Area Of Semideciduous Forest Research Articles

Extension of the geographical distribution of two anuran species for Rio Grande do Sul State, Brazil, with comments on natural history

We record for the first time Crossodactylus schmidti (Anura: Hylodidae) and Proceratophrys avelinoi (Anura: Cycloramphidae) from Rio Grande do Sul State, Brazil, based on individuals captured in an area of Mesophytic Semideciduous Forest, the Parque Estadual do Turvo, located in the northwest region of the state. These records extend the geographical range for both species in about 60 km from the nearest known locality, the Municipality of San Vicente, Misiones, Argentina. We provide a characterization of the calling site used by males of Crossodactylus schmidti, and we also determined the niche breadth of P. avelinoi regarding to the use of water bodies.

Ocorrência e caracterização de galhas entomógenas em uma área de floresta estacional semidecídua em Goiânia, Goiás, Brasil

Em uma área de floresta estacional semidecídua do Campus Samambaia da Universidade Federal de Goiás, Goiânia, Goiás foram coletados 34 tipos de galhas entomógenas, durante o período de 2005-2007. As galhas ocorreram em 20 espécies de plantas de 12 famílias, sendo Leguminosae (9), Styracaceae (6) e Ulmaceae (4) as que apresentaram o maior número de morfotipos de galhas. Galhas foliares e caulinares foram as mais comuns. Em relação à morfologia foram coletadas galhas globóides, discóides, elipsóides, cilíndricas e coniformes. A coloração variou entre o verde, amarela, marrom e vermelha. As galhas estavam agrupadas ou isoladas e eram glabras ou pilosas. Os Cecidomyiidae (Diptera) foram os principais cecidógenos e os parasitóides encontrados pertenciam às famílias Eulophidae, Torymidae, Pteromalidae, Encyrtidae (Hymenoptera). Este é o primeiro relato de galhas em quatro espécies de plantas hospedeiras para a região Neotropical.

Dinâmica da comunidade arbórea de uma floresta semidecidual em Uberlândia, MG, Brasil

O objetivo do trabalho foi de verificar as mudanças ocorridas na comunidade arbórea em um intervalo de 14 anos. O estudo foi realizado em uma área de floresta semidecidual utilizando 50 parcelas de 10 m×10 m, onde foram amostradas todas as árvores com DAP > 3,18 cm em 1990 e em 2004. No primero inventário encontrou-se 95 espécies, 818 indivíduos e área basal de 14,43 m² . No segundo levantamento amostrou-se 95 espécies, 866 indivíduos e área basal de 13,42 m² . No período de 14 anos, 10 espécies desapareceram e o mesmo número ingressou na comunidade. O índice de diversidade de Shannon, na primeira amostragem foi de 4,05 e na segunda 3,72. A taxa média anual de mortalidade foi de 4,1% e a de recrutamento 4,5%. A meia-vida, o tempo de duplicação, a estabilidade e a reposição, para o número de indivíduos foi 16,92, 15,04, 1,86 e 15,98 anos, respectivamente. O fragmento florestal manteve a riqueza de espécies, porém houve mudanças no índice de diversidade, número de indivíduos e área basal podendo possivelmente ser o resultado do processo de fragmentação e do isolamento dessa comunidade.

Anatomia comparada do lenho de Piptadenia gonoacantha (Mart.) J.F.Macbr. em dois tipos de vegetação

A anatomia ecológica tem como objetivo correlacionar as estruturas morfológicas e anatômicas das plantas com dados climáticos, geográficos e do solo. Nesse contexto, avaliaram-se as diferenças qualitativas e quantitativas no lenho de árvores de pau-jacaré -Piptadenia gonoacantha procedentes do Parque Estadual Cantareira (PEC) e da Estação Ecológica de Caetetus (EEC), áreas respectivamente de Floresta ombrófila densa e Floresta estacional semidecidual. Os parâmetros anatômicos foram analisados seguindo técnicas usuais em anatomia de madeira e os dados avaliados por meio de análise de variância (ANOVA) e teste de comparações múltiplas. Os resultados revelaram diferenças estatisticamente significativas, sendo que indivíduos do PEC apresentaram maior frequência de vasos, raios mais baixos, largos e mais frequentes, além de fibras com maior diâmetro. Os indivíduos da EEC mostraram maior índice de vulnerabilidade e vasos com pontoações menores. As diferenças encontradas no lenho dos espécimes dos dois locais podem ser decorrentes de variações de temperatura, pluviosidade, altitude, latitude e longitude, embora um número maior de indivíduos deva ser analisado para se estabelecer possíveis tendências ecológicas.

Térmitas construtores de ninhos conspícuos em duas áreas de Mata Atlântica com diferentes níveis de perturbação antrópica

The effects of selective logging on termite assemblages that build conspicuous nests were studied in two areas of semideciduous Atlantic Forest, located in the Reserva Biológica Guaribas, Northeastern Brazil. The two study areas went through selective logging until 1985 (A17) and 1972 (A30). In 2002, termite nests were studied in two plots of 1 ha (100 x 100 m), being one plot in each area. The nests were placed in each plot and the species were categorized in feeding groups. The structure of the study assemblages was different between the two areas. Diversity and richness of builder species were greater in the A30 area. Species that consume humus were more sensitive to selective logging. Nest abundance of humus feeding species was significantly higher in the A30 area, whereas nests of wood feeding species were significantly more abundant in the area A17. Nest ratio between humus and wood feeding species was 1:3 in the A30 area and 1:12 in the A17 area. Nests with greater volume were observed in the area A30, whereas abundance of inactive nests was significantly higher in A17. The time for habitat resilience after the selective logging influenced patterns of assemblage structure of termites in similar ways as described in other studies in tropical forests.

INFLUENCE OF SOILS AND TOPOGRAPHIC GRADIENTS ON TREE SPECIES DISTRIBUTION IN A BRAZILIAN ATLANTIC TROPICAL SEMIDECIDUOUS FOREST

AbstractThis study investigated the effect of environmental variables such as soil class, soil water availability, topography and slope on spatial distribution patterns of tree species in a Brazilian Seasonal Semideciduous Forest area. Floristic and structural data for a tree community were obtained by sampling 100 plots 10 × 10 m in which every tree with trunk diameter (dbh) ⩾ 4.77 cm at 130 cm above ground level was sampled. The area under study showed a marked soil gradient, directly associated with the topography: flat hilltops with Al3+-rich Dystric Latosols give way to steep colluvial slopes with shallower and more Dystric Cambic Latosols without Al3+, changing over, at the bottom of the hollows, to Epieutrophic Cambisols richer in nutrients. The floristic-sociological parameters analysed for the soil habitats did not differ statistically from each other. The diversity and equability indices were 3.6 and 0.84, 3.48 and 0.85, 3.49 and 0.84 for the Dystric Latosol, Dystric Cambic Latosol and Epieutrophic Cambisol, respectively. The soil variables (related to the fertility and texture) and the soil water regime (drainage) were probably the principal factors determining the spatial distribution patterns of tree species in the forest.

Biodiversity and spatial distribution of vascular epiphytes in two biotopes of the Cameroonian semi-deciduous rain forest

The diversity and spatial distribution of vascular epiphytes were surveyed in two biotopes (dryland forest and swamp-inundated forest) of the semi-deciduous rain forest area in Cameroon. Eight sites in each biotope were selected, which included 530 individuals of phorophytes in dryland forest and 460 in swamp-inundated forest. A total of 148 epiphyte species were recorded, which showed that semi-deciduous rain forests represent a major source of African-epiphyte diversity. Dryland forest hosted 110 epiphyte species, while the swamp-inundated forest harboured 108. A total of 56 species were found only in the dryland forest and 60 were restricted to the swamp-inundated forest. At family level, Orchidaceae exhibited the highest-species richness within both biotopes. Pteridophytes were more abundant in the swamp-inundated forest. A TWINSPAN analysis of the floristic similarities separated the two investigated forest types very clearly. No significant difference existed between the two biotopes regarding vertical distribution of epiphytes within single trees. The swamp-inundated forests may serve as a refuge for many epiphytes that occur in the outer canopy of the dryland forests, both because they are inherently less vulnerable to timber extraction, and enjoy better protection by legislation.

A new species of Amblyseius Berlese (Acari: Phytoseiidae) from Brazil

Phytoseiid mites have received considerable world wide attention because of their potential as natural enemies of phytophagous mites (McMurtry, 1984). The Amblyseius obtusus group Chant is the largest species group in the genus Amblyseius. Chant & McMurtry (2004) divided the group into seven subgroups based on spermathecal morphology. The andersoni subgroup of Chant & McMurtry, 2004 is characterized by a spermatheca with the calyx dish-, cup-, bell-, or V-shaped, with the length/width ratio at the mid-point of the calyx < 3:1. A total of 24 species of the andersoni subgroup are known from the Neotropical region, 13 of these from Brazil (Moraes et al., 2004). A new species of this subgroup, Amblyseius paulofariensis sp. nov., is described and illustrated in this paper, from specimens collected in the semi-deciduous forest area of “Estação Ecológica de Paulo de Faria”, a protected natural area in the State of São Paulo, southeastern Brazil, on three species of Euphorbiaceae: Acalypha diversifolia Jacq., Actinostemon communis (Müll. Arg.) and Alchornea glandulosa Poepp. & Endl.. In the region where this mites was found, the climate is of the type Cwa-Aw of Köppen, with two distinct seasons: one wet, from October to March, and the other dry, from April to September. The annual mean temperature is 25°C, with a maximum mean of 30°C and a minimum mean of 20°C (Barcha & Arid, 1971; Arid & Barcha, 1973).

Taxocenose de anuros de uma mata semidecídua do interior do Estado de São Paulo e comparações com outras taxocenoses do estado, sudeste do Brasil

O presente estudo foi realizado em um fragmento de floresta semidecídua, Mata São José (MSJ), e em áreas adjacentes ao fragmento localizado no município de Rio Claro, Estado de São Paulo, Brasil. Informações sobre a composição e distribuição espacial e temporal de espécies de anuros foram coletadas entre agosto de 2002 e julho de 2003. Foram registradas 24 espécies, sendo que a maioria foi observada em atividade de vocalização e reprodução nas áreas abertas adjacentes ao fragmento. Apenas três espécies, Hypsiboas lundii, H. prasinus e Proceratophrys boiei foram observadas utilizando ambientes no interior do fragmento para a reprodução e apenas H. prasinus foi registrada também em ambientes adjacentes ao fragmento. A maioria das espécies foi registrada durante a estação chuvosa da região e os ambientes temporários foram os mais utilizados para reprodução. A composição de espécies da MSJ foi comparada com a de outras 10 localidades com as seguintes fisionomias vegetais e status de conservação: floresta tropical preservada, ecótono de floresta ombrófila e floresta estacional semidecídua pouco preservada, Cerrado preservado e áreas antropizadas principalmente pela implantação de agricultura e pastagem. A composição de espécies da MSJ e da área de floresta estacional semidecídua foram mais similares entre si e com áreas perturbadas e área de Cerrado que quando comparadas a composição de espécies da área de floresta tropical preservada. Não houve correlação entre as distâncias e a similaridade na composição da anurofauna das localidades comparadas. Proceratophrys boiei e H. lundii aparentemente são as espécies mais afetadas pelo processo de fragmentação ambiental no Estado de São Paulo, provavelmente devido a sua ecologia e dependência de ambientes mais florestados.

Trap-nesting bees (Hymenoptera, Apoidea) in areas of dry semideciduous forest and caatinga, Bahia, Brazil

In this study were examined the species richness and seasonal abundance of cavity-nesting bees in areas of dry semi-deciduous forest and caatinga in the State of Bahia, Brazil. Sampling was done employing two types of trap-nests: bamboo canes and tubes made of black cardboard with dimensions of either 58 x 6 mm or 105 x 8 mm. The traps were inspected once a month. One hundred and forty-six nests of 11 bee species were collected in the forest, and 121 nests of seven species were collected in the caatinga. Five species of cleptoparasitic bees were also reared from these nests. The highest nesting frequencies occurred in the wet season in both areas. Nests parasitism was important only for Centris tarsata Smith, 1874, and was higher at the caatinga site than in the forest. The mortality of pre-emergent adults was high, especially in C. tarsata,Tetrapedia diversipes Klug, 1810 and Euglossa cordata (Linnaeus, 1758). Information on the number of cells per nest, the size, shape, and arrangement of brood cells in the nests, as well as the number of adults produced and the number of generations per year are also presented. Species richness, temporal patterns of nesting, and percentage of parasitism were compared with other habitats.

Reproductive condition of Akodon montensis Thomas and Bolomys lasiurus (Lund) (Rodentia, Muridae) based on histological and histometric analyses of testes and external characteristics of gonads

The reproductive activity of two species of wild rodents was studied in the Serra do Rola-Moca State Park (PERM), in the state of Minas Gerais, Brazil. From October 1998 to October 1999 specimens of Akodon montensis (Thomas 1913) were captured in an area of seasonal semi-deciduous forest, while specimens of Bolomys lasiurus (Lund 1840) were captured in a cerrado area (a savannah-like grassland). The determination of the reproductive condition was based on histological and histometric analyses of testes and external characteristics of gonads. The volume of the testes, diameter of the seminiferous tubules and depth of the seminiferous epithelium were measured. Akodon montensis showed a seasonal annual reproductive cycle divided into four stages (recrudescence, activity or proliferation, regression and rest) with the reproductive activity mainly occurring during the rainy season. In contrast, B. lasiurus presented reproductive activity during almost the whole year. For both species the volume of the testes was an effective indicator of their reproductive condition. We suggest that the histological and histometric analysis of the gonads of males, together with the observations of external characteristics of gonads of males and females, may assist in identifying the reproductive condition of these animals.

Tree population and community dynamics in a Brazilian tropical semideciduous forest

Tree population and community dynamics in a Brazilian tropical semideciduous forest). The dynamics of the tree community and 30 tree populations were examined in an area of tropical semideciduous forest located on the margin of the Rio Grande, SE Brazil, based on surveys done in 1990 and 1997 in three 0.18 ha plots. The main purpose was to assess whether variations in dynamics were related to topography and the effects of a catastrophic flood in 1992. Rates of mortality and recruitment of trees and gain and loss of basal area in two topographic sites, lower (flooded) and upper (non-flooded), were obtained. Projected trajectories of mean and accelerated growth in diameter were obtained for each species. In both topographic sites, mortality rates surpassed recruitment rates, gain rates of basal area surpassed loss rates, and size distributions changed, with declining proportions of smaller trees. These overall changes were possibly related to increased underground water supply after the 1992 flood as well as to a c. 250-year-old process of primary succession on abandoned gold mines. Possible effects of the 1992 flood showed up in the higher proportions of dead trees in the flooded sites and faster growth rates in the flood-free sites. Species of different regeneration guilds showed particular trends with respect to their demographic changes and diameter growth patterns. Nevertheless, patterns of population dynamics differed between topographic sites for only two species.

Population dynamics, age structure and sex ratio of the bromeliad-dwelling jumping spider, Psecas chapoda (Salticidae)

In this study, the population fluctuations, phenology and sex ratio of the bromeliad-dwelling jumping spider Psecas chapoda were investigated in an area of semi-deciduous forest in south-eastern Brazil. Psecas chapoda occurred and reproduced on Bromelia balansae (Bromeliaceae) throughout the year. The number of egg sacs increased at the beginning of the rainy season (September to December), but the population size and phenology were stable over time and correlated weakly with rainfall and temperature. The principal factor affecting the dynamics of P. chapoda was the blooming of B. balansae, which expelled spiders because of the drastic change in plant architecture. Male spiders were more frequent than females during the juvenile phase, whereas females were more frequent than males during the subadult and adult phases, suggesting a sex ratio that favoured males. The biotic and abiotic factors that influence the population dynamics and sex-dependent vulnerability determination are discussed.

Nesting biology of Centris (Hemisiella) tarsata Smith (Hymenoptera, Apidae, Centridini)

Nests of Centris tarsata Smith, 1874 were obtained from trap-nests in areas of dry semi-deciduous forest (Baixa Grande) and caatinga (Ipirá), in the State of Bahia. Nesting occurred in bamboo canes and in tubes of black cardboard with 5.8 cm (= small tube) and 10.5 cm (= large tube) in length and 0.6 and 0.8 cm in diameter, respectively. In both areas C. tarsata nested during the wet season producing four generations in Baixa Grande and three generations in Ipirá. The immatures of one generation underwent diapause at both sites. The bees constructed their nests with a mixture of sand and oil. In general, the cells were elongated and arranged in linear series with its opening pointing towards the nest entrance. Completed nests had two to three cells in small tubes, one to seven cells in large tubes, and two to 13 cells in bamboo canes. The nest plug resembled an uncompleted cell and was externally covered with oil. The cells were provisioned with pollen, oil, and nectar. Nests were parasitized by Mesocheira bicolor (Fabricius, 1804) (Hymenoptera: Apidae) and other not identify bee species.

Variations in tree community composition and structure in a fragment of tropical semideciduous forest in southeastern Brazil related to different human disturbance histories

In an area of tropical seasonal semideciduous forest, the soil characteristics, floristic composition, physiognomic structure, and the distribution of three regeneration and three dispersal guilds were studied for four stands within the forest that had documented histories of varying degrees of human disturbance. The aim was to study forest regeneration in areas of preserved forest and secondary forest, with parts of both types of forest experiencing either ‘intensive’ or ‘occasional’ cattle trampling. The study was carried out in the Sebastião Aleixo da Silva Ecological Station, Bauru, São Paulo State, Brazil. Two stands were called ‘secondary’ because they corresponded to forest tracts that were felled and occupied by crops and pastures in the past and then abandoned to forest regeneration ca. 40 years before this study. The other two stands, called ‘preserved’, corresponded to areas of the fragment where the forest has been maintained with only minor human impacts. The arboreal component of the tree community (diameter at breast height or dbh≥5 cm) was sampled in 20 plots of 40 m×40 m, and the subarboreal component (diameter at the base of the stem or dbs<5 cm and height≥0.5 m) in subplots of 40 m×2 m. Physiognomic features, such as canopy height and density of climbing plants, were registered all over a 5 m×5 m gridline laid on the sample plots. Soil bulk samples were collected for chemical and textural analyses. Most detected differences contrasted the secondary to the preserved forest stands. The soils of the secondary stands showed higher proportions of sand and lower levels of mineral nutrients and organic matter than those of the preserved stands, probably due to higher losses by leaching and erosion. Compared to the secondary stands, the preserved ones had higher proportions of tall trees, higher mean canopy height, lower species diversity, higher abundance of autochorous and shade-tolerant climax species, and lower abundance of pioneer and light-demanding climax species. Despite the high proportion of species shared by the preserved and secondary stands (108 out of 139), they differed consistently in terms of density of the most abundant species. On the other hand, the secondary and preserved stands held similar values for tree density and basal area, suggesting that 40 years were enough to restore these features. Effects of cattle trampling on the vegetation were detected for the frequency of trees of anemochorous and zoochorous species, which were higher in the stands under occasional and intensive cattle trampling, respectively. The density of thin climbers was lower in the stands with intensive trampling.

A high resolution Holocene pollen record from Lago do Pires, SE Brazil: vegetation, climate and fire history

Lago do Pires (17° 57′ S, 42° 13′ W) is situated at 390 m a.s.l. in the foothills of the Serra do Espinhaco, 250 km from the Brazilian Atlantic coast. The original vegetation of the study area has been almost destroyed by pastoral activity. Relicts of a dense 20–30 m tall tropical semidciduous forest are present only on a few hill tops. The dry season of the Lago do Pires region lasts for 4 months and the annual precipitation is 1250 mm. A high resolution pollen record from a 16 m long sediment core, composed of 77 samples, subdivided in 7 zones and 4 subzones, allows a reconstruction of Holocene paleoenvironments. For the early Holocene (9720-8810 B.P.), the results indicate that the region surrounding the lake was dominated by a herb savanna (campo cerrado) withCuratella americana (cerrado tree) and high fire frequency. Species ofCecropia, Urticales and a few others, form small gallery forests along the water courses. This vegetation pattern is consistent with a long dry season (perhaps 6 months) and a low annual precipitation. Between 8810 and 7500 years B.P. gallery forests expanded in the valleys and suggest a period of higher rainfall with shortened dry season (perhaps 5 months). Fire was less frequent. Reduction of gallery forests followed (7500-5530 B.P.), probably related to a return of drier climatic conditions (5–6 months dry season, lower precipitation). Fires were more frequent. Between 5530 and 2780 years B.P. in the vallyes were forests and on the hills still an open cerrado. The dry season probably was about 5 months and the rainfall was higher than in the previous period. Later (2780-970 B.P.) the more open cerrado on the hills changed to more closed cerrado. A dense and closed semideciduous forest existed in the region only in the latest Holocene period (since 970 B.P.) under the current climatic conditions. The vegetation was no longer influenced by fire. A very strong human impact by deforestation and use of fire occurred in the last decades. Today cerrado vegetation is generally restricted to central Brazil and exists in several small isolated ‘Islands’ (Hueck, 1956) in the area of semideciduous forest in SE Brazil which were more widespread during the drier periods of the Holocene. The wettest period of Holocene occurs in the present millenium.

Differentiation of streamside and upland vegetation in an area of montane semideciduous forest in southeastern Brazil

Summary The differences in plant community structure and soil properties between streamside and upland topographical sites were analysed in an area of montane semideciduous forest on the margins of the Camargos Reservoir, southeastern Brazil. The studied forest patch lies at the headwaters of two narrow streams and is surrounded by montane grasslands. The plant community was surveyed by one 30 × 150 m and one 30 × 165 m transects, both made up of 15 × 15 m contiguous quadrats. The first transect extended along one of the streams while the other linked the two streams by traversing the interfluve. Soil samples were collected from all quadrats and their texture and chemical properties were analysed in the laboratory. The streamside soils were tropical Podzolic Soils, characterised by clay depletion of the top layer with its accumulation in the deeper horizons. The upland soils were Cambisols, a 'maturing' soil type with no clear zonation. A canonical correspondence analysis indicated that the species' abundance distribution was significantly correlated with the two topographical sites as well as with some soil properties. The most abundant species appeared to vary from fairly exclusive streamside or upland preferentials to broadly indifferent for the two habitats. A tentative ecological classification of the 69 most abundant species according to their preference for streamside or upland habitat and to their growth strategy in the forest dynamics, is presented. An overall analysis of this classification along with the differences in soil properties between the two topographic sites gives evidence that the forest probably expanded from the two valley bottoms towards the upland sector occupying sites that were previously covered with montane grasslands.

Comparison of the woody flora and soils of six areas of montane semideciduous forest in southern Minas Gerais, Brazil

Qualitative and quantitative descriptions of the woody flora and soil analyses are provided for six areas of montane semideciduous forest in the upper Rio Grande region, southern Minas Gerais, Brazil. Comparisons are made of the floristic composition of these six areas and 24 other forest areas of southeastern Brazil using ordination by detrended correspondence analysis (DCA) and hierarchical classifications, both agglomerative (upgma) and divisive (twinspan). The variation in community structure of five of the six forest areas was analysed using a two-way table yielded by twinspan. The floristic analyses indicated the strongest link between the forests of the upper Rio Grande region and other montane forest formations of southeastern Brazil as well as secondary links with the gallery forests that extend into the cerrado domain and the submontane semideciduous forests of the Rio Parana basin. Variations in community structure among the five forest areas were apparently associated mainly with riverside effects and soil fertility.Descrições qualitativas e quantitativas da flora lenhosa e análises de solos são apresentadas para seis áreas de floresta semidecídua montana na regiāo do alto rio Grande, sul de Minas Gerais, Brasil. Sāo feitas comparações florísticas das seis florestas e de outras 24 áreas de floresta do sudeste brasileiro usando ordenação por análise de correspondência (DCA) e classificações hierárquicas, tanto aglomerativa (upgma) como divisiva (twinspan). As variações em estrutura comunitária de cinco das seis florestas foram analisadas usando uma tabela bidirecional produzida por twinspan. As análises florísticas indicaram uma ligação mais forte entre as florestas do alto rio Grande e outras formações florestais montanas do sudeste do Brasil, bem como laços florísticos secundários com as florestas de galena que penetram o domínio dos cerrados e com as florestas semidecíduas submontanas do vale do rio Paraná. As variaç˜es em estrutura comunitária entre as cinco florestas mostraram-se aparentemente associadas principalmente com o efeito da margem dos rios e com a fertilidade dos solos.

Effect of flooding regime and understorey bamboos on the physiognomy and tree species composition of a tropical semideciduous forest in Southeastern Brazil

The interrelationship between river flooding regime, topography, soil properties and the distribution of tree and bamboo species was analysed in an area of tropical semideciduous forest on the margins of the Rio Grande, in Madre de Deus de Minas, Southeastern Brazil. A survey was carried out in a single forest plot (1.597 ha, 71 adjacent 225 m2 quadrats) located in the inner side of a river bend and extending from the point bar to the top of the slope. All trees (≥5 cm diameter at the base of the trunk) and bamboo culms were registered. Soil samples were collected and analysed for their properties and the river level was monitored during a two year period. In the point bar the forest was dominated by only two tree species, Salix humboldtiana and Inga affinis, that tended to occur in distinct areas. Differences in soil properties between these areas suggest variation in sedimentation dynamics. In the sloping part of the plot, a canonical correspondence analysis (CCA) indicated that the floristic composition was significantly correlated with three topographic sectors and their corresponding flood regimes. The Lower Slope corresponds to the sharp transition to the point bar forest, endures partial and annual floods and shows a very distinct flora that includes many light-demanding species. The Middle Slope is only occasionally reached by exceptional river floods and is characterised by a high density of the bamboo Merostachys neesii. The comparatively low density and basal area of trees, particularly for the smaller ones, provide evidence that the bamboos are problably interfering with the trees by restricting their recruitment. The Ridgetop lies entirely above the highest flooding level registered. The density of bamboos is lower and the understorey trees abundant.