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Dans la zone de Botambi (forêt classée), située au sud-ouest de Bangui, capitale de Centrafrique, la déforestation liée à la pratique de l'agriculture itinérante sur brûlis entraine depuis quelques années le recul de la couverture forestière au profit des jachères pauvres à Chromolaena odorata et des savanes herbeuses. Cette disparition de la forêt est un manque à gagner pour les communautés autochtones et locales qui vivent et dépendent très significativement des ressources issues de la forêt. C'est également une perte pour la nation qui tire une part importante de ses revenus de l'exploitation du bois et pour l'ensemble de l'humanité (protection contre l'érosion des sols, préservation de la biodiversité, séquestration du carbone, etc.). Devant une telle situation, le PDRSO (Projet de Développement Régional du Sud-Ouest) a initié différentes techniques agroforestières dans les villages de Talo, de Botéké et de Salanga, où différents gradients de déforestation et de dégradation peuvent être observés. Ainsi, à Botéké et à Salanga, le projet a procédé à une expérimentation de la technique agroforestière de Régénération Naturelle Assistée durant les sarclages des champs (RNA sarclage ou RNAs). L'avantage de la RNAs est qu'elle permet une régénération rapide lorsque les rejets, semis et/ou drageons des espèces arborées forestières sont épargnés par les agriculteurs lors des activités de sarclage des champs. Le but de cette étude consiste à caractériser la ressource arborée dans les champs traités par la RNA sarclage et de la comparer à celle des champs témoins dans les villages de Talo, de Botéké et de Salanga. Pour atteindre cet objectif, plusieurs campagnes de sensibilisations ont été menées afin d'amener les agriculteurs de Botéké et de Salanga à appliquer cette technique. Au total, 11 agriculteurs de Botéké et 11 de Salanga ont adhéré à la technique et la RNAs a été ainsi installée dans leurs champs dès juin 2019. Les résultats des inventaires floristiques réalisés de juin 2019 à juin 2021 au sein des parcelles agricoles traitées par la RNAs montrent une nette augmentation du nombre d'individus ligneux au cours du temps et par rapport aux témoins. Sur les parcelles avec RNAs, la densité est passée de 177 arbres/ha en juin 2019 à 392 arbres/ha en juin 2021. Au sein des parcelles témoins, une augmentation de la densité des ligneux a été observé mais celle-ci reste très faible par rapport aux parcelles RNA sarclage. Elle est de 97 arbres/ha en juillet 2020 puis de 131 arbres/ha en juin 2021. L'analyse des traits de vie des espèces au sein des parcelles RNAs met en évidence une dominance des mégaphérophytes (58%), un mode de dissémination dominé par des espèces zoochores (75%), un tempérament caractérisé par des espèces pionnières (65%) et une distribution phytogéographique dominée par les espèces à large distribution (58%). Cette même tendance a été observée également au sein des parcelles témoins et a permis de tirer comme conclusion une nette transformation ou conversion de la forêt en jachères pauvres (Botéké) et en savanes herbeuses (Talo). L'analyse de la cinétique de végétation des villages de Botéké et Salanga montre que les parcelles RNAs de Salanga se trouvant en milieu forestier, peu ou pas dégradé, offrent plus de diversité contrairement à celles de Botéké situées dans un milieu forestier dégradé et dans des jachères pauvres. Par ailleurs, cette étude vise à comprendre les pratiques culturales exercées par les agriculteurs. L'objectif étant de savoir si celles-ci permettent une résilience des ligneux et une diffusion à grande échelle de la technique de RNAs pour obtenir ce résultat. Pour mener à bien cette partie, une enquête a été réalisée auprès des agriculteurs des villages de Talo, de Botéké et de Salanga. Concernant les pratiques culturales des agriculteurs dans les trois villages, celles-ci sont restées ancestrales et ne permettent plus à la forêt de se reconstituer. Les défrichements suivis obligatoirement du brûlis, les sarclages des champs sans tenir compte des rejets, semis et/ou drageons et l'implication de la main d'oeuvre salariée durant les défrichements et sarclages entrainent la perte de la couverture forestière dans la zone forestière de Botambi. La technique RNAs expérimentée par le PDRSO est une alternative qui a été appréciée par les agriculteurs qui l'ont expérimenté pour sa simplicité et sa capacité à enrichir les jachères en ligneux utiles). Cependant, seuls les détenteurs de droits fonciers se déclarent prêts à l'utiliser. Pour cette dernière catégorie, la RNAs peut être vulgarisée auprès des agriculteurs, pour une gestion durable des territoires forestiers en République Centrafricaine.

Cette étude se propose d’évaluer les caractéristiques de la végétation herbacée dans le Ferlo Nord au Sénégal. La végétation joue un rôle essentiel dans la vie des populations sahéliennes car elle constitue une ressource fourragère très importante pour les animaux. Elle est aussi très utilisée par la population locale comme bois de chauffage, bois d’oeuvre et dans l’alimentation. C’est ainsi que la gestion durable des ressources végétales d’une localité nécessite la connaissance de la flore pour appuyer les politiques de développement durable. C’est à cet effet que des inventaires de la strate herbacée ont été réalisés sous couvert et hors couvert sur une parcelle de cinq hectares mise en défens. La méthodologie d’inventaire adoptée a été la technique du « tour de champ » sur une période de quatre ans (2014–2017). Les résultats ont permis de dénombrer 66 espèces réparties dans 43 genres et 20 familles. Parmi ces espèces, les dicotylédones ont été dominantes avec 46 espèces (69,7 %), alors que les monocotylédones n’ont été représentées que par 20 espèces (30,3 %). Les familles les plus représentatives ont été les Poaceae avec 17 espèces, suivies des Fabaceae avec 7 espèces et des Malvaceae avec 6 espèces. Les thérophytes ont représenté 91 % des types biologiques, alors que les chaméphytes et les géophytes n’ont représenté que 4,5 % chacun. Au plan biogéographique, les espèces d’affinités africaines et pantropicales ont été dominantes avec respectivement 30,3 % et 24,2 % des espèces de la flore.

In drylands, water availability is the main limiting factor for plant growth. Topographic depressions in the Sahel that reveal a more favorable water balance display greater tree diversity compared to their surroundings. However, the environmental factors that drive differences in botanical composition between depressions remain unknown. Here, we investigated the depression features, and the landscape and connectivity metrics responsible for woody vegetation composition in a savanna of Senegal. We mapped depressions in a 700 km2 area and inventoried woody vegetation in 61 depressions varying in area. Simple linear models were applied between (i) indicators of richness and botanical composition and (ii) depression attributes, landscape and connectivity metrics. We found that the area of a depression increased species richness. The number of vegetation strata and the presence of a temporary pond also positively influenced species richness. Yet, while large depressions always had high richness, some small depressions did too. We were not able to identify additional factors to explain this diversity between small depressions. In the context of decreasing richness and composition shift observed in the Sahel over recent decades, depressions, as biodiversity hotspots, are key elements in ecosystem functioning. Further studies are needed to understand other potential drivers of species diversity, such as soil water availability.

Aim We sought to determine the relationship of forest composition and alpha diversity (the species diversity of a local assemblage) to altitude, soil, and spatial factors over a 440–2,950 m a.s.l gradient. Location Altitudinal gradient on the Caribbean slope of the Talamanca Cordillera, Costa Rica. Taxon Angiosperm and gymnosperm trees, palms, and tree ferns. Methods We measured and identified all stems ≥10 cm dbh in 32 0.25‐ha undisturbed rain forest plots over the gradient. We determined compositional patterns using Non‐Metric Multidimensional Scaling (NMS) ordination, and used linear regressions to explore the relationship between four alpha diversity metrics and altitude. With variation partitioning (VARPART), we determined the compositional variation explained by altitude, soil, and spatial variables quantified using Principle Components of Neighbor matrices. Results We identified 425 species. NMS axis 1 separated a lowland zone (440–1,120 m asl) from a transitional one dominated by holarctic Oreomunnea mexicana (1,400–1,600 m asl) and Quercus‐dominated forests at altitudes >2,100 m asl. The lowland zone was separated into two clusters of plots on NMS axis 2, the first in the 430–620 m asl range and the second at 1,000–1,120 masl. Regressions showed that all alpha diversity metrics were strongly negatively related to altitude (R 2 > 0.78). Overall, adjusted R 2 from VARPART was 0.43, with 0.30, 0.21, and 0.17 for altitude, soil, and space respectively. The respective adjusted R 2 of individual matrices, on controlling for the other two, was 0.06, 0.05 and 0.09 (p 2,150 m asl—with a transitional zone at 1,400–1,600 m asl, where lowland tropical and montane holarctic species are found together. Montane forests are very distinct in their composition and low alpha diversity. Vegetation and soil respond to altitude, and therefore temperature, as an integrated system, a model that goes beyond niche assembly as shown by the significant effect of space in the VARPART.

International audience; Accurate estimates of feed intake are important in order to develop accurate ration formulations, for selecting livestock according to production efficiency, and for reducing environmental impact of livestock. The present study assessed the accuracy of n-alkanes to estimate individual herbage intake and diet botanical composition of cattle fed natural forages, typical to Madagascar. The effect of two different forage allowances and seasons on the herbage intake was also tested. Eight Norwegian red pie sires (232 ± 20 kg BW) were orally dosed twice daily with paper pellets containing 456.61 ± 21.64 mg of C32 alkane as external marker. Animals were housed in individual pens and fed with mixtures of five forages species typically used by farmers in the rainy season (Aristida multicaulis, Hyparrhenia rufa, Imperata cylindrical, Urochloa brizantha and Stylosanthes guyanensis) and the dry season (Chrysopogon serrulatus, Cynodon dactylon, Imperata cylindrica, Lolium multiflorum and Leersia hexandra Sw). The sires were randomly assigned to two different forage allowances: (i) ad libitum with a refusal of 5 % and (ii) 1.1 % DM of body weight (BW). The n-alkane pairs C31:C32 and C32:C33 and the ratio C32/Acid Insoluble Ash (AIA) in plants and faeces were used to estimate the herbage intake. The botanical composition of the diet was estimated using the n-alkane profile from C27 to C35 in individual plant species and faeces, by least squares optimization. The n-alkane pairs underestimated (P < 0.0001) the herbage intake by 25 % in the dry season, for both forage allowances and 26 % for animals receiving ad libitum diet, regardless of the season. In contrast, the intake estimates based on both n-alkane pairs did not differ from the measured intake for animals receiving low forage allowance during the rainy season. The C32/AIA underestimated the actual herbage intake, by 50 %, for animal consuming ad libitum diet, for both seasons (P < 0.0001). The n-alkane faecal recovery (AFR) corrections factors set affected (P < 0.01) the estimated proportions of each plant species, that comprised the diet in both seasons. The application of appropriate AFR permitted to have a better accuracy of diet botanical composition estimates. It is concluded that plant wax n-alkanes are advantageous for estimating both diet botanical composition and herbage intake in cattle. However, for improving the prediction, it is important to measure the actual AFR before the calculation.

International audience; Secondary forests are a prominent component of tropical landscapes, and they constitute a major atmospheric carbon sink. Rates of carbon accumulation are usually inferred from chronosequence studies, but direct estimates of carbon accumulation based on long-term monitoring of stands are rarely reported. Recent compilations on secondary forest carbon accumulation in the Neotropics are heavily biased geographically as they do not include estimates from the Guiana Shield. We analysed the temporal trajectory of aboveground carbon accumulation and floristic composition at one 25-ha secondary forest site in French Guiana. The site was clearcut in 1976, abandoned thereafter, and one large plot (6.25 ha) has been monitored continuously since. We used Bayesian modelling to assimilate inventory data and simulate the long-term carbon accumulation trajectory. Canopy change was monitored using two aerial lidar surveys conducted in 2009 and 2017. We compared the dynamics of this site with that of a surrounding old-growth forest. Finally, we compared our results with that from secondary forests in Costa Rica, which is one of the rare long-term monitoring programs reaching a duration comparable to our study. Twenty years after abandonment, aboveground carbon stock was 64.2 [95% credibility interval: 46.4;89.0] MgC/ha, and this stock increased to 101.3 [78.7;128.5] MgC/ha twenty years later. The time to accumulate half of the mean aboveground carbon stored in the nearby old-growth forest (185.6 [155.9;200.2] MgC/ha) was estimated at 35.0 [20.9;55.9] years. During the first 40 years, the contribution of the long-lived pioneer species Xylopia nitida, Goupia glabra and Laetia procera to the aboveground carbon stock increased continuously. Secondary forest mean-canopy height measured by lidar increased by 1.14 m in eight years, a canopy-height increase consistent with an aboveground carbon accumulation of 7.1 MgC/ha (or 0.89 MgC/ha/yr) during this period. Long-term AGC accumulation rate in Costa Rica was almost twice as fast as at our site in French Guiana. This may reflect higher fertility of Central American forest communities or a better adaptation of the forest tree community to intense and frequent disturbances. This finding may have important consequences for scaling-up carbon uptake estimates to continental scales.

Questions: What are the effects of abandonment on plant diversity in seminatural grasslands? Do the effects of abandonment on taxonomic and functional diversity vary along environmental gradients of climate and soil? Location: West and mid-Norway. Methods: Plant composition was surveyed in 110 subplots of 4 m2 in 14 sites across grazed and abandoned semi-natural grasslands. Climate data were extracted and soil composition analysed. To reduce the number of explanatory variables and deal with collinearity, we performed PCA. Data on the plant species vegetative height (H), leaf dry matter content (LDMC), specific leaf area (SLA), seed mass (SM) and number of seeds per plant (SNP) for 175 species were extracted from the LEDA database. Measures of plant diversity (species richness, CWM of functional traits and functional diversity (evenness and range)) were calculated for each subplot. To estimate the effects of abandonment on plant diversity and examine how these effects are moderated by gradients in soil and climate, we fitted mixed models to the data including site as a random effect. Results: Species richness in the subplots was lower in abandoned semi-natural grasslands, especially on more calcareous soils. CWM H, LDMC and SM were higher in abandoned semi-natural grasslands. CWM LDMC was only higher in the driest subplots. The ranges in H, SLA and SM, as well as evenness in LDMC were also higher in abandoned semi-natural grasslands,but the range in LDMC was lower. Conclusions: It is important to assess both taxonomic and functional diversity to understand ecosystem processes. The species pool in ecosystems influenced by a long history of intermediate grazing includes a high proportion of low stature, grazing-tolerant plant species. Abandonment of extensive land-use practices will cause a decline in taxonomic diversity (plant species richness) in such systems due to increased abundance of plants with high stature that outcompete the lower, grazing-tolerant plants. This process is predominant especially if moisture, soil fertility and pH are at intermediate levels. Changes in species communities due to abandonment will also influence ecosystem functioning, such as nutrient turnover and fodder production resilience.

Cypress (Cupressus sp.pl) is a genus within the Cupressaceae family. This family covers all of the Earth's continents except for Antarctica, and it includes about 160 species. The most important taxa for allergic diseases belong to five different genera: Cupressus, Hesperocyparis, Juniperus, Cryptomeria, and Chamaecyparis. Cupressaceae species share a common pollen type that can even include the genus Taxus (Taxaceae) when this plant is also present. As Juniperus oxycedrus pollinates in October, Cupressus sempervirens in January and February, Hesperocyparis arizonica (prev. Cupressus arizonica) in February and March, and Juniperus communis in April, the symptomatic period is long-lasting. Due to global warming, the pollination period tends to last longer, and there is a trend for Cupressaceae bioclimate niches to migrate north. In Mediterranean areas, C. sempervirens (Italian cypress or Mediterranean cypress) is by far the most common pollinating species. It accounts for half of the total pollination level. The group 1 major allergens belong to the pectate-lyase family, and members share 70 to 97% sequence homology within the different Cupressaceae. Group 2 allergens correspond to the polygalacturonase protein family, while group 3, a minor allergen, belongs to the family of "thaumatin-like proteins," a pathogenesis-related protein 5. Group 4 allergens are Ca++-binding protein (4 EF-hands). Aside from these four groups, about 15 other allergens have been reported. Prominent among these is a basic low-molecular mass cross-reactive allergen that was identified recently, and which is suspected to be involved in pollen food syndromes which are common with peach and citrus. The prevalence of cypress allergy in the general population ranges from 0.6 to 3%, depending on the degree of exposure to the pollen. Depending on the geographic area and the studied population, 9 to 65% of outpatients consulting an allergist may have sensitization to cypress pollen. Repeated cross-sectional studies performed at different time intervals have demonstrated a threefold increase in the percentage of cypress allergy around the Mediterranean area. Risk factors include a genetic predisposition and/or a strong exposure to pollen, and the natural history of cypress allergy allows identification of a subgroup of patients as allergic rather than atopic. Concerning the clinical expression, rhinitis is the most prevalent symptom, while conjunctivitis is the most disabling. Pharmacological treatment of cypress allergies is not different from that of other seasonal allergies. Immunotherapy has been used, initially by subcutaneous injections, but currently mostly through the sublingual route. Although clinical trials have included only a limited number of patients, it has proven effective and safe. Avoidance can be implemented at the individual level, as well as at the community level, through the use of alternative plants, low-pollinating cypresses, or by trimming hedges before pollination.

Aim: In tropical Africa, savannas cover huge areas, have high plant species richness and are considered as a major natural resource for most countries. There is, however, little information available on their floristics and biogeography at the continental scale, despite the importance of such information for our understanding of the drivers of species diversity at various scales and for effective conservation and management. Here, we collated and analysed floristic data from across the continent in order to propose a biogeographical regionalization for African savannas. Location: We collated floristic information (specifically woody species lists) for 298 samples of savanna vegetation across Africa, extending from 18° N to 33° S and from 17° W to 48° E. Taxa: We focused on native woody species. Methods: We used ordination and clustering to identify the floristic discontinuities and gradual transitions across African savannas. Floristic relationships, specificity and turnover, within and between floristic clusters, were analysed using a (dis-)similarity-based approach. Results: We identified eight floristic clusters across African savannas which in turn were grouped into two larger macro-units. Ordinations at species and genus levels showed a clear differentiation in woody species composition between the North/West macro-unit and the South/East macro-unit. This floristic discontinuity matches to the High (i.e. N&W) and Low (S&E) division of Africa previously proposed by White () and which tracks climatic and topographical variation. In the N&W savannas, the floristic gradient determined by rainfall was partitioned into the Sudanian (drier) and Guinean (wetter) clusters. Within the highly heterogeneous S&E savannas and woodlands, six clusters were identified: Ugandan, Ethiopian, Mozambican, Zambezian, Namibian and South African. Main conclusions: The proposed pan-African classification of savannas and woodlands might assist the development of coordinated management and conservation policies., SCOPUS: ar.j, info:eu-repo/semantics/published

Resolving phylogenetic relationships allows the investigation of how species diversity has evolved in various ecosystems. The genera Entandrophragma and Khaya consist of tree species distributed in different African biomes (lowland rain forest, dry forest and savanna, montane forest), and are suitable to examine how (single or multiple events) and when the processes of diversification led to biome transitions. Based on the sequencing of plastome (pDNA: c. 160,000 bp), ribosomal DNA (rDNA: c. 5300 bp), and habitat characteristic data for each species, we have: (i) reconstructed phylogenetic relationships between species and estimated the divergence period between the main lineages, and (ii) reconstructed ancestral states regarding biome preferences. The phylogenetic trees obtained with both markers support monophyly of the five sections of Entandrophragma previously defined based on fruit and floral characters. Nevertheless, the position of some species from the pDNA and rDNA tree topologies varied within sections. In Khaya, pDNA and rDNA show very divergent topologies, possibly due to a more recent diversification involving incomplete lineage sorting and/or recurrent hybridization events. Khaya diversified during the Pliocene and Pleistocene according to both markers; whereas, according to rDNA data, the Entandrophragma sections diverged during the early Miocene and species within sections diverged from the late Miocene to the Pleistocene. Divergence date estimates tended to be more recent using pDNA data. Biome transitions could not be reconstructed in Khaya as the species tree remains unresolved. Contrarily, three independent biome transitions were inferred in Entandrophragma. The first transition from rain to dry forests occurred during the Miocene and two other transitions were inferred during the Pleistocene, one from rain forest to dry forest and another from rain forest to mountain forest. Overall, we demonstrate that multiple biome transitions occurred, starting from a rain forest biome, possibly reflecting the global trend of aridification of Africa throughout the Cenozoic. © 2019 Elsevier GmbH, SCOPUS: ar.j, info:eu-repo/semantics/published

Although agriculture is a major factor in environmental change, the level of its impact is likely to vary with farming practices. Thus, we sought to determine how farming practices might affect the natural compartment of agroecosystems and the sustainable use of land. In particular, we examined ant biodiversity and community composition as related to orchard design and management practices in the mango- and citrus-based orchard agroecosystems of Senegal. Ants were collected using pitfall traps in 49 orchards classed in four types based on their design and management. The results showed that the effect of practices was significant, albeit weak, and a typology of orchards based on design and management practices was congruent with a typology based on the composition of ant communities. The different types of orchard were seen to differ in the richness and diversity ant species. Moreover, ant richness and diversity was positively correlated with tree richness. We were also able to identify some ant species as being related to agricultural practices. For instance, Monomorium salomonis (L.) was closely associated with high irrigation, fertilization and pesticide use, whereas Paltotyreus tarsatus was associated with greater tree richness, high local ground coverage by the tree canopy, more leaf litter and great variation in the local tree planting density. This study appears to be the first attempt to characterise the relations existing between orchard design and management practices and the functioning of Sahelian fruit-based agroecosystems thereby furthering the goal of providing recommendations for sustainable management strategies.

Dans le but de répondre aux besoins en agriculture, l’INRA met en place plusieurs projets. Le projet expérimental Patuchev a pour but d’évaluer et de concevoir des systèmes d’élevage caprins innovant viables qui respectent l’environnement et le bien-être animal.[br/] Afin de faciliter la gestion du pâturage et la prise de décision des éleveurs, l’estimation de la biomasse d’une parcelle peut se révéler très utile. Afin de l’estimer, la hauteur d’herbe moyenne et la densité de la parcelle sont nécessaires. Une valeur communément utilisée de la densité est 250 kg matière sèche/cm/ha[br/] L’objectif de ce stage est de déterminer la pertinence de cette valeur à partir des données du dispositif expérimental Patuchev et de déterminer si l’on doit prendre en compte la présence d’espèces fourragères spécifiques., In order to responds the needs in agriculture, INRA is implementing several projects. The purpose of the Patuchev Experimental Project is to evaluate and propose, sustainable goat farming systems that respect the environment and animal welfare.[br/] In order to facilitate grazing management and decision-making for farmers, estimating the biomass of a plot can be very useful. To estimate it, the average grass height and parcel density are necessary. A commonly used value of density is 250 kg dry matter / cm / ha[br/] The objective of this internship is to determine the suitability of this value from the Patuchev experimental device data and to determine whether the presence of specific forage species should be taken into consideration.

Le domaine de Namalok (4 500 ha), situé au nord-est de la Tanzanie, a été protégé par TPC Limited, une société sucrière privée, pour en faire une réserve privée de faune et de flore. La végétation locale est constituée de savanes arbustives à Salvadora persica, de fourrés de Suaeda monoica et de savanes arborées plus au moins denses à Acacia xanthophloea, Faidherbia albida et Acacia tortilis. Afin de répondre à un objectif de gestion suite à la réintroduction de grands herbivores, la composition floristique de ces formations ligneuses a été étudiée en association avec une approche cartographique du degré d’accessibilité des formations ligneuses par les herbivores, exprimé en classes de densité établies selon l’indice perpendiculaire de végétation (IPV). Les résultats révèlent tout d’abord une corrélation très élevée entre la densité calculée des ligneux et l’IPV (r2 = 0,96) et confirment l’intérêt de l’approche proposée d’analyse d’images satellitaires. Dans une perspective plus locale, ils montrent aussi que, sur le plan floristique, les niveaux successifs des densités cartographiées sont composés de 70 espèces végétales et relèvent d’un fond floristique d’espèces pantropicales. Ces savanes montrent également une distribution spécifique relativement équitable et très diverse, avec des fréquences spécifiques voisines les unes des autres. Les savanes arborées représentent 38 % de la surface du domaine. Par ordre croissant de densité, les savanes de moins de 100 arbres/ha couvrent 836 ha, celles comptant 100 à 200 arbres/ha occupent 654 ha et celles ayant des densités de 200 à 300 arbres/ha sont assez peu importantes et n’occupent que 206 ha. Les savanes de densité supérieure à 300 arbres/ha représentent des étendues beaucoup moins vastes, soit seulement 22 ha.

Funding Information: Natural Environment Research Council (NERC), Grant/Award Number: NE/ N004655/1; NERC Consortium Grants “AMAZONICA”; BIO‐RED; European Research Council (ERC); The Gordon and Betty Moore Foundation; European Union's Seventh Framework Programme, Grant/ Award Number: 282664; Royal Society, Grant/Award Number: CH160091; Royal Society Wolfson Research Merit Award. Most of the planet's diversity is concentrated in the tropics, which includes many regions undergoing rapid climate change. Yet, while climate-induced biodiversity changes are widely documented elsewhere, few studies have addressed this issue for lowland tropical ecosystems. Here we investigate whether the floristic and functional composition of intact lowland Amazonian forests have been changing by evaluating records from 106 long-term inventory plots spanning 30 years. We analyse three traits that have been hypothesized to respond to different environmental drivers (increase in moisture stress and atmospheric CO2 concentrations): maximum tree size, biogeographic water-deficit affiliation and wood density. Tree communities have become increasingly dominated by large-statured taxa, but to date there has been no detectable change in mean wood density or water deficit affiliation at the community level, despite most forest plots having experienced an intensification of the dry season. However, among newly recruited trees, dry-affiliated genera have become more abundant, while the mortality of wet-affiliated genera has increased in those plots where the dry season has intensified most. Thus, a slow shift to a more dry-affiliated Amazonia is underway, with changes in compositional dynamics (recruits and mortality) consistent with climate-change drivers, but yet to significantly impact whole-community composition. The Amazon observational record suggests that the increase in atmospheric CO2 is driving a shift within tree communities to large-statured species and that climate changes to date will impact forest composition, but long generation times of tropical trees mean that biodiversity change is lagging behind climate change. Publisher PDF

Mediterranean forests are found in the Mediterranean basin, California, the South African Cape Province, South and southwestern Australia and parts of Central Chile. They represent 1.8 % of the world forest areas of which the vast majority is found in the Mediterranean basin, where historical and paleogeographic episodes, long-term human influence and geographical and climatic contrasts have created ecosystemic diversity and heterogeneity. Even if evergreen is dominant, deciduous trees are also represented, with different forest types including dense stands with a closed canopy (forests sensu stricto) and pre-forestal or pre-steppic structures with lower trees density and height. The Mediterranean basin is also a hot spot of forest species and genetic diversity, with 290 woody species versus only 135 for non-Mediterranean Europe. However, the characteristics of the Mediterranean area (long-standing anthropogenic pressure, significant current human activity and broad biodiversity) make it one of the world’s regions most threatened by current changes. Four examples of Mediterranean forest types, present in south and north of the Mediterranean basin and more or less threatened, are developed in order to show that linking “hard sciences” and humanities and social sciences is necessary to understand these complex ecosystems. We show also that these forests, in spite of specific climatic constraints, can also be healthy and productive and play a major ecological and social role. Furthermore, even if the current human activity and global change constitute a risk for these exceptional ecosystems, Mediterranean forests represent a great asset and opportunities for the future of the Mediterranean basin.

International audience; Background and aims – The thermophilous woodlands of the Mediterranean region constitute reservoirs of genetic resources for several fruit trees. Among them, the carob tree (Ceratonia siliqua) is a key component of traditional Mediterranean agroecosystems but its ecology was never assessed at the scale of its whole distribution area. Fortunately, phytosociological literature shelters invaluable resources for several issues in conservation, among them the possibility to analyse plant biodiversity at regional or continental scale. Here, we present the results of a comprehensive survey of the phytosociological literature associated to carob tree.Methods – We collected 1542 floristic relevés performed in 18 geographical areas distributed around the Mediterranean in which the presence of C. siliqua was recorded. Species composition of the plant communities was analysed by multivariate ordination and hierarchical classification, and species diversity was evaluated by rarefaction and prediction analyses of Hill numbers.Key results – Multivariate analyses revealed that plant communities associated with the carob tree are well differentiated between the Western and Eastern basins. A wider range of floristic differentiation is revealed in the Western basin where the vegetation reaches its maximal heterogeneity. By comparison, in the Eastern basin the plant assemblages associated with the carob tree are more homogeneous and with a lower species richness but a higher Simpson diversity.Conclusions – The large ecological range of the Mediterranean carob trees is potentially an important evolutionary legacy for the conservation of genetic resources and seed sourcing for new uses such as restoration ecology.

Tree vigor is often used as a covariate when tree mortality is predicted from tree growth in tropical forest dynamic models, but it is rarely explicitly accounted for in a coherent modeling framework. We quantify tree vigor at the individual tree level, based on the difference between expected and observed growth. The available methods to join nonlinear tree growth and mortality processes are not commonly used by forest ecologists so that we develop an inference methodology based on an MCMC approach, allowing us to sample the parameters of the growth and mortality model according to their posterior distribution using the joint model likelihood. We apply our framework to a set of data on the 20-year dynamics of a forest in Paracou, French Guiana, taking advantage of functional trait-based growth and mortality models already developed independently. Our results showed that growth and mortality are intimately linked and that the vigor estimator is an essential predictor of mortality, highlighting that trees growing more than expected have a far lower probability of dying. Our joint model methodology is sufficiently generic to be used to join two longitudinal and punctual linked processes and thus may be applied to a wide range of growth and mortality models. In the context of global changes, such joint models are urgently needed in tropical forests to analyze, and then predict, the effects of the ongoing changes on the tree dynamics in hyperdiverse tropical forests.

Biological and structural factors of the invading vine Merremia peltata in forested habitats in Mayotte. — Lianas are hyperdynamic elements of tropical vegetation that strongly react to changes in forest structure. In Mayotte (Western Indian Ocean), the indigenous vine Merremia peltata (Convolvulaceae) greatly expanded its range in recent decades and sometimes causes the collapse of the forest canopy. Surveys were conducted in 52 4 m-radius plots arranged in Voundzé forest and Bénara Monts Departmental Forest, along an ecological gradient of invasion of M. peltata from free to very strongly invaded areas. The propagation modes of the liana, the vertical structure of forest stands, but also topographic parameters, were identified and quantified. No plantlet resulting from germination was observed. The creeping stems, present in high density (1.9 stems / m) were systematically layered in the ground. A set of 37 native plant species have been recorded as supports, the most common one being Grisollea myrianthea. From the primary host, which has an average diameter of 6.0 ± 4.9 cm at 1.30 m above ground, the creeper joins another support remote of a mean distance of 97 cm. The index of colonization and the index of forest structure which were used, which sum the rate of vegetation cover at different heights, were negatively correlated (n = 52, Pearson coefficient r = -0.319, P < 0.05). Natural forests, which show a complex vertical structure, were actually less colonized than secondary forests, which have a poorer vertical structure. The negative correlation between the same index of colonization and altitude (n = 35, Pearson coefficient r = -0.439, P < 0.05) is interpreted as a relationship confused with the previous, as natural forests are located at altitude unlike secondary forests. The colonization of forest ecosystems by M. peltata is facilitated by a high aptitude for vegetative propagation, coupled with higher propensity of secondary forests to be colonized by lianas. Uncertainty remains about the future of the sites where this vine has led to the collapse of forest stands. However, only new ecosystems mixing indigenous and alien species, are expected to emerge., Les lianes sont en général des éléments hyperdynamiques de la végétation tropicale qui réagissent fortement aux changements de structure des peuplements. À Mayotte (océan Indien occidental), la liane indigène Merremia peltata (Convolvulaceae) a fortement étendu son aire de répartition depuis quelques décennies et provoque parfois l’effondrement de la canopée forestière. Des relevés ont été assurés dans 52 placettes circulaires de 4 m de rayon disposées au sein de la forêt domaniale de Voundzé et de la forêt départementale des Monts Bénara, et recouvrant un gradient écologique d’enlianement à M. peltata, depuis des zones indemnes jusqu’à des situations localement très fortement enlianées. Les modes de propagation de la liane, la structure verticale des peuplements forestiers, mais aussi des paramètres d’ordre topographique y ont été relevés et quantifiés. Aucune plantule issue de reproduction sexuée n’a été observée. En revanche, les tiges rampantes, dont l’abondance est traduite par une densité s’élevant à 1,9 points d’interception par mètre linéaire, se révèlent systématiquement marcottées au sol. Un ensemble de 37 espèces végétales indigènes ont été recensées comme pouvant servir de support à cette liane, la plus fréquente étant Grisollea myrianthea. À partir de l’hôte primaire, dont le diamètre moyen et l’écart-type à 1,30 m sont de 6,0 et 4,9 cm, la liane rejoint un autre support en moyenne éloigné de 97 cm. L’indice d’enlianement et l’indice de structure forestière que nous avons utilisés, sommant les taux de recouvrement selon diverses strates de végétation, se sont révélés négativement corrélés (n = 52, coefficient de corrélation linéaire de Pearson r = -0,319, P < 0,05). Les faciès de forêts dites naturelles, à structure verticale complexe, étaient de fait moins enlianés que les faciès relevant de forêts secondaires, à structure verticale plus lâche. La corrélation négative observée entre le même indice d’enlianement et l’altitude (n = 35, coefficient de corrélation linéaire de Pearson r = -0,439, P < 0,05) s’interprète comme une relation se confondant avec la précédente, les forêts naturelles étant situées en altitude, contrairement aux forêts secondaires. L’enlianement des écosystèmes forestiers par M. peltata est donc facilité par une aptitude élevée à la propagation végétative, conjuguée à une plus forte propension des forêts secondaires à être colonisées. L’incertitude demeure quant au devenir des sites où cette liane a entraîné l’effondrement des peuplements forestiers. Seuls des écosystèmes inédits mêlés d’essences allogènes semblent pouvoir en émerger., Tassin Jacques,Laizé Alexandre. Facteurs biologiques et structuraux de l’invasion de la liane Merremia peltata dans les habitats forestiers de Mayotte. In: Revue d'Écologie (La Terre et La Vie), supplément n°12, 2015. Les invasions biologiques et leur gestion au carrefour des sciences naturelles et des sciences humaines et sociales. Colloque organisé à Rennes (Université de Rennes 1) du 20 au 22 octobre 2014. pp. 151-161.

Thailand has undergone significant forest cover changes in recent decades, and this is likely to have altered the hydrological functioning of many watersheds; however, such potential impacts are not fully understood. To contribute towards a better understanding of the potential hydrological impacts of forest cover changes, this study examines the temporal trends of several hydrological indices in eight watersheds of Thailand over the period from 1982 to 2013. A number of hydrological indices (runoff coefficient, baseflow index, flow duration indices, streamflow elasticity, dryness index) were analysed using a combined Thiel–Sen/Mann–Kendall trend-testing approach, to assess the magnitude and significance of patterns in the observed data. These trend tests indicated that the change in the hydrological response of watersheds varied with the change in structure and composition of forest species. A significant increase in runoff (viz. average flow) was observed in those watersheds covered with natural forests, whereas a significant reduction in runoff (viz. baseflow and low runoff) was observed in those watersheds where the land cover was changed to Para rubber plantations and reforested areas. It is also noteworthy that the watersheds covered by natural forest showed more streamflow elasticity than plantations or reforested areas. These results highlight the importance of considering both forest types/dynamics and watershed characteristics when assessing hydrological impacts.

The populations of light-demanding trees that dominate the canopy of central African forests are now aging. Here, we show that the lack of regeneration of these populations began ca. 165 ya (around 1850) after major anthropogenic disturbances ceased. Since 1885, less itinerancy and disturbance in the forest has occurred because the colonial administrations concentrated people and villages along the primary communication axes. Local populations formerly gardened the forest by creating scattered openings, which were sufficiently large for the establishment of light-demanding trees. Currently, common logging operations do not create suitable openings for the regeneration of these species, whereas deforestation degrades landscapes. Using an interdisciplinary approach, which included paleoecological, archaeological, historical, and dendrological data, we highlight the long-term history of human activities across central African forests and assess the contribution of these activities to present-day forest structure and composition. The conclusions of this sobering analysis present challenges to current silvicultural practices and to those of the future. DOI: http://dx.doi.org/10.7554/eLife.20343.001, eLife digest The world’s forests contain trillions of trees. Some of those trees require more light than others to mature, and certain species can only grow to reach the forest canopy if they have access to sunlight throughout their whole life. Central Africa is home to the second largest tropical rainforest in the world. Previous studies showed that few young trees of light-demanding species were growing to replace the old trees in this forest. As a result this population is aging and at risk of disappearing, which is a major concern. Many light-demanding tree species in the Central African forest are cut down for their valuable timber. However, if young trees do not grow to replace the mature ones that are logged, even logging operations that follow national and international environmental rules cannot guarantee the sustainability of these trees. As such, Morin-Rivat et al. set out to understand what changed in the Central African forest in the past to stop the regeneration of the light-demanding trees. The analyses focused on four species classified as light-demanding trees in part of Central Africa called the northern Congo Basin. Most of the trees in these species were about 165 years old. This was the case even though the different species grow at different rates, and it means that they all grew from young trees that settled in the middle of the 19th century. So what was it that changed after this period to stop this population of light-demanding trees in the Central African forest from regenerating? By combining information from a number of datasets and historical records, Morin-Rivat et al. arrived at the following conclusion. Before the mid-19th century, many people lived in the forest and their activities created clearings that turned the forest into a relatively patchy landscape. However from about 1850 onwards, when Europeans started to colonize the region, people and villages were moved out of the forests and closer to rivers and roads for administrative and commercial purposes. Moreover, many people were killed in conflicts or died because of newly introduced diseases, which also led to fewer people in the forest. As a result, the forest became less disturbed. With fewer clearings, fewer light-demanding trees would have had enough access to sunlight to grow to maturity. The findings of Morin-Rivat et al. show that disturbance is needed to maintain certain forest habitats and tree species, including light-demanding species of tree. As common logging operations do not create openings large enough to guarantee that such species will be able to establish themselves naturally, complementary treatments are needed. These might include selectively logging mature trees around young members of light-demanding species, or planting threatened species. DOI: http://dx.doi.org/10.7554/eLife.20343.002

International audience; Context: The biodiversity hotspot for conservation of New Caledonia has facing high levels of forest fragmentation. Remnant forests are critical for biodiversity conservation and can help in understanding how does forest fragmentation affect tree communities.Objective: Determine the effect of habitat configuration and availability on tree communities.Methods: We mapped forest in a 60 km2 landscape and sampled 93 tree communities in 52 forest fragments following stratified random sampling. At each sampling point, we inventoried all trees with a diameter at breast height ≥10 cm within a radius of 10 m. We then analysed the response of the composition, the structure and the richness of tree communities to the fragment size and isolation, distance from the edge, as well as the topographical position.Results: Our results showed that the distance from the forest edge was the variable that explained the greatest observed variance in tree assemblages. We observed a decrease in the abundance and richness of animal-dispersed trees as well as a decrease in the abundance of large trees with increasing proximity to forest edges. Near forest edges we found a shift in species composition with a dominance of stress-tolerant pioneer species.Conclusions: Edge-effects are likely to be the main processes that affect remnant forest tree communities after about a century of forest fragmentation. It results in retrogressive successions at the edges leading to a dominance of stress-tolerant species. The vegetation surrounding fragments should be protected to promote the long process of forest extension and subsequently reduce edge-effects.

Patterns in above-ground biomass of tropical forests over short altitudinal gradients are poorly known. The aim of this study was to investigate the variation of above-ground biomass with altitude in old-growth forests and determine the importance of changes in floristic composition as a cause of this variation. We used a dataset from 15 1-ha permanent plots established from lowland (200 m asl) to submontane forests (900 m asl) in the Ngovayang Massif, south-western Cameroon. We analysed variation over altitude in two specific functional traits, the potential maximum tree height and the wood density. Forest above-ground biomass decreased from 500–600 Mg ha−1 in lowland plots to around 260 Mg ha−1 at the highest altitudes. The contribution to above-ground biomass of large-tree species (dbh ≥ 70 cm) decreased with altitude, while the contribution of smaller trees was constant. Contribution of the Fabaceae subfamily Caesalpinioideae decreased with altitude, while those of Clusiaceae, Phyllanthaceae and Burseraceae increased. While potential maximum tree height significantly decreased, wood specific gravity displayed no trend along the gradient. Finally, the decrease in above-ground biomass along the short altitudinal gradient can be at least partially explained by a shift in species composition, with large-tree species being filtered out at the highest altitudes. These results suggest that global change could lead to significant shifts in the properties of montane forests over time.