Species Diversity In Tropical Forests Research Articles

Travelling waves due to negative plant–soil feedbacks in a model including tree life-stages

The emergence and maintenance of tree species diversity in tropical forests is commonly attributed to the Janzen–Connell (JC) hypothesis, which states that growth of seedlings is suppressed in the proximity of conspecific adult trees. As a result, a JC distribution due to a density-dependent negative feedback emerges in the form of a (transient) pattern where conspecific seedling density is highest at intermediate distances away from parent trees. Several studies suggest that the required density-dependent feedbacks behind this pattern could result from interactions between trees and soil-borne pathogens. However, negative plant–soil feedback may involve additional mechanisms, including the accumulation of autotoxic compounds generated through tree litter decomposition. An essential task therefore consists in constructing mathematical models incorporating both effects showing the ability to support the emergence of JC distributions.In this work, we develop and analyse a novel reaction–diffusion-ODE model, describing the interactions within tropical tree species across different life stages (seeds, seedlings, and adults) as driven by negative plant–soil feedback. In particular, we show that under strong negative plant–soil feedback travelling wave solutions exist, creating transient distributions of adult trees and seedlings that are in agreement with the Janzen–Connell hypothesis. Moreover, we show that these travelling wave solutions are pulled fronts and a robust feature as they occur over a broad parameter range. Finally, we calculate their linear spreading speed and show its (in)dependence on relevant nondimensional parameters.

UAV-based height measurement and height–diameter model integrating taxonomic effects: exploring vertical structure of aboveground biomass and species diversity in a Malaysian tropical forest

The complex stratification of tropical forests is a key feature that directly contributes to high aboveground biomass (AGB) and species diversity. This study aimed to explore the vertical patterns of AGB and tree species diversity in the tropical forest of Pasoh Forest Reserve, Malaysia. To achieve this goal, we used a combination of field surveys and drone technology to gather data on species diversity, tree height (H), and tree diameter at breast height (D). As all trees in the 6 ha plot were tagged and identified, we used the data to classify the taxonomy and calculate species diversity indices. We used unmanned aerial vehicle-based structure-from-motion photogrammetry to develop a Digital Canopy Height Model to accurately estimate H. The collected data and previous datasets were then used to develop Bayesian height–diameter (HD) models that incorporate taxonomic effects into conventional allometric and statistical models. The best models were selected based on their performance in cross-validation and then used to estimate AGB per tree and the total AGB in the plot. Results showed that taxonomic effects at the family and genus level improved the HD models and consequent AGB estimates. The AGB was the highest in the higher layers of the forest, and AGB was largely contributed by larger trees, especially specific families such as Dipterocarpaceae, Euphorbiaceae, and Fabaceae. In contrast, species diversity was the highest in the lower layers, whereas functional diversity was the highest in the middle layers. These contrasting patterns of AGB and species diversity indicate different roles of forest stratification and layer-specific mechanisms in maintaining species diversity. This study highlights the importance of considering taxonomic effects when estimating AGB and species diversity in tropical forests. These findings underscore the need for a more comprehensive understanding of the complex stratification of tropical forests and its impact on the forest ecosystem.

Some of the Mechanisms for Coexistence of Tree Species Diversity in Tropical Forests: A Review of Effects of Tree Density Dependence

Tree communities contribute to maintenance of species diversity in tropical forests. Coexistence of many tree species is not without competition. Therefore, coexistence of tree species and size diversities occur sequentially or simultaneously in tropical natural forests. Understanding coexistence and competition mechanisms of tree species requires knowledge of interactions within and between species. However, many conservation efforts and strategies failed due to inability to identify and maintain functional coexistence mechanisms among tree species in the forest. Also, most trees died because of pressure on their habitats and not because of limiting growth resources. Hence, species identity, minimum distance and size of the neighbouring trees which are responsible for coexistence of competing trees in most tropical forests have not been explicitly reviewed. Therefore, this review evaluated some of the density dependent mechanisms for coexistence of tree species alpha diversity in tropical forests. Many interactive mechanisms are responsible for coexistence tree species in tropical forests. Inter- and intra-specific competitions are the most significant and both facilitate positive and negative density dependence. Therefore, switching from negative to positive density dependence may occur in some situations. Positive and negative density effects regulate species abundance and coexistence through conspecific and heterospecific structures. Aggregates of conspecific and heterospecific neighbours constitute forest spatial structure. Negative density interactions are mutually exclusive and basically ranged from effect of species identity of neighbours, distance to neighbours and tree size of the neighbours to reference trees in the community structures. Some mechanisms shorten distances for heterospecific than conspecific interactions. Conspecific structures improved survival and growth of rare tree species. Interactive mechanisms in tree community and population structures facilitate species diversity and size inequality, respectively.

Microclimate, soil chemistry, and microbiota fail to explain Euphorbia dendroidesJanzen‐Connell pattern in a shrubland

AbstractNegative plant–soil feedback can cause density and distance effects that lead to Janzen–Connell (JC) distribution. The JC hypothesis has been proposed to explain the high species diversity in tropical forests, but it has been rarely tested in species‐rich Mediterranean shrublands. In this study, we assessed whether the JC hypothesis could explain Euphorbia dendroides recruitment pattern under conspecific conditions, that is, mother plant and the canopy of Pistacia lentiscus, Juniperus phoenicea, Myrtus communis, Rosmarinus officinalis, and Olea europaea. We examined whether soil chemistry and/or soil microbiota, characterized by both bacterial and fungal communities, explained the observed JC pattern. We also explored differences in microclimate among shrub species by monitoring air temperature and light availability at different times of the year. Euphorbia recruits were almost absent under the canopy of conspecifics, being more abundant at the edge of the canopy, which fits the JC pattern. Interestingly, we also found a high density of Euphorbia recruitment under heterospecific canopies, that is, O. europaea and J. phoenicea, but a very low density under other heterospecific canopies, for example, R. officinalis and P. lentiscus. Although shrubs have a species‐specific microbiota signature under their canopy, neither the accumulation of species‐specific pathogens nor soil chemical properties explain the observed JC pattern. Despite finding that shrubs buffer high temperatures in summer, the observed microclimatic difference failed to explain the recruitment pattern. We conclude that JC is prevalent in this species‐rich Mediterranean shrubland, but the underlying mechanism remains to be investigated and clarified.

Improving Forest Above-Ground Biomass Retrieval Using Multi-Sensor L- and C- Band SAR Data and Multi-Temporal Spaceborne LiDAR Data

Due to the great structural and species diversity of tropical forests and limitations of the methods used to estimate aboveground biomass, there is uncertainty in quantifying its carbon sequestration potential. Measuring carbon sequestered in the terrestrial ecosystem and monitoring its dynamics is one of the key objectives in sustainable development goals. Synthetic Aperture Radar (SAR) has evolved as a key satellite technology in measuring and monitoring terrestrial carbon sink stored as biomass in plants. This study attempts to model forest above-ground biomass (AGB) using a random forest machine-learning approach where the predictor variables are from C-band (Radarsat-2), L-band (ALOS-2/PALSAR-2), and multi-temporal spaceborne LiDAR data from the GEDI platform. Training and validation data for the machine learning approach are obtained from the field measured inventory campaigns to evaluate the modeled forest biomass accuracies. The results show that variables from L-band (HH, HV), C-band (HV), and canopy height from the GEDI LiDAR platform performed effectively to model forest AGB with the coefficient of determination (R2) of 0.81 and root mean squared error (rmse) of 19.35 Mg/ha (%rmse – 17.17). In the case of single frequency SAR data, the analysis shows that the model derived from the L-band SAR data and LiDAR performed comparably better than the combination of C-band SAR and LiDAR data with an R2 of 0.78 and rmse of 21.36 Mg/ha (%rmse – 18.94). The results, thus, demonstrate the potential of SAR data (both single frequency and multiple frequencies) in combination with GEDI LiDAR data in effectively modeling AGB over highly biodiverse tropical forest regions.

A test of the Janzen‐Connell hypothesis in a species‐rich Mediterranean woodland

AbstractThe Janzen‐Connell (JC) hypothesis predicts that conspecific negative density dependence contributes to the maintenance of plant diversity by lowering the recruitment of locally abundant plant species. The JC hypothesis is a widely evoked explanation for the high species diversity in tropical forests, but remains poorly tested in other species‐rich systems such as Mediterranean woodlands. As such, we tested if the JC operates and the role of soil‐borne oomycetes in a species‐rich Mediterranean woodland of Western Australia, where post‐fire recruitment can lead to high seedling densities, using the common Banksia attenuata as a case study. We attempted to decipher the effects of oomycete pathogens and distance from conspecific trees on intraspecific seedling survival and growth. Contrary to the JC hypothesis, we found little evidence of negative density dependence, but our results suggest positive density dependence survival under conspecific trees. Oomycete‐driven mortality in seedlings was also found regardless of the type of tree. Our results suggest that short‐term seedling recruitment patterns in this species‐rich, fire‐prone ecosystem do not follow the JC hypothesis. Future studies should explore whether negative conspecific density and distance dependence could play a greater role in later stages of the post‐fire recovery process.

Carbon Stocks, Species Diversity and Their Spatial Relationships in the Yucatán Peninsula, Mexico

Integrating information about the spatial distribution of carbon stocks and species diversity in tropical forests over large areas is fundamental for climate change mitigation and biodiversity conservation. In this study, spatial models showing the distribution of carbon stocks and the number of species were produced in order to identify areas that maximize carbon storage and biodiversity in the tropical forests of the Yucatan Peninsula, Mexico. We mapped carbon density and species richness of trees using L-band radar backscatter data as well as radar texture metrics, climatic and field data with the random forest regression algorithm. We reduced sources of errors in plot data of the national forest inventory by using correction factors to account for carbon stocks of small trees (<7.5 cm DBH) and for the temporal difference between field data collection and imagery acquisition. We created bivariate maps to assess the spatial relationship between carbon stocks and diversity. Model validation of the regional maps obtained herein using an independent data set of plots resulted in a coefficient of determination (R2) of 0.28 and 0.31 and a relative mean square error of 38.5% and 33.0% for aboveground biomass and species richness, respectively, at pixel level. Estimates of carbon density were influenced mostly by radar backscatter and climatic data, while those of species richness were influenced mostly by radar texture and climatic variables. Correlation between carbon density and species richness was positive in 79.3% of the peninsula, while bivariate maps showed that 39.6% of the area in the peninsula had high carbon stocks and species richness. Our results highlight the importance of combining carbon and diversity maps to identify areas that are critical—both for maintaining carbon stocks and for conserving biodiversity.

Bats in Three Protected Areas of The Central Amazon Ecological Corridor in Brazil

Bats have the second highest mammalian species richness globally, and account for about half of the mammal species diversity in tropical forests. In the Neotropical region, Brazil is the second most bat species-rich country, and the Brazilian Amazonia harbours most of the Brazilian bat diversity. However, many areas of the Amazon have sampling gaps in biodiversity inventories, and this is the situation of most Protected Areas (PAs) of the Central Amazon Ecological Corridor (CAEC) of Brazil. In the CAEC, there are PAs that are relatively intact, globally relevant for biodiversity, having high priority for conservation at the regional scale, but are greatly deficient in faunal inventories. In this sense, species inventories are the first step to consolidate management plans for PAs, as well as the conservation of the species occurring there. Thus, in this study we survey the bat assemblages in three PAs in the CAEC of Brazil: Jutai River Extractive Reserve (JRER), Jutai-Solimoes Ecological Station (JSES) and Auati-Parana Extractive Reserve (APER). In addition, we compared the bat diversity of these three areas with a compilation of data from 44 localities in the Amazon biome in two different biogeographic contexts. The first involves three geographic regions separated by large Amazonian rivers (Eastern Amazonia, Western Amazonia and the Guiana Shield) and the second based on three biogeographic dominions (Boreal Brazilian, Southeastern Amazonia and South Brazilian). We recorded 36 species at JRER in ten nights of sampling, 33 species at JSES in nine nights, and 55 species at APER in 17 nights. Of the total number of species, 20 were captured exclusively at APER, seven at JSES and only four at JRER, with 21 species being common to the three PAs. One species (Artibeus bogotensis) was recorded for the first time in Brazil. In a biogeographic context, species composition differed among biogeographic regions. This suggests that when designing strategies of conservation to protect the rich diversity of the large-scale bat fauna of the Amazon, considering the location of PAs, as well as the biogeographic regions is key. Although there have been major efforts in Brazil to identify priority conservation areas, for most priority areas of Amazon, bat surveys have not been performed, highlighting the urgent need for further studies.

Toward accurate species-level metabarcoding of arthropod communities from the tropical forest canopy.

Metabarcoding of arthropod communities can be used for assessing species diversity in tropical forests but the methodology requires validation for accurate and repeatable species occurrences in complex mixtures. This study investigates how the composition of ecological samples affects the accuracy of species recovery.Starting with field‐collected bulk samples from the tropical canopy, the recovery of specimens was tested for subsets of different body sizes and major taxa, by assembling these subsets into increasingly complex composite pools. After metabarcoding, we track whether richness, diversity, and most importantly composition of any size class or taxonomic subset are affected by the presence of other subsets in the mixture.Operational taxonomic units (OTUs) greatly exceeded the number of morphospecies in most taxa, even under very stringent sequencing read filtering. There was no significant effect on the recovered OTU richness of small and medium‐sized arthropods when metabarcoded alongside larger arthropods, despite substantial biomass differences in the mixture. The recovery of taxonomic subsets was not generally influenced by the presence of other taxa, although with some exceptions likely due to primer mismatches. Considerable compositional variation within size and taxon‐based subcommunities was evident resulting in high beta‐diversity among samples from within a single tree canopy, but this beta‐diversity was not affected by experimental manipulation.We conclude that OTU recovery in complex arthropod communities, with sufficient sequencing depth and within reasonable size ranges, is not skewed by variable biomass of the constituent species. This could remove the need for time‐intensive manual sorting prior to metabarcoding. However, there remains a chance of taxonomic bias, which may be primer‐dependent. There will never be a panacea primer; instead, metabarcoding studies should carefully consider whether the aim is broadscale turnover, in which case these biases may not be important, or species lists, in which case separate PCRs and sequencing might be necessary. OTU number inflation remains an issue in metabarcoding and requires bioinformatic development, particularly in read filtering and OTU clustering, and/or greater use of species‐identifying sequences generated outside of bulk sequencing.

Consequences of a Reduced Number of Plant Functional Types for the Simulation of Forest Productivity

Tropical forests represent an important pool in the global carbon cycle. Their biomass stocks and carbon fluxes are variable in space and time, which is a challenge for accurate measurements. Forest models are therefore used to investigate these complex forest dynamics. The challenge of considering the high species diversity of tropical forests is often addressed by grouping species into plant functional types (PFTs). We investigated how reduced numbers of PFTs affect the prediction of productivity (GPP, NPP) and other carbon fluxes derived from forest simulations. We therefore parameterized a forest gap model for a specific study site with just one PFT (comparable to global vegetation models) on the one hand, and two versions with a higher amount of PFTs, on the other hand. For an old-growth forest, aboveground biomass and basal area can be reproduced very well with all parameterizations. However, the absence of pioneer tree species in the parameterizations with just one PFT leads to a reduction in estimated gross primary production by 60% and an increase of estimated net ecosystem exchange by 50%. These findings may have consequences for productivity estimates of forests at regional and continental scales. Models with a reduced number of PFTs are limited in simulating forest succession, in particular regarding the forest growth after disturbances or transient dynamics. We conclude that a higher amount of species groups increases the accuracy of forest succession simulations. We suggest using at a minimum three PFTs with at least one species group representing pioneer tree species.

Floristic composition and ecological assessment of tree species diversity in tropical forests of Srikakulam and Vizianagaram districts of Andhra Pradesh, India

Background and Aim: Phytosociological investigation of vegetation serves as a pre-requisite for investigating the details of theprimary productivity of an ecosystem. The present study deals with Environmental Statistics and Ecological Assessment of treespecies diversity in Srikakulam and Vizianagaram districts of Andhra Pradesh, India. Methods: The present investigation dealswith the comparison of species diversity indices of plant species i.e., Simpson’s index, Shannon –wiener index, species richnesswith other counter parts. Importance Value Index = Relative density + Relative frequency + Relative dominance Based on thefrequency classes of tree species were determined. According to Raunkiaer classify to There are 5 frequency classes, i.e. 'A' classwith the species of frequency ranging from 1-20%; 'B' class 21- 40%; 'C' class 41-60%; 'D' class 61-80% and 'E' class 81- 100%based on the frequency pattern of the community, the homogeneity and heterogeneity of the vegetation. Results: The studyresulted in documentation of total 165 tree species, belonging to 119 genera and 50 families were recorded, and 160 are dicots and5 are monocots. The ecological studies have taken up to visualize the positive impact of protection on tree diversity. Conclusion:An understanding of the distribution of tree species and their assemblages must play an important role in elucidating the largerpatterns of distribution of diversity. The quantitative inventory of tree species diversity revealed a considerable variation in thecomposition of dominant species and density in various forest areas and the estimations of IVI have helped to understanding theecological significance of the species, present in different communities.

Soil-borne pathogens restrict the recruitment of a subtropical tree: a distance-dependent effect.

The Janzen-Connell hypothesis suggests that density- and/or distance-dependent juvenile mortality driven by host-specific natural enemies can explain high species diversity in tropical forests. However, such density and distance effects may not occur simultaneously and may not be driven by the same mechanism. Also, reports of attempts to identify and quantify the differences between these processes in tropical forests are scarce. In a primary subtropical forest in China, we (1) experimentally examined the relative influence of the distance to parent trees vs. conspecific seedling density on mortality patterns in Engelhardia fenzelii, (2) tested the role of soil-borne pathogens in driving density- or distance-dependent processes that cause seedling mortality, and (3) inspected the susceptibilities of different tree species to soil biota of E. fenzelii and the effects of soil biota from different tree species on E. fenzelii. The results from these field experiments showed that distance- rather than density-dependent processes driven by soil pathogens strongly affect the seedling survival of this species in its first year. We also observed increased survival of a fungicide treatment for E. fenzelii seedlings in the parent soil but not for the seedlings of the other three species in the E. fenzelii parent soil, or for E. fenzelii seedlings in the parent soil of three other species. This study illustrates how the distance-dependent pattern of seedling recruitment for this species is driven by soil pathogens, a mechanism that likely restricts the dominance of this abundant species.

A neutral vs. non-neutral parametrizations of a physiological forest gap model

Tropical forests are vital ecosystems which provide numerous ecological functions and forest models can be used to simulate their dynamics. However, due to the high species diversity of tropical forests and the common lack of detailed knowledge about these species, simulating the behavior of each species separately is not feasible. Therefore, species with common characteristics are usually aggregated into species groups.Although the number of species groups is likely to be an important characteristic of forest models, little research has been done on its effect on the results of the model. In this article, we compare the effect of the number of species groups using a physiological forest gap model and review our results using 28 years of field data from a 50ha forest plot in Panama as well as a chronosequence over four centuries from the same area. The number of simulated groups ranged from 1 to 4, 9 and 16. The parameterization with a single species group is a “neutral” parameterization with all simulated trees being ecophysiologically identical.The number of groups turned out to be an important characteristic of the model which influences its results on a fundamental level. Steady-states characteristics of forests like stem-numbers and stem-size distributions can be successfully simulated with even a single species group while modeling the long-term dynamics requires a higher number of groups. On the downside, a higher number of groups makes parameterization and fitting of the model more difficult. We conclude that the number of species groups is a vital characteristic of a forest model which has far-reaching consequences for its results and needs to be chosen with care.

Community divergence in a tropical forest following a severe cyclone

Cyclones are relatively infrequent, may cause massive and widespread disturbance to tropical regions, and are recognized as important determinants of the structure of tropical rainforest communities. Climate change scientists predict that the intensity of cyclones will increase in the future; understanding the long-term implications of these major disturbances for tropical forest composition and structure will be vital in anticipating and adapting to future changes and impacts. We established a long-term monitoring site in a rainforest area impacted by severe tropical Cyclone Larry which crossed the North Queensland coast of Australia in March 2006. We monitored recruitment, growth and mortality of nearly 17 000 seedlings in 90 quadrats across the study area for almost 5 years following the cyclone and measured the impact of variation in cyclone disturbance and debris load on community diversity, composition and dispersion as the forest recovered. We show that the level of structural disturbance sustained by the forest has a strong and immediate influence on community dynamics. Quadrats in severely disturbed areas, which were characterized by multiple treefalls and extensive canopy loss, had higher levels of diversity and variation in community assemblage than quadrats in areas characterized primarily by branch loss and defoliation. A rapid divergence in community composition between quadrats in the most- and least-severely disturbed areas resulted in the development of statistically distinct community states across relatively small scales. This provides further evidence that severe cyclones are important in maintaining species diversity in tropical forests.

On Tropical Forests and Their Pests

Interactions with pest species may help to explain the high plant species diversity in tropical forests.

The effect of habitat filtering on tree seedling distribution in a subtropical evergreen broadleaf forest in China

Niche theory hypothesized that habitat specialization would contribute to the high species diversity of tropical forests and adult tree patterns. However, the effect of habitat selection during early life stages on plant communities and the influence on seedling regeneration remains unresolved. We studied seedling distribution patterns in four habitat types of GTS 24 hm² forest dynamic plots. (1) The torus-translation test was used to detect the species-habitat associations. Out of 24 seedling species, 11 species were significantly associated with a certain habitat, with seven species showing positive associations. (2) Indicator species analysis was used to investigate the strength of seedling species habitat specialization. We found eight representative indicator species and eight pairs of species combinations of particular habitat types. (3) Compared with early studies based on trees with d.b.h.≥1 cm (non-seedling trees), we found habitat associations differed across plant-life stages. We conclude that habitat filtering influences the distribution and regeneration patterns at very early life stages, affecting the diversity of the whole community in this subtropical evergreen broadleaf forest in China.

Relationship between aboveground biomass and measures of structure and species diversity in tropical forests of Vietnam

Tropical forests play an important role in storing carbon through aboveground biomass (AGB) and are considered the highest biodiversity ecosystem on earth. However, the quantitative relationship between AGB and structure–species diversity is poorly understood. Twenty-eight 1-ha plots from old-growth tropical evergreen broadleaf forests and dry dipterocarp deciduous forests, distributed in six ecological regions throughout Vietnam, were used for large tree census (diameter at breast height⩾10cm). Measures of biodiversity (species richness, Shannon index, and evenness) and of structure–species diversity (biomass–species and abundance–biomass–species diversities) were used to determine the patterns and strengths of relationship between each measure and AGB. The linear, logarithmic, and exponential patterns were found, however the former dominated. Negative linear and exponential patterns represented relationship between evenness and AGB, while positive linear and logarithmic relationships were most suitable for others. In general, site – specific relationships (R2>0.6) were much stronger than inter – site relationships (R2<0.6). Meanwhile, relationships between measures of biodiversity and AGB (the lowest R2=0.14) were generally weaker than that between measures of structure–species diversity and AGB (the lowest R2=0.31). This finding indicates that structure–species diversity is a sound index representing the role of tropical forest in storing biomass and may suggest that uneven-aged and multistoried plantations should be encouraged for carbon sequestration.

Distinctive Bacterial Communities in the Rhizoplane of Four Tropical Tree Species

It is known that the microbial community of the rhizosphere is not only influenced by factors such as root exudates, phenology, and nutrient uptake but also by the plant species. However, studies of bacterial communities associated with tropical rainforest tree root surfaces, or rhizoplane, are lacking. Here, we analyzed the bacterial community of root surfaces of four species of native trees, Agathis borneensis, Dipterocarpus kerrii, Dyera costulata, and Gnetum gnemon, and nearby bulk soils, in a rainforest arboretum in Malaysia, using 454 pyrosequencing of the 16S rRNA gene. The rhizoplane bacterial communities for each of the four tree species sampled clustered separately from one another on an ordination, suggesting that these assemblages are linked to chemical and biological characteristics of the host or possibly to the mycorrhizal fungi present. Bacterial communities of the rhizoplane had various similarities to surrounding bulk soils. Acidobacteria, Alphaproteobacteria, and Betaproteobacteria were dominant in rhizoplane communities and in bulk soils from the same depth (0-10cm). In contrast, the relative abundance of certain bacterial lineages on the rhizoplane was different from that in bulk soils: Bacteroidetes and Betaproteobacteria, which are known as copiotrophs, were much more abundant in the rhizoplane in comparison to bulk soil. At the genus level, Burkholderia, Acidobacterium, Dyella, and Edaphobacter were more abundant in the rhizoplane. Burkholderia, which are known as both pathogens and mutualists of plants, were especially abundant on the rhizoplane of all tree species sampled. The Burkholderia species present included known mutualists of tropical crops and also known N fixers. The host-specific character of tropical tree rhizoplane bacterial communities may have implications for understanding nutrient cycling, recruitment, and structuring of tree species diversity in tropical forests. Such understanding may prove to be useful in both tropical forestry and conservation.

Soil profile, relief features and their relation to structure and distribution of Brazilian Atlantic rain forest trees

In tropical forests, the environmental heterogeneity can provide niche partitioning at local scales and determine the diversity and plant species distribution. Thus, this study aimed to investigate the variations of tree species structure and distribution in response to relief and soil profile features in a portion of the largest remnant of Brazilian Atlantic rain forest. All trees ³ 5 cm diameter at breast height were recorded in two 0.99 ha plots. Topographic survey and a soil characterization were accomplished in both plots. Topsoil samples (0-20 cm) were taken from 88 quadrats and analyzed for chemical and particle size properties. Differences for both diversity and tree density were identified among three kinds of soils. A canonical correspondence analysis (CCA) indicated that the specific abundance varied among the three kinds of soils mapped: a shallow Udept - Orthent / Aquent gradient, probably due to differences in soil drainage. Nutrient content was less likely to affect tree species composition and distribution than relief, pH, Al3+, and soil texture. Some species were randomly distributed and did not show restriction to relief and soil properties. However, preferences in niche occupation detected in this study, derived from the catenary environments found, rise up as an important explanation for the high tree species diversity in tropical forests.

How uniform is species diversity in tropical forests?

Las preguntas acerca de la diversidad de especies ha atraído a los ecologistas desde hace más de un siglo. Uno de los factores que genera preguntas es la distribución de las especies, misma que se podría ser un resultado del llamado “efecto de los botánicos” o efecto del esfuerzo de colección, así por ejemplo una zona donde existan muchos orquideólogos, con seguridad tiene una gran diversidad, pero al mismo tiempo gran esfuerzo de colección. Otro fenómeno común asociado al esfuerzo de colección de encuentra en la distribución de especies endémicas, que aparecen como más diversas al borde de los carreteros, y que declinan su diversidad hacia el interior del bosque. En este estudio probamos esta hipótesis utilizando datos de especies de orquídeas bolivianas. Se encontró diferencias entre especies terrestres y epífitas. En el caso de las terrestres, tanto la diversidad como el número de individuos disminuyó hacia el interior del bosque. Sin embargo, las especies epífitas incrementaron su abundancia y diversidad hacia el interior del bosque. Las razones que explican los patrones observados son evidentes, ya que hacia el interior del bosque hay mayor densidad de árboles por lo tanto hay menor cantidad de luz que llega al suelo, por lo cual la diversidad de las especies terrestres declina. Así, los hábitats cercanos a claros de bosque son más propicios para especies terrestres, mientras que los que se encuentran al interior del bosque son apropiados par alas especies epífitas debido a una mayor disponibilidad de árboles hospederos.