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Background and Aims Bark allows species to survive fire, protecting their inner tissues and allowing new branches to resprout from aerial buds. Thus, bark production is likely to be selected with aerial bud protection in fire-prone ecosystems. By considering the coexistence of fire-prone and fire-free ecosystems, in addition to the different impacts of flames on different growth forms, in this study we tested whether: (1) species from areas with higher fire frequencies have a faster bark production; (2) bark growth rate differs between trees and shrubs; (3) generalists adjust their bark production according to their environment (fire-prone or fire-free ecosystems); and (4) fast bark production results in better aerial bud protection. Methods We sampled two different types of forests and savannas in the Cerrado and registered every woody individual with height between 1.5 and 3 m tall (directly exposed to the flames). For the 123 species registered, we sampled three different individuals in each vegetation type where the species occurred to assess their bark production and aerial bud protection. We then checked, for each species, their preferred habitat (savanna and forest specialists or generalists) and their predominant growth form. Key Results A minimal threshold of 0.13 mm per growth unit of bark production differentiated woody communities from savannas and forests. Shrubs and trees did not differ in terms of bark growth rate, despite being exposed to the flames in a different manner. Generalist species in savannas were able to produce bark above the threshold. However, when these species were in forests they produced bark below the threshold. Finally, a higher bark growth rate accounted for a better aerial bud protection. Conclusions Generalist species are likely to be capable of displaying plasticity in their bark production, which could be important for their success in contrasting ecosystems. The relationship between aerial bud protection and bark growth rate suggests that bark production plays an important role in protecting the dormant buds, in addition to being selected in fire-prone ecosystems.

If trees minimize self-shading, new foliage in shaded parts of the crown should remain minimal. However, many species have abundant foliage on short shoots inside their crown. In this paper, we test the hypothesis that short shoots allow trees to densify their foliage in self-shaded parts of the crown thanks to reduced costs. Using 30 woody species in Mediterranean and tropical biomes, we estimated the contribution of short shoots to total plant foliage, calculated their costs relative to long shoots including wood cost, and used 3D plant simulations calibrated with field measurements to quantify their light interception, self-shading and yield. In species with short shoots, leaves on short shoots account for the majority of leaf area. The reduced cost of short stems enables the production of leaf area with 36% less biomass. Simulations show that although short shoots are more self-shaded, they benefit the plant because they cost less. Lastly, the morphological properties of short shoots have major implications for whole plant architecture. Taken together, our results question the validity of only assessing leaf costs to understand leaf economics and call for more integrated observations at the crown scale to understand light capture strategies in woody plants.

Different ecosystems evolved and are maintained by fire, with their vegetation hosting species with a wide diversity of persistence strategies allowing them to insulate their body and resprout new branches after fire disturbance. Changes in fire regime are predicted due to climate change, either by promoting more frequent and/or severe fires or by reducing the number fire events due to the limitation of fuel load. Predicting the future of fire-driven ecosystems is a complex task as species’ survival depends on many factors that vary in space and time. Since plants are constantly experiencing new environments as they grow through meristem development, woody plant modularity, modules morpho-physiological aspects and their integration should be considered when investigating species strategies in fire-prone ecosystems: according to their position and their tissue composition, plants’ modules experience fire differently and will contribute differently to other modules and the whole plant survival, with consequences cascading over the overall vegetation structure. Growth modules may hold the key to understanding how fast plants can get protected from fire, ultimately helping us to predict which species will persist across changing fire regimes. We present an empirical example showing how different fire-return intervals translate into distinct pressures on the timing, protection, and location of modules and discuss how these can translate into modifications in the vegetation structure due to climate change.

International audience; A longstanding research divide exists in plant ecology: either focusing on plant clonality, with no ambition to address nonclonal plants, or focusing on all plants, ignoring that many ecological processes can be affected by the fact that some plants are clonal while others are not. This gap cascades into a lack of distinction and knowledge about the similarities and differences between clonal and nonclonal plants. Here we aim to bridge this gap by identifying areas that would benefit from the incorporation of clonal growth into one integrated research platform: namely, response to productivity and disturbance, biotic interactions, and population dynamics. We are convinced that this will provide a roadmap to gain valuable insights into the ecoevolutionary dynamics relevant to all plants.

The role of mammal herbivory in plant evolution is largely unrecognised. Spines on stems are a common and important feature found in ∼9% of eudicot woody plant species worldwide. Spines evolved independently multiple times during the Cenozoic. The timing and extent of spiny plant diversification varied among continents, pointing towards continental rather than global drivers. Spine evolution is closely related to radiation of extant ungulates and extinct ground sloths, rather than climate variation. Diversification began in the Paleogene in herbivore species-rich Eurasia and North America, emerging later in the Neogene in species-poorer South America, Africa and Australia. Spiny lineages expanded their ecological footprint over non-spiny plants, mainly through intercontinental migrations, indicating that spines likely provided a competitive advantage with increasing, and novel, mammal herbivory pressure.

Aim The aim of this study was to further advance our understanding of the species‐rich, and ecologically important angiosperm family Combretaceae to provide new insights into their evolutionary history. We assessed phylogenetic relationships in the family using target capture data and produced a dated phylogenetic tree to assess fruit dispersal modes and patterns of distribution. Location Tropical and subtropical regions. Time Period Cretaceous to present. Major Taxa Studied Family Combretaceae is a member of the rosid clade and comprises 10 genera and more than 500 species, predominantly assigned to generaCombretumandTerminalia, and occurring on all continents and in a wide range of ecosystems. Methods We use a target capture approach and the Angiosperms353 universal probes to reconstruct a robust dated phylogenetic tree for the family. This phylogenetic framework, combined with seed dispersal traits, biome data and biogeographic ranges, allows the reconstruction of the biogeographical history of the group. Results Ancestral range reconstructions suggest a Gondwanan origin (Africa/South America), with several intercontinental dispersals within the family and few transitions between biomes. Relative abundance of fruit dispersal types differed by both continent and biome. However, intercontinental colonizations were only significantly enhanced by water dispersal (drift fruit), and there was no evidence that seed dispersal modes influenced biome shifts. Main Conclusions Our analysis reveals a paradox as drift fruit greatly enhanced dispersal distances at intercontinental scale but did not affect the strong biome conservatism observed.

Made available in DSpace on 2022-04-28T19:45:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Species growing in fire-prone savannas usually persist by resprouting from their buds. In this study, we evaluated how various persistence traits allow bud protection for improved survival in fire-prone ecosystems. Using an integrative morphological and macroanatomical approach, we analysed how woody plants protect their buds. We tested bud protection at the community level and evaluated: (a) how bud protection changes along a fire frequency gradient, (b) if it differs between shrubs and trees and (c) whether the level of bud protection is related to post-fire responses of 28 woody savanna species. A mix of traits involving bud protection may enable woody species persistence in fire-prone ecosystems. Savanna species better protected their buds than forest species by developing bark and trichomes that allowed resprouting after fire. Regarding growth forms, shrub species capable of resprouting above-ground had their buds better protected than trees. Bud protection is not only linked with their position to the bark, but also with the presence of trichomes. Profuse trichomes covering buds were related to savanna species. Some species with no bud protection by bark but with trichomes covering their buds were able to resprout after fire. The presence of accessory buds is also a trait more related to savannas, possibly influencing the resprouting after fire as they are better protected and increase the bud bank. Finally, different persistence traits interact with one another to better protect the buds, requiring a detailed screening of the traits to assess species responses to fire. Synthesis. During fire, species have their aerial biomass consumed by the flames. To be able to resprout new branches and persist in the environment, they must have well-protected buds. In this study, we evaluated different ways that woody species protect their buds and related them with their resprouting strategy after fire. We investigated the protection by the bark, the presence of trichomes and accessory buds. By studying the woody community in a gradient of savannas and forests we found that buds can be protected by bark, trichomes or soil. Species can present a mix of these traits and strategies, which enhances their resprouting after fire. A free Plain Language Summary can be found within the Supporting Information of this article. Lab of Vegetation Ecology Instituto de Biociências Universidade Estadual Paulista (UNESP) CNRS UMR7618 Institute of Ecology and Environmental Sciences Paris Sorbonne University Lab of Vegetation Ecology Instituto de Biociências Universidade Estadual Paulista (UNESP)

International audience; Tree architectures reflect the main abiotic and biotic selection pressures determining tree growth and survival. Studies have shown that trees growing in herbivore-dominated ecosystems, such as savannas, develop denser, more divaricate ‘cage’-like architectures in response to chronic browsing pressure (also known as ‘brown world’ architectures). In contrast, trees growing under resource-limited conditions develop traits that allow them to better compete for abiotic resources (referred to as ‘green world’ architectures); for example, light limitation can induce trees to form more pole-like structures that allow them to grow faster in height. In temperate forests, abiotic drivers have traditionally been assumed to be the main factors affecting plant architecture. However, gap dynamics typically characterize old-growth temperate forests, where disturbances such as storms create gaps with temporary high-light availability, but also attracting intense mammalian browsing. Under such conditions, one would expect tree saplings to exhibit high architectural plasticity enabling them to develop a ‘cage’ in response to high herbivore pressure, but when herbivore pressure declines switch to a more pole-like structure that allows them to grow quickly in height and compete for light.We tested the ability of five dominant European tree species to induce a ‘cage’ architecture (hereafter referred to as ‘cage plasticity’) under contrasting light and herbivory regimes in a full-factorial experiment in Białowieża Forest. We planted 720 young tree saplings in six replicated blocks in which we manipulated ungulate browsing (exclosure vs. control) and light levels (gap vs. closed forest).Two out of the five species (hornbeam Carpinus betulus and lime Tilia cordata) were able to develop a cage when exposed to ungulate herbivores but only under high-light conditions. These two species had the highest survival rates in the herbivory treatment over a 10-year period.Synthesis. Cage plasticity in temperate forest tree species may reflect an overlooked adaptation to mammal herbivory originating in a past when large mammals exerted strong selection pressures in European ecosystems. Our findings challenge the view of closed-canopy forest communities being solely driven by abiotic drivers and call for a re-evaluation of the importance of large herbivores in shaping the functional traits of temperate tree species.

Given that the rate of resource capture constrains plant growth and defence, understanding the linkage between the leaf economic spectrum (LES) and defence and how it contributes to growth is central to predicting species performance. In spite of the prevalence of spiny plants in many plant communities, little is known about how the LES relates to defence and growth rate across these species. We grew 42 spiny species, from diverse environments, under common garden conditions for 15 weeks and measured LES (leaf N, SLA and assimilation rate), defence and growth traits. We assessed general relationships between LES and growth rate and tested whether structural defences (spines, leaf fibre and lignin content) and quantitative chemical defences (condensed tannins) are linked to the LES and growth and if different spine types (i.e. leaf spines, stipular spines, prickles and thorns), with distinct anatomical origins, partition out across the LES. We observed two independent trait axes that together explained ~68% of trait variation across species. The first axis showed that structural defences (spines, leaf fibre and lignin content) trade off with leaf productivity along the LES. Axis 2 revealed that condensed tannins is orthogonal and less integrated with the LES‐structural defence axis. Bivariate trait analyses disclosed positive covariations between LES traits and sapling growth rate. All structural defence traits were negatively related to sapling growth. Across spine types, species with leaf spines were associated with the conservative end of the LES, characterized by high structural defences and lower leaf productivity relative to other spine types. Synthesis: Our study shows that the LES and structural defences are coupled in spiny species such that constitutive growth – defence strategies range from fast‐growing species with low allocation to defences to slow‐growing species that invest heavily in structural defences (dominated by leaf spiny species).

Background and Aims The defensive role of spines has previously been related to leaves, young shoots and reproductive organs. However, some woody species harbour spines on their trunks where none of those organs are present. Several explanations are plausible: they could be (1) climbing aids, (2) remnants from defence of leaves or reproductive organs during an earlier development phase, or (3) an as-yet undescribed defence. Here we investigate whether they could play a role against either bark feeding or preventing climbing animals accessing food resources in the tree canopy. Methods We described 31 woody species with spines on their trunk, growing in a botanical garden, to test whether morphological strategies could be identified and suggest what could be their most likely function. As testing their function is difficult experimentally for large pools of species, we performed virtual experiments to evaluate the potential roles of trunk spines against bark removal and climbing animals of different sizes. We then compared for each species and their confamilial non-spiny species the nutritional profiles of leaf, bark and reproductive organs to test whether trunk spines were associated with a nutritious organ (more likely targeted by herbivores). Key Results We identified four morphological syndromes of trunk spines. Two corresponded to already known functions (anchorage for lianas and crown defence against large ground mammals), and two strategies are newly described trait syndromes with traits suggesting a defence against bark feeding and climbing mammals. By simulation, we show how each strategy could translate into defence against debarking and prevent herbivores from climbing. Conclusions We identified trunk spine strategies and the criteria to classify them, their most likely function and the likely feeding mode and size of animal against which different trunk spine strategies may be effective. We discuss further perspectives for testing their function and their ecological significance.

Background: Biotic and abiotic disturbances such as frequent wildfires and herbivory contribute to maintain trees and grasses coexistence in savanna ecosystems. In comparison to stems and leaves, exposed to fire and herbivory, the roots, protected by being belowground, are less affected by these disturbances. Therefore, indirect estimation of belowground biomass (BGB) of savanna trees from simple allometric relations based on stem measurements can lead to major biases. Aims: In this study we explored how the Leaf ontogenetic change index (LOCI), a quantitative index based on leaf heteroblastic development, can provide an accurate estimate of BGB in Cussonia arborea, a widespread species in West African humid savannas. Methodology: We examined leaf morphometrics on post-fire resprouts of 40 individuals to assess whether LOCI can inform on plant age. We then analyzed by log-level regressions the variation of LOCI in relation to plant stem volume. Subsequently, we studied the variation of BGB according to stem volume, and as a function of both stem volume and LOCI, which allowed us to evaluate the contribution of LOCI to BGB estimation. BGB was obtained destructively by digging up roots and weighing total dry mass of 25 individuals including small and large trees. Statistical analyses were done with the R software. Place and Duration of Study: Study was performed in the Lamto Scientific Reserve, Côte d’Ivoire, between May 2020 and June 2021. Results: Using the stem volume as single explanatory variable of BGB, the regression model provided an adjusted R2 of 0.71. Association of the stem volume with LOCI increased the adjusted R2 from 0.71 to 0.90. Conclusion: Combining LOCI with a measure of stem size provides better estimate of BGB in C. arborea compared to estimate based on stem size only. Since a large proportion of woody species in frequently disturbed environments exhibit an overall strategies promoting persistence, future works should evaluate how these strategies are modulated during ontogeny and can explain biomass variation over time.

International audience; Premise To further advance the understanding of the species-rich, economically and ecologically important angiosperm order Myrtales in the rosid clade, comprising nine families, approximately 400 genera and almost 14,000 species occurring on all continents (except Antarctica), we tested the Angiosperms353 probe kit. Methods We combined high-throughput sequencing and target enrichment with the Angiosperms353 probe kit to evaluate a sample of 485 species across 305 genera (76% of all genera in the order). Results Results provide the most comprehensive phylogenetic hypothesis for the order to date. Relationships at all ranks, such as the relationship of the early-diverging families, often reflect previous studies, but gene conflict is evident, and relationships previously found to be uncertain often remain so. Technical considerations for processing HTS data are also discussed. Conclusions High-throughput sequencing and the Angiosperms353 probe kit are powerful tools for phylogenomic analysis, but better understanding of the genetic data available is required to identify genes and gene trees that account for likely incomplete lineage sorting and/or hybridization events.

Fires in savannas limit tree cover, thereby promoting flammable grass accumulation and fuelling further frequent fires. Meanwhile, forests and thickets form dense canopies that reduce C4-grass fuel loads and creating a humid microclimate, thereby excluding fires under typical climatic conditions.However, extreme fires occasionally burn into these closed-canopy systems. Although these rare fires cause substantial tree mortality and can make repeat fires more likely, the long-term consequences of an extreme fire for closed canopy vegetation structure and potential to convert to savanna (hereafter “savannization”) remain largely unknown.Here, we analysed whether an extreme fire could, alone, alter species composition, vegetation structure, and fire regimes of closed-canopy ecosystems in an intact savanna-forest-thicket mosaic, or whether successive fires after an initial extreme fire were necessary to trigger a biome transition between from forest to savanna.We found that forests that only burned once recovered, whereas those that burned again following an initial extreme fire transitioned from closed-canopy forests towards open, grassy savannas.While thickets had less tree mortality in fires than forests, repeat fires nonetheless precipitated a transition towards savannas.Colonization of the savanna tree community lagged behind the grass community, but also began to transition.SynthesisOur results suggest that rare extreme fires, followed by repeated burning can indeed result in savannization in places where savanna and forest represent alternative stable states.

International audience; Plant architecture strongly influences ecological performance, yet its role in plant evolution has been weakly explored. By testing both phylogenetic and environmental signals, it is possible to separate architectural traits into four categories: development constraints (phylogenetic signal only); convergences (environmental dependency only); key confluences to the environmental driver (both); unknown (neither).We analysed the evolutionary history of the genus Euphorbia, a model clade with both high architectural diversity and a wide environmental range. We conducted comparative analyses of 193 Euphorbia species worldwide using 73 architectural traits, a dated phylogeny, and climate data.We identified 14 architectural types in Euphorbia based on trait combinations. We found 22 traits and three types representing convergences under climate groups; 21 traits and four types showing phylogenetic signal but no relation to climate; and 16 traits and five types with both climate and phylogenetic signals. Major drivers of architectural trait evolution likely include water stress in deserts (selected for succulence, continuous branching), frost disturbance in temperate systems (selected for simple, prostrate, short‐lived shoots) and light competition (selected for arborescence). Simple architectures allowed resilience to disturbance, and frequent transitions into new forms. Complex architectures with functional specialisation developed under stable climates but have low evolvability.

International audience; Ideas on hominin evolution have long invoked the emergence from forests into open habitats as generating selection for traits such as bipedalism and dietary shifts. Though controversial, the savanna hypothesis continues to motivate research into the palaeo-environments of Africa. Reconstruction of these ancient environments has depended heavily on carbon isotopic analysis of fossil bones and palaeosols. The sparsity of the fossil record, however, imposes a limit to the strength of inference that can be drawn from such data. Time-calibrated phylogenies offer an additional tool for dating the spread of savanna habitat. Here, using the evolutionary ages of African savanna trees, we suggest an initial tropical or subtropical expansion of savanna between 10 and 15 Ma, which then extended to higher latitudes, reaching southern Africa ca. 3 Ma. Our phylogenetic estimates of the origin and latitudinal spread of savannas broadly correspond with isotopic age estimates and encompass the entire hominin fossil record. Our results are consistent with the savanna hypothesis of early hominin evolution and reignite the debate on the drivers of savanna expansion. Our analysis demonstrates the utility of phylogenetic proxies for dating major ecological transitions in geological time, especially in regions where fossils are rare or absent or occur in discontinuous sediments. The emergence of savannas and other tropical grassy biomes has been a topic of intense research interest, not least because it coincides with early hominin evolution. The savanna hypothesis of human evolution suggests that the transition from a predominately arboreal lifestyle in forest to one in open habitats favoured an upright posture and selected for bipedalism along with a shift in diet that necessitated travel over greater distances across the landscape 1. The early support for the savanna hypothesis waned, in part, due to confusion as to the definition of prehistoric savannas-as open grassland or as a grassland-tree mosaic-nonetheless, it continues to influence thinking about the selective landscape that shaped human evolution, and generate large interest in the palaeo-environments of Africa where our ancestors emerged 2-6. However, while our understanding of hominin evolution is continually updated by new fossil finds, the palaeontological reconstruction of the ancient African environment has been greatly limited by the sparse record of fossil bones and palaeosols that capture the signature of these past ecosystems 7. open 1

Dominants are key species that shape ecosystem functioning. Plant dominance is typically assessed on aboveground features. However, belowground, individual species may not scale proportionally in relation to their aboveground dimension. This is especially important in ecosystems where most biomass is allocated belowground, including grassy and shrubby biomes.

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In this study we explore species richness and traits across two urban gradients in the City of Cape Town. The first is the natural-urban boundary and the second is a socio-economic gradient informed by historical race-based apartheid planning. Plant species and cover were recorded in 156 plots sampled from conservation areas, private gardens, and public open green space. The socio-economic gradient transitioned from wealthier, predominantly white neighbourhoods to poorer, predominantly black neighbourhoods. The socio-economic gradient was selected to fall within one original vegetation type to ensure a consistent biophysical template. There is a marked shift between the natural and urban plant communities in the City of Cape Town, with little structural affinity. Urban landscapes are dominated by grass, with low diversity compared to natural counterparts. A significant ecological gradient of reduced biodiversity, traits, and in turn functionality, was found across the socio-economic gradient. Wealthier communities benefit from more private green space, more public green space, and a greater plant diversity. Poorer communities have limited green space on all fronts, and lower plant and trait diversity. Plant communities with limited diversity are less resilient and if exposed to environmental perturbation would lose species, and associated ecosystem services faster than a species rich community. These species-poor plant communities mirror historical apartheid planning that is resistant to change. Based on how biodiversity, functionality, and associated ecosystem services and ecosystem stability are linked, the results of this study suggests how significant environmental injustice persists in the City of Cape Town.

Background and Aims Herbivory by large mammals imposes a critical recruitment bottleneck on plants in many systems. Spines defend plants against large herbivores, and how early they emerge in saplings may be one of the strongest predictors of sapling survival in herbivore-rich environments. Yet little effort has been directed at understanding the variability in spine emergence across saplings. Methods We present a multispecies study examining whether and how sapling size, spine type and species' environmental niche (light and precipitation environment) influence early emergence and biomass investment in spines. A phylogenetically diverse pool of 45 species possessing different spine types (spines, prickles and thorns; that are derived from distinct plant organs: leaf, epidermis or cortex, and branch, respectively), were grown under common-garden conditions, and patterns of spine emergence and biomass allocation to spines at 5 and 15 weeks after transplanting were characterized. Key Results Spine type and species' resource niche were the main factors driving early emergence and investment patterns. Spines emerged earliest in leaf spine-bearing species, and latest in thorn-bearing species. The probability of early spine emergence increased with decreasing precipitation, and was greater in species from open than from closed habitats. Sapling investment in spines changed with plant mass but was contingent on spine type and habitat type. Conclusions Different spine types have strikingly different timing of expression, suggesting that developmental origins of spines play a critical role in sapling defences. Furthermore, species from different precipitation and light environments (open vs. closed habitats) showed contrasting patterns of early spine expression, suggesting that resource limitation in their native range may have driven divergent evolution of early defence expression.

Globally, as trends of urbanisation continue to intensify, there has been increasing concern over the impacts of urban expansion on biodiversity and greater attention towards addressing these impacts. Ecological infrastructure such as urban rivers and their catchments may enhance biodiversity, ecological functioning and ecosystem service delivery within cities. Birds are good indicators of urban habitat quality because their ecology is well-studied and they are habitat selective. This study assesses the ecological value of a small urban river catchment in Cape Town, South Africa, in terms of its effect on the taxonomic and functional diversity of birds. 178 bird counts were carried out at 89 sites and 95 species were recorded. The nine functional groups considered were present in equal proportions in the catchment and in the whole of southern Africa, making the catchment a microcosm of the region’s avifauna in terms of functional composition. Using RLQ and fourth-corner analyses, we showed that the river was responsible for the occurrence of certain species and functional groups that would not otherwise occur in the suburbs. Nutrient movers, insectivores, scavengers and seed dispersers responded strongly to a gradient of distance from the river and the position on the river. Contrary to the homogenised assemblage that might be expected of an urban area, the catchment contains a taxonomically and functionally diverse bird assemblage. The combination of a river, a heterogeneous urban matrix and an adjacent national park makes this catchment an exemplar of the value of ecological infrastructure for urban biodiversity.

Shade cast by trees, which suppresses grass growth, and fire fuelled by grass biomass, which prevents tree sapling establishment, are mutually exclusive and self-reinforcing drivers of biome distribution in savanna-forest mosaics. We investigated how shade depth, represented by canopy leaf area index (LAI), is generated by adult trees across savanna-forest boundaries and how a shade gradient filters tree functioning, and grass composition and biomass. Forest trees exerted greater shading through increased stem density and greater light interception per unit biomass. A critical transition at LAI c. 1.5 was linked to tree shifts from savanna to forest species, functional shifts from fire-tolerant to light-competitive species, and grass composition shifts from C4 to C3 pathways. A second transition to grass fuel loads too low to support fires, occurred at a lower canopy density (LAI > 0.5), accompanied by shifts in C4 subtype dominance. This pattern suggests that shade suppression of grass biomass is an essential first step for the maintenance of alternative stable states.

Lactation is a mammalian attribute, and the few known nonmammal examples have distinctly different modalities. We document here milk provisioning in a jumping spider, which compares functionally and behaviorally to lactation in mammals. The spiderlings ingest nutritious milk droplets secreted from the mother’s epigastric furrow until the subadult stage. Milk is indispensable for offspring survival in the early stages and complements their foraging in later stages. Maternal care, as for some long-lived vertebrates, continues after the offspring reach maturity. Furthermore, a female-biased adult sex ratio is acquired only when the mother is present. These findings demonstrate that mammal-like milk provisioning and parental care for sexually mature offspring have also evolved in invertebrates, encouraging a reevaluation of their occurrence across the animal kingdom, especially in invertebrates.

Summary Where large browsers are abundant, the survival of trees depends on their ability to deploy defences, either chemical or structural. Structural defences include the arrangement of dense and intricate architecture, termed ‘cage’ architecture. Previous studies showed that trees developing in herbivore-rich environments tend to have more cage architecture but its precise effect on mammalian herbivores remains unknown. In this paper, we experimentally test how cage architecture affects the bite rate of goats, a generalist mammalian herbivore. We selected 11 palatable tree species with contrasting architectures. We described their caginess using an index combining spinescence and woodiness of their stems. Finally, we evaluated how the caginess of trees slows down herbivores when feeding on the inner leaves in tree crowns. We observed that the bite rate of goats on inner leaves of the cagiest trees was so severely reduced that they could not satisfy their daily nutritional requirements. We discuss how this could affect the preference of wild herbivores for less cagy trees, especially at the end of the dry season. A lay summary is available for this article.

Aims Savanna and forest biomes co-occur across many subtropical landscapes in Africa, and can be differentiated by their fire regime: fires are more frequent in savannas compared to forests. Bark thickness is a key trait of savanna trees, promoting their survival in this context. The rate of bark production (increment·yr−1) should therefore be critical for determining how quickly a developing sapling would be protected or bark could regenerate between two fires. Despite this, the rate of bark production has seldom been measured in studies of fire-tolerant vs fire-intolerant species. Location Hluhluwe-iMfolozi Game reserve, South Africa. Methods We examined the distribution of woody species in a South African park over 253 sites, stratified by biome. We described the bark traits of the 63 most abundant species and related them to the fire frequencies of the sites where they occur. Results Bark growth rate was a good predictor of woody plant persistence in fire-prone savanna ecosystems. A key exception was root-suckering species, which have their structure physically protected underground and can thus survive frequent fires while producing little bark. Conclusion Species of different forest types and savanna have different bark characteristics, highlighting the important role played by fire in shaping biome distribution.

Plant functional traits provide a valuable tool to improve our understanding of ecological processes at a range of scales. Previous handbooks on plant functional traits have highlighted the importance of standardising measurements of traits to improve our understanding of ecological and evolutionary processes. In open ecosystems (i.e. grasslands, savannas, open woodlands and shrublands), traits related to disturbance (e.g. herbivory, drought, and fire) play a central role in explaining species performance and distributions and are the focus of this handbook. We provide brief descriptions of 34 traits and list important environmental filters and their relevance, provide detailed sampling methodologies and outline potential pitfalls for each trait. We have grouped traits according to plant functional type (grasses, forbs and woody plants) and, because demographic stages may experience different selective pressures, we have separated traits according to the different plant life stages (seedlings saplings and adults). We have attempted to not include traits that have been covered in previous handbooks except for where updates or additional information was considered beneficial.

Savannas first began to spread across Africa during the Miocene. A major hypothesis for explaining this vegetation change is the increase in C4 grasses, promoting fire. We investigated whether mammals could also have contributed to savanna expansion by using spinescence as a marker of mammal herbivory. Looking at the present distribution of 1,852 tree species, we established that spinescence is mainly associated with two functional types of mammals: large browsers and medium-sized mixed feeders. Using a dated phylogeny for the same tree species, we found that spinescence evolved at least 55 times. The diversification of spiny plants occurred long after the evolution of Afrotherian proboscideans and hyracoids. However, it is remarkably congruent with diversification of bovids, the lineage including the antelope that predominantly browse these plants today. Our findings suggest that herbivore-adapted savannas evolved several million years before fire-maintained savannas and probably, in different environmental conditions. Spiny savannas with abundant mammal herbivores occur in drier climates and on nutrient-rich soils, whereas fire-maintained savannas occur in wetter climates on nutrient-poor soils.

Tree densities in tropical and sub-tropical vegetation have, until recently, long been understood as increasing proportionally in response to precipitation. Current understanding is that trees are organised into alternative states with divergent properties that are linked, in the case of savannas, to frequent grass-fuelled fires or the absence of fire in non-savannas. In this paper we explored the hypothesis of functional divergence in three biomes, defined structurally by their dominant growth forms: savannas, ‘thicket’ and forest, within the vegetation of a South African park (Hluhluwe-iMfolozi). Thicket and forest both lack a continuous C4 grassy layer and are therefore non-savannas. ‘Thicket’, as defined here, has shorter trees than forests (4–6 m vs. > 10 m) and, often a dense understorey of sub-shrubs. We analysed tree species composition in 253 sites across these three biomes. We then compared herbivore use and fire frequency among the three biomes. Finally we characterised functional traits for 58 tree species including several linked to fire and herbivore responses. In support of the emerging alternative states paradigm for both tree density and phylogenetic composition, we found that the three structurally defined biomes had separate tree species assemblages. Differences in growth form, especially the presence or absence of C4 grasses had key consequences for consumers with high fire frequency in savannas, low in thickets and none in forest and high grazing in savannas, high browsing in thickets and very low herbivory in forests. Trait analysis was consistent with these differences among biomes. Consumers appear to be important environmental filters by admitting some tree species to a biome and excluding others, depending on their functional traits. Positive feedbacks between vegetation and consumers may explain the coexistence of biomes in areas with similar climate and geology.

Plant structural defences against mammals play an important role in ecosystem functioning as they simultaneously mediate the fitness of both animals and plants. The efficiency of structural defences can be described by the amount of plant material an animal can remove in one bite. Quantifying bite size by direct observation is difficult requiring controlled access to both the plants of interest and the herbivores. A method called the bite size index (BSI) has been proposed using human bites to simulate the bite size of medium-sized mammalian herbivores. In this paper, we evaluated the utility of the BSI for assessing the efficacy of plant structural defences. We analysed the intra- and inter-specific variability of the BSI in an African savanna (Hluhluwe–iMfolozi, South Africa) rich in herbivores, its repeatability between recorders, how the results reflect known properties of plant structural defences and how well the index correlates with the bite size of goats and its efficacy for explaining species distribution on a fire–herbivory gradient. The BSI was readily applied to a large set (n = 55) of plant species and proved to be consistent among recorders (8 of the 9 recorders obtained similar estimates). Bite sizes of goats and human observers were strongly correlated for 14 plant species (R 2 = 0.70) with divergent leaf and branch types. An analysis of BSI for 55 plant species disclosed two main contributory factors: leaf dimensions and spinescence. The BSI was significantly related to plant species distribution on a fire–herbivore gradient in an African savanna.

Summary Contrasting fire regimes maintain patch mosaics of savanna, thicket and forest biomes in many African subtropical landscapes. Species dominating each biome are thus expected to display distinct fire-related traits, commonly thought to be bark related. Recent Australian savanna research suggests that bud position, not bark protection alone, determines fire resilience via resprouting. We tested first how bud position influences resprouting ability in 17 tree species. We then compared the effect of both bark-related protection and bud position on the distribution of 63 tree species in 253 transects in all three biomes. Tree species with buds positioned deep under bark had a higher proportion of post-fire aboveground shoot resprouting. Species with low bud protection occurred in fire-prone biomes only if they could root-sucker. The effect of bud protection was supported by a good relationship between species bud protection and distribution across a gradient of fire frequency. Bud protection and high bark production are required to survive frequent fires in savanna. Forests are fire refugia hosting species with little or no bud protection and thin bark. Root-suckering species occur in the three biomes, suggesting that fire is not the only factor filtering this functional type.

International audience; Plant architecture is related to the performance of long-lived plants; its role in promoting species coexistence and in successional patterns is now widely recognized. However, because plant architecture involves branching processes, it is highly variable at the intra-specific level. In this paper, we address two questions: what is the best way to describe plant architecture to obtain meaningful information for explaining population cover: at the whole-plant level, or at the level of its unitary constituent parts? Further, are there architectural designs related to populations’ success? We evaluated the relative impact of ontogeny and whole-plant traits on the cover achieved by the populations of five shrub species developing on 25 abandoned farmlands in southwestern Québec (Canada). We compared four ways of analyzing plant architecture: 1–2) using morphological traits described at the scale of a module (an elementary architectural unit made up of all the different types of shoots), with or without taking into account the ontogeny of the whole organism, 3) using the rate of changes during ontogeny as traits, and 4) using whole-plant traits describing branching processes at a scale larger than modules. We then used variation partitioning to discriminate the actual effects of these traits on percent cover of the species from hidden effects due to plant ontogenesis and population spatial structure. Our results suggest that the predominant variables that effectively describe population cover vary from one species to another. At the same time, whole-plant architectural traits and the rate of change of morphological traits during ontogeny both have an important effect on population cover. These findings suggest that acknowledging the developmental pattern of woody species can clarify the impact of intra-specific trait variation on population cover

In the Neotropics, the genus Hydrangea of the popular ornamental hortensia family is represented by climbing species that strongly cling to their support surface by means of adhesive roots closely positioned along specialized anchoring stems. These root-climbing hortensia species belong to the nearly exclusive American Hydrangea section Cornidia and generally are long lianescent climbers that mostly flower and fructify high in the host tree canopy. The Mexican species Hydrangea seemannii , however, encompasses not only long lianescent climbers of large vertical rock walls and coniferous trees, but also short ‘shrub-like’ climbers on small rounded boulders. To investigate growth form plasticity in root-climbing hortensia species, we tested the hypothesis that support variability (e.g. differences in size and shape) promotes plastic responses observable at the mechanical, structural and anatomical level. Stem bending properties, architectural axis categorization, tissue organization and wood density were compared between boulder and long-vertical tree-climbers of H. seemannii . For comparison, the mechanical patterns of a closely related, strictly long-vertical tree-climbing species were investigated. Hydrangea seemannii has fine-tuned morphological, mechanical and anatomical responses to support variability suggesting the presence of two alternative root-climbing strategies that are optimized for their particular environmental conditions. Our results suggest that variation of some stem anatomical traits provides a buffering effect that regulates the mechanical and hydraulic demands of two distinct plant architectures. The adaptive value of observed plastic responses and the importance of considering growth form plasticity in evolutionary and conservation studies are discussed.

Qualitative and quantitative studies of the pattern of invasive plant development is now considered a key aspect in understanding invasiveness. This work was performed to determine relationships between shrub architectural plasticity and proliferating behaviour. We selected five shrub species (Cornus sericea L., Cornaceae ; Prunus virginiana L., Rosaceae ; Rhamnus cathartica L., Rhamnaceae ; Rhus typhina L., Anacardiaceae ; Zanthoxylum americanum Mill., Rutaceae) known to arrest plant succession under certain conditions in Southern Québec, Canada. Architectural analysis revealed species' structural units and their ontogenic changes. These ontogenic changes need to be calibrated if a full description of phenotypic plasticity is to be obtained. Analysis of the plant structural units reveals that they are of different functional significance: the higher the level of organization, the greater the capacity for phenotypic plasticity and competition. We defined three architectural strategies related to individual behaviours and which can relevantly explain the population proliferation of shrubs.; L'étude qualitative et quantitative du mode de développement des plantes envahissantes est actuellement considérée comme une étape clef dans la compréhension des phénomènes d'invasion. L'objectif de ce travail est de préciser les relations qui existent entre la structure architecturale des buissons et leur caractère proliférant. Nous avons sélectionné cinq espèces buissonnantes (Cornus sericea L., Cornaceae ; Prunus virginiana L., Rosaceae ; Rhamnus cathartica L., Rhamnaceae ; Rhus typhina L., Anacardiaceae ; Zanthoxylum americanum Mill., Rutaceae) qui sont connues pour leur aptitude à bloquer la succession végétale sous certaines conditions au Sud du Québec (Canada). L'analyse architecturale a permis chez ces espèces de caractériser les unités structurelles et leurs modifications ontogéniques. Ces modifications ontogéniques doivent être prise en compte afin d'obtenir une description complète de la plasticité phénotypique chez ces espèces. L'analyse des différentes unités structurelles révèle qu'elles ne possèdent pas la même signification fonctionnelle : les niveaux d'organisation les plus grands sont responsables majoritairement des capacités de plasticité phénotypique de la plante et de sa compétition. Ces analyses ont abouti à la définition de trois stratégies architecturales correspondant à des comportements individuels et qui sont également pertinentes pour expliquer la prolifération des populations

A-10-02; International audience; Background and Aims: Qualitative and quantitative studies of the pattern of invasive plant development is considered a key aspect in understanding invasiveness. An architectural analysis was therefore performed in order to understand the relationship between shoot architecture and invasiveness in red-osier dogwood, Cornus sericea (Cornaceae). Methods:The structural and ontogenic characteristics of individuals in invading and non-invading populations in the native range of the species were compared to test the implication of developmental plasticity on invasiveness. Key Results and Conclusions: The results show that the shrub has a modular architecture governed by strong developmental rules. Cornus sericea is made up of two levels of organization, each with its own intrinsic sequence of differentiation. These intrinsic mechanisms were used as a framework for comparison and it was found that, in response to the light environment, developmental plasticity was elevated, resulting in two architectural strategies. This developmental plasticity concerns the growth direction and the size of the modules, the speed of their time-course changes, their branching and flowering. Under an open canopy, C. sericea rapidly develops large vertical structures and abundant flowering. This strategy leads the plant to be invasive by excluding competitors and disseminating in the landscape. In the understorey, C. sericea slowly develops long horizontal structures which creep across the soil surface, while assimilating structures are poorly developed. This strategy does not lead to invasiveness but may allow the plant to survive in the understorey and reach sunny patches

A-09-11; International audience; Architectural descriptors were used to understand root system structure and development in white yam (Dioscorea rotundata Poir., Dioscoreaceae), a tuber monocot. Observations were made on seedlings and plant derived from tuber fragments, cultivated in greenhouses over a developmental cycle. This study demonstrated that both seedlings and plants derived from tubers have two distinct root systems that are highly organized. The first (seminal or tubercular) has been called the temporary root system which is small and short lived. The architectural unit here is made up of two root axis categories. The second (adventitious in both cases) has been called the definitive root system. It is larger and has a far longer lifespan than temporary root systems. The architectural unit here is made up of three root axis categories. Adventitious root systems are formed by structural repetitions of their own architectural unit. The temporary and definitive root systems possess the same structural and functional properties and become established and succeed one another in time following an identical developmental sequence. Neo tuber development is coupled with the root system development. Our results highlight to what extent it is important to study simultaneously the different parts of a root system in order to understand its development. This study confirms how architectural tools can be used to understand root system structure and development and prove accurate informations on root system development for use in agricultural management.