The interspecific growth-mortality trade-off is not a general framework for tropical forest community structure

Demographic dynamics of a tropical montane rainforest: resilience to drought and implications for biodiversity conservation

Understanding how montane rainforests respond to disturbances is essential for identifying mechanisms that sustain biodiversity and ecosystem services under climate change. This study examined the structure, diversity, and dynamics of a tropical montane rainforest in Caparaó National Park, Brazil, over 10 years, following a severe drought. We analyzed biotic (e.g., species richness and canopy cover) and abiotic variables (e.g., elevation and slope) influencing demographic processes across forest strata and species groups. Data were collected from two inventories of permanent plots, and analyses included diversity indices, demographic rates, and linear models to assess relationships between environmental factors and forest dynamics. The results showed no significant changes in stem density or total basal area, indicating structural stability. Diversity indices were high (Shannon = 5.00; Pielou = 0.84) and exceeded those of nearby montane forests. Mortality rates (2.06 % yr-1) aligned with patterns in tropical forests at dynamic equilibrium, while recruitment (1.68 % yr-1) and basal area gain (2.80 % yr-1) highlighted the forest's resilience to drought. Tree survival was higher at lower elevations, on sun-exposed slopes, in soils with lower acidity, under dense canopies, and in areas with greater species richness (p = 0.042). Conversely, tree growth was more pronounced at higher elevations and in less dense canopies (p = 0.013). These findings underscore the importance of preserving montane forests as potential climate refugia due to their structural complexity and topographic heterogeneity, which buffer microclimatic extremes and enhance ecosystem resilience under climate change scenarios.

Nitrogen allocation among leaves and roots mediates the interaction between plant life history trade-off and density dependence

Introduction

Carbon, nitrogen and phosphorus, as the basic components of plants, determine plant growth and adaptation strategies, while there are certain differences in nutrient allocation among different plant organs. However, little is known about the manner in which resource allocation mediates the plant life history strategy.

Methods

Here, we collected three census field survey datasets from the Heishiding 50-ha dynamic plot showing functional traits and nutrient allocation among leaves and roots (⍺nutrient) from 92 woody species to determine the relationship between nutrient allocation and the plant life history strategy.

Results

Carbon allocation ⍺carbon was mainly determined by intraspecific variation while nitrogen allocation ⍺nitrogen and phosphorus allocation ⍺phosphorus was determined by interspecific variation. Species allocating more nitrogen to leaves showed greater resource acquisition traits, while species allocating more nitrogen to roots showed greater resource conservation traits. We found a trade-off between the plant relative growth rate and conspecific density dependence; fast-growing species showed higher mortality with conspecific neighbors but tended to allocate more nitrogen to leaves rather than roots.

Discussion

Our study revealed interspecific variation in nutrient allocation among leaves and roots as well as their relationship with functional traits and the plant life history strategy.

Nitrogen addition accelerates aboveground biomass sequestration in old-growth forests by stimulating ectomycorrhizal tree growth

Examining whether nitrogen (N) enrichment promotes secondary tree growth in both young (YF) and old-growth forests (OF) is crucial. This will help determine how N addition influences plant carbon sequestration across successional phases in temperate forests. We conducted an eight-year N addition experiment (0, 25, 50, 75 kg N ha-1 yr-1) in YF and OF in northeast China to investigate the effects of enhanced in situ N deposition on tree growth. Our results indicated that N addition accelerated the accumulation of annual mean aboveground biomass (ΔAGB) of trees only in OF. Specifically, for the species co-occurring in both YF and OF plots, their ΔAGB in OF peaked under the medium N treatment (3.69 Mg ha-1 yr-1), which was 2.3 times higher than that of YF (1.58 Mg ha-1 yr-1). Regarding mycorrhizal types, only the ΔAGB of EcM-associated trees peaked under the high N treatment (2.81 Mg ha-1 yr-1), increasing by 126.6% compared to the control (1.24 Mg ha-1 yr-1). This increase in biomass primarily came from large trees with a DBH ≥15 cm, most of which are EcM -associated species, such as Pinus koraiensis. In conclusion, continuous N addition increases nutrient supply and alleviates N limitation in old growth forest, leading to faster biomass accumulation. The growth of large-diameter trees with EcM-associated may contribute significantly to aboveground biomass accmulation under N addition. Nutrient limitation is dependent on stand age, mycorrhizal type and size, so these factors must be considered when assessing forest nutrient limitations.

Putting seedlings on the map: Trade-offs in demographic rates between ontogenetic size classes in five tropical forests

All species must partition resources among the processes that underly growth, survival, and reproduction. The resulting demographic trade-offs constrain the range of viable life-history strategies and are hypothesized to promote local coexistence. Tropical forests pose ideal systems to study demographic trade-offs as they have a high diversity of coexisting tree species whose life-history strategies tend to align along two orthogonal axes of variation: a growth-survival trade-off that separates species with fast growth from species with high survival and a stature-recruitment trade-off that separates species that achieve large stature from species with high recruitment. As these trade-offs have typically been explored for trees ≥1 cm dbh, it is unclear how species' growth and survival during earliest seedling stages are related to the trade-offs for trees ≥1 cm dbh. Here, we used principal components and correlation analyses to (1) determine the main demographic trade-offs among seed-to-seedling transition rates and growth and survival rates from the seedling to overstory size classes of 1188 tree species from large-scale forest dynamics plots in Panama, Puerto Rico, Ecuador, Taiwan, and Malaysia and (2) quantify the predictive power of maximum dbh, wood density, seed mass, and specific leaf area for species' position along these demographic trade-off gradients. In four out of five forests, the growth-survival trade-off was the most important demographic trade-off and encompassed growth and survival of both seedlings and trees ≥1 cm dbh. The second most important trade-off separated species with relatively fast growth and high survival at the seedling stage from species with relatively fast growth and high survival ≥1 cm dbh. The relationship between seed-to-seedling transition rates and these two trade-off aces differed between sites. All four traits were significant predictors for species' position along the two trade-off gradients, albeit with varying importance. We concluded that, after accounting for the species' position along the growth-survival trade-off, tree species tend to trade off growth and survival at the seedling with later life stages. This ontogenetic trade-off offers a mechanistic explanation for the stature-recruitment trade-off that constitutes an additional ontogenetic dimension of life-history variation in species-rich ecosystems.

Integrating conspecifics negative density dependence, successional and evolutionary dynamics: Towards a theory of forest diversity

Tree successional diversity is evident even to casual observers and has a well-understood physiological basis. Various life history trade-offs, driven by interspecific variation in a single trait, help maintain this diversity. Conspecific negative density dependence (CNDD) is also well-documented and reduces tree vital rates independently of succession strategies. The CNDD hypothesis is frequently justified by specialist natural enemies at a separate trophic level. We integrate these processes into an analytical demographic model, spanning short-term plant physiological responses to the dynamics of a large forest mosaic connected to a metacommunity. Surprisingly, multiple trade-offs do not necessarily increase diversity, as suboptimal trait combinations lead to strategies that cannot compete for successional niches, explaining the weak correlation between functional traits and succession position. Succession alone can sustain half of the species in the metacommunity, with diversity increasing linearly with CNDD strength. The steeper increase with larger metacommunities suggests CNDD plays a greater role in tropical forests. However, if each successional type contains multiple equivalent species, CNDD maintains diversity but becomes less effective in promoting successional diversity, consistent with some tropical forests being less successional diverse. Additionally, CNDD enhances the likelihood of successful speciation and shifts life-history trait frequency by affecting more late-successional species.

A Growth-Survival Trade-Off Along an Elevation Gradient Is Altered by Earthquake Disturbance in a Monodominant Southern Beech Forest

Tree growth-survival relationships link two demographic processes that individually dictate the composition, structure and functioning of forest ecosystems. While these relationships vary intra-specifically, it remains unclear how this reflects environmental variation and disturbance. We examined the influence of a 700-m elevation gradient and an Mw = 6.7 earthquake on intra-specific variability in growth-survival relationships. We expected that survival models that incorporated recent growth would be better supported than those only using other factors known to influence tree survival. We used a permanent plot network that representatively sampled a monodominant Nothofagus forest in New Zealand's Southern Alps in 1974 and that was remeasured seven times through to 2009. The relationships were assessed using pre-earthquake growth and survival, pre-earthquake growth and post-earthquake survival (0-5 years post-earthquake), and post-earthquake growth and survival (5+ years post-earthquake). Survival was related to growth of 4504 trees on 216 plots using Bayesian modelling. We hypothesised there would be a positive, logistic relationship between growth and survival. Pre-earthquake, we found a positive, logarithmic growth-survival relationship at all elevations. At higher elevations, trees grew more slowly but had higher survival than trees at lower elevations, supporting our hypothesised demographic trade-off with elevation. The earthquake altered growth-survival relationships from those found pre-earthquake and 0-5 years post-earthquake survival held little relationship with growth. A strong, logarithmic growth-survival relationship developed 5+ years post-earthquake because of enhanced survival of fast-growing trees yet low survival of slow-growing trees. Synthesis. Our findings demonstrate a trend in growth-survival relationships along an elevation gradient. If we assume a gradual climate warming is the equivalent of a forest stand shifting to a lower elevation, then data from our pre-earthquake period suggest that tree growth-survival relationships at any elevation could adjust to faster growth and lower survival. We also show how these novel growth-survival relationships could be altered by periodic disturbance.

The pace of life for forest trees

Tree growth and longevity trade-offs fundamentally shape the terrestrial carbon balance. Yet, we lack a unified understanding of how such trade-offs vary across the world's forests. By mapping life history traits for a wide range of species across the Americas, we reveal considerable variation in life expectancies from 10 centimeters in diameter (ranging from 1.3 to 3195 years) and show that the pace of life for trees can be accurately classified into four demographic functional types. We found emergent patterns in the strength of trade-offs between growth and longevity across a temperature gradient. Furthermore, we show that the diversity of life history traits varies predictably across forest biomes, giving rise to a positive relationship between trait diversity and productivity. Our pan-latitudinal assessment provides new insights into the demographic mechanisms that govern the carbon turnover rate across forest biomes.

Trait-Mediated Variation in Seedling Performance in Costa Rican Successional Forests: Comparing Above-Ground, Below-Ground, and Allocation-Based Traits

The interspecific relationship between functional traits and tree seedling performance can be inconsistent, potentially due to site-to-site or microsite variation in environmental conditions. Studies of seedling traits and performance often focus on above-ground traits, despite the importance of below-ground resource acquisition and biomass allocation to above versus below-ground functions. Here we investigate how varying environmental conditions across sites induce intraspecific variation in organ-level (above-ground, below-ground) and biomass allocation traits, affecting interspecific relationships between these traits and seedling performance. We analyzed trait expression for 12 organ-level and three allocation traits and their relationships with height growth (1716 seedlings) and mortality (15,862 seedlings) for 26 tree species across three sites along a forest successional gradient in Costa Rica. We found significant intraspecific differences across sites in all allocation traits, but only in three of seven above-ground and three of five below-ground organ-level traits. Allocation traits were better predictors of seedling performance than organ-level traits. Relationships between allocation traits and both growth and mortality varied among all sites, but for organ-level traits, only relationships with growth varied among sites. These results underscore that biomass allocation plays a key role in the earliest life stages of trees and that site-specific conditions can influence how functional traits mediate seedling establishment during succession.

Leaf and twig traits predict habitat adaptation and demographic strategies in tropical freshwater swamp forest trees

Differences in demographic and environmental niches facilitate plant species coexistence in tropical forests. However, the adaptations that enable species to achieve higher demographic rates (e.g. growth or survival) or occupy unique environmental niches (e.g. waterlogged conditions) remain poorly understood. Anatomical traits may better predict plant environmental and demographic strategies because they are direct measurements of structures involved in these adaptations. We collected 18 leaf and twig traits from 29 tree species in a tropical freshwater swamp forest in Singapore. We estimated demographic parameters of the 29 species from growth and survival models, and degree of association toward swamp habitats. We examined pairwise trait-trait, trait-demography and trait-environment links while controlling for phylogeny. Leaf and twig anatomical traits were better predictors of all demographic parameters than other commonly measured leaf and wood traits. Plants with wider vessels had faster growth rates but lower survival rates. Leaf and spongy mesophyll thickness predicted swamp association. These findings demonstrate the utility of anatomical traits as indicators of plant hydraulic strategies and their links to growth-mortality trade-offs and waterlogging stress tolerance that underlie species coexistence mechanisms in tropical forest trees.

Residual water losses mediate the trade-off between growth and drought survival across saplings of 12 tropical rainforest tree species with contrasting hydraulic strategies

Knowledge of the physiological mechanisms underlying species vulnerability to drought is critical for better understanding patterns of tree mortality. Investigating plant adaptive strategies to drought should thus help to fill this knowledge gap, especially in tropical rainforests exhibiting high functional diversity. In a semi-controlled drought experiment using 12 rainforest tree species, we investigated the diversity in hydraulic strategies and whether they determined the ability of saplings to use stored non-structural carbohydrates during an extreme imposed drought. We further explored the importance of water- and carbon-use strategies in relation to drought survival through a modelling approach. Hydraulic strategies varied considerably across species with a continuum between dehydration tolerance and avoidance. During dehydration leading to hydraulic failure and irrespective of hydraulic strategies, species showed strong declines in whole-plant starch concentrations and maintenance, or even increases in soluble sugar concentrations, potentially favouring osmotic adjustments. Residual water losses mediated the trade-off between time to hydraulic failure and growth, indicating that dehydration avoidance is an effective drought-survival strategy linked to the 'fast-slow' continuum of plant performance at the sapling stage. Further investigations on residual water losses may be key to understanding the response of tropical rainforest tree communities to climate change.

Tree demographic strategies largely overlap across succession in Neotropical wet and dry forest communities

Secondary tropical forests play an increasingly important role in carbon budgets and biodiversity conservation. Understanding successional trajectories is therefore imperative for guiding forest restoration and climate change mitigation efforts. Forest succession is driven by the demographic strategies-combinations of growth, mortality and recruitment rates-of the tree species in the community. However, our understanding of demographic diversity in tropical tree species stems almost exclusively from old-growth forests. Here, we assembled demographic information from repeated forest inventories along chronosequences in two wet (Costa Rica, Panama) and two dry (Mexico) Neotropical forests to assess whether the ranges of demographic strategies present in a community shift across succession. We calculated demographic rates for >500 tree species while controlling for canopy status to compare demographic diversity (i.e., the ranges of demographic strategies) in early successional (0-30 years), late successional (30-120 years) and old-growth forests using two-dimensional hypervolumes of pairs of demographic rates. Ranges of demographic strategies largely overlapped across successional stages, and early successional stages already covered the full spectrum of demographic strategies found in old-growth forests. An exception was a group of species characterized by exceptionally high mortality rates that was confined to early successional stages in the two wet forests. The range of demographic strategies did not expand with succession. Our results suggest that studies of long-term forest monitoring plots in old-growth forests, from which most of our current understanding of demographic strategies of tropical tree species is derived, are surprisingly representative of demographic diversity in general, but do not replace the need for further studies in secondary forests.

Survival, growth, and functional traits of tropical wet forest tree seedlings across an experimental soil moisture gradient in Puerto Rico

Droughts are predicted to become more frequent and intense in many tropical regions, which may cause shifts in plant community composition. Especially in diverse tropical communities, understanding how traits mediate demographic responses to drought can help provide insight into the effects of climate change on these ecosystems. To understand tropical tree responses to reduced soil moisture, we grew seedlings of eight species across an experimental soil moisture gradient at the Luquillo Experimental Forest, Puerto Rico. We quantified survival and growth over an 8-month period and characterized demographic responses in terms of tolerance to low soil moisture-defined as survival and growth rates under low soil moisture conditions-and sensitivity to variation in soil moisture-defined as more pronounced changes in demographic rates across the observed range of soil moisture. We then compared demographic responses with interspecific variation in a suite of 11 (root, stem, and leaf) functional traits, measured on individuals that survived the experiment. Lower soil moisture was associated with reduced survival and growth but traits mediated species-specific responses. Species with relatively conservative traits (e.g., high leaf mass per area), had higher survival at low soil moisture whereas species with more extensive root systems were more sensitive to soil moisture, in that they exhibited more pronounced changes in growth across the experimental soil moisture gradient. Our results suggest that increasing drought will favor species with more conservative traits that confer greater survival in low soil moisture conditions.

The links between wood traits and species demography change during tree development in a lowland tropical rainforest

One foundational assumption of trait-based ecology is that traits can predict species demography. However, the links between traits and demographic rates are, in general, not as strong as expected. These weak associations may be due to the use of traits that are distantly related to performance, and/or the lack of consideration of size-related variations in both traits and demographic rates. Here, we examined how wood traits were related to demographic rates in 19 tree species from a lowland forest in eastern Amazonia. We measured 11 wood traits (i.e. structural, anatomical and chemical traits) in sapling, juvenile and adult wood; and related them to growth and mortality rates (MR) at different ontogenetic stages. The links between wood traits and demographic rates changed during tree development. At the sapling stage, relative growth rates (RGR) were negatively related to wood specific gravity (WSG) and total parenchyma fractions, while MR decreased with radial parenchyma fractions, but increased with vessel lumen area (VA). Juvenile RGR were unrelated to wood traits, whereas juvenile MR were negatively related to WSG and axial parenchyma fractions. At the adult stage, RGR scaled with VA and wood potassium concentrations. Adult MR were not predicted by any trait. Overall, the strength of the trait-demography associations decreased at later ontogenetic stages. Our results indicate that the associations between traits and demographic rates can change as trees age. Also, wood chemical or anatomical traits may be better predictors of growth and MR than WSG. Our findings are important to expand our knowledge on tree life-history variations and community dynamics in tropical forests, by broadening our understanding on the links between wood traits and demography during tree development.

Breakdown of the growth-mortality trade-off along a soil phosphorus gradient in a diverse tropical forest

An ecological paradigm predicts that plant species adapted to low resource availability grow slower and live longer than those adapted to high resource availability when growing together. We tested this by using hierarchical Bayesian analysis to quantify variations in growth and mortality of ca 40 000 individual trees from greater than 400 species in response to limiting resources in the tropical forests of Panama. In contrast to theoretical expectations of the growth-mortality paradigm, we find that tropical tree species restricted to low-phosphorus soils simultaneously achieve faster growth rates and lower mortality rates than species restricted to high-phosphorus soils. This result demonstrates that adaptation to phosphorus limitation in diverse plant communities modifies the growth-mortality trade-off, with important implications for understanding long-term ecosystem dynamics.

Demographic trade-offs and functional shifts in a hurricane-impacted tropical forest

BACKGROUND AND AIMS

Understanding shifts in the demographic and functional composition of forests after major natural disturbances has become increasingly relevant given the accelerating rates of climate change and elevated frequency of natural disturbances. Although plant demographic strategies are often described across a slow-fast continuum, severe and frequent disturbance events influencing demographic processes may alter the demographic trade-offs and the functional composition of forests. We examined demographic trade-offs and the shifts in functional traits in a hurricane-disturbed forest using long-term data from the Luquillo Forest Dynamics Plot (LFPD) in Puerto Rico.

METHODS

We analysed information on growth, survival, seed rain and seedling recruitment for 30 woody species in the LFDP. In addition, we compiled data on leaf, seed and wood functional traits that capture the main ecological strategies for plants. We used this information to identify the main axes of demographic variation for this forest community and evaluate shifts in community-weighted means for traits from 2000 to 2016.

KEY RESULTS

The previously identified growth-survival trade-off was not observed. Instead, we identified a fecundity-growth trade-off and an axis representing seedling-to-adult survival. Both axes formed dimensions independent of resprouting ability. Also, changes in tree species composition during the post-hurricane period reflected a directional shift from seedling and tree communities dominated by acquisitive towards conservative leaf economics traits and large seed mass. Wood specific gravity, however, did not show significant directional changes over time.

CONCLUSIONS

Our study demonstrates that tree demographic strategies coping with frequent storms and hurricane disturbances deviate from strategies typically observed in undisturbed forests, yet the shifts in functional composition still conform to the expected changes from acquisitive to conservative resource-uptake strategies expected over succession. In the face of increased rates of natural and anthropogenic disturbance in tropical regions, our results anticipate shifts in species demographic trade-offs and different functional dimensions.

Winds of change. A commentary on 'Demographic trade-offs and functional shifts in a hurricane-impacted tropical forest'

This article comments on:

María Natalia Umaña, Jessica Needham, Jimena Forero-Montaña, Christopher J. Nytch, Nathan G. Swenson, Jill Thompson, María Uriarte and Jess K. Zimmerman. Demographic trade-offs and functional shifts in a hurricane-impacted tropical forest, Annals of Botany, Volume 131, Issue 7, 6 June 2023, Pages 1051–1060, https://doi.org/10.1093/aob/mcad004

How woody plants adjust above- and below-ground traits in response to sustained drought

Future increases in drought severity and frequency are predicted to have substantial impacts on plant function and survival. However, there is considerable uncertainty concerning what drought adjustment is and whether plants can adjust to sustained drought. This review focuses on woody plants and synthesises the evidence for drought adjustment in a selection of key above-ground and below-ground plant traits. We assess whether evaluating the drought adjustment of single traits, or selections of traits that operate on the same plant functional axis (e.g. photosynthetic traits) is sufficient, or whether a multi-trait approach, integrating across multiple axes, is required. We conclude that studies on drought adjustments in woody plants might overestimate the capacity for adjustment to drier environments if spatial studies along gradients are used, without complementary experimental approaches. We provide evidence that drought adjustment is common in above-ground and below-ground traits; however, whether this is adaptive and sufficient to respond to future droughts remains uncertain for most species. To address this uncertainty, we must move towards studying trait integration within and across multiple axes of plant function (e.g. above-ground and below-ground) to gain a holistic view of drought adjustments at the whole-plant scale and how these influence plant survival.

Plant Species' Capacity for Range Shifts at the Habitat and Geographic Scales: A Trade-Off-Based Framework

Climate change is causing rapid shifts in the abiotic and biotic environmental conditions experienced by plant populations, but we lack generalizable frameworks for predicting the consequences for species. These changes may cause individuals to become poorly matched to their environments, potentially inducing shifts in the distributions of populations and altering species' habitat and geographic ranges. We present a trade-off-based framework for understanding and predicting whether plant species may undergo range shifts, based on ecological strategies defined by functional trait variation. We define a species' capacity for undergoing range shifts as the product of its colonization ability and the ability to express a phenotype well-suited to the environment across life stages (phenotype-environment matching), which are both strongly influenced by a species' ecological strategy and unavoidable trade-offs in function. While numerous strategies may be successful in an environment, severe phenotype-environment mismatches result in habitat filtering: propagules reach a site but cannot establish there. Operating within individuals and populations, these processes will affect species' habitat ranges at small scales, and aggregated across populations, will determine whether species track climatic changes and undergo geographic range shifts. This trade-off-based framework can provide a conceptual basis for species distribution models that are generalizable across plant species, aiding in the prediction of shifts in plant species' ranges in response to climate change.

Growth portfolios buffer climate-linked environmental change in marine systems

Large-scale, climate-induced synchrony in the productivity of fish populations is becoming more pronounced in the world's oceans. As synchrony increases, a population's "portfolio" of responses can be diminished, in turn reducing its resilience to strong perturbation. Here we argue that the costs and benefits of trait synchronization, such as the expression of growth rate, are context dependent. Contrary to prevailing views, synchrony among individuals could actually be beneficial for populations if growth synchrony increases during favorable conditions, and then declines under poor conditions when a broader portfolio of responses could be useful. Importantly, growth synchrony among individuals within populations has seldom been measured, despite well-documented evidence of synchrony across populations. Here, we used century-scale time series of annual otolith growth to test for changes in growth synchronization among individuals within multiple populations of a marine keystone species (Atlantic cod, Gadus morhua). On the basis of 74,662 annual growth increments recorded in 13,749 otoliths, we detected a rising conformity in long-term growth rates within five northeast Atlantic cod populations in response to both favorable growth conditions and a large-scale, multidecadal mode of climate variability similar to the East Atlantic Pattern. The within-population synchrony was distinct from the across-population synchrony commonly reported for large-scale environmental drivers. Climate-linked, among-individual growth synchrony was also identified in other Northeast Atlantic pelagic, deep-sea and bivalve species. We hypothesize that growth synchrony in good years and growth asynchrony in poorer years reflects adaptive trait optimization and bet hedging, respectively, that could confer an unexpected, but pervasive and stabilizing, impact on marine population productivity in response to large-scale environmental change.

Trait-mediated leaf retention of atmospheric particulate matter in fourteen tree species in southern China

Particulate air pollution is a serious threat to human health, especially in urban areas, and trees can act as biological filters and improve air quality. However, studies on greening tree species selection are rare. We measured three particular matter adsorption metrics (PM_2.5, PM_2.5-10, and PM_>10 captured per leaf area) and six functional traits for each of fourteen species and estimated their minimum light requirements based on field surveys. We found that shade-tolerant species captured more coarse particles (PM_2.5-10) than light-demanding species. For traits, a strong negative correlation was found between photosynthetic capacity and adsorption capacity for all three PM size fractions, indicating that in comparison to acquisitive species, conservative species captured larger amounts of particles. Moreover, denser wood species and smaller leaves were more efficient in capturing large particles (PM_>10), while species with "expensive" leaves (high leaf N or P) were more efficient in capturing fine particles (PM_2.5), indicating that capturing large and fine particles was related to mechanical stability traits and leaf surface traits, respectively. Our results demonstrated that the metabolism (e.g., photosynthetic capacity) and chemistry (e.g., leaf N and leaf P) of leaves help explain species capacity to capture PM. We encourage future studies to investigate the ecosystem functions and stress tolerance of tree species with the same framework and trait-based methods.

Multiscale predictors of small tree survival across a heterogeneous tropical landscape

Uncertainties about controls on tree mortality make forest responses to land-use and climate change difficult to predict. We tracked biomass of tree functional groups in tropical forest inventories across Puerto Rico and the U.S. Virgin Islands, and with random forests we ranked 86 potential predictors of small tree survival (young or mature stems 2.5-12.6 cm diameter at breast height). Forests span dry to cloud forests, range in age, geology and past land use and experienced severe drought and storms. When excluding species as a predictor, top predictors are tree crown ratio and height, two to three species traits and stand to regional factors reflecting local disturbance and the system state (widespread recovery, drought, hurricanes). Native species, and species with denser wood, taller maximum height, or medium typical height survive longer, but short trees and species survive hurricanes better. Trees survive longer in older stands and with less disturbed canopies, harsher geoclimates (dry, edaphically dry, e.g., serpentine substrates, and highest-elevation cloud forest), or in intervals removed from hurricanes. Satellite image phenology and bands, even from past decades, are top predictors, being sensitive to vegetation type and disturbance. Covariation between stand-level species traits and geoclimate, disturbance and neighboring species types may explain why most neighbor variables, including introduced vs. native species, had low or no importance, despite univariate correlations with survival. As forests recovered from a hurricane in 1998 and earlier deforestation, small trees of introduced species, which on average have lighter wood, died at twice the rate of natives. After hurricanes in 2017, the total biomass of trees ≥12.7 cm dbh of the introduced species Spathodea campanulata spiked, suggesting that more frequent hurricanes might perpetuate this light-wooded species commonness. If hurricane recovery favors light-wooded species while drought favors others, climate change influences on forest composition and ecosystem services may depend on the frequency and severity of extreme climate events.

Links across ecological scales: Plant biomass responses to elevated CO2

The degree to which elevated CO₂ concentrations (e[CO₂ ]) increase the amount of carbon (C) assimilated by vegetation plays a key role in climate change. However, due to the short-term nature of CO₂ enrichment experiments and the lack of reconciliation between different ecological scales, the effect of e[CO₂ ] on plant biomass stocks remains a major uncertainty in future climate projections. Here, we review the effect of e[CO₂ ] on plant biomass across multiple levels of ecological organization, scaling from physiological responses to changes in population-, community-, ecosystem-, and global-scale dynamics. We find that evidence for a sustained biomass response to e[CO₂ ] varies across ecological scales, leading to diverging conclusions about the responses of individuals, populations, communities, and ecosystems. While the distinct focus of every scale reveals new mechanisms driving biomass accumulation under e[CO₂ ], none of them provides a full picture of all relevant processes. For example, while physiological evidence suggests a possible long-term basis for increased biomass accumulation under e[CO₂ ] through sustained photosynthetic stimulation, population-scale evidence indicates that a possible e[CO₂ ]-induced increase in mortality rates might potentially outweigh the effect of increases in plant growth rates on biomass levels. Evidence at the global scale may indicate that e[CO₂ ] has contributed to increased biomass cover over recent decades, but due to the difficulty to disentangle the effect of e[CO₂ ] from a variety of climatic and land-use-related drivers of plant biomass stocks, it remains unclear whether nutrient limitations or other ecological mechanisms operating at finer scales will dampen the e[CO₂ ] effect over time. By exploring these discrepancies, we identify key research gaps in our understanding of the effect of e[CO₂ ] on plant biomass and highlight the need to integrate knowledge across scales of ecological organization so that large-scale modeling can represent the finer-scale mechanisms needed to constrain our understanding of future terrestrial C storage.

Dynamic Energy Budget models: fertile ground for understanding resource allocation in plants in a changing world

Climate change is having dramatic effects on the diversity and distribution of species. Many of these effects are mediated by how an organism's physiological patterns of resource allocation translate into fitness through effects on growth, survival and reproduction. Empirically, resource allocation is challenging to measure directly and so has often been approached using mathematical models, such as Dynamic Energy Budget (DEB) models. The fact that all plants require a very similar set of exogenous resources, namely light, water and nutrients, integrates well with the DEB framework in which a small number of variables and processes linked through pathways represent an organism's state as it changes through time. Most DEB theory has been developed in reference to animals and microorganisms. However, terrestrial vascular plants differ from these organisms in fundamental ways that make resource allocation, and the trade-offs and feedbacks arising from it, particularly fundamental to their life histories, but also challenging to represent using existing DEB theory. Here, we describe key features of the anatomy, morphology, physiology, biochemistry, and ecology of terrestrial vascular plants that should be considered in the development of a generic DEB model for plants. We then describe possible approaches to doing so using existing DEB theory and point out features that may require significant development for DEB theory to accommodate them. We end by presenting a generic DEB model for plants that accounts for many of these key features and describing gaps that would need to be addressed for DEB theory to predict the responses of plants to climate change. DEB models offer a powerful and generalizable framework for modelling resource allocation in terrestrial vascular plants, and our review contributes a framework for expansion and development of DEB theory to address how plants respond to anthropogenic change.