biomass in Two Widespread Woody Plants in Hawaii

Allometric models are important for quantifying biomass and carbon storage in terrestrial ecosystems. Generalized allometry exists for tropical trees, but species‐ and site‐specific models are more accurate. We developed species‐specific models to predict aboveground biomass in two of the most ubiquitous natives in Hawaiian forests and shrublands, Metrosideros polymorpha and Dodonaea viscosa. The utility of the M. polymorpha allometry for predicting biomass across a range of sites was explored by comparing size structure (diameter at breast height vs. tree height) of the trees used to develop the models against trees from four M. polymorpha‐dominated forests along a precipitation gradient (1630–2380 mm). We also compared individual tree biomass estimated with the M. polymorpha model against existing generalized equations, and the D. viscosa model with an existing species‐specific model. Our models were highly significant and displayed minimal bias. Metrosideros polymorpha size structures from the three highest precipitation sites fell well within the 95% confidence intervals for the harvested trees, indicating that the models are applicable at these sites. However, size structure in the area with the lowest precipitation differed from those in the higher rainfall sites, emphasizing that care should be taken in applying the models too widely. Existing generalized allometry differed from the M. polymorpha model by up to 88 percent, particularly at the extremes of the data range examined, underestimating biomass in small trees and overestimating in large trees. The existing D. viscosa model underestimated biomass across all sizes by a mean of 43 percent compared to our model. The species‐specific models presented here should enable more accurate estimates of biomass and carbon sequestration in Hawaiian forests and shrublands.     

Allometric Biomass,Biomass Expansion Factor and Wood Density Models for the OP42 Hybrid Poplar in Southern Scandinavia

Biomass and biomass expansion factor functions are important in wood resource assessment, especially with regards to bioenergy feedstocks and carbon pools. We sampled 48 poplar trees in seven stands with the purpose of estimating allometric models for predicting biomass of individual tree components, stem-to-aboveground biomass expansion factors (BEF) and stem basic densities of the OP42 hybrid poplar clone in southern Scandinavia. Stand age ranged from 3 to 31 years, individual tree diameter at breast height (dbh) from 1.2 to 41 cm and aboveground tree biomass from 0.39 to 670 kg. Models for predicting total aboveground leafless, stem and branch biomass included dbh and tree height as predictor variables and explained more than 97 % of the total variation. The BEF was approaching 2.0 for the smallest trees but declined with increasing tree size and stabilized around 1.2 for trees with dbh >10 cm. Average stem basic density was more than 400 kg m^?3 for the smallest trees but declined with increasing tree height and stabilized around 355 kg m^?3, at a tree height of about 20 m. Existing biomass functions from the literature all underestimated the measured sample tree biomass. Possible explanations include not only differences in competition among trees in the examined stands and site conditions but also differences in sampling procedures. We observed that basic density increased with height above the ground. This trend may have led to the observed underestimation by existing biomass functions including only few samples from the lower end of the stems.     

林木分化对兴安落叶松异速生长方程和生物量分配的影响

林木因对资源竞争而产生分化,从而影响林木的异速生长方程和生物量分配,但其影响程度还不清楚。采用林木相对直径法将38株兴安落叶松(Larix gmelinii)样木在林分中的分化等级分为优势木、中等木和被压木,量化林木分化对林木异速生长方程和生物量分配的影响。结果显示:生物量组分异速生长方程多以胸径(DBH)为自变量为好,但以枝下高处的树干直径为自变量估测其枝、叶生物量时更精确。在一定的胸径范围内,同一胸径下不同林木分化等级的地下部分各组分生物量没有显著差异(P0.05),但优势木分配更多的生物量给枝和叶,中等木比优势木分配更多的生物量给树干,中等木比被压木分配更多的生物量给地上部分,而且被压木和中等木的树高显著高于优势木。除根茎生物量之外,不同林木分化等级的生物量组分(包括枝、叶、树干和根系)的相对分配比例无显著差异(P0.05),根冠比保持相对稳定。这些结果表明,主要由竞争而引起的林木分化改变了兴安落叶松地上生物量组分的异速生长和分配,但其相对分配格局较为保守。     

Allometric equations and biomass expansion factors of Japanese red pine on the local level

This study was conducted to evaluate site-specific allometric equations and biomass expansion factors (BEF) of Japanese red pine (Pinus densiflora S. et Z.) at five sites in the Hadong, Hamyang, Jinju, Sancheong, and Uiryeong regions, situated in the western part of Gyeongnam province, Korea. Biomass in each tree component, i.e., needle, branch, stem wood, and stem bark, was quantified by destructive tree harvesting. Site-specific as well as generalized allometric equations were developed for each tree component across the entire sites. Both allometric regression equations were significant (P < 0.05), with diameter at breast height (DBH) accounting for 69–99% of the variation (as indicated by coefficients of determination, r ²) in aboveground biomass. The stem densities at different sites were significantly different (P < 0.05) from each other, but no significant difference was observed for stem bark density. The aboveground BEFs also showed a significant variation (P < 0.05) at a landscape scale and ranged from 1.19 to 1.46 among the sites. The results suggest that application of site-specific allometric equations and aboveground BEFs are likely to improve the reliability of biomass estimates on the local level.     

Replicated throughfall exclusion experiment in an Indonesian perhumid rainforest: wood production,litter fall and fine root growth under simulated drought

Climate change scenarios predict increases in the frequency and duration of ENSO‐related droughts for parts of South‐East Asia until the end of this century exposing the remaining rainforests to increasing drought risk. A pan‐tropical review of recorded drought‐related tree mortalities in more than 100 monitoring plots before, during and after drought events suggested a higher drought‐vulnerability of trees in South‐East Asian than in Amazonian forests. Here, we present the results of a replicated (n = 3 plots) throughfall exclusion experiment in a perhumid tropical rainforest in Sulawesi, Indonesia. In this first large‐scale roof experiment outside semihumid eastern Amazonia, 60% of the throughfall was displaced during the first 8 months and 80% during the subsequent 17 months, exposing the forest to severe soil desiccation for about 17 months. In the experiment's second year, wood production decreased on average by 40% with largely different responses of the tree families (ranging from −100 to +100% change). Most sensitive were trees with high radial growth rates under moist conditions. In contrast, tree height was only a secondary factor and wood specific gravity had no influence on growth sensitivity. Fine root biomass was reduced by 35% after 25 months of soil desiccation while fine root necromass increased by 250% indicating elevated fine root mortality. Cumulative aboveground litter production was not significantly reduced in this period. The trees from this Indonesian perhumid rainforest revealed similar responses of wood and litter production and root dynamics as those in two semihumid Amazonian forests subjected to experimental drought. We conclude that trees from paleo‐ or neotropical forests growing in semihumid or perhumid climates may not differ systematically in their growth sensitivity and vitality under sublethal drought stress. Drought vulnerability may depend more on stem cambial activity in moist periods than on tree height or wood specific gravity.     

Allometric growth and carbon storage in the mangrove Sonneratia apetala

Allometric growth reflects different allocation patterns and relationships of different components or traits of a plant and is closely related to ecosystem carbon storage. As an introduced species, the growth and carbon storage of Sonneratia apetala are still unclear. To derive allometric relationships of the mangrove S. apetala and to estimate carbon storage in mangrove ecosystems, we harvested 12 individual Sonneratia apetala trees from four different diameter classes in the Futian National Nature Reserve, Guangdong, China. Allometric growth models were fitted. The results showed that diameter at breast height (DBH) and wood density were better variables for predicting plant biomass (including above- and below-ground biomass) than plant height. There were significant power function relationships between biomass and DBH, with a mean allometric exponent of 2.22, and stem biomass accounted for 97% of the variation in S. apetala total biomass. Nearly isometric scaling relationships were developed between stem biomass and other biomass components. To better understand the carbon stocks of the S. apetala ecosystem, we categorized all trees into five age classes and quantified vegetation carbon storage. The S. apetala vegetation carbon storage ranged from 96.48 to 215.35 Mg C ha^?1, and the carbon storage significantly increased with stand age. The allometric equations developed in this study are useful to estimate biomass and carbon storage of S. apetala ecosystems.

     

广西主要树种(组)异速生长模型及森林生物量特征

基于广西11类主要树种(组)5个龄组(245株样木、345块样地)的生物量实测调查,建立了各树种(组)的生物量优化异速生长模型,探讨广西森林生态系统总生物量及不同森林类型、不同龄组、不同层次的生物量组成与分配。结果表明:(1)广西11类树种(组)叶、枝、干、根、全株生物量(除了杉树叶、桉树叶生物量)、地上-地下、胸径-树高的优化回归模型均为幂函数,经t检验均达到显著水平(P0.05),其中11类树种(组)以全株生物量的模拟效果最好;(2)广西森林总生物量为1425.37 Tg,平均生物量为105.36 Mg/hm2,各森林类型总生物量为松树林(366.14 Tg)硬阔(291.08 Tg)软阔(239.75 Tg)石山林(165.51 Tg)杉木林(164.01 Tg)桉树林(99.55 Tg)栎类(46.34 Tg)八角林(20.21 Tg)油茶林(19.59 Tg)竹林(13.19 Tg),均随年龄的增加而增加,各层次生物量均以乔木层占绝对优势,所占比例为78.30%—97.47%,各龄组地上生物量均大于地下生物量;(3)考虑统计学与实际应用之间的平衡及异速生长模型的可解释量、回归系数的显著性,以胸径为变量的生物量模型能有效估算广西主要树种(组)各器官及总生物量;(4)优化筛选的广西各树种(组)的地上-地下优化异速生长模型及推算的地上-地下生物量比,对于估计广西森林地下生物量具有重要参考价值。     

Variation in wood density determines spatial patterns inAmazonian forest biomass

Uncertainty in biomass estimates is one of the greatest limitations to models of carbon flux in tropical forests. Previous comparisons of field‐based estimates of the aboveground biomass (AGB) of trees greater than 10 cm diameter within Amazonia have been limited by the paucity of data for western Amazon forests, and the use of site‐specific methods to estimate biomass from inventory data. In addition, the role of regional variation in stand‐level wood specific gravity has not previously been considered. Using data from 56 mature forest plots across Amazonia, we consider the relative roles of species composition (wood specific gravity) and forest structure (basal area) in determining variation in AGB. Mean stand‐level wood specific gravity, on a per stem basis, is 15.8% higher in forests in central and eastern, compared with northwestern Amazonia. This pattern is due to the higher diversity and abundance of taxa with high specific gravity values in central and eastern Amazonia, and the greater diversity and abundance of taxa with low specific gravity values in western Amazonia. For two estimates of AGB derived using different allometric equations, basal area explains 51.7% and 63.4%, and stand‐level specific gravity 45.4% and 29.7%, of the total variation in AGB. The variation in specific gravity is important because it determines the regional scale, spatial pattern of AGB. When weighting by specific gravity is included, central and eastern Amazon forests have significantly higher AGB than stands in northwest or southwest Amazonia. The regional‐scale pattern of species composition therefore defines a broad gradient of AGB across Amazonia.     

Regional Variations in Biomass Distribution in Brazilian Savanna Woodland

The Cerrado, the savanna biome in central Brazil, mostly comprised of woodland savanna, is experiencing intense and fast land use changes. To understand the changes in Cerrado carbon stocks, we present an overview of biomass distribution in different Cerrado vegetation types (i.e., grasslands, shrublands and forestlands). We surveyed 26 studies including 170 Cerrado sites. The grasslands presented mean total biomass of 24 Mg/ha, with 70 percent allocated in the belowground portion. In shrublands, the mean total biomass was 58 Mg/ha being 58 percent in the belowground portion. Finally, in forestlands the mean total biomass was 98 Mg/ha with 18 percent as belowground biomass. The surveyed studies presented 12 allometric equations for biomass estimate, most involving both diameter and height. Data on wood density for Cerrado shrubs and trees are not abundant and the average value was 0.66 g/cm³, similar to that found in the central portion of the Amazon Forest. We also examined the relationship between total precipitation and dry‐season intensity with biomass variation in the Cerrado shrubland using data from tropical rainfall measurement mission (TRMM) for the period 2000–2010. Dry‐season precipitation amount in cerrado areas in severe drought regions explained 29 percent of the variation in aboveground woody biomass. This finding is important in the face of the predictions of longer and more severe dry seasons in the region due to climate change.     

Soil is the main predictor of secondary rain forest estimated aboveground biomass across a Neotropical landscape

We studied the relative effects of landscape configuration, environmental variables, forest age, and spatial variables on estimated aboveground biomass (AGB) in Costa Rican secondary rain forests patches. We measured trees ≥5 cm dbh in 24, 0.25 ha plots and estimated AGB for trees 5–24.9 cm dbh and for trees >25 cm dbh using two allometric equations based on multispecies models using tree dbh and wood‐specific gravity. AGB averaged 87.3 Mg/ha for the 24 plots (not including remnant trees) and 123.4 Mg/ha including remnant trees (20 plots). There was no effect of forest age on AGB. Variation partitioning analysis showed that soils, climate, landscape configuration, and space together explained 61% of tree AGB variance. When controlling for the effects of the other three variables, only soils remained significant. Soil properties, specifically K and Cu, had the strongest independent effect on AGB (variation partitioning, R² = 0.17, p = 0.0310), indicating that in this landscape, AGB variation in secondary forest patches is influenced by soil chemical properties. Elucidating the relative influence of soils in AGB variation is critical for understanding changes associated with land cover modification across Neotropical landscapes, as it could have important consequences for land use planning since secondary forests are considered carbon sinks. Abstract in Spanish is available with online material.     

Carbon of Chaillu forests based on a phytosociological analysis in Republic of Congo,more than meets the eye?

The objectives were to quantify aboveground, belowground and dead wood carbon pools near Mayoko in the Chaillu massif of Republic of Congo and explore relationships between carbon storage and plant diversity of all growth forms. A total of 190 plots (25 m by 25 m) were sampled (5072 stems, 211 species) and data analysed using recommended central-African forest allometric equations. Mean stem diameter at breast height was 33.6 cm, mean basal area 47.7 m² ha⁻¹ and mean density of individuals 407 ha⁻¹. Mean aboveground carbon (AGC) ranged from 13.93–412.66 Mg C ha⁻¹, belowground carbon from 2.86–96.97 Mg C ha⁻¹ and dead wood from 0.00–7.59 Mg C ha⁻¹. The maximum AGC value recorded in a plot was 916 Mg C ha⁻¹. The analysis performed using phytosociological association as basis rather than broad vegetation type is unique. AGC values for undisturbed terra firme forest sites featured among the highest recorded for African tropical forests. Considering only tree diversity, a weak, yet significant, relationship existed between AGC and species richness, Shannon-Wiener index of diversity and Fisher's alpha. However, if diversity of all plant growth forms is considered, no relationship between carbon and plant diversity existed.     

An analysis of structure: biomass structure relationships for characteristic species of the western Kalahari,Botswana

Savannah ecosystems are important carbon stocks on the Earth, and their quantification is crucial for understanding the global impact of climate and land‐use changes in savannahs. The estimation of aboveground/belowground plant biomass requires tested allometric relationships that can be used to determine total plant biomass as a function of easy‐to‐measure morphological indicators. Despite recent advances in savannah ecology, research on allometric relations in savannahs remains confined to a few site‐specific studies where basal area is typically used as the main morphometric parameter with plant biomass. We investigate allometric relations at four sites along a 950‐km transect in the Kalahari across mean rainfall gradient 170 mm yr^?1–550 mm yr^?1. Using data from 342 harvested trees/shrubs, we relate basal area, height and crown diameter to aboveground biomass. These relationships are strongest in trees and weakest in small shrubs. Strong allometric relationships are also determined for morphologically similar groups of woody vegetation. We show that crown diameter can be used as an alternative to basal area in allometric relationships with plant biomass. This finding may enhance the ability to determine aboveground biomass over large areas using high‐resolution aerial or satellite imagery without requiring ground‐based measurements of basal area.