David Yue Phin Tng

Climate change has led to more unpredictable and in many cases more extreme environmental stress on both forests and savannas, which occur as a vegetation mosaic in many tropical regions. It is therefore important to understand the comparative ecological strategies of plants in these disparate habitats. Studying a pair of congeneric Grevillea (Proteaceae) in the forest (Grevillea baileyana) and in the savanna (Grevillea glauca), which do not overlap in their habitat, we examined 20 functional stem and leaf traits, including less-studied anatomical and flammability traits. We found that the forest Grevillea had a higher leaf area, stomatal density, and vessel area, while the savanna species exhibited denser wood, more parenchyma, higher leaf mass per unit area, and thicker bark (p < 0.001 for most trait comparisons). However, we found that the forest species was equally flammable as the savanna species, with the latter only having a higher maximum burn temperature. Overall, our results are consistent with the forest species having more acquisitive and the savanna species having more resource-conservative trait strategies. Further examination of intraspecific trait variation will also aid in understanding how these species may respond to the effects of climatic change in their respective habitats.

Leaves and stems span an extraordinary range of sizes and forms, yet how this diversity is coordinated in whole plants remains unclear, lacking both general theory and empirical tests across the full diversity of plant lineages. Here, we derive predictions from Metabolic Scaling Theory (MST)1 and test them using a globally standardized dataset spanning 1,473 species and nearly all woody plant families worldwide. Across lineages, climates, and growth forms, we show that twig cross-sectional area scales isometrically with leaf area (slope = 1), while leaf size scales to the 1/3 power with twig length, and to the -4/3 power with stem tissue density, all in conformity with predictions from MST. Plant height influences the intercepts, but not the slopes, of leaf-stem scaling relationships, indicating that twigs from taller plants have narrower twigs for a given leaf area, consistent with selection maintaining constant sapwood volume per unit leaf area. Our findings provide empirical support for an adaptive spectrum of leaf–stem coordination in plants, shaped by major tradeoffs and selection pressures, including plant height, that govern plant carbon allocation globally.

Summary: Wood density is central for estimating vegetation carbon storage and a plant functional trait of great ecological and evolutionary importance. However, the global extent of wood density variation is unclear, especially at the intraspecific level. We assembled the most comprehensive wood density collection to date, including 109 626 records from 16 829 plant species across woody life forms and biomes (GWDD v.2, available here: doi: 10.5281/zenodo.16919509 ). Using the GWDD v.2, we explored the sources of wood density variation within individuals, within species and across environmental gradients. Intraspecific variation accounted for c . 15% of overall wood density variation (SD = 0.068 g cm ⁻³ ). Variance was 50% smaller in sapwood than heartwood, and 30% smaller in branchwood than trunkwood. Individuals in extreme environments (dry, hot and acidic soils) had higher wood density than conspecifics elsewhere (+0.02 g cm ⁻³ , c . 4% of the mean). Intraspecific environmental effects strongly tracked interspecific patterns ( r = 0.83) but were 70–80% smaller and varied considerably among taxa. Individual plant wood density was difficult to predict (root mean square error > 0.08 g cm ⁻³ ; single‐measurement R ² = 0.59). We recommend: (1) systematic sampling of multiple individuals and tissues for local applications; and (2) expanded taxonomic coverage combined with integrative models for robust estimates across ecological scales.

Wood density is central for estimating vegetation carbon storage and a plant functional trait of great ecological and evolutionary importance. However, the global extent of wood density variation is unclear, especially at the intraspecific level. We assembled the most comprehensive wood density collection to date (GWDD v.2), including 109,626 records from 16,829 plant species across woody life forms and biomes. Using the GWDD v.2, we explored the sources of variation in wood density within individuals, within species, and across environmental gradients. Intraspecific variation accounted for up to 15% of overall wood density variation (sd = 0.068 g cm ^-3 ). Sapwood densities varied 50% less than heartwood densities, and branchwood densities varied 30% less than trunkwood densities. Individuals in extreme environments (dry, hot, acidic soils) had higher wood density than conspecifics elsewhere (+0.02 g cm ^-3 , ∼4% of the mean). Intraspecific environmental effects strongly tracked interspecific patterns (r = 0.83) but were only 20–30% as large and varied considerably among taxa. Individual plant wood density was difficult to predict (RMSE > 0.08 g cm ^-3 ; single-measurement R ² = 0.59). We recommend (i) systematic within-species sampling for local applications, and (ii) expanded taxonomic coverage combined with integrative models for robust estimates across ecological scales.

Wood density influences how quickly woody plants grow, how long they live and how much carbon they store, yet its global variation remains poorly mapped. Here we combined 109,626 wood density measurements from 16,829 species with 300,949 vegetation plots to produce a km-scale map of community-weighted wood density for every woody biome. Our model led to a prediction accuracy 32–51 % higher than previous global products, and a 1.8–3.7-fold wider wood density range (0.28–1.00 g cm ⁻³ ; global mean: 0.57 g cm ⁻³ ) than previously assumed. Spatial cross-validation showed low bias (±2.5 % of the mean), and uncertainties decreased from 20% in poorly sampled drylands and boreal regions to 5% in data-rich temperate forests. Mean annual temperature was the best predictor of community-weighted mean wood density, increasing by 0.01 g cm ⁻³ for every 1°C change. We deliver a low-bias, high-resolution wood density layer for Earth system models, together with spatially explicit error maps. This study represents a major step forward for carbon accounting and trait-based forecasts of vegetation change.

In the traditional classification system of the Lauraceae family based on morphology and anatomy, the phylogenetic position of the genus Sassafras has long been controversial. Chloroplast (cp) evolution of Sassafras has not yet been illuminated. In this study, we first sequenced and assembled the complete cp genomes of Sassafras, and conducted the comparative cp genomics, phylogenomics, and divergence time estimation of this ecological and economic important genus. The whole length of cp genomes of the 10 Sassafras ranged from 151,970 bp to 154,011 bp with typical quadripartite structure, conserved gene arrangements and contents. Variations in length of cp were observed in the inverted repeat regions (IRs) and a relatively high usage frequency of codons ending with T/A was detected. Four hypervariable intergenic regions (ccsA-ndhD, trnH-psbA, rps15-ycf1, and petA-psbJ) and 672 cp microsatellites were identified for Sassafras. Phylogenetic analysis based on 106 cp genomes from 30 genera within the Lauraceae family demonstrated that Sassafras constituted a monophyletic clade and grouped a sister branch with the Cinnamomum sect. Camphora within the tribe Cinnamomeae. Divergence time between S. albidum and its East Asian siblings was estimated at the Middle Miocene (16.98 Mya), S. tzumu diverged from S. randaiense at the Pleistocene epoch (3.63 Mya). Combined with fossil evidence, our results further revealed the crucial role of the Bering Land Bridge and glacial refugia in the speciation and differentiation of Sassafras. Overall, our study clarified the evolution pattern of Sassafras cp genomes and elucidated the phylogenetic position and divergence time framework of Sassafras.

Premise: The increased frequency of droughts and wildfires in recent decades poses a significant risk to agricultural lands and private property. Given the negative impact of fires on food production and associated livelihoods, it is crucial to assess the flammability of crop species and find ways of mitigating risk of fire in agricultural lands. Methods: We quantified the shoot‐level flammability of 65 tropical species of fiber, food, and spice crops by assessing maximum temperature, burn time, and burnt biomass and assessed key leaf traits from a subset of these species to assess how specific leaf area (SLA), leaf area (LA), and leaf dry mass to fresh mass ratio (DM:FM) influences these flammability measures. Results: Groundcover, shrubs, and vines were generally less flammable than canopy and subcanopy plants. DM:FM was a consistent and significant predictor of all three flammability measures regardless of plant life form. Conclusions: Our results equip farmers and policymakers with information to construct agricultural landscapes that are more fire resilient and options for pursuing nature‐based solutions to mitigate fire risk, such as planting green firebreaks with fire‐retardant species.

Tropical forest and savanna biomes are pivotal in the functioning of the Earth system. Tropical forests are one of the largest terrestrial biosphere carbon pools, whereas savannas exchange carbon between the biosphere and atmosphere via frequent and extensive landscape fires. Both are biodiverse and under increasing threat due to land clearing and anthropogenic climate change. Reliable mapping of tropical forest and savanna is essential to provide understanding of how anthropogenic impacts are affecting the extent of these biomes. Using Google Maps satellite imagery, we manually classified 24,239 random points as forest, savanna, or anthropogenic landscapes within the tropics. Because fire and climate are correlated, we developed separate geospatial models to rank the importance of climate, topography, and human influence on vegetation present. This modelling confirmed that those areas with more fires had lower probabilities of tropical forest, that forest was most likely in areas with high mean annual rainfall with little seasonal variation in precipitation, and that anthropogenic factors disrupt this environmental predictability. We found there were environments where tropical forest and savanna were equally probable are geographically restricted. These relationships suggest that future drier climates projected under anthropogenic climate change, combined with clearing and burning that have reduced tropical forest extent to a subset of its theoretical distribution, will lead to irreversible loss of tropical forests. Our modelling provides global mapping that can be used track further changes to distribution of rainforests.