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— Cecropia is a group of fast-growing pioneer trees that are important in forest regeneration and a common ant-plant mutualism in the Neotropics. To investigate the evolution of mutualism between Cecropia and associated ants, a phylogenetic framework is necessary. Cecropia species are difficult to distinguish morphologically and conventional genetic markers are insufficiently variable to resolve the phylogenetic relationships among species. Our study aimed to compare the phylogenetic utility of restriction site associated DNA (RAD) sequencing to prior work based on commonly sequenced gene regions. RAD sequence data resolved and supported species-level relationships better than previous studies. We identified a deeply divergent non-myrmecophytic clade including C. sciadophylla and African Musanga. Results from geographically widespread and morphologically heterogenous C. obtusifolia and C. angustifolia suggest that current synonymy has lumped phylogenetically divergent lineages. Reconstruction of ant associations on the highly supported Cecropia phylogeny inferred equal probability of the ancestor of Cecropia being myrmecophytic or not. More intensive genetic study is needed to refine species concepts in Cecropia.

As currently circumscribed, Acrogenospora (Acrogenosporaceae, Minutisphaerales, Dothideomycetes) is a genus of saprobic hyphomycetes with distinctive conidia. Although considered common and cosmopolitan, the genus is poorly represented by sequence data, and no neotropical representatives are present in public sequence databases. Consequently, Acrogenospora has been largely invisible to ecological studies that rely on sequence-based identification. As part of an effort to identify fungi collected during ecological studies, we identified strains of Acrogenospora isolated in culture from seeds in the soil seed bank of a lowland tropical forest in Panama. Here we describe Acrogenospora terricola sp. nov. based on morphological and phylogenetic analyses. We confirm that the genus has a pantropical distribution. The observation of Acrogenospora infecting seeds in a terrestrial environment contrasts with previously described species in the genus, most of which occur on decaying wood in freshwater environments. This work highlights the often hidden taxonomic value of collections derived from ecological studies of fungal communities and the ways in which rich sequence databases can shed light on the identity, distributions and diversity of cryptic microfungi.

Previous theoretical work has highlighted the potential for natural enemies to mediate the coexistence of species with similar life histories via density‐dependent effects on survivorship. For plant pathogens to play this role, they must differ in their ability to infect or induce disease in different host plant species. In tropical forests characterized by high diversity, these effects must extend to phylogenetically closely related species pairs. Mortality at the seed and seedling stage strongly influences the abundance and distribution of tropical tree species, but the host preferences and spatial distributions of fungi are rarely determined. We examined how host species identity, relatedness and seed viability influence the composition of fungal communities associated with seeds of four co‐occurring pioneer trees (Cecropia insignis, C. longipes, C. peltata and Jacaranda copaia). Seeds were buried in mesh bags in five common gardens in the understorey of a lowland tropical forest in Panama and retrieved at intervals from 1 to 30 months. A subset of the seeds in each bag was used to determine germination success. One half of each remaining seed was tested for viability; and the other half was used to culture and identify seed‐infecting fungi. Seeds were infected by fungi after burial. Although fungal communities differed in viable versus dead seeds, and across burial locations, community composition primarily varied as a function of plant species identity (30.7% of variation in community composition vs. 4.5% for viability and location together), even for congeneric Cecropia species. Phylogenetic reconstruction showed that relatedness of fungi mostly reflected differences between Jacaranda (Bignoniaceae) and Cecropia (Urticaceae). Although the proportion of germinable seeds decreased gradually over time for all species, intraspecific variation in survival was high at the same location (e.g. ranging from 0% to 100% for C. peltata) suggesting variable exposure or susceptibility to seed pathogens. Synthesis. Our study provides evidence under field conditions that congeneric tree species with similar life history traits differ markedly in seed‐associated fungal communities when exposed to the same soil‐borne fungi. This is a critical first step supporting pathogen‐mediated coexistence of closely related tree species.

Plant defense theory explores how plants invest in defenses against natural enemies but has focused primarily on the traits expressed by juvenile and mature plants. Here we describe the diverse ways in which seeds are chemically and physically defended. We suggest that through associations with other traits, seeds are likely to exhibit defense syndromes that reflect constraints or trade-offs imposed by selection to attract dispersers, enable effective dispersal, ensure appropriate timing of seed germination, and enhance seedling performance. We draw attention to seed and reproductive traits that are analogous to defense traits in mature plants and describe how the effectiveness of defenses is likely to differ at pre- and postdispersal stages. We also highlight recent insights into the mutualistic and antagonistic interactions between seeds and microbial communities, including fungi and endohyphal bacteria, that can influence seed survival in the soil and subsequent seedling vigor.

Animals, such as termites, have largely been overlooked as global-scale drivers of biogeochemical cycles1,2, despite site-specific findings3,4. Deadwood turnover, an important component of the carbon cycle, is driven by multiple decay agents. Studies have focused on temperate systems5,6, where microbes dominate decay7. Microbial decay is sensitive to temperature, typically doubling per 10°C increase (decay effective Q10 = ~2)8–10. Termites are important decayers in tropical systems3,11–13 and differ from microbes in their population dynamics, dispersal, and substrate discovery14–16, meaning their climate sensitivities also differ. Using a network of 133 sites spanning 6 continents, we report the first global field-based quantification of temperature and precipitation sensitivities for termites and microbes, providing novel understandings of their response to changing climates. Temperature sensitivity of microbial decay was within previous estimates. Termite discovery and consumption were both much more sensitive to temperature (decay effective Q10 = 6.53), leading to striking differences in deadwood turnover in areas with and without termites. Termite impacts were greatest in tropical seasonal forests and savannas and subtropical deserts. With tropicalization17 (i.e., warming shifts to a tropical climate), the termite contribution to global wood decay will increase as more of the earth’s surface becomes accessible to termites. Acknowledgements. For materials, field, and lab assistance, we thank the Australian Landscape Trust Team, Juan Martínez de Aragón, Eric Roy, Hugh Wilson, Kylie Brice, Bethanie Coleman, Brendan Delroy, Coline Deveautour, Suzanne Donn, Generci Assis Neves, Ricardo Marques Barreiros, Ricardo Marques Barreiros, Generci Assis Neves from Resineves Agroflorestal company, Alfred Lochner, Pousada Vale do Céu, Humberto Robles, María M. Rivera, and Grant Kirker. Steve Allison and Tom Crowther provided comments on the manuscript and Abbey Yatsko helped with figure and manuscript formatting. Funding for this work was provided by US National Science Foundation (DEB-1655759, 2149151, 1713502, 1713435, 1647502, 1546686, 1831952), George Washington University, USDA Forest Service, Centre College Faculty Development Funds, Australia Terrestrial Ecosystem Research Network (TERN) National Collaborative Research Infrastructure Strategy (NCRIS), Royal Society-FCDO Africa Capacity Building Initiative, New Phytologist Foundation, Fondecyt grant:1160329, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES), Department of Ecology and Conservation of the Federal University of Lavras, CNPq, FAPEMIG, Australian Academy of Science 2017 Thomas Davies Research Grant, Australian Research Council (DP160103765), UK National Environment Research Council (NE/L000016/1), Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil (NERC - FAPESP)19/07773-1, Environment Research and Technology Development Fund (ERTDF; JPMEERF15S11420) of the Environmental Restoration and Conservation Agency (ERCA) of Japan, COLCIENCIAS (No. FP44842-046-2017), Spanish Government (grant PID2019-110521GB-I00), Catalan Government (grant SGR 2017-1005), Fundación Ramón Areces (grant ELEMENTAL-CLIMATE), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT) PICT 2019- 2472, National Agency for the Promotion of Research, Technological Development and Innovation, Scientific and Technological Research Project 2018-01561 (PICT 2018- 01561), iDiv German Research Foundation (DFG– FZT 118, 202548816), European Research Council (ERC), European Union's Horizon 2020 research and innovation program (grant agreement no. 677232).

Tropical forest productivity is often thought to be limited by soil phosphorus (P) availability. Phosphorus availability might therefore constrain potential increases in growth as the atmospheric CO₂ concentration increases, yet there is little experimental evidence with which to evaluate this hypothesis. We hypothesized that while all species would respond more strongly to elevated CO₂ when supplied with extra P, the responses of individual species would also depend on their habitat associations with either high‐ or low‐P soils. We further hypothesized that this effect would be exacerbated by a reduction in transpiration rate under elevated CO₂, as transpiration may aid in P acquisition. We used a pot experiment to test the effects of P addition on the physiological and growth response to elevated CO₂ of eight tropical tree species with contrasting distributions across a soil P gradient in Panamanian lowland forests. Seedlings were grown in an ambient (400 ppm) or elevated (800 ppm) CO₂‐controlled glasshouse in either a high‐ or low‐P treatment to quantify the effects of P limitation on relative growth rate (RGR), transpiration, maximum photosynthetic rate and foliar nutrients. We found evidence of limitation by P and CO₂ on growth, photosynthesis, foliar nutrients and transpiration. However, the affinity of a species for P, defined as the species distribution relative to P availability, was not correlated with RGR or transpiration responses to elevated CO₂ in either the low‐P or high‐P treatments. Transpiration rates decreased under elevated CO₂, but foliar P was greater for some species under elevated CO₂, suggesting a greater capacity for upregulation of P acquisition in species associated with low‐P soils. Our results show that tropical forest responses to elevated CO₂ will be species‐specific and not necessarily explained by P affinities based on distribution, which poses challenges for predictions of community‐wide responses. A free Plain Language Summary can be found within the Supporting Information of this article.

Plant-associated fungi often harbor endohyphal bacteria (EHB) that modulate fungal phenotypes. We quantified the effects of EHB on interactions between fungi and seeds of neotropical pioneer trees, which fungi colonize naturally in forest soil. Seeds were exposed to six fungal isolates that harbored EHB, and to clones of those fungi from which EHB were removed by antibiotic treatment. Seed colonization by fungi was evaluated for five tree species, and germination and viability were evaluated for three tree species. EHB influenced seed colonization by fungi in 5 of 30 fungus-tree species combinations, but the magnitude of their effects was small and the direction of effects depended upon fungal isolate-tree species pairs. EHB had rare and context-dependent effects on seed germination and viability, but their effects were strong when observed. Rare but powerful effects of EHB on fungal interactions with seeds highlight important and context-dependent aspects of plant and fungal ecology.

1. Polyphenols are one of the most common groups of secondary metabolites in plants and thought to play a key role in enhancing plant fitness by protecting plants against enemies. Although enemy-inflicted mortality at the seed stage can be an important regulator of plant populations and a key determinant of community structure, few studies have assessed community-level patterns of polyphenol content in seeds. 2. We describe the distribution of the main seed polyphenol groups across 196 tree and liana species on Barro Colorado Island (Panama) and community-level patterns in two aspects of their biological activity (protein precipitation and oxidative capacity). Taking advantage of substantial variation in morphological and ecological traits in the studied plant community, we test for correlations and trade-offs between seed polyphenols and non-chemical plant traits hypothesised to make plant species more or less likely to invest in polyphenol production. 3. The majority of species have polyphenols in their seeds. The incidence and concentrations of polyphenols were related to a set of non-chemical plant traits. Polyphenols were most likely to be present (and where present, to be expressed in high concentrations) in species with large seeds, short seed dormancy times, low investment in mechanical seed defences, high wood density, high leaf mass per area, tough leaves, and slow growth rates. 4. Synthesis: Our study reveals a potential trade-off between chemical and mechanical seed defences and shows that plant species that invest in physical defences at later life stages (high wood density and tough leaves) tend not to invest in physical defences of seeds but instead produce secondary metabolites likely to act as seed defences. Overall, our results conform to predictions from the resource availability hypothesis, which states that species in resource-limited environments (such as slow-growing shade-tolerant tree species) will invest more in defences than fast-growing pioneer species.

The diverse soilborne fungi that recruit to seeds after dispersal include some of the most important agents of seed mortality, as well as strains that enhance germination or inhabit seeds without detriment. Ecological factors that influence seed colonization are not well understood yet are fundamental to the interactions between soilborne fungi and seeds that ultimately influence plant demography and community structure. Here we present current perspectives on seed defense syndromes and related frameworks for predicting colonization success of fungi, with a focus on seeds of tropical pioneer trees. We present a case study that tests whether fungal host range can be predicted by field observations of host use, seed defense syndromes, or phylogenetic relatedness of fungi or hosts. We show that phylogenetic relatedness of hosts, but not fungi, is a strong predictor of fungal colonization of seeds. We posit that the impacts of individual fungi and microbial consortia on seed viability and germination may in turn reflect fungal interactions with the suites of plant defenses codified recently under the broad framework of seed dormancy-defense syndromes. Our findings set the stage for experiments that track colonization, germination, and seedling establishment in the field, important for understanding impacts of fungi on the recruitment of tropical trees.

Seeds of tropical pioneer trees have chemical and physical characteristics that determine their capacity to persist in the soil seed bank. These traits allow seeds to survive in the soil despite diverse predators and pathogens, and to germinate and recruit even decades after dispersal. Defenses in seedlings and adult plants often are described in terms of tradeoffs between chemical and physical defense, but the interplay of defensive strategies has been evaluated only rarely for seeds. Here we evaluated whether classes of seed defenses were negatively correlated across species (consistent with tradeoffs in defense strategies), or whether groups of traits formed associations across species (consistent with seed defense syndromes). Using 16 of the most common pioneer tree species in a neotropical lowland forest in Panama we investigated relationships among four physical traits (seed fracture resistance, seed coat thickness, seed permeability, and seed mass) and two chemical traits (number of phenolic compounds and phenolic peak area), and their association with seed persistence. In addition, seed toxicity was assessed with bioassays in which we evaluated the activity of seed extracts against representative fungal pathogens and a model invertebrate. We did not find univariate tradeoffs between chemical and physical defenses. Instead, we found that seed permeability – a trait that distinguishes physical dormancy from other dormancy types – was positively associated with chemical defense traits and negatively associated with physical defense traits. Using a linear discriminant analysis and a hierarchical cluster analysis we found evidence to distinguish three distinct seed defense syndromes that correspond directly with seed dormancy classes (i.e., quiescent, physical, and physiological). Our data suggest that short and long‐term persistence of seeds can be achieved via two strategies: having permeable seeds that are well defended chemically, corresponding to the physiologically dormant defense syndrome; or having impermeable seeds that are well defended physically, corresponding to the physically dormant defense syndrome. In turn, transient seeds appear to have a lower degree of chemical and physical defenses, corresponding to the quiescent defense syndrome. Overall, we find that seed defense and seed dormancy are linked, suggesting that environmental pressures on seed persistence and for delayed germination can select for trait combinations defining distinct dormancy‐defense syndromes.

The Janzen–Connell (JC) hypothesis provides a conceptual framework for explaining the maintenance of tree diversity in tropical forests. Its central tenet—that recruits experience high mortality near conspecifics and at high densities—assumes a degree of host specialization in interactions between plants and natural enemies. Studies confirming JC effects have focused primarily on spatial distributions of seedlings and saplings, leaving major knowledge gaps regarding the fate of seeds in soil and the specificity of the soilborne fungi that are their most important antagonists. Here we use a common garden experiment in a lowland tropical forest in Panama to show that communities of seed-infecting fungi are structured predominantly by plant species, with only minor influences of factors such as local soil type, forest characteristics, or time in soil (1–12 months). Inoculation experiments confirmed that fungi affected seed viability and germination in a host-specific manner and that effects on seed viability preceded seedling emergence. Seeds are critical components of reproduction for tropical trees, and the factors influencing their persistence, survival, and germination shape the populations of seedlings and saplings on which current perspectives regarding forest dynamics are based. Together these findings bring seed dynamics to light in the context of the JC hypothesis, implicating them directly in the processes that have emerged as critical for diversity maintenance in species-rich tropical forests.

Patterns of leaf production and leaf fall directly influence leaf area index and forest productivity. Here, we focused on Cecropia sciadophylla individuals inhabiting the extremes of the gradient in seasonality in rainfall at which C. sciadophylla occurs. In Colombia and French Guiana we compared the intra-annual variation in leaf production as well as the intra-annual fluctuation in internode length on a total of 69 saplings ranging in size from 1 to 2 m. The mean rate of leaf production was ~2 leaves mo−1 in both populations, and the rate of leaf production was constant throughout the year. Our results showed monthly variation in internode length and the number of live leaves per sapling in the seasonal habitat and variation only in internode length in the everwet habitat. Because the rate of leaf production is constant at both localities, the difference in number of live leaves per sapling at the seasonal site must reflect seasonal variation in leaf life span. We show that in Cecropia, internode length can serve as an indicator of precipitation seasonality. Finally an open question is whether leaf production in other pioneer species is also independent of climatic seasonal cues. This information could allow us to link growth and climate of secondary forest species and better understand how past and future climate can affect plant growth trajectories.

Interactions between fungi and tropical trees help shape some of the most biodiverse communities on earth. These interactions occur in the presence of additional microbes that can modify fungal phenotypes, such as endohyphal bacteria (EHB). Here we examine the occurrence, diversity, and taxonomic composition of EHB in fungi that colonize seeds and leaves of plants in tropical forests. We use PCR and fluorescence microscopy to detect EHB in fungi, and a phylogenetic approach to explore evolutionary relationships among seed- and leaf-inhabiting fungi and their bacterial partners. Analyses focusing on two prevalent orders of fungi (Hypocreales and Xylariales) revealed that seed- and leaf-inhabiting fungi have a shared evolutionary history, yet differ in the prevalence, richness, and composition of their endohyphal symbionts. Phylogenetic analyses detected that the endohyphal habit is widespread, here encompassing members of seven phyla of bacteria (including three classes of Proteobacteria). Occurring in seed- vs. leaf-associated fungi has not resulted in detectable structure in the evolution of EHB, and no congruence was observed in the phylogenetic relationships of these apparently facultative, horizontally transmitted symbionts, and their fungal hosts. Our results are consistent with multiple origins of fungus-bacterium associations and argue for evaluating focal pairs to determine how particular EHB affect the establishment or maintenance of fungal symbioses in seeds and leaves.

Summary It was recently proposed that boron might be the most important nutrient structuring tree species distributions in tropical forests. Here we combine observational and experimental studies to test this hypothesis for lowland tropical forests of Panama. Plant-available boron is uniformly low in tropical forest soils of Panama and is not significantly associated with any of the > 500 species in a regional network of forest dynamics plots. Experimental manipulation of boron supply to seedlings of three tropical tree species revealed no evidence of boron deficiency or toxicity at concentrations likely to occur in tropical forest soils. Foliar boron did not correlate with soil boron along a local scale gradient of boron availability. Fifteen years of boron addition to a tropical forest increased plant-available boron by 70% but did not significantly change tree productivity or boron concentrations in live leaves, wood or leaf litter. The annual input of boron in rainfall accounts for a considerable proportion of the boron in annual litterfall and is similar to the pool of plant-available boron in the soil, and is therefore sufficient to preclude boron deficiency. We conclude that boron does not influence tree species distributions in Panama and presumably elsewhere in the lowland tropics.

Summary Soils influence tropical forest composition at regional scales. In Panama, data on tree communities and underlying soils indicate that species frequently show distributional associations to soil phosphorus. To understand how these associations arise, we combined a pot experiment to measure seedling responses of 15 pioneer species to phosphorus addition with an analysis of the phylogenetic structure of phosphorus associations of the entire tree community. Growth responses of pioneers to phosphorus addition revealed a clear tradeoff: species from high-phosphorus sites grew fastest in the phosphorus-addition treatment, while species from low-phosphorus sites grew fastest in the low-phosphorus treatment. Traits associated with growth performance remain unclear: biomass allocation, phosphatase activity and phosphorus-use efficiency did not correlate with phosphorus associations; however, phosphatase activity was most strongly down-regulated in response to phosphorus addition in species from high-phosphorus sites. Phylogenetic analysis indicated that pioneers occur more frequently in clades where phosphorus associations are overdispersed as compared with the overall tree community, suggesting that selection on phosphorus acquisition and use may be strongest for pioneer species with high phosphorus demand. Our results show that phosphorus-dependent growth rates provide an additional explanation for the regional distribution of tree species in Panama, and possibly elsewhere.

The recent opinion piece by Sheil and Padmanaba (2011) argues that greater attention is required for invasive species management procedures that are relevant to and realistic for developing countries. They use the example of the Neotropical tree Cecropia as an introduction to West Java to illustrate their point. In our invited response we contend that the assumptions and data on the dynamics of Cecropia in Java presented in their paper, as well as their review of global Cecropia introductions, are of reduced scientific value. Even so, we agree with the paper's opinion that the naturalised species of Cecropia in West Java represent a considerable invasion risk and that funding must be improved so that the capacity for invasion ecology research and management of invasive alien species in developing countries is more effective. Unlike Sheil and Padmanaba (2011), however, we conclude that there is already enough evidence to be concerned by the threat of Cecropia to natural ecosystems, but that knowledge of th...

Plant phenology is concerned with the timing of recurring biological events. Though phenology has traditionally been studied using intensive surveys of a local flora, results from such surveys are difficult to generalize to broader spatial scales. In this study, contrastingly, we assembled a continental-scale dataset of herbarium specimens for the emblematic genus of Neotropical pioneer trees, Cecropia , and applied Fourier spectral and cospectral analyses to investigate the reproductive phenology of 35 species. We detected significant annual, sub-annual and continuous patterns, and discuss the variation in patterns within and among climatic regions. Although previous studies have suggested that pioneer species generally produce flowers continually throughout the year, we found that at least one third of Cecropia species are characterized by clear annual flowering behaviour. We further investigated the relationships between phenology and climate seasonality, showing strong associations between phenology and seasonal variations in precipitation and temperature. We also verified our results against field survey data gathered from the literature. Our findings indicate that herbarium material is a reliable resource for use in the investigation of large-scale patterns in plant phenology, offering a promising complement to local intensive field studies.

Germination from the soil seed bank (SSB) is an important determinant of species composition in tropical forest gaps, with seed persistence in the SSB allowing trees to recruit even decades after dispersal. The capacity to form a persistent SSB is often associated with physical dormancy, where seed coats are impermeable at the time of dispersal. Germination literature often speculates, without empirical evidence, that dormancy-break in physically dormant seeds is the result of microbial action and/or abrasion by soil particles. We tested the microbial/soil abrasion hypothesis in four widely distributed neotropical pioneer tree species (Apeiba membranacea, Luehea seemannii, Ochroma pyramidale, and Cochlospermum vitifolium). Seeds were buried in five common gardens in a lowland tropical forest in Panama, and recovered at 1, 3, 6, and 12 months after burial. Seed permeability, microbial infection, seed coat thickness, and germination were measured. Parallel experiments compared the germination fraction of fresh and aged seeds without soil contact, and in seeds as a function of seed permeability. Contrary to the microbial/soil abrasion hypothesis the proportion of permeable seeds, and of seeds infected by cultivable microbes, decreased as a function of burial duration. Furthermore, seeds stored in dark and dry conditions for 2 years showed a higher proportion of seed germination than fresh seeds in identical germination conditions. We determined that permeable seeds of A. membranacea and O. pyramidale had cracks in the chalazal area or lacked the chalazal plug, whereas all surfaces of impermeable seeds were intact. Our results are inconsistent with the microbial/soil abrasion hypothesis of dormancy loss and instead suggest the existence of multiple dormancy phenotypes, where a fraction of each seed cohort is dispersed in a permeable state and germinates immediately, while the impermeable seed fraction accounts for the persistent SSB. Thus, we conclude that fluctuations in the soil temperature in the absence of soil abrasion and microbial infection are sufficient to break physical dormancy on seeds of tropical pioneer trees.

The seed stage is often critical in determining the regeneration success of plants. Seeds must survive an array of seed predators and pathogens and germinate under conditions favourable for seedling establishment. To maximise recruitment success plants protect seeds using a diverse set of chemical and physical defences. However, the relationship between these defence classes, and their association with other life history traits, is not well understood. Data on seed coat thickness and fracture resistance, and the abundance and diversity of potential defensive compounds were collected for 10 tree species of Macaranga from Borneo. The data were used to test whether there is a trade-off in physical versus chemical defence investment, and to determine how investment varies with seed mass, and light requirement for regeneration. Across species there was no correlation between seed coat thickness and abundance of potential defensive compounds, indicating the absence of a direct trade-off between defence classes. While chemical defences were not correlated to other traits, physical defences were positively correlated with light requirement for regeneration. For a subset of five Macaranga species we evaluated the relative investment in chemical and physical defence to seed persistence in the soil, measured as the time to half initial seed viability (seed half-life). Half-life was negatively related to the ratio of potential defensive compound abundance to seed coat thickness, suggesting that species with long persistence invested in physical defence more than stored chemical defences. These results indicate that investment in seed defences are associated with species' light requirements for regeneration, rather than scaling positively with seed mass. Furthermore, chemical defences, although highly variable among species, do not appear to be critical to long term persistence of Macaranga seeds, and may be important in defending seeds from natural enemies distinct from those found in the soil.

International audience; Forest successional processes following disturbance take decades to play out, even in tropical forests. Nonetheless, records of vegetation change in this ecosystem are scarce, increasing the importance of the chronosequence approach to study forest recovery. However, this approach requires accurate dating of secondary forests, which until now was a difficult and/or expensive task. Cecropia is a widespread and abundant pioneer tree genus of the Neotropics. Here we propose and validate a rapid and straightforward method to estimate the age of secondary forest patches based on morphological observations of Cecropia trees. We found that Cecropia-inferred ages were highly correlated with known ages of the forest. We also demonstrate that Cecropia can be used to accurately date disturbances and propose twenty-one species distributed all over the geographical range of the genus as potential secondary forest chronometer species. Our method is limited in applicability by the maximal longevity of Cecropia individuals. Although the oldest chronosequence used in this study was 20 years old, we argue that at least for the first four decades after disturbance, the method described in this study provides very accurate estimations of secondary forest ages. The age of pioneer trees provides not only information needed to calculate the recovery of carbon stocks that would help to improve forest management, but also provides information needed to characterize the initial floristic composition and the rates of species remigration into secondary forest. Our contribution shows how successional studies can be reliably and inexpensively extended without the need to obtain forest ages based on expensive or potentially inaccurate data across the Neotropics.

International audience; Context : Functional - structural models (FSM) of tree growth have great potential in forestry, but their development, calibration and validation are hampered by the difficulty of collecting experimental data at organ scale for adult trees. Due to their simple architecture and morphological properties, " model plants " such as Cecropia sciadophylla are of great interest to validate new models and methodologies, since exhaustive descriptions of their plant structure and mass partitioning can be gathered. * Aims : Our objective was to develop a model-based approach to analysing the influence of environmental conditions on the dynamics of trophic competition within C. sciadophylla trees. * Methods : We defined an integrated environmental factor that includes meteorological medium-frequency variations and a relative index representing the local site conditions for each plant. This index is estimated based on model inversion of the GreenLab FSM using data from 11 trees for model calibration and 7 trees for model evaluation. * Results : The resulting model explained the dynamics of biomass allocation to different organs during the plant growth, according to the environmental pressure they experienced. * Perspectives : By linking the integrated environmental factor to a competition index, an extension of the model to the population level could be considered.

International audience; Although there is an increasing number of models simulating the functional and structural development of trees at organ scale, few of them can be fully calibrated, evaluated and validated. A major obstacle resides in the intrinsic complexity of trees due to their high stature, large number of organs and long life span that limits the possibilities of experimental work and the access to measurement data. This is why 'model plants' such as the neotropical genus Cecropia are of great interest. This genus has a simple architecture and some qualities that allow collecting exhaustive datasets at the organ scale. In this paper, we evaluate the GreenLab model on data recorded on 11 individuals measured in 2007 in French Guiana. The branching and flowering patterns are analyzed using an index of trophic competition.

A-08-06; International audience; Cecropia species, ranging from Mexico to northern Argentina and the West Indies, are pioneer trees that colonize cleared areas with high light. To determine their ages to help pinpoint the date of the area's disturbance, we need to understand their developmental and architectural changes over time. The simple architecture of Cecropia conforms to the model of Rauh; that is, it has orthotropic axes with lateral flowering and rhythmic branching. The axes are made of a succession of nodes and internodes whose length and associated lateral productions remain measurable for years. Thus, by describing the tree trunk node by node, we can depict the sequence of events involved in tree development. For 25 trees of C. sciadophylla, from two stations in French Guiana and Colombia, we recorded internode length and any presence of branches, and flowers for each node. Using autocorrelation coefficients, we found a high periodicity in flowering and branching, with inflorescences at every 25 nodes, stages of branches spaced by a multiple of 25 nodes, and alternation of long and short nodes every 25 nodes. Considering that flowering is annual for many Cecropia species, the main conclusion of this work is that C. sciadophylla has strong annual growth, branching, and flowering rhythms. In addition, the age of the tree can be estimated retrospectively by observing its adult morphology.

Le genre Néotropical Cecropia Loefl. regroupe des arbres pionniers qui colonisent les milieux ouverts et perturbés. Ils constituent un modèle d'étude dans des champs disciplinaires très variés. Malgré le volume et la diversité des recherches menées sur ce genre, il est paradoxal de constater que l'identification des espèces reste extrêmement difficile et constitue un frein à l'ensemble de ces études. La monographie de Berg & Franco-Rosselli (2005) retient 61 espèces et 2 sous-espèces. La circonscription proposée repose essentiellement sur des caractères morphologiques. L'objectif de thèse est d'organiser un cadre de travail par une série d'outils logiciels et analytiques pour i) extraire la substantifique moelle de la monographie par une approche numérique et ii) revoir la circonscription des espèces par une approche en taxonomie intégrative couplant taxonomie numérique et modèle de niches à une échelle continentale. Nos résultats montrent que la monographie est cohérente, avec des taxons bien séparés d'un point de vue morphologique, mais avec une mise en synonymie massive qui n'est pas argumentée. Notre analyse permet d'identifier les caractères les plus discriminants à utiliser en taxonomie numérique et permis de construire une clef d'identification multientrées pour le genre. La modélisation de la niche climatique montre un fort recouvrement entre les espèces et pas d'identité climatique réellement propre à l'une d'entre elles. Nous identifions également plusieurs espèces à haut potentiel invasif. Ce travail appelle à intégrer des approches en biologie moléculaire pour mieux comprendre la dynamique évolutive où l'hybridation fréquente génère un continuum morphologique.