Tree Functional Traits Research Articles

Sensitivity Analysis of Sentinel-2 Imagery to Assess Urban Tree Functional Traits: A Physical Approach Based on Local Climate Zones

Urban trees contribute to urban well-being but face challenging environments that can reduce their lifespan and increase young tree mortality. Although many studies have used remote sensing data to monitor the functional status of trees in rural areas, few have done so in urban areas to assess the health or estimate the biomass of large green areas. This study assessed the suitability of using Sentinel-2 images to characterize two urban tree functional traits—leaf chlorophyll content (Cab) and leaf area density (LAD)—in isolated trees and tree rows. Simulated Sentinel-2 images were generated using the DART radiative transfer model, considering 16 tree-endogenous and 14 tree-exogenous parameters, with 15 vegetation indices (VIs) analyzed. Sensitivity analysis was performed in four contrasting urban environments using local climate zone taxonomy. The accuracy of the simulated images was validated with real Sentinel-2 images, field measurements, and ancillary data collected for four tree species in Rennes, France. The results showed that the tree parameters significantly influenced Sentinel-2 spectral bands, with NGBDI and OSAVI VIs being most sensitive to Cab and LAD. The model showed high accuracy, with a mean RMSE of 0.016 for key spectral bands. The results also highlighted the importance of considering ancillary data to capture specific urban characteristics.

Soil conditions modify species diversity effects on tree functional trait expression

Examples of positive effects of biodiversity on ecosystem functions have kept accumulating in the last two decades, and functional traits are considered suitable tools to explain their underlying mechanisms. However, traits are rarely studied at the scale where these mechanisms (e.g., complementarity) are likely to originate, that is, between two interacting individuals. In an 18-month greenhouse experiment, we investigated how species diversity (i.e., monospecific or heterospecific tree pairs) affects within-individual leaf traits expression and variation and how this effect is modified by soil conditions. While resource addition through phosphorus fertilization partly strengthened the diversity effects, inoculation of soil microbiota (potentially leading to increased resource accessibility) resulted in counter effects. Hence, in contrast to our expectations, we did not find synergistic effects of the two soil treatments, but we found distinct effects on species following an acquisitive or conservative growth strategy. Overall, our study showed that the effect of species diversity on young trees’ adaptability and resource-use strategy needs to be considered alongside soil biotic and abiotic aspects. The influence of soil conditions on species diversity effects is essential to understand mechanisms behind complementarity at the individual level, which ultimately translate to the community scale.

Mixed forests provide higher levels of growth and yield than monocultures across a broad range of conditions

Compared with single-species forests, mixed forests tend to provide more forest ecosystem functions and services. However, there is a lack of detailed understanding of the basic mechanisms of the impact of species diversity on tree growth and forest productivity. The main drivers of this relationship are also still under discussion. Here, we synthesized information from 93 studies to quantify the increase in tree size, crown size and stand productivity in mixed stands, and conducted a meta-analysis on the response of tree growth and forest productivity to species mixing. Tree size, crown size and stand productivity increased by 7.4 % (2.4–12.5 %), 12.6 % (5.6–20.1 %), and 33.0 % (18.7–49.0 %), respectively, in mixed stands compared with single-species stands. Our results show that when all observations are included, the mean effect sizes of tree size, crown size, and stand productivity were greater than when only the equal stand density observations were included. Stand age and stand density were the most important moderators affecting tree size in mixed forests. Stand age, shade tolerance and soil acidity were the most important moderators influencing the effect sizes of crown size, and shade tolerance was the most important moderator influencing the effect sizes of stand productivity. We found that these positive mixing effects were also modulated by tree functional traits, stand characteristics, and climatic conditions. For different growth variables, the moderators that affect their growth in the mixed forests were different. Therefore, in the afforestation practices for differing management objectives, foresters should give priority to the factors that have the most important impact on them to achieve their goals. Our results have implications for linking biodiversity-ecosystem functioning relationships and forest management practices and may aid the development of more appropriate afforestation strategies.

Functional diversity enhances dryland forest productivity under long-term climate change.

Short-term experimental studies provided evidence that plant diversity increases ecosystem resilience and resistance to drought events, suggesting diversity to serve as a nature-based solution to address climate change. However, it remains unclear whether the effects of diversity are momentary or still hold over the long term in natural forests to ensure that the sustainability of carbon sinks. By analyzing 57 years of inventory data from dryland forests in Canada, we show that productivity of dryland forests decreased at an average rate of 1.3% per decade, in concert with the temporally increasing temperature and decreasing water availability. Increasing functional trait diversity from its minimum (monocultures) to maximum value increased productivity by 13%. Our results demonstrate the potential role of tree functional trait diversity in alleviating climate change impacts on dryland forests. While recognizing that nature-based climate mitigation (e.g., planting trees) can only be partial solutions, their long-term (decadal) efficacy can be improved by enhancing functional trait diversity across the forest community.

Shade tree trait diversity and functions in agroforestry systems: A review of which traits matter

Abstract Shade trees in agroforestry systems confer ecosystem services, such as enhanced soil fertility from diverse litter inputs, microclimate regulation via shade, and disease mitigation through trophic and abiotic interactions. With this thriving role of agroforestry in sustainable agriculture, particularly for tree crops, systematic and reliable methods to select shade trees for specific agroecosystem outcomes are crucial. Plant functional traits offer a framework to describe, select and manage shade trees. Over the last decade, shade tree leaf functional traits and whole plant traits have been assessed in agroforestry systems. Yet, we lack amalgamated information on (i) what we know about shade tree trait relationships with functions to achieve desired agroecosystem outcomes, (ii) how decades of shade tree selection by farmers impacts agroforests inter‐ and intraspecific trait diversity, and (iii) which shade tree traits should be considered for achieving farmer priorities. We consolidate literature on Coffea arabica (coffee) and Theobroma cacao (cocoa) agroforestry systems to summarize the role of shade tree functional traits in three key ecosystem functions: soil fertility, microclimate modification and crop productivity. We compile global and regional datasets on tree functional trait diversity to show the functional space of agroforestry tree species compared with the overall functional space observed in plants. Despite, or maybe because of, high shade tree diversity, shade tree trait characterization remains coarse and commonly measured at the community scale in the literature. Based on published trait data, we show that farmers adjust the functional composition of shade trees to increase the recycling of soil nutrients (high leaf nitrogen), the production of wood (skewing towards lower wood densities) and the production of fruits (tendency towards high seed size). Common shade trees in coffee and cocoa systems fall in the mid‐range of leaf acquisitive to conservative strategies, providing evidence that expanding shade tree portfolios can improve, or even accelerate, functions. Synthesis and applications: Based on the agroforestry literature and on trait‐environment relationships, we propose a matrix of shade tree traits that influence desirable agroecosystem outcomes for farmers, which can guide fine‐scale coordination of trait expression and agroforestry functions.

Height-diameter model of broad-leaved mixed forest based on species classification in Maoershan, Northeast China.

The complex stand structure and high species diversity of natural forests pose great challenges for analyzing stand growth and formulating reasonable plans for forest management. The height-diameter relationship is of great significance for predicting stand growth and formulating forest management measures. Based on survey data of 48 broad-leaved mixed forest plots in Maoershan, we classified 23 tree species into four groups based on species structure, growth characteristics and bionomics. We established a generalized model including stand, tree competition, species mixing and species diversity variables by reparameterization method, and a two-level mixed effect model of plot and tree species group. We tested the prediction ability of the model by leave-one-out cross-validation method. The results showed that the Ratkowsky (1990) model was the optimal basic model. The introduction of dominant height, basal area of trees larger than the object tree, basal area proportion of each species, and Shannon index could better explain the height-diameter relationship of broad-leaved mixed forest in Maoershan. The introduction of the mixed effect model of plot and tree species group could significantly improve the prediction accuracy of the model, with a Ra2 of 0.83. Under the same gradient of environmental factors, intolerant tree species exhibited higher tree heights than shade-tolerant tree species. In this study, we used the constructed tree height-diameter model to analyze the effects of species mixing and tree functional traits on tree height, which provided a theoretical basis for accurately predicting height of different tree species and analyzing the growth relationships in broadleaved mixed forests.

Global patterns and environmental drivers of forest functional composition

AbstractAimTo determine the relationships between the functional trait composition of forest communities and environmental gradients across scales and biomes and the role of species relative abundances in these relationships.LocationGlobal.Time periodRecent.Major taxa studiedTrees.MethodsWe integrated species abundance records from worldwide forest inventories and associated functional traits (wood density, specific leaf area and seed mass) to obtain a data set of 99,953 to 149,285 plots (depending on the trait) spanning all forested continents. We computed community‐weighted and unweighted means of trait values for each plot and related them to three broad environmental gradients and their interactions (energy availability, precipitation and soil properties) at two scales (global and biomes).ResultsOur models explained up to 60% of the variance in trait distribution. At global scale, the energy gradient had the strongest influence on traits. However, within‐biome models revealed different relationships among biomes. Notably, the functional composition of tropical forests was more influenced by precipitation and soil properties than energy availability, whereas temperate forests showed the opposite pattern. Depending on the trait studied, response to gradients was more variable and proportionally weaker in boreal forests. Community unweighted means were better predicted than weighted means for almost all models.Main conclusionsWorldwide, trees require a large amount of energy (following latitude) to produce dense wood and seeds, while leaves with large surface to weight ratios are concentrated in temperate forests. However, patterns of functional composition within‐biome differ from global patterns due to biome specificities such as the presence of conifers or unique combinations of climatic and soil properties. We recommend assessing the sensitivity of tree functional traits to environmental changes in their geographic context. Furthermore, at a given site, the distribution of tree functional traits appears to be driven more by species presence than species abundance.

Tree functional traits across Caribbean island dry forests are remarkably similar

AbstractAimTo examine the climatic and biogeographic drivers of plant trait variation across Caribbean tropical dry forests, a system characterised by high rates of plant endemism despite low moisture availability, high rainfall variability and persistent exposure to hurricanes.LocationCaribbean tropical dry forests.TaxonWoody plants.MethodsWe used a database of 572 woody vegetation plots spanning across the Caribbean, including Florida. We then extracted seed mass, specific leaf area and wood density from global trait databases. We supplemented additional trait data from herbaria collections and calculated phylogenetic imputation of traits. Furthermore, we calculated presence–absence community means and functional diversity and correlated these metrics with bioclimatic variables in addition to island and dry forest area using generalised additive models.ResultsDespite occurring in climatically distinct regions, Caribbean tropical dry forests are functionally similar, and the trait space of many dry forests are nested within the functional space of others. In line with island biogeographic theory, island area, dry forest area and island isolation were correlated with functional diversity. Although temperature and precipitation were important determinants of trait variation and functional diversity, environmental variables differently impacted trait variation and the variance explained was generally low.Main ConclusionsThe high functional overlap among Caribbean dry forests is remarkable given the broad climatic gradient across these islands. High functional overlap suggests that environmental and biogeographic filters constrain plant form and function in these intrinsically fascinating systems. The trait space of these insular dry forest systems points to dispersal‐limitation, in addition to high temperature and water limitations, and favouring persistence strategies to withstand high frequency hurricane disturbance.

Anthropogenic disturbance modifies tree functional traits in the only remnant swamp forest of Bangladesh

The relationship between ecosystem functions and plant functional traits has been well documented and is considered to be one of the most vital topics in ecology. However, the correlation between anthropogenic disturbance and tree functional trait diversity remains largely unclear. The present study investigates the role of anthropogenic disturbance on selected tree functional traits in Ratargul Swamp Forest (RSF) – the only remnant tropical freshwater swamp forest ecosystem in Bangladesh. We established 50 plots and collected six plant traits, i.e., tree height, specific leaf area (SLA), wood density (WD), leaf dry matter content (LDMC), seed mass, and bark thickness. A two-way analysis of variance (ANOVA) was carried out to test the interaction between plant functional traits and anthropogenic disturbance in RSF. Our study found that anthropogenic disturbance has a significant (p< 0.05) influence on deciduous swamp forest tree species’ functional traits but none on evergreen tree species’ functional traits. For deciduous trees, disturbance has a significant positive effect on CWM.SLA (p< 0.05) and CWM.Height (p< 0.05) and a negative impact on CWM.Bark-thickness and CWM.Seed-mass (p< 0.05). There were no significant effects of disturbance on CWM.WD and CWM.LDMC. We believe the present study will contribute toward improving our understanding of the effect of disturbances on tree functional trait diversity in tropical human-dominated landscapes where anthropogenic pressure is increasing at an unprecedented rate. It will also function as an essential conservation for related decision-making of Ratargul Swamp Forest in northeastern Bangladesh and elsewhere in the tropics with a similar context.

Assisted tree migration can reduce but not avert the decline of forest ecosystem services in Europe

European forests are facing multiple natural and anthropogenic pressures that are expected to become more severe in the next decades. Tree diversity is projected to decline in many areas across the continent. How this will affect the provision of forest services remains an open question, whose answer depends, among others, on the practical and theoretical challenges of incorporating assisted migration into climate adaptation strategies. Here, we tackle the issue by combining a large dataset of tree species occurrences, future climatic projections, and data on tree functional traits and tree-specific forest services into a novel modelling framework. We estimate that, by the end of the century and under a natural dispersal scenario, the provision of forest services would decrease on average by 15% in Europe (for RCP 4.5; 23% for RCP 8.5), and up to 52% (70% for RCP 8.5) in the Mediterranean. To explore if and how management could reduce the projected losses, we simulated a suite of alternative assisted migration strategies aimed at identifying, for each locality, the tree species communities offering the best compromise in terms of resilience to climate change and delivery of specific combinations of ecosystem services. Such strategies could reduce losses of services by 10% (15%) on average in Europe, and even increase service availability in the Alpine and Boreal regions but not in the Mediterranean, where losses will remain as high as 33% (54% for RCP 8.5). Our findings highlight how science-driven management strategies could be vital to reduce an otherwise dramatic, European-wide decline of forest services. Our results are qualitatively robust to different assumptions on future carbon emissions and related climate trajectories. That is, our simulated assisted migration strategies identify similar tree species communities under different pathways (RCP 4.5 vs RCP 8.5). This makes our approach a powerful tool for forest management, as it generates advice that is valid regardless of whether, and to what extent, human society will steer away from business-as-usual emission trajectories.

Effects of Tree Functional Traits on Soil Respiration in Tropical Forest Plantations

Fast-growing tree species, including Eucalyptus sp. and Acacia sp., are widely used to rehabilitate degraded tropical forestland quickly, while mitigating climate change. However, the extent of carbon losses through soil respiration (RS) often remains unknown. Moreover, the promotion of these non-native species has raised concerns over their impact on other ecosystem services, including N2-fixation-induced soil acidification and nutrient cycling. This study compared two non-native and native species, with one of each being N2-fixing, growing in 11-year-old monospecific plantations in NE Thailand. Hourly RS was measured monthly over one year and combined with stand characteristics, as well as soil microclimatic and chemical properties. Mixed-effects models were used to capture this hierarchical, diurnal, and seasonal dataset. RS rates were influenced by soil temperature and moisture following a parabolic relation, and negatively affected by acidity. Overall, RS varied significantly according to species-specific microclimates and productivity. Despite the high input of organic matter, non-native species failed to ameliorate extreme soil moisture or temperature; limiting microbial decomposition and reducing RS. Hopea odorata produced moderate levels of carbon sequestration, but maintained soil fertility. The choice of tree species can significantly affect carbon sequestration and storage, as well as nutrient cycling, and careful species selection could optimize these ecosystem services.

Temporal changes in the dominance of tree functional traits, but no changes in species diversity during woody plant encroachment in a Brazilian savanna

AbstractQuestions: Woody encroachment in savannas has been associated with changing taxonomic composition and ecosystem function. Interestingly, there is little understanding of how encroachment impacts plant functional diversity and how those changes relate to plant demography, a crucial mediator between taxonomic composition and ecosystem function.Location: Southeastern Brazil.Methods: Using a landscape scale fire suppression experiment in a diverse Brazilian savanna, we quantify how change in species composition over seven years impacted vegetative and reproductive tree functional diversity as determined by new recruits, dead and surviving trees.Results: Over seven years, tree above‐ground biomass increased by 15%, while total species richness did not change. Despite minor changes, species composition remained overall similar (82%), with few species contributing significantly to plot dissimilarity over time. There were small changes in vegetative traits, where the community‐weighted mean increased in maximum tree height (↑ 2.1%) and specific leaf area (↑ 5.3%), and decreased in wood density (↓ 1.3%) and bark thickness (↓ 9.4%). Changes in reproductive traits were larger than in vegetative traits, with an increase in the prevalence of monoecy (↑ 32.6%), dioecy (↑ 44.2%), large seeds (↑ 20.3%), animal‐mediated seed dispersal (↑ 4.9%) and pollination by very small insects (↑ 45.5%), and a decrease in the prevalence of hermaphroditism (↓ 9%), small seeds (6.8%) and pollination by small insects (12.5%). The overall decrease in bark thickness and increase in monoecy and dioecy were mainly driven by characters of the new recruits, while the overall increase in specific leaf area (SLA) and decrease in small seeds appeared largely determined by the loss of trees possessing those traits.Conclusions: Encroachment leads to changes that are likely increasing ecosystem vulnerability to fire and drought. Further, the compositional changes observed appear to drive marked change in reproductive traits, indicating increasing dependence on animals for dispersal and reproduction. Understanding post‐hoc encroachment impacts in an era of widespread pervasive encroachment is fundamental to reconciling ecosystem functions such as nutrient cycling and pollination services as there is a loss of species with open ecosystem life‐history strategies. Among savannas, there remains an urgent need to understand relationships between woody cover and ecosystem function to determine thresholds in woody cover promoting resilient savanna ecosystems.

Abiotic and biotic drivers of tree trait effects on soil microbial biomass and soil carbon concentration

AbstractForests are ecosystems critical to understanding the global carbon budget, due to their carbon sequestration potential in both aboveground and belowground compartments, especially in species‐rich forests. Soil carbon sequestration is strongly linked to soil microbial communities, and this link is mediated by the tree community, likely due to modifications of microenvironmental conditions (i.e., biotic conditions, soil properties, and microclimate). We studied soil carbon concentration and the soil microbial biomass of 180 local neighborhoods along a gradient of tree species richness ranging from 1 to 16 tree species per plot in a Chinese subtropical forest experiment (BEF‐China). Tree productivity and different tree functional traits were measured at the neighborhood level. We tested the effects of tree productivity, functional trait identity, and dissimilarity on soil carbon concentrations, and their mediation by the soil microbial biomass and microenvironmental conditions. Our analyses showed a strong positive correlation between soil microbial biomass and soil carbon concentrations. In addition, soil carbon concentration increased with tree productivity and tree root diameter, while it decreased with litterfall C:N content. Moreover, tree productivity and tree functional traits (e.g., fungal root association and litterfall C:N ratio) modulated microenvironmental conditions with substantial consequences for soil microbial biomass. We also showed that soil history and topography should be considered in future experiments and tree plantations, as soil carbon concentrations were higher at sites where historical (i.e., at the beginning of the experiment) carbon concentrations were high, themselves being strongly affected by the topography. Altogether, these results implied that the quantification of the different soil carbon pools is critical for understanding microbial community–soil carbon stock relationships and their dependence on tree diversity and microenvironmental conditions.

Hydraulic role in differential stomatal behaviors at two contrasting elevations in three dominant tree species of a mixed coniferous and broad-leaved forest in low subtropical China

Quantifying the variation in stomatal behavior and functional traits of trees with elevation can provide a better understanding of the adaptative strategies to a changing climate. In this study, six water- and carbon-related functional traits were examined for three dominant tree species, Schima superba, Pinus massoniana and Castanopsis chinensis, in a mixed coniferous and broad-leaved forest at two elevations (70 and 360 ​m above sea level, respectively) in low subtropical China. We hypothesized that trees at higher elevations would develop more efficient strategies of stomatal regulations and greater water transport capacity to cope with more variable hydrothermal conditions than those at lower elevations. Results show that the hydraulic conductivity did not differ between trees at the two elevations, contrary to our expectation. The C. chinensis trees had greater values of leaf mass per unit area (LMA), and the S. superba and C. chinensis trees had greater values of wood density (WD), relative stem water content (RWC), and ratio of sapwood area to leaf area (Hv) at the 360-m elevation than at 70-m elevation. The mean canopy stomatal conductance was greater and more sensitive to vapor deficit pressure at 360 ​m than at 70 ​m for both S. superba and C. chinensis, while stomatal sensitivity did not differ between the two contrasting elevations for P. massoniana. The midday leaf water potential (ψL) in P. massoniana was significantly more negative at 360 ​m than at 70 ​m, but did not vary with increasing elevation in both S. superba and C. chinensis. Variations in Hv can be related to the differential stomatal behaviors between the two elevations. The variations of stomatal behavior and ψL with elevation suggested the isohydric strategy for the two broad-leaved species and the anisohydric strategy for the conifer species. The species-specific differences in LMA, WD, RWC, and Hv between the two elevations may reflect conservative resource use strategies at the higher elevation. Our findings revealed a close relationship between hydraulic and stomatal behavior and may help better understand the functional responses of forests to changing environmental conditions.

Leaf phenology rather than mycorrhizal type regulates soil nematode abundance, but collectively affects nematode diversity in seven common subtropical tree species

The underlying mechanisms of the relationships between tree species and the soil micro-food web in forest ecosystems remain uncertain, primarily ascribed to an insufficient understanding on how tree functional traits drive soil nematode communities, including in subtropical forests. We investigated the impacts of seven subtropical tree species (evergreen: Pinus massoniana, Mytilaria laosensis, Ilex chinensis, Michelia macclurei; and deciduous: Liquidambar formosana, Quercus acutissima, and Betula luminifera) on the soil nematode communities. We found that the abundance of soil nematodes was not affected by mycorrhizal types, but it was around 83% higher under the deciduous trees than the evergreen trees, indicating the importance of leaf phenology to the abundance of soil nematodes. Nonetheless, both the evergreen and the arbuscular mycorrhizal trees increased soil nematode diversity, resulting from changes in root traits and soil properties. Furthermore, root traits (root C, root N, and root C:N ratio), and soil properties (total C, total N, moisture content, and bulk density) were the best predictors of the community composition of soil nematodes, indicating a key role of resource quality and soil microhabitat in regulating soil nematodes. In contrast, the ectomycorrhizal trees had lower plant parasite and Wasilewska indices, and evenness, whereas the evergreen trees slightly improved the evenness of soil nematodes. This study suggests that tree species affect the soil food web through changes in soil conditions and plant functional traits in subtropical forests.

Relationships between tree functional traits and leaf nitrogen and phosphorus resorption efficiencies in subtropical young plantations

We examined the relationship between tree functional traits and leaf nitrogen and phosphorus resorption efficiencies across 29 species in 3-year-old pure plantations in subtropical China. The results showed that the average nitrogen (NRE) and phosphorus (PRE) resorption efficiencies in 29 young plantations were 50.5% and 57.3%, respectively. The average NRE of 22 arbuscular mycorrhizal (AM) tree species was 52.7%, significantly higher than that of the seven ectomycorrhizal (EM) tree species (45.1%). NRE was positively correlated with fine root tissue density across the 29 tree species. PRE was positively correlated with root diameter in the seven EM tree species. Functional traits of 22 AM tree species were not associated with NRE and PRE. Among all of the 29 tree species, mycorrhizal type, specific leaf area, fine root tissue density, leaf thickness, and the interaction effects of mycorrhizal type with leaf thickness explained 27% variation in NRE. Specific root length, fine root carbon content, fine root carbon to nitrogen ratio, mycorrhizal type, leaf carbon content, and the interaction effects of mycorrhizal type with leaf carbon content explained 35% variation in PRE. Root functional trait of subtropical species could predict nitrogen and phosphorus resorption efficiencies. The model with multiple functional traits could better reveal the relative importance of different biological factors on nutrient resorption efficiency.

Edge tree functional traits and their association with edaphic factors in seasonally dry forests in northern Thailand

The relationships between plant traits and soil properties in forest edges can provide insights into tree species recovery in edge habitats. In this study, we investigated the relationships between plant functional traits and soil conditions related to tree species recovery at the edges of two seasonally dry forests, a mixed deciduous forest (MDF) and a deciduous dipterocarp forest (DDF) in northern Thailand. We analyzed differences in functional trait diversity and community-level trait values between forests and performed RLQ analysis to assess the associations among species abundance, plant traits, and soil variables. We found that the MDF site had greater functional diversity and was dominated by plants with high specific leaf area (SLA) and leaf dry-matter content (LDMC) at the community level, whereas the DDF site had lower diversity and was dominated by plants with high wood density (WD) and leaf thickness (LT). The RLQ results indicated that at the MDF site, tree species with greater SLA (e.g., Pterocarpus macrocarpus, Dalbergia cultrata, and Phanera bracteata) were associated with soil clay content and nutrient status (i.e., nitrogen and calcium). Species with greater LDMC and leaf size (e.g., Xylia xylocarpa, Schleichera oleosa, and Chukrasia tabularis) were associated with soil organic matter content. At the DDF site, species with greater WD and LT (e.g., Dipterocarpus obtusifolius, Shorea siamensis, and Buchanania lanzan) were associated with soil sand content and bulk density. These patterns reflect the interplay between soil conditions and plant traits in the edge habitats of seasonally dry forests. Our results indicate that the edge effects on plant communities within seasonally dry forests depend on soil conditions and species-specific plant traits.

Tropical tree species differ in damage and mortality from lightning.

Lightning is an important agent of mortality for large tropical trees with implications for tree demography and forest carbon budgets. We evaluated interspecific differences in susceptibility to lightning damage using a unique dataset of systematically located lightning strikes in central Panama. We measured differences in mortality among trees damaged by lightning and related those to damage frequency and tree functional traits. Eighteen of 30 focal species had lightning mortality rates that deviated from null expectations. Several species showed little damage and three species had no mortality from lightning, whereas palms were especially likely to die from strikes. Species that were most likely to be struck also showed the highest survival. Interspecific differences in tree tolerance to lightning suggest that lightning-caused mortality shapes compositional dynamics over time and space. Shifts in lightning frequency due to climatic change are likely to alter species composition and carbon cycling in tropical forests.

Diversity-productivity relationships in forests of the southeastern United States: Leveraging national inventory data and tree functional traits

Numerous studies have evaluated the relationship between tree species diversity and productivity, with general trends suggesting a positive relationship. While most studies only use species richness, this study also analyzed how productivity changes with functional diversity and Shannon-Wiener's diversity index, to compare the impact of these different indicators of tree species diversity. This study used data from the USDA Forest Service Forest Inventory and Analysis (FIA) database collected in Alabama, Louisiana, and Mississippi to estimate plot-level productivity and diversity. Structural equation modeling was used to determine the strength of the relationship between different measures of tree species diversity and forest productivity directly and indirectly. This study found that species richness had the greatest influence on forest productivity, but it was largely an indirect effect mediated by stand density. Functional diversity did not have a substantial relationship with productivity while Shannon- Wiener's diversity index was negatively related to productivity when modeled with the other diversity indicators and mediated through stand density. The methodology of this research provides a framework for a similar analysis expanded spatially to other regions of the US to include more forest types for comparison of trends with the use of FIA data.

Shrubs Should Be Valued: The Functional Traits of Lonicera fragrantissima var. lancifolia in a Qinling Huangguan Forest Dynamics Plot, China

Previous studies have focused on the functional traits of trees, while undergrowth shrubs have not received the same attention. We collected 97 shrubs from 6 habitats in 3 diameter classes to measure the functional traits of Lonicera fragrantissima var. lancifolia, which is one of the dominant species in the shrub layer of the Qinling Huangguan plot. We found that leaf thickness (LT) decreased with an increase in diameter classes. Other functional traits did not change significantly with the diameter classes. Most of the functional traits changed with the habitats, which may be influenced by topography and soil. On the whole, Lonicera fragrantissima var. lancifolia showed low variation, which indicates that its growth was stable and good. The relationships between functional traits within species was in accordance with the leaf economic spectrum. The positive correlation between soil total nitrogen (STN) and C:N verified the “nutrition luxury hypothesis”.