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In many grasslands, species with specific traits occupy unique temporal positions within communities. Such intra-annual segregation is predicted to be greatest in systems with high intra-annual climate variability because fluctuating environmental conditions provide opportunities for temporal niche partitioning among species. However, because most studies on intra-annual community dynamics have been conducted at individual sites, relationships between intra-annual climate variability and seasonal community dynamics at global scales have not yet been identified. Furthermore, the same characteristics that promote species-specific responses to fluctuations in environmental conditions may also drive species-specific responses to global change drivers such as eutrophication. Research provides evidence that eutrophication alters inter-annual plant community dynamics yet understanding of how it alters intra-annual dynamics remains limited.We used early-season and late-season compositional data collected from 10 grassland sites around the world to ask how intra-annual variability in precipitation and temperature as well as nutrient enrichment shape intra-annual species segregation, or seasonal β-diversity, in plant communities. We also assessed whether changes in the abundances of specific functional groups including annual forbs, perennial forbs, C3 and C4 graminoids, and legumes underpin compositional differences between early- and late-season communities and treatments. We found that intra-annual temperature variability and seasonal β-diversity were positively related but observed no relationship between intra-annual precipitation variability and seasonal β-diversity. This suggests that positive relationships between α-diversity and intra-annual temperature variability identified in earlier studies may be underpinned by the positive influence of intra-annual temperature variability on temporal segregation of species within growing seasons. We found that nutrient enrichment increased seasonal β-diversity via increased turnover of species between early- and late-season communities. This finding mirrors patterns observed at inter-annual scales and suggests fertilization can alter compositional dynamics via similar mechanisms at varied temporal scales. Finally, fertilization reduced the abundance of C4 graminoids and legumes and eliminated intra-annual differences in these groups. In contrast, fertilization resulted in intra-annual differences in C3 graminoids which were not observed in control conditions, and increased abundance of C3 graminoids and annual forbs overall. Our study provides new insight into how intra-annual climate variability and nutrient enrichment influence biodiversity and seasonal dynamics in global grasslands.

Rangelands account for a large portion of global carbon stocks and have high potential for carbon sequestration if managed properly. Grazing has variable effects on soil organic carbon depending on climate, geography, and soil type; therefore, grazers in various regions may need to be managed differently to ensure optimum carbon sequestration. This study aimed to assess the impacts of cattle grazing on soil carbon in seminatural subtropical humid rangelands in Florida. We measured root biomass, bulk density, soil organic carbon (SOC), and total carbon (TC) concentrations and used the equivalent soil mass method to assess organic carbon stock (OCS) and total carbon stock at three depths (0−5 cm, 5−15 cm, and 15−30 cm) inside and outside of five 15-yr-old grazing exclosures. We also surveyed the vegetation at each sampling location and litter biomass inside and outside of exclosures. We found that grazing increased bulk density, decreased root biomass, but did not affect litter amount. SOC and TC concentrations did not differ significantly between ungrazed and grazed plots. On an equivalent soil mass basis, we found greater soil carbon stocks in grazed plots within the shallower part of the soil (0−5 cm). Removal of grazing resulted in a clear difference in vegetation composition between grazed and ungrazed plots, with grazed plots having higher grass cover (on average 60% in grazed vs. 13% in ungrazed) and ungrazed having higher forb cover (on average 78% in ungrazed vs. 32% in grazed). Results provide evidence that grazing increased soil carbon stocks in the top layer of soil, but longer-term studies are needed to assess the impact of grazing on SOC concentrations. To further clarify the impact of grazing on drivers of soil carbon in subtropical humid seminatural grasslands, we recommend further study of grazing impacts on productivity, root production and turnover, and microbial responses.

Plant–plant interactions influence community assembly and species responses to environmental change. However, species interactions are complex phenomena influenced by context and scale. We conducted a one-year replacement experiment between two grasses in subtropical grasslands (native Axonopus fissifolius and non-native Paspalum notatum) in central Florida, USA. We evaluated interactions between these species at three ecological scales, ‘pairwise interactions,’ ‘patch’ (33 cm × 33 cm), and ‘plot’ (1 m x 3 m) and along a gradient (15 levels) of increasing non-native and decreasing native plot ground cover within enclosures in semi-native pastures. We transplanted 18 individuals of each species per plot (18 × 30 plots = 1080 plants in total) in a 2 × 2 design intersecting direct pairwise interactions (additional transplanted neighbor: absent/present) with recipient patch type (Axonopus fissifolius/Paspalum notatum). Leaf length, leaf number, and plant biomass were measured at the beginning and the end of the experiment along with soil nutrients and pH at patch level. Over 92% of the transplants survived. We observed an interactive effect between patch type (non-native vs. native dominated) and plant abundance at plot level on plant performance, suggesting that indirect effects at larger spatial scales can influence effects at smaller scales. Surprisingly, both species exhibited enhanced performance with increasing abundance of the non-native species at plot level. We discuss several mechanisms explaining these indirect effects including Paspalum notatum-induced changes in soil pH, soil feedbacks from the soil microbial community, preconditioning effects of the native species on the recipient soil, and positive density dependence effects after transplantation.

The effects of altered nutrient supplies and herbivore density on species diversity vary with spatial scale, because coexistence mechanisms are scale dependent. This scale dependence may alter the shape of the species–area relationship (SAR), which can be described by changes in species richness (S) as a power function of the sample area (A): S = cAz, where c and z are constants. We analysed the effects of experimental manipulations of nutrient supply and herbivore density on species richness across a range of scales (0.01–75 m²) at 30 grasslands in 10 countries. We found that nutrient addition reduced the number of species that could co-occur locally, indicated by the SAR intercepts (log c), but did not affect the SAR slopes (z). As a result, proportional species loss due to nutrient enrichment was largely unchanged across sampling scales, whereas total species loss increased over threefold across our range of sampling scales.

Isolated, seasonal wetlands within agricultural landscapes are important ecosystems. However, they are currently experiencing direct and indirect effects of agricultural management surrounding them. Because wetlands provide important ecosystem services, it is crucial to determine how these factors affect ecological communities. Here, we studied the long-term effects of land-use intensification, cattle grazing, prescribed fires, and their interactions on wetland plant diversity, community dynamics, and functional diversity. To do this, we used vegetation and trait data from a 14-year-old experiment on 40 seasonal wetlands located within seminatural and intensively managed pastures in Florida. These wetlands were allocated different grazing and prescribed fire treatments (grazed vs. ungrazed, burned vs. unburned). Our results showed that wetlands within intensively managed pastures have lower native plant diversity, floristic quality, evenness, and higher nonnative species diversity and exhibited the most resource-acquisitive traits. Wetlands embedded in intensively managed pastures were also characterized by lower species turnover over time. We found that 14 years of cattle exclusion reduced species diversity in both pasture management intensities and had no effect on floristic quality. Fenced wetlands exhibited lower functional diversity and experienced a higher rate of community change, both due to an increase in tall, clonal, and palatable grasses. The effects of prescribed fires were often dependent on grazing treatment. For instance, prescribed fires increased functional diversity in fenced wetlands but not in grazed wetlands. Our study suggests that cattle exclusion and prescribed fires are not enough to restore wetlands in intensively managed pastures and further highlights the importance of not converting seminatural pastures to intensively managed pastures. Our study also suggests that grazing levels applied in seminatural pastures maintained high plant diversity and prevented tree and shrub encroachment and that in the absence of grazing, prescribed fire became crucial to maintaining higher species evenness.

Litter decomposition is a fundamental process underpinning multiple ecosystem services. Despite a long history of research on decomposition, direct and indirect effects of multiple interactive land management on wetland decomposition yet remain less well understood. Here, we used a long-term whole-ecosystem wetland experiment in south-central Florida to investigate interactive effects of land-use intensification, cattle grazing and prescribed fire on in situ wetland plant litter decomposition. We further examined the direct and indirect pathways of land management effects on litter decomposition through changes in associated litter traits, soil properties, and soil microbial attributes using structural equation models. We used the litterbag technique that quantifies decomposition rates (k-values) and recalcitrant fractions (A-values). Our results showed that land-use intensification increased k-values in ungrazed wetlands and decreased k-values in grazed wetlands, but consistently reduced A-values regardless of other treatments. Prescribed fire individually suppressed litter decomposition by reducing k and increasing A. Further, these effects occurred through altering litter, soil, and microbial properties. Our results revealed that litter traits and soil properties were the first two strongest factors in determining wetland decomposition processes. Particularly, litter P and Mg contents and soil P and K contents were the best predictors for k, while litter Ca and lignin contents and soil pH, N and water content best predicted A. Moreover, microbial traits exhibited interactive effects with litter and soil properties to affect wetland litter decomposition. Our research suggests that cattle grazing could buffer against stimulating effect of land-use intensification on decomposition rates and thus avoid nutrient releases pulses. Our study further indicates that land-use intensification and fire suppression in subtropical wetlands could promote organic matter depletion and thus nutrient loss, highlighting the need to reduce anthropogenic disturbances to natural wetlands to maintain their capacity for providing associated regulating and supporting services.

Wetlands embedded in agroecosystems provide vital ecosystem services (i.e., freeze protection, water retention, nutrient cycling, biodiversity support). However, they are particularly susceptible to invasion by nonnative species. West Indian marsh grass [Hymenachne amplexicaulis (Rudge) Nees] is a major wetland invader in Florida. Despite the documented consequences of H. amplexicaulis invasions, the landscape factors influencing the spread of this species are poorly understood. In this study, we asked whether landscape factors associated with wetland isolation, connectivity, and land management influence the presence of H. amplexicaulis among wetlands embedded in pastures. We recorded the presence or absence of H. amplexicaulis in 158 seasonal wetlands embedded in different pasture types (semi-natural vs. intensively managed). Wetland area, isolation from neighboring wetlands, isolation from the nearest source ditch, and connectivity were determined using a geographic information system (GIS). We related landscape factors to H. amplexicaulis using generalized linear models and model selection based on the second-order Akaike information criterion. Hymenachne amplexicaulis was first detected at the study site in the early 2000s. By 2018, we observed this species in 66% of the surveyed wetlands. The likelihood of observing H. amplexicaulis was higher in wetlands embedded in semi-natural pastures and higher in less isolated wetlands, especially when connected to a ditch. These results indicate that H. amplexicaulis spreads both overland (during seasonal flooding) and via the ditch network. Future work is needed to understand whether seeds or stolons are the primary invasion propagule and whether the species forms a persistent seed bank that could slow down restoration efforts. Additionally, further research is required to understand the ecological impact of this highly invasive plant in Florida wetlands.

AIM: The relative importance of stochastic and deterministic niche processes can affect the assembly of communities in response to land use context and change. In this study, we quantified the relative importance of dispersal‐ vs niche‐based processes in structuring forest plant metacommunities and sought to understand how these processes have changed in these forests over the past 50 years. LOCATION: Wisconsin, USA. METHODS: We used plant understorey community survey data in both the 1950s and 2000s from 142 upland forest stands in southern and northern Wisconsin forests to relate compositional similarity to geographic and environmental distances among sites (reflecting dispersal and niche‐based processes, respectively). We then partitioned the variance to determine their relative importance over time. Finally, we classified species into three dispersal groups based on seed mass, dispersal mode, and plant height to assess how these affect community structure. RESULTS: Both niche and dispersal processes influence the structure of Wisconsin's forest plant understories. Niche‐based processes related to environmental differences among sites dominate the mostly continuous northern upland forests. In contrast, dispersal processes dominate community assembly in the more fragmented southern upland forests. Dispersal processes increased in importance in both regions and especially in more fragmented southern upland forests over the past 50 years. We detected no differences among dispersal groups in how similarity decays with geographic distance. CONCLUSIONS: In regions retaining heavy forest cover, niche‐based assembly still predominates while in areas with smaller scattered patches of forest, stochastic dispersal plays a greater role. Dispersal‐based processes increasingly dominate forest metacommunity dynamics in both regions.

Wisconsin's plant communities are responding to shifting disturbance regimes, habitat fragmentation, aerial nitrogen deposition, exotic species invasions, ungulate herbivory, and successional processes. To better understand how plant functional traits mediate species' responses to changing environmental conditions, we collected a large set of functional trait data for vascular plant species occupying Wisconsin forests and grasslands. We used standard protocols to make 76,213 measurements of 34 quantitative traits. These data provide rich information on genome size, physical leaf traits (length, width, circularity, thickness, dry matter content, specific leaf area, etc.), chemical leaf traits (carbon, nitrogen, phosphorus, potassium, calcium, magnesium, ash), life history traits (vegetative and flower heights, seed mass), and traits affecting plant palatability (leaf fiber, fat, and lignin). These trait values derive from replicate measurements on 12+ individuals of each species from multiple sites and 45+ individuals for a selected subset of species. Measurements typically reflect values for individuals although some chemical traits involved composite samples from several individuals at the same site. We also qualitatively characterized each species by plant family, woodiness, functional group, and Raunkiaer lifeform. These data allow us to characterize trait dimensionality, differentiation, and covariation among temperate plant species (e.g., leaf and stem economic syndromes). We can also characterize species' responses to environmental gradients and drivers of ecological change. With survey and resurvey data available from400 sites in Wisconsin, we can analyze variation in community trait distributions and diversity over time and space. These data therefore allow us to assess how trait divergence vs. convergence affects community assembly and how traits may be related to half-century shifts in the distribution and abundance of these species. The data set can be used for non-commercial purposes. The data set is licensed as follows: CC-By Attribution 4.0 International. We request users cite both the OSF data set and this Ecology data paper publication.

The effects of habitat fragmentation on species richness and composition have been extensively studied. However, little is known about how fragmentation affects functional diversity patterns. Fragmentation can indeed affect functional diversity directly (e.g. by promoting traits associated to long-distance dispersal when fragment isolation increases) or indirectly (e.g. by decreasing species richness, hence trait diversity, when fragment area decreases). Here, we used structural equation modeling to determine whether factors associated to forest fragmentation, namely area, habitat heterogeneity, spatial isolation and age have a direct effect on forest herb functional diversity. Using occurrence data from 243 forest fragments located in northern France and six plant life-history traits, we estimated species richness and calculated functional diversity in each of these 243 forest fragments. We found that species richness was the primary driver of functional diversity in these fragments, with a strong positive and direct relationship between species richness and functional diversity. Interestingly, both fragment isolation and age had a direct negative effect on functional diversity independent of their effects on species richness. Isolation selected life-history traits associated with long-distance dispersal, while age selected for life-history traits typical of forest habitat specialists. Isolated and/or older forest fragments are thus at greater risk of local species and functional extinctions, and hence making these forest fragments particularly vulnerable to future global changes.

Aim Biotic homogenization – the tendency for communities to converge in species composition – has occurred in many ecosystems, creating management challenges. The extent to which this convergence in species composition is related to convergence in trait composition (‘functional homogenization’), however, remains unresolved. Location North America, Wisconsin.

Ungulate browsing affects many plant species, shifting patterns of relative abundance, plant community diversity, and ecosystem processes. Despite the strength and diversity of ungulate impacts, we lack comprehensive methods and a unified network for tracking and comparing ungulate impacts across the Great Lakes region. The Great Lakes Network Office (GLN) of the National Park Service has identified white-tailed deer as a keystone herbivore that could threaten the health of Great Lakes forests. To supplement their permanent vegetation monitoring program, GLN monitors deer and moose browsing pressure on woody and herbaceous plants at nine national parks in the region. We used data from these surveys to investigate relationships among patterns of browsing across species and sites with the goal of inferring efficient and reliable indicators of ungulate impacts. We also investigated the relationships between patterns of browsing on woody vegetation and among-site variation in the presence and abundance of understory species. Our results showed that ungulates clearly prefer certain woody species, but these vary across the region in response to local community composition. Ungulate impacts on understory species are correlated with woody browsing impacts but also vary with local ecological conditions. To build a more efficient and accurate composite indicator of overall ungulate impacts, we combined data on woody plant browsing with data on the abundance of specific understory species to infer overall levels of threat from ungulate browsing. Such combined indicators improve our ability to monitor the impacts of ungulate browsing, particularly if such methods can be expanded and standardized across the region.

Plant traits are particularly important in determining plant community structure. However, how can one identify which traits are the most important in driving community assembly? Here we propose a method 1) to quantify the direction and strength of trait selection during community assembly and 2) to obtain parsimonious lists of traits that can predict species relative abundances in plant communities. We tested our method using floristic data from 32 plots experiencing different treatments (fertilisation and grazing) in southern France. Twelve functional traits were measured on 68 species. We determined the direction and strength of selection on these 12 traits using a metric derived from a maximum entropy model (i.e. lambda). We then determined our parsimonious list of traits using a backward selection of traits based on these lambda values (for all treatments and in each treatment separately). We finally compared our method to two other methods: one based on iterative RLQ and the other based on an entropy-based forward selection of traits. We found major differences in the direction and strength of selection across the 12 traits and treatments. From the 12 traits, plant vegetative and reproductive heights, leaf dry matter content leaf nitrogen content, specific leaf area, and leaf phosphorus content were particularly important for predicting species relative abundances when considering all treatments together. Our method yielded results similar to those produced by the entropy-based approach but differed from those produced by the iterative RLQ, whose selected traits could not significantly predict species relative abundances. Together these results suggest that the assembly of these communities is primarily driven by a small number of key functional traits. We argue that our method provides an objective way of determining a parsimonious list of traits that together accurately predict community structure and which, despite its complementarities with entropy-based method, offers significant advantages.

Summary1. Al th o ug h h ab itat frag me n tatio n is reco gn ized as a ma jor th reat to bio dive rsity, few stu dies h av eex am ined th e relative imp o rtan ce o f loca l, land scap e an d histo rica l facto rs in co nt ro lling loca lsp ec ies as semb lage s, an d h o w th ese facto rs intera ct,in pa tchy ec o sy stem s. We q ua n tiÞe d th e directan d ind irec t effects o f pa tch size ,p atch h etero ge n eity,ag ricu ltu ra linten sity an d p atch ag e o n plan tsp ec ies rich n ess an d co mp o sitio n o ffo rest pa tche s em b ed d ed in ag ricu ltu ra lland scap es.2. In six 5 a 5 k m- sa mp ling lan ds ca pe wi n do ws , we su rv ey ed ea ch fo rest p atch fo r va scular p lantsp ec ies an d co llec ted th ree sets of ind ep en d en t va riab les, d escribing p atch size an d h etero ge n eity,lan ds ca pe co mp o sition an d h isto ry .T he six wi n do ws w ere ar ra ng ed alon g a gr ad ien t o f ag ricu ltu reint en sity in ru ra llan ds ca pe s of th e P icar d y region (N Fr an ce ).3. We u sed n on -m etric mu ltidim en sion al scaling (N MS ) to d etec t ma jor en viro n me n tal gr ad ient su n de rlying va riation in sp ec ies co mp o sition am on g pa tche s. We th en co n stru cted stru ctu ra l eq u a-tion mo de ls (S E M) to q ua nt ify th e direct an d ind irec t effects of th e th ree sets of va riab les o n loca lp lant d iversity,wh ich wa s su cc essive ly inco rp or ated as pa tch scor es alon g th e Þ rst th ree NM S ax es,w oo dy sp ec ies rich ne ss,fo rest he rb sp ec ies rich ne ss,an d no n- fo rest h erb sp ec ies rich ne ss.4. A ma jor insu en ce o f th e lan ds ca pe ma trix on loca l sp ec ies co mp os ition wa s reve aled b y NM San d su bs eq ue nt S EM ,ma inly th ro u gh no n -for esthe rb sp ec ies, w hich ex plain ed mo st of th e be tw ee np atch s or istic d issimi larity.S pe cies rich ne ss increa sed wi th pa tch he tero ge n eity,wh erea s pa tch ar ean ev er h ad a direct effect. Fo rest he rb s we re mo re resp o ns ive to pa tch ag e an d co nn ec tivity tha no th er sp ec ies, wh erea s n on -for est an d wo o d y sp ec ies we re mo re insu en ce d by ag ricu ltu re inten sityin th e su rro u nd ing ma trix.5. S ynthesis.We us ed o ne o f th e larg est da ta sets ev er co llec ted in temp erate frag me n ted fo rests tob u ild, fo r th e Þ rsttime ,a stru ctur al mo de linco rp or ating allsu sp ec ted dr ivers of loca lplan t co mm u -n ities. We sh o we d th at th e n u mb er an d iden tity of loca lsp ec ies co ex istin g in su cc essio na lfrag me n tso f a fo rest me taco mm un ity at a give n time is co nt ro lled by a u n iqu e co mb ination o f int erac tin gloc al, lan ds ca pe an d histo rica l factor s. Pr eservin g the larg est, old est frag me n ts an d fav o ur ing sp e-cies mo ve me n ts in th e su rro un d ing ma trix is th e be st wa y to co ns erve fo rest sp ec ialists in ch an gingru ra llan ds ca pe s.Key-wor ds: agricu ltural intens ity, disper sal lim itation, habita t fragm entat ion, he dgerow net-work, metacommun ity, plant communi ty divers ity, specie sÐarea relationshi p, specie sÐtimerelationshi p, struc tural equati on modellingIntroduc tion

We evaluate the predictive power and generality of Shipley's maximum entropy (maxent) model of community assembly in the context of 96 quadrats over a 120-km2 area having a large (79) species pool and strong gradients. Quadrats were sampled in the herbaceous understory of ponderosa pine forests in the Coconino National Forest, Arizona, U.S.A. The maxent model accurately predicted species relative abundances when observed community-weighted mean trait values were used as model constraints. Although only 53% of the variation in observed relative abundances was associated with a combination of 12 environmental variables, the maxent model based only on the environmental variables provided highly significant predictive ability, accounting for 72% of the variation that was possible given these environmental variables. This predictive ability largely surpassed that of nonmetric multidimensional scaling (NMDS) or detrended correspondence analysis (DCA) ordinations. Using cross-validation with 1000 independent runs, the median correlation between observed and predicted relative abundances was 0.560 (the 2.5% and 97.5% quantiles were 0.045 and 0.825). The qualitative predictions of the model were also noteworthy: dominant species were correctly identified in 53% of the quadrats, 83% of rare species were correctly predicted to have a relative abundance of < 0.05, and the median predicted relative abundance of species actually absent from a quadrat was 5 x 10(-5).

Questions: How can one explicitly quantify, and separately measure, stress and disturbance gradients? How do these gradients affect functional composition in early successional plant communities and to what extent? Can we accurately predict trait composition from knowledge of these gradients? Location: Southern Quebec, Canada. Methods: Using eight environmental variables measured in 48 early successional plant communities, we estimated stress and disturbance gradients through structural equation modelling. We then measured 10 functional traits on the most abundant species of these 48 communities and calculated their community-level mean and variance weighted by the relative abundance of each species. Finally, we related these community-weighted means and variances to the estimated stress and disturbance gradients using general linear models or generalized additive models. Results: We obtained a well-fitting measurement model of the stress and disturbance gradients existing in our sites. Of the 10 studied traits, only average plant reproductive height was strongly correlated with the stress (r2=0.464) and disturbance (r2=0.543) gradients. Leaf traits were not significantly related to either the stress or disturbance gradients. Conclusions: The well-fitting measurement model of the stress and disturbance gradients, combined with the generally weak trait–environment linkages, suggests that community assembly in these early successional plant communities is driven primarily by stochastic processes linked to the history of arrival of propagules and not to trait-based environmental filtering.

C. I. Millar and N. L. Stephenson (“Temperate forest health in an era of emerging megadisturbance,” Review, 21 August, p. [823][1]) review the increasing susceptibility of temperate forests to stresses such as increasing droughts, insect outbreaks, and more frequent and intense fires (“

Recent global warming is acting across marine, freshwater, and terrestrial ecosystems to favor species adapted to warmer conditions and/or reduce the abundance of cold-adapted organisms (i.e., “thermophilization” of communities). Lack of community responses to increased temperature, however, has also been reported for several taxa and regions, suggesting that “climatic lags” may be frequent. Here we show that microclimatic effects brought about by forest canopy closure can buffer biotic responses to macroclimate warming, thus explaining an apparent climatic lag. Using data from 1,409 vegetation plots in European and North American temperate forests, each surveyed at least twice over an interval of 12–67 y, we document significant thermophilization of ground-layer plant communities. These changes reflect concurrent declines in species adapted to cooler conditions and increases in species adapted to warmer conditions. However, thermophilization, particularly the increase of warm-adapted species, is attenuated in forests whose canopies have become denser, probably reflecting cooler growing-season ground temperatures via increased shading. As standing stocks of trees have increased in many temperate forests in recent decades, local microclimatic effects may commonly be moderating the impacts of macroclimate warming on forest understories. Conversely, increases in harvesting woody biomass—e.g., for bioenergy—may open forest canopies and accelerate thermophilization of temperate forest biodiversity. ispartof: Proceedings of the National Academy of Sciences of the United States of America vol:110 issue:46 pages:18561-18565 ispartof: location:United States status: published

Leaf traits of tropical tree species display an important inter-specific diversity, as detected for instance in the large range of values of leaf mass : area ratio (LMA). They also demonstrate a large irradiance-elicited plasticity, but there is still debate whether this plasticity differs among species. To address this question, leaf traits were recorded on saplings from 12 rainforest tree species in French Guiana, grown under approximately 5, 10 and 20% relative irradiance. Fifteen structural and physiological leaf traits related to photosynthesis were measured. The irradiance-elicited plasticity was quantified using a relative distance plasticity index. A large inter-specific diversity was detected for all leaf traits. A principal component analysis opposed species with a large mass-based photosynthesis, respiration, N content and photosynthetic nitrogen use efficiency, to species with a large leaf mass : area ratio, LMA. The two pioneer species used in this study displayed the largest photosynthetic capacity (and lowest LMA) and ranked at one end of the species continuum. Relative irradiance affected almost all traits with the exception of mass-based photosynthesis. A weak interaction was found between species and relative irradiance and the species ranking was maintained among relative irradiance treatments for the majority of the traits. A principal component analysis of the values of relative-distance plasticity index failed to reveal any consistent patterns of traits or species. We concluded that irradiance-elicited plasticity of leaf traits was similar among species irrespective of LMA and successional status, despite the occurrence of a large inter-specific diversity for the investigated traits.