High tree alpha-diversity in Amazonian Ecuador

In a 1 ha square plot of terra firme forest at 260 m elevation in Amazonian Ecuador, all trees with diameter at breast height (dbh) 5 cm were studied. There were 1561 individuals, 473 species, 187 genera and 54 families. Of these, 693 individuals, 307 species, 138 genera and 46 families had a dbh 10 cm. This is the highest number of tree species ever recorded for a tropical rain forest sample of this size. In both dbh classes, the most species-rich families were: Fabaceae sensu lato (including Mimosaceae and Caesalpiniaceae), Lauraceae and Sapotaceae; the most species-rich genera, were Pouteria, Inga and Protium. The vertical space was partitioned among species: 166 species were found only in the 5–10 dbh cm class and were mostly sub-canopy treelets, and 307 species with dbh 10 cm were mostly large canopy trees.     

<Emphasis Type="Italic">Berlinia korupensis</Emphasis> (Leguminosae <Emphasis Type="Italic">–</Emphasis> Caesalpinioideae), a new tree species from Cameroon

Summary  The tree species Berlinia korupensis Mackinder & Burgt is described as new. The species is endemic to the southern part of Korup National Park in Cameroon. Seventeen trees have been found so far, the largest being 42 m high and having a trunk diam. of 88 cm. The new species is assessed as Critically Endangered (CR D) under the criteria of IUCN. Two distribution maps are included; one map indicating the single locality in Cameroon near the Nigerian border where the new species was found and another map of the permanent plot where 14 of the 17 trees were recorded. A line drawing is also included, along with colour photographs of the flowers and the trunk.

Woody Species Alpha‐diversity and Species Abundance Distributions in an African Semi‐deciduous Tropical Rain Forest

Understanding plant species diversity patterns and distributions is critical for conserving and sustainably managing tropical rain forests of high conservation value. We analyzed the alpha‐diversity, species abundance distributions, and relative ecological importance of woody species in the Budongo Forest, a remnant forest of the Albertine Rift in Uganda. In 32 0.5‐ha plots, we recorded 269 species in 171 genera and 51 families with stems of ≥2.0 cm in diameter at breast height (dbh). There were 53 more species with stems of ≥2.0 cm dbh than with stems of ≥10 cm dbh, of which 33 were treelets and 20 were multi‐stemmed shrubs. For both minimum stem diameter cut‐offs (i.e., ≥2 cm dbh vs. ≥10 cm dbh), the Fabaceae, Euphorbiaceae, Ulmaceae, and Meliaceae families and the species Cynometra alexandri, Lasiodiscus mildbraedii, and Celtis mildbraedii had the highest relative ecological importance. The relative ecological importance of some species and families changed greatly with the minimum stem diameter measured. Alpha‐diversity, species richness, and species abundance distributions varied across historical management practice types, forest community types, and as a function of minimum stem diameter. Species richness and Shannon–Weiner diversity index were greater for species with stems of ≥2.0 cm dbh than of ≥10 cm dbh. The decrease in species evenness with an increasing number of plots was accompanied by an increase in species richness for trees of both minimum diameters. This forest is characterized by a small number of abundant species and a relatively large proportion of infrequent species, many of which are sparsely distributed and with restricted habitats. We recommend lowering the minimum stem diameter measured for woody species diversity studies in tropical forests from 10 cm dbh to 2 cm dbh to include a larger proportion of the species pool.     

Liana cover in the canopies of rainforest trees is not predicted by local ground‐based measures

Lianas (woody climbers) are structural parasites of trees that compete with them for light and below‐ground resources. Most studies of liana–tree interactions are based on ground‐level observations of liana stem density and size, with these assessments generally assumed to reflect the amount of liana canopy cover and overall burden to the tree. We tested this assumption in a 1‐ha plot of lowland rainforest in tropical Australia. We recorded 1072 liana stems (≥1 cm diameter at breast height {dbh}) ha^?1 across all trees (≥10 cm dbh) on the plot and selected 58 trees for detailed study. We estimated liana canopy cover on selected trees that hosted 0–15 liana individuals, using a 47‐m‐tall canopy crane. Notably, we found no significant correlations between liana canopy cover and three commonly used ground‐based measurements of liana abundance as follows: liana stem counts per tree, liana above‐ground biomass per tree and liana basal area per tree. We also explored the role of tree size and liana infestation and found that larger trees (≥20 cm dbh) were more likely to support lianas and to host more liana stems than smaller trees (≤20 cm dbh). This pattern of liana stem density, however, did not correlate with greater liana coverage in the canopy. Tree family was also found to have a significant effect on likelihood of hosting lianas, with trees in some families 3–4 times more likely to host a liana than other families. We suggest that local ground‐based measures of liana–tree infestation may not accurately reflect liana canopy cover for individual trees because they were frequently observed spreading through neighbouring trees at our site. We believe that future liana research will benefit from new technologies such as high‐quality aerial photography taken from drones when the aim is to detect the relative burden of lianas on individual trees.     

Revised treatment of <Emphasis Type="Italic">Memecylon</Emphasis> sect. <Emphasis Type="Italic">Afzeliana</Emphasis> (<Emphasis Type="Italic">Melastomataceae: Olisbeoideae</Emphasis>), including three new species from Cameroon

Summary  Seven new names at species rank are proposed in Memecylon sect. Afzeliana Jacq.-Fél., a group of forest shrubs and small trees confined to Guineo-Congolian Africa. The group is centred in Cameroon, where 17 of the 20 species occur. A new flower type, the “star-flower” in Memecylon is revealed, and its taxonomic and ecological importance discussed. Three new, locally endemic species from the South West Province of Cameroon are described, mapped and illustrated: M. kupeanum R. D. Stone, Ghogue & Cheek, M. bakossiense R. D. Stone, Ghogue & Cheek, and M. rheophyticum R. D. Stone, Ghogue & Cheek. Two new names, M. accedens R. D. Stone, Ghogue & Cheek and M. hyleastrum R. D. Stone & Ghogue and one new combination, M. mamfeanum (Jacq.-Fél.) R. D. Stone, Ghogue & Cheek are provided at species level for three taxa originally proposed as varieties of M. afzelii G. Don. The taxon M. arcuatomarginatum var. simulans Jacq.-Fél. is also elevated to species status, as M. simulans (Jacq.-Fél.) R. D. Stone & Ghogue. Conservation assessments are provided for all the newly named taxa. A key is provided to the species of Memecylon sect. Afzeliana.     

Selection of mature and old stands by Corsican Nuthatch Sitta whiteheadi in harvested forests

In harvested forests, the bird community is largely determined by stand structure, which itself is determined by forestry practices. This study aimed to identify habitat variables determining the presence of Corsican Nuthatch Sitta whiteheadi – a threatened island endemic – in harvested Corsican Pine Pinus nigra laricio woods, with the aim of mitigating the impact of timber harvest on the bird. Comparison of occupied and unoccupied plots showed that this bird is found mostly in pure Corsican Pine stands, and is absent when more than 50% of trees are not this species. Nests were built in decaying pine snags between 20 and 100 cm diameter at breast height (dbh), but birds avoided stands with live pines < 70 cm dbh, and selected stands with pines > 80 cm dbh. Conservation of Corsican Nuthatch therefore depends on maintaining harvest rotations of more than 200 years, reducing the size of felling coupes in clear‐cutting systems or, preferably, practising selective cutting, maintaining a sufficient density of old trees and snags, and checking the encroachment of other tree species into Corsican Pine stands.     

Vegetation dynamics in the Bangladesh Sundarbans mangroves: a review of forest inventories

The Sundarbans, the largest contiguous mangrove forest in the world, covers 6,017 km² of the coastal zone of Bangladesh. Heritiera fomes Buch.-Ham., Excoecaria agallocha L. and Ceriops decandra (Griff.) Ding Hou jointly cover 95% of the forest area. In this study, the results of four forest inventories have been analyzed to understand observed vegetation dynamics of the Sundarbans from 1926 to 1997. The diversity of forest types has been gradually reduced over time, but H. fomes and E. agallocha have maintained their dominance over large portions of the forest. H. fomes is spread over 67% of the vegetated area of the forest, concentrated mostly in the northeastern area, and constitutes 75% of the density of trees with >15 cm dbh. The distribution and stem density of H. fomes show negative relationships with that of E. agallocha and C. decandra. In terms of coverage, E. agallocha is the most common species, spread over 74% of the vegetated area of the forest, and constitutes 39% of the density of trees with >2.5 cm dbh. On a longer timeframe (1926–1997), the dominance (coverage and density of larger diameter trees) of H. fomes as well as that of E. agallocha is declining. Even on parameters such as density of trees with >15 cm dbh, the dominance of E. agallocha is declining at a much greater rate than H. fomes. This observation contradicts the successional schemes proposed by different authors. This might indicate that theorizing successional schemes based on short-term observations on vegetation dynamics is not sufficient. The effect of human interference, changes in hydroedaphic condition and species interaction should be taken into consideration during explaining observed vegetation dynamics. Moreover, the need to understand vegetation trajectories at the micro-scale should be emphasized.     

Rhabdias rhampholeonis n. sp. and Rhabdias mariauxi n. sp. (Nematoda, Rhabdiasoidea), first lung worms from leaf chameleons: Description, molecular evidence and notes on biology

Rhabdias rhampholeonis n. sp. from Rhampholeon (Rh.) spectrum, Cameroon, and Rhabdias mariauxi n. sp. from Rieppeleon brevicaudatus, Tanzania, are the first lung worms from leaf chameleons. The new species are similar to the majority of species parasitic in chamaeleonids by having a long (≥10 mm) and thick body (≥500 µm), long oesophagus (≥800 µm), wide buccal capsule (≥40 µm) and low buccal ratio (<0.5). They most closely resemble Rhabdias chamaeleonis and Rhabdias cristati parasitic in Trioceros spp. from East Africa and Cameroon, respectively. Main distinctive characters are a buccal capsule composed of two segments and the head shape. The dorso-ventrally flattened buccal capsule of R. mariauxi n. sp. is unique in Rhabdias parasitising Chamaeleonidae. Sequences of the 12S rDNA and mitochondrial cytochrome c oxidase subunit 1 (coxI) genes were obtained and compared to those of Rhabdias okuensis, the only sequences published for chamaeleonid lung worms. The smallest nucleotide interspecific distances were found between R. mariauxi n. sp. and the former species of Trioceros from Cameroon. Hermaphroditism in females in the lungs, and R. mariauxi n. sp. free-living stages are like in other species from Chamaeleonidae, but the number of infective larvae produced per free-living female (one or two) was not fixed.     

Short‐term Dynamics and the Effects of Biotic and Abiotic Factors on Plant Physiognomic Groups in a Hurricane‐impacted Lower Montane Tropical Forest

We assessed the short‐term effects of biotic (density, plant size) and abiotic factors (light), on the dynamics of physiognomically different plant groups (palms, tree ferns, lianas, and trees) in a hurricane‐impacted tropical wet montane forest, John Crow Mountains, Jamaica. All plants ≥2 cm (dbh) found within 45, 25 × 25 m permanent sample plots (2.8125 ha), established according to a randomized block design along an elevation gradient, were tagged and measured (dbh) in 2006 and re‐assessed in 2012 after Hurricane Dean (2007). Hemispheric light was measured in 2007 and 2008. Tree and liana size class distributions changed due to high mortality in the smallest size classes and their densities declined; however, palm and tree fern density remained unchanged. The dynamics of trees were only related to tree fern and liana dynamics (e.g., tree mortality was negatively related to liana recruitment etc.). Although pre‐ and posthurricane light was related to palm density and the density of the other plant groups, respectively, there were no significant changes in light. Tree survivorship increased with increasing dbh while posthurricane light and overall density influenced the growth and survivorship of tree species. Species importance value did not change, suggesting that direct regeneration may be the model of forest recovery following this small‐scale disturbance. Over the short term, tree species showed life history trade‐offs that aid species coexistence after this moderate/low disturbance event. Our study highlights that hurricanes with low impacts can have differential short‐ and possibly long‐term effects on different plant groups.     

<Emphasis Type="Italic">Psychotria kupensis</Emphasis> (<Emphasis Type="Italic">Rubiaceae</Emphasis>) a new dwarf,litter-gathering species from western Cameroon

Summary   Psychotria kupensis Cheek is described as a new species in Psychotria sect. Confertiflorae Hiern. Attention is drawn to its monopodial, dwarf, litter-gathering and adventitious root-forming habit and to its anomalous stipules. The species appears to be endemic to the submontane evergeen forest of Mt Kupe in Cameroon. Its conservation status is assessed.     

Spatial segregation of pines and oaks under different fire regimes in the Sierra Madre Occidental

Surface fire can modify spatial patterns and self-thinning in pine-oak ecosystems. Spatial pattern analyses were used to compare pattern development and interspecific spatial interactions in trees and seedlings in five Madrean pine-oak stands with different recent fire histories. Interspecific and intraspecific patterns were compared in small (< 15 cm dbh) and large (< 15 cm dbh) diameter classes of the pines (Pinus durangensis, P. teocote, and P. leiophylla) and oaks (Quercus sideroxylla, Q. crassifolia, and Q. laeta) that collectively dominated the five stands. Numbers of juvenile trees in 2.5 × 2.5 m subplots were correlated with cumulative distances to adult trees. Small pine and oak trees were intraspecifically clustered at all scales, irrespective of fire regime. Large pines were strongly clustered only in stands with longer fire-free intervals, and patterns of large versus small pine trees were regular or random in frequent fire stands. These patterns were consistent with fire-induced mortality of maturing trees under frequent fire. Large and small pines were segregated from small oaks at short and long distances in one stand with a 32-year fire-free interval, implying that two or more dynamic factors had produced regular patterns at different scales. Such regular spatial patterns at short distances were not seen in other stands. Therefore, there was little evidence for direct competition between oaks and pines. The results reported here are consistent with studies from other pine-oak ecosystems showing that different fire regime and site factors interact to influence stand development processes and relative dominance of pines and oaks. In some stands, the continued absence of fire could foster increasing tree densities and an intensification of local neighborhood effects, producing segregation of pine and oak species at longer distances. This revised version was published online in August 2006 with corrections to the Cover Date.     

Occurrence of the marbled rose-chafer (Protaetia lugubris Herbst, Coleoptera, Cetoniidae) in rural avenues in northern poland

The occurrence of Protaetia lugubris, an endangered species developing in hollow trees, was studied in a network of rural avenues in northern Poland. We detected 1002 trees from nine species with hollows suitable for beetle development (25% of all trees inspected). Among them, 74 trees (7.4%) from seven species were occupied by P. lugubris. The distribution of P. lugubris was random with respect to tree species identity. The beetle preferred trees above 200 cm in circumference with a tendency towards higher occupancies of the bigger trees having circumferences above 300 cm. P. lugubris did not show any significant preferences according to hollow entrance area, exposition and road surface type. Our results indicate that P. lugubris is a generalist species colonizing all suitable hollows. Its occurrence indicates suitable conditions for many other species associated with tree cavities and decaying wood.     

Variation of heartwood and sapwood in 18-year-old Eucalyptus globulus trees grown with different spacings

Heartwood and sapwood development was studied in 18-year-old Eucalyptus globulus trees from pulpwood plantations with different spacings (3 × 2, 3 × 3, 4 × 3, 4 × 4 and 4 × 5 m), on cross-sectional discs taken at breast height. The trees possessed a large proportion of heartwood, on average 60% of the wood cross-sectional surface. Spacing was a statistically significant source of variation of heartwood area, which ranged between 99 and 206 cm² for the closer (3 × 2) and wider (4 × 5) spacings, respectively. There was a positive and high statistical significant correlation between heartwood diameter and tree diameter (heartwood diameter = −0.272 + 0.616 dbh; r ² = 0.77; P < 0.001), and larger trees contained more heartwood regardless of spacing. Heartwood proportion in cross-section remained practically constant between spacings but increased with tree diameter class: 55.1, 62.2, 65.0 and 69.5% for diameter at breast height classes <15, 15–20, 20–25 and >25 cm, respectively. The sapwood width did not depend on tree diameter growth and remained practically constant at an average of 18 mm (range 15–21 mm), but sapwood area showed a good linear regression with tree diameter. Therefore, tree growth enhancement factors, such as wide spacings, will induce formation of larger heartwoods that can negatively impact raw-material quality for pulping. The increase in heartwood in relation with tree dimensions should therefore be taken into account when designing forest management guidelines.     

Four new submontane species of <Emphasis Type="Italic">Psychotria</Emphasis> (<Emphasis Type="Italic">Rubiaceae</Emphasis>) with bacterial nodules from Western Cameroon

Summary  Four new Psychotria species with conspicuous bacterial nodules in their leaf-blades, P. njumei Cheek, P. ngollengollei Cheek, P. darwiniana Cheek and P. babatwoensis Cheek are described, mapped and illustrated from the submontane forests of the Cameroon Highlands. Their taxonomic and conservation status are assessed.     

Complex spatial structure in a population of <Emphasis Type="Italic">Didymopanax pittieri</Emphasis>, a tree of wind-exposed lower montane rain forest

Didymopanax pittieri is a common shade-intolerant tree colonizing treefall gaps in the elfin forests on windswept ridgecrests in the lower montane rain forests of the Cordillera de Tilarán, Costa Rica. All D. pittieri taller than >0.5 m in a 5.2-ha elfin forested portion of a gridded study watershed in the Monteverde Cloud Forest Preserve were located, mapped, and measured. This local population of D. pittieri is spatially inhomogeneous, in that density increases with increasing wind exposure; D. pittieri are more abundant near ridge crests than lower on windward slopes. The important and ubiquitous phenomenon of spatial inhomogeneity in population density is addressed and corrected for in spatial analyses by the application of the inhomogeneous version of Ripley’s K. The spatial patterns of four size classes of D. pittieri (<5 cm dbh, 5–10 cm dbh, 10–20 cm dbh, and >20 cm dbh) were investigated. Within the large-scale trend in density driven by wind exposure, D. pittieri saplings are clumped at the scale of treefall gaps and at the scale of patches of aggregated gaps. D. pittieri 5–10 cm dbh are randomly distributed, apparently due to competitive thinning of sapling clumps during the early stages of gap-phase regeneration. D. pittieri larger than 10 cm dbh are overdispersed at a scale larger than that of patches of gaps. Natural disturbance can influence the distribution of shade intolerant tree populations at several different spatial scales, and can have discordant effects at different life history stages.     

Diameter Growth of Juvenile Trees after Gap Formation in a Bolivian Rain Forest: Responses are Strongly Species‐specific and Size‐dependent

We evaluated growth responses to gap formation for juvenile individuals of three canopy rain forest species: Peltogyne cf. heterophylla, Clarisia racemosa and Cedrelinga catenaeformis. Gaps were formed during selective logging operations 7 yr before sampling in a Bolivian rain forest. We collected wood samples for tree‐ring analyses at different distances to the stump (<10, 10–40 and >40 m) and from trees with different diameters (5–30 cm diameter at breast height [dbh]). Tree‐rings width was measured in at least two radii and converted to average diameter growth. Changes in 7‐yr median diameter growth before and after selective logging were analyzed. Diameter growth rates significantly increased by 0.7–0.8 mm/yr after gap formation for P. heterophylla and C. catenaeformis, but not for C. racemosa. We applied a multiple regression analysis to explain variation in growth responses of P. heterophylla and C. catenaeformis by distance to logging gap and tree size. For P. heterophylla we found that growth increase occurring close to logging gaps was strongest for large juvenile trees (20–25 cm dbh) and almost absent in small juveniles. For C. catenaeformis, variation in growth responses was not related to tree size or distance to gaps. Our results show that growth responses to gap formation strongly differ across species and tree sizes. This finding calls for caution in the interpretation of growth releases in tree‐ring series, as gap formation does not necessarily invoke growth responses and if such growth responses occur, their strength is species‐ and size specific.     

Protecting a single endangered species and meeting multiple conservation goals: an approach with Guaiacum sanctum in Yucatan Peninsula,Mexico

Aim New protected areas should consider safeguarding high conservation value sites based on multiple criteria and not just the presence of a single endangered or charismatic species. However, the extent to which complementary criteria coincide is usually unknown. We use the case of Guaiacum sanctum (Zygopyllaceae), an endangered timber tree species, to explore whether the protection of forests where this species is most abundant would meet other complementary conservation goals, such as capturing regional plant biodiversity, protecting other threatened/endemic species or safeguarding ecosystem services. Location Yucatan Peninsula, southern Mexico. Methods We conducted an analysis of the structure, composition and diversity of tree communities (including stems ≥5 cm dbh) at eight G. sanctum forest sites. We identified endemic and threatened tree species and quantified above‐ground tree biomass and carbon storage in these G. sanctum forests. Results Guaiacum sanctum forests contain 35–59 tree species on plots as small as 1000 m². The species composition of tree communities changed rapidly (high β‐diversity) across soil boundaries and rainfall regimes. Twenty‐one endemic and eight threatened tree species were recorded in our inventories. Individuals of G. sanctum represented up to 55% of the above‐ground carbon for trees ≥5 cm dbh. The high basal area of G. sanctum forests plus the high wood density, abundance, large size and longevity (more than 500 years) of G. sanctum and other tree species enhance the potential importance of these forests for carbon storage. Main conclusions A conservation strategy focused on protecting important populations of G. sanctum in the Yucatan Peninsula would have significant co‐benefits for conservation of regional tree species biodiversity and provision of critical ecosystem services. Our study illustrates a multiple criteria approach useful for the selection of areas with high conservation value on the basis of endemic, threatened species, species richness and ecosystem services.     

Endophytic fungi of teak leaves Tectona grandis L. and rain tree leaves Samanea saman Merr.

Summary In order to study the foliar endophytes from teak (Tectona grandis L.) and rain tree (Samanea saman Merr.) growing in the campus of Chulalongkorn University, healthy leaves were collected at two-monthly intervals during January to December. The number of genera and species, together with their colonization frequency (CF%) in mature teak and rain tree leaves were greater than those in the young leaves. More endophytic isolates in the leaves of both trees were recovered during the rainy season. The fungal genera found in both young and mature teak leaves were Alternaria, Colletotrichum, Nigrospora, Phomopsis and mycelia sterilia. Phomopsis was the dominant genus in both young (newly emerged) and mature leaves. Fusarium, Penicillium, Schizophyllum commune and members of the Xylariaceae were found only in mature leaves. For the rain tree leaves, species of Phomopsis and mycelia sterilia were found in both young newly emerged and mature leaves. Colletotrichum and Penicillium were found only in mature leaves, whereas Nigrospora was found only in young newly emerged leaves. In this study, Phomopsis was the dominant genus in the leaves of both tree species. A total of 37 isolates of endophytic fungi isolated from teak and rain tree leaves were tested for the production of antimicrobial activities. Out of these, 18 isolates could produce inhibitory substances effective against Bacillus subtilis, Staphylococcus aureus and Escherichia coli and 3 isolates inhibited growth of Candida albicans in vitro.     

Variable rainfall has a greater effect than fire on the demography of the dominant tree in a semi‐arid Eucalyptus savanna

Rainfall, fire and competition are emphasized as determinants of the density and basal area of woody vegetation in savanna. The semi‐arid savannas of Australia have substantial multi‐year rainfall deficits and insufficient grass fuel to carry annual fire in contrast to the mesic savannas in more northern regions. This study investigates the influence of rainfall deficit and excess, fire and woody competition on the population dynamics of a dominant tree in a semi‐arid savanna. All individuals of Eucalyptus melanophloia were mapped and monitored in three, 1‐ha plots over an 8.5 year period encompassing wet and dry periods. The plots were unburnt, burnt once and burnt twice. A competition index incorporating the size and distance of neighbours to target individuals was determined. Supplementary studies examined seedling recruitment and the transition of juvenile trees into the sapling layer. Mortality of burnt seedlings was related to lignotuber area but the majority of seedlings are fire resistant within 12 months of germination. Most of the juveniles (≤1 cm dbh) of E. melanophloia either died in the dry period or persisted as juveniles throughout 8.5 years of monitoring. Mortality of juveniles was positively related to woody competition and was higher in the dry period than the wet period. The transition of juveniles to a larger size class occurred at extremely low rates, and a subsidiary study along a clearing boundary suggests release from woody competition allows transition into the sapling layer. From three fires the highest proportion of saplings (1–10 cm dbh) reduced to juveniles was only 5.6% suggesting rates of ‘top‐kill’ of E. melanophloia as a result of fire are relatively low. Girth growth was enhanced in wet years, particularly for larger trees (>10 cm dbh), but all trees regardless of size or woody competition levels are vulnerable to drought‐induced mortality. Overall the results suggest that variations in rainfall, especially drought‐induced mortality, have a much stronger influence on the tree demographics of E. melanophloia in a semi‐arid savanna of north‐eastern Australia than fire.     

Tree species diversity and forest structure in relation to microtopography in a tropical freshwater swamp forest in French Guiana

Diversity of tree association and forest structure were analysed in relation to microtopography and flooding intensity in a tropical freshwater swamp forest in the Sinnamary river basin, French Guiana. A 530-m-long vegetation transect was established through a hummock-hollow terrain. Nine 10 m× 50 m sample plots, perpendicular to the main transect, were located so that each was as microtopographically uniform as possible. Trees with dbh (diameter at 1.3 m) 10 cm were censused in all plots and trees with 2 cm dbh < 10 cm in three plots. Sixty tree species belonging to 39 genera and 30 families were recorded. The study area was divided into low and high sites according to microtopography and flooding intensity. According to the Czekanowski similarity matrix, the tree association in low, most frequently flooded, sites differed from that in the high sites under intermediate or low flooding intensity. The low sites had higher stand density and lower species richness than the high sites. Trees with dbh 10 cm in low sites were small and stand basal area (SBA) was about the same in low (69.6 m² ha^–1) and high (64.3 m² ha^–1) sites. The low areas were dominated by Pterocarpus officinalis (38% of stems with dbh 10 cm and 36% of SBA) and Malouetia tamaquarina (26 and 15%). Diospyros guianensis (13.4% of stems with dbh 10 cm and 6.1% of SBA), a Caraipa sp. (14.0 and 7.9%), Lecythis corrugata (6.6 and 3.5%) and emergent Caryocar microcarpum (0.9 and 13.9%) were abundant in high sites. Nodulated legume trees, P. officinalis, Hydrochorea corymbosa and Inga disticha, comprised 44% of stems in the low sites. The abundant nodulation suggests that symbiotic dinitrogen fixation may be an adaptation to N-depleted waterlogged soils. Other adaptive responses were litter accumulation between the buttresses of P. officinalis, which formed hummocks above surface water, and clonal growth habit of M. tamaquarina, which resulted in formation of monospecific groves in low sites.