Floristic composition and diversity of three swamp forests in northwest Guyana

This paper reviews the floristic composition, vegetation structure, and diversity of three types of swamp forest that cover a considerable part of Guyana's North-West District. Trees, shrubs, lianas, herbs, and hemi-epiphytes were inventoried in three hectare plots: one in Mora forest, one in quackal swamp, and one in manicole swamp. The Mora forest, flooded annually by white water, was dominated by relatively few, large individuals of Mora excelsa. The very dense, thin-stemmed quackal forest, almost permanently flooded by black water, was characterized by Tabebuia insignis and Symphonia globulifera and contained few palms. The somewhat less dense manicole swamp, flooded regularly by brackish water, was distinguished by large numbers of Euterpe oleracea. Although the three swamps showed little overlap in floristic composition and densities of dominant species, they represent some of the lowest diversity forest in the Neotropics, with an -diversity of 7.4 for the Mora forest, 8.2 for the quackal forest and 5.7 for the manicole swamp. When compared with similar vegetation types in the Guiana Shield, the swamp forests in this study show some interesting differences in species composition and density. The wetlands of the North-West District form the last stretch of natural coastline in Guyana and play an important role in the protection of riverine ecosystems. Furthermore, there is commercial potential for the extraction of non-timber forest products from these low-diversity forests. Nevertheless, in prolonged dry periods, large tracts of quackal forest are being burnt to give way to almost treeless, flooded savannas. For these reasons, adequate management and conservation strategies must be developed for the area.     

Pattern of tree species diversity in riparian forest fragments of different widths (SE Brazil)

Width is an essential element of the spatial configuration of riparian forests and may be fundamental in determining their corridor function. In the present study we tested the effect of forest width on floristic structure (tree species composition and diversity) in 15 fragments of riparian forest in an agricultural fragmented landscape of SE Brazil. All these fragments were chosen in a geomorphological homogeneous river reach under similar soil, topographic and human disturbance conditions in order to minimize the influence of these factors. The forest widths considered ranged from 30 to 650 m. The results showed that total species richness and climax species richness were significantly greater when we consider larger fragments, as has been observed in other studies. Nevertheless, species diversity and evenness were not significantly correlated with forest width. The analysis of species composition showed that the narrowest fragments were characterized by species well adapted to temporary flood conditions, while medium and wide fragments showed a composition typical of drier upland areas. Therefore, the effect of forest width on floristic structure appears to be more strongly linked to the effect of river floods in the case of the fragments studied. The existence in riparian corridors of a drier forest, in general richer and more diversified than the annually flooded forest, seems to favor the maintenance of regional species diversity in fragmented landscapes.     

The combined role of topography and overstorey tree composition in promoting edaphic and floristic variation in a Mediterranean forest

This study aimed to address which factors, other than topography, contribute to the floristic variation of forested slopes. The natural forest studied is located in the Sudoeste Alentejano e Costa Vicentina Nature Park (southwestern Portugal). We sampled topographic, edaphic, floristic and community structure variables along three bottom–top hillside transects. Multivariate analyses of soil variables (by PCA), and of woody species composition and floristic–environmental relationships (by CCA and pCCA) were performed. Environmental–floristic trends strongly associated with the elevation gradient were identified. At lower altitudes, the lowest species richness, the highest soil fertility, and the tallest and most dense (least available light) canopy occurred. The spatial variation in woody species composition and abundance was closely associated with Zn availability in the soil and litter groundcover, but these varibles had significant spatial structure in the studied forest. The non-spatially structured species variance was better predicted by soil NO₃^– and NH₄⁺. The spatial variation of species data not shared with environmental variables was also calculated. We suggest that the influence of topographic gradient on the variation of edaphic variables and on the distribution and abundance of woody species was mediated by overstorey tree composition. Locally dominant tree species, in particular Quercus faginea and Quercus suber, may function as ecosystem engineers promoting environmental changes (i.e., Zn availability in soil, litter accumulation and light availability) that influence overall floristic variation.     

Assessment of flora diversity in a minor river valley using ecological indicator values, Geographical Information Systems and Digital Elevation Models

Ellenberg indicator values (EIV) have been widely used to estimate habitat variables from floristic data and to predict vegetation composition based on habitat properties. Geographical Information Systems (GIS) and Digital Elevation Models (DEM) are valuable tools for studying the relationships between topographic and ecological characters of river systems. A 3-meter resolution DEM was derived for a. 3-km-long break section of the Szum River (SE Poland) from a 1:10,000 topographic map. Data on the diversity and ecological requirements of the local vascular flora were obtained while making floristic charts for 32 sections of the river valley (each 200 m long) and physical and chemical soil measurements; next, the data were translated into EIV. The correlations of the primary and secondary topographic attributes of the valley, species richness, and EIV (adapted for the Polish vascular flora) were assessed for all species recognized in each valley section. The total area and proportion of a flat area, mean slope, slope curvature, solar radiation (SRAD), and topographic wetness index (TWI) are the most important factors influencing local flora richness and diversity. The highest correlations were found for three ecological indicators, namely light, soil moisture, and soil organic content. The DEM seems to be useful in determination of correlations between topographic and ecological attributes along a minor river valley.     

Spatial distribution and floristic composition of trees and lianas in different forest types of an Amazonian rainforest

A quantitative inventory of trees and lianas was conducted (1) to compare floristic composition, diversity and stem density variation between three different forest types (tierra firme, floodplain and swamp), and (2) to analyse the relationships between floristic similarity and forest structure in two regions ~60 km apart in Yasuní National Park, Amazonian Ecuador. A total of 1,087 species with a diameter at breast height ≥ 2.5 cm were recorded in 25 0.1-ha plots. Tierra firme was the habitat with the highest number of species and stem density for trees and lianas, followed by floodplain and swamp in both regions. Two hypotheses that have been independently proposed to describe plant distribution in tropical rain forests, together explain species spatial distribution in this study. The fact that the 30 most important species per forest type (totalling 119 species) accounted for 48.2% of total individuals supports the oligarchy hypothesis. Likewise, 28 out of these 119 species are reported as restricted to a single forest type, which supports the environmental-determinism hypothesis. In general, both canopy and understorey trees and lianas showed rather similar floristic patterns across different forest types and regions.     

Effects of the duration of flooding on species richness and floristic composition in three hectares in the Jau´ National Park in floodplain forests in central Amazonia

Rivers in Central Amazonia show annual water level fluctuations of up to 14m; the flooding period ranges from 50 to 270 days between the rising and falling phases. Differences in duration and type of flood in Amazonian floodplain forests result in a mosaic of habitats which include lakes, grasslands, forests, streams etc. To study the floristic composition, structure, variation on number of species and diversity in a forest that is seasonally flooded by a black-water river in Brazilian Amazonia, 200km NE of Manaus, I surveyed three hectares in habitats which included lake, river margin, and stream. The number of species per hectare ranged from 44 to 137. The number of trees varied from 796 to 1130. Total basal area ranged from 22.3m2 to 41.8m2. Leguminosae was the most abundant and dominant family in the river margin and stream plot, while Euphorbiaceae and Leguminosae were, respectively the most abundant and dominant families in the lake plot. The most dominant species in the river margin and stream plots was Aldina latifolia (Leguminosae), while Amanoa oblongifolia (Euphorbiaceae) was the most abundant and dominant species in the lake plot. Mean water level and flooding period decreased significantly from lake to the river margin to the stream. The mean number of species and the Shannon diversity increase significantly from the lake to the river margin to the stream habitats plots. Similarity indexes varied from 0.3 to 0.55% between the three plots sampled in this study.     

Monitoring and predictive mapping of floristic biodiversity along a climatic gradient in ENSO's terrestrial core region,NW Peru

The tropical dry forests of NW Peru are heavily shaped by the El Niño Southern Oscillation (ENSO), where especially El Niño brings rain to arid to semi-arid areas. However, the resulting effects on biodiversity patterns remain largely unknown as well as the effect of environmental variables on the floristic composition under varying rainfall patterns. Therefore, we studied the spatio-temporal effects of different ENSO episodes on floristic biodiversity along a climatic gradient ranging from the coastal desert to the Andean foothills. We sampled 50 vegetation plots in four years representing different ENSO episodes. To highlight the spatio-temporal changes in floristic composition and beta diversity across ENSO episodes, we predicted ordination scores with a Generalized Additive Model. We applied variation partitioning to test if topographic or edaphic variables gained in importance during more humid ENSO episodes. Additionally, we executed an irrigation–fertilization experiment to quantify the beneficial effects of the water–nutrient interaction under different simulated ENSO rainfall scenarios. Plant species richness increased under humid conditions during the humid La Niña (2012) and the moderate El Niño (2016), and slightly decreased under the very humid conditions during the coastal El Niño (2017). The spatial prediction revealed that specific vegetation formations became more pronounced with increasing water input, but that a large water surplus led to the disruption of the strict order along the climatic gradient. Edaphic and topographic variables gained in importance with increased water availability (2012 and 2016), however, this effect was not further amplified under very wet conditions (2017). The experiment showed that plant cover under Super Niño conditions was three times higher when fertilized. Overall, our spatial predictions concede detailed insights into spatio-temporal ecosystem dynamics in response to varying rainfall caused by different ENSO episodes while the results of the experiment can support farmers regarding a sustainable agrarian management.     

Relationships between spatial configuration of tropical forest patches and woody plant diversity in northeastern Puerto Rico

The destruction and fragmentation of tropical forests are major sources of global biodiversity loss. A better understanding of anthropogenically altered landscapes and their relationships with species diversity and composition is needed in order to protect biodiversity in these environments. The spatial patterns of a landscape may control the ecological processes that shape species diversity and composition. However, there is little information about how plant diversity varies with the spatial configuration of forest patches especially in fragmented tropical habitats. The northeastern part of Puerto Rico provides the opportunity to study the relationships between species richness and composition of woody plants (shrubs and trees) and spatial variables [i.e., patch area and shape, patch isolation, connectivity, and distance to the Luquillo Experimental Forest (LEF)] in tropical forest patches that have regenerated from pasturelands. The spatial data were obtained from aerial color photographs from year 2000. Each photo interpretation was digitized into a GIS package, and 12 forest patches (24–34 years old) were selected within a study area of 28 km². The woody plant species composition of the patches was determined by a systematic floristic survey. The species diversity (Shannon index) and species richness of woody plants correlated positively with the area and the shape of the forest patch. Larger patches, and patches with more habitat edge or convolution, provided conditions for a higher diversity of woody plants. Moreover, the distance of the forest patches to the LEF, which is a source of propagules, correlated negatively with species richness. Plant species composition was also related to patch size and shape and distance to the LEF. These results indicate that there is a link between landscape structure and species diversity and composition and that patches that have similar area, shape, and distance to the LEF provide similar conditions for the existence of a particular plant community. In addition, forest patches that were closer together had more similarity in woody plant species composition than patches that were farther apart, suggesting that seed dispersal for some species is limited at the scale of 10 km.     

Ecological features affect patterns of plant communities in Mediterranean temporary rock pools

In this paper, the results of a study on the ecology, floristic composition and spatial assemblages of temporary limestone rock pool plant communities of a central Mediterranean area (S Sicily, the Maltese Islands and Lampedusa) are presented. A total of 76 temporary pools were studied, distributed between the infra-mediterranean and thermo-mediterranean bioclimatic belt. For each temporary rock pools, the floristic composition and cover of the species were determined using standard relevé methods. Moreover, for 50 of these pools, pH, conductivity, soil depth, water-level, altitude and floristic richness and diversity index were assessed. The plant communities were analysed using unweighted pair group method using arithmetic averages and Euclidean distance classification and ordination methods such as canonical correspondence analysis (CCA). A total of four plant communities with specific floristic composition were established, each one with a different dominant species: Callitriche truncata; Elatine gussonei; Tillaea vaillantii and Lythrum hyssopifolia. According to the CCA, the spatial patterns of plant communities follow an ecological gradient related to water level and depth/size of the rock pools: these are the main ecological features affecting the distribution of the plant communities of rock pools. In addition, floristic richness and diversity index showed a slight increase in trend from temporary pools submerged for long periods towards pools submerged for short periods.     

Effects of different components of diversity on productivity in artificial plant communities

In an experiment on artificial plant communities, the effects of three components of plant diversity—plant species diversity, plant functional group diversity and plant functional diversity—on community productivity and soil water content were compared. We found that simple regression analysis showed a positive diversity effect on ecosystem processes (productivity and soil water content). However, when three components of diversity were included in the multiple regression analyses, the results showed that functional group diversity and functional diversity had more important effects on productivity and resource use efficiency. These results suggested that, compared with species number, functional differences among species and the range of functional traits carried by plants are the basis of biodiversity effects on ecosystem functioning. These diversity effects of increasing functional group diversity or functional diversity were likely because species differing greatly in size, life form, phenology and capacity to capture and use resources efficiently in diverse communities realize complementary resource use in temporal, spatial, and biological ways.     

Tree community features of two stands of riverine forest under different flooding regimes in Southern Brazil

Two 1 ha plots of a Southern Brazilian subtropical riverine forest, subject to different frequency and duration of floods, were compared to detect the differences in physiognomic structure, tree community composition, richness and diversity. Each plot was made up of 100 contiguous 10×10 m subplots, where 3451 trees with pbh 15 cm were measured and identified. The survey observed 30 tree species, in the frequently flooded plot and 48 in the occasionally flooded plot. A detailed topographical and soil survey was carried out in both plots and indicated that the levels of organic matter and most mineral nutrients were higher in the frequently flooded stand. The forest understory was denser in the occasionally flooded stand which also showed taller emergent trees. Multivariate ordination and grouping techniques showed that the species’ abundance distribution was strongly related to the topographical variation. There was a clear pattern of species turnover according to topographic position, indicating that tree species developed different abilities to survive flooding events. As a result, the two plots also differed in their tree frequency per species regeneration, vertical distribution and dispersion groups. Both species richness and diversity decreased with increasing flood frequency, also showing a patchy distribution within both stands. At a local scale, flooding regime is regulating the spatial variation of α-diversity by forming different seral stages of predictable species composition. Compared to regularly flooded riverine and floodplain forests, riverine forests, with unpredictable flooding regimes, may show higher diversity at a local scale and more abundant opportunistic species of high environmental plasticity.     

Early seral trends in plant community diversity on a recontoured surface mine

The initial floristic composition and structure of vegetation on a recontoured surface mine in southwestern Wyoming was experimentally manipulated to test ideas concerning successional convergence. Experimental treatments involving the planting pattern and density of shrubs and the storage of topsoil were evaluated on the basis of their ability to divert the successional trajectories of the redeveloping vegetation and to increase species diversity. The change in compositional similarity along a topographic gradient was also monitored.The influence of initial composition and soil storage generally declined with time; successional convergence among treatments over the four years of the study was largely monotonic. The planting of shrubs and the storage of topsoil did, however, influence the rate of plant succession. There were no persistent differences in alpha diversity among the experimental treatments. Compositional dissimilarity along the topographic gradient, as expressed by beta diversity, increased with time.     

Avian Composition Co‐varies with Floristic Composition and Soil Nutrient Concentration in Amazonian Upland Forests

Spatial heterogeneity in the plant species composition of tropical forests is expected to influence animal species abundance and composition because vegetation constitutes the primary habitat feature for forest animals. Floristic variation is tied to variation in soils, so edaphic properties should ultimately influence animal species composition as well. The study of covariation in floristic and faunistic turnover has been hindered by the difficulty of completing coordinated surveys in hyperdiverse tropical communities, but this can be overcome with the use of a few plant taxa that function as surrogates for general floristic turnover. We used avian and plant transect surveys and soil sampling in a western Amazonian upland (terra firme) forest landscape to test whether spatial variation in bird community composition is associated with floristic turnover and corresponding edaphic gradients. Partial Mantel tests and Non‐metric Multidimensional Scaling showed floristic distinctiveness between two forest types closely associated with differences in soil cation concentrations, and differences in both floristic composition and cation concentrations were further linked to compositional differences in avian species, independent of geographic distances among sites. Ten percent of bird species included in Indicator Species Analyses showed significant associations with one of the two forest types. The upland forest types that we sampled, each corresponding to a different geological formation, are intermediate relative to edaphically extreme environments in the region. Models of avian diversification should take into account this environmental heterogeneity, as should conservation planning approaches that aim to represent faunal diversity. Abstract in Spanish is available in the online version of this article.     

Ecological impacts of desert plantation forests on biodiversity

This investigation involves the comparison of the diversity of understorey vegetation of four desert planted forests with the adjacent desert areas. Spatial and temporal variations in species composition and structure were compared, and alpha and beta diversities were compared for the field data collected from sampled sites. The diversity of native desert species decreased from 66% in desert areas to 44% of the total recorded plants inside the forests. Meanwhile, the percentage of agricultural weed species increased in forests to >twofold more than that recorded in desert areas. Plant communities in forest stands shared <50% of their species with adjacent vegetation in desert stands. The percentage of variation in species composition was >340% in some forests compared with the desert areas. Alpha diversity and β‐diversity were significantly higher in forest stands than in the desert. Spatial and temporal variations in species diversity were correlated with type of tree canopy and irrigation system. Planted forests had significant negative effects on the diversity of native desert shrubs and trees. Using flood irrigation and more spacing between trees might help in conserving the floristic diversity of desert shrubs and trees at the forest floor.     

Selective recruitment and resurgence of tropical river phytoplankton: evidence from the Nile system of lakes,rivers, reservoirs and ponds

The recruitment of major species-components of phytoplankton is considered with reference to diverse water-bodies—rivers, headwater lakes, reservoirs and lateral waters—of the Nile system. The importance of massive ‘inocula’, carried in flowing and inter-communicating waters, is emphasised; the most direct evidence is from quantitative population dynamics in longitudinally sampled river-reservoir systems. Other indications of extraneous derivation are taken from geographical distribution and apparent invasions of newly recorded species. For five reservoirs, there are records of initial colonisation (in two) and of the annual colonisation of seasonally impounded water (in three). There was a selective recruitment of reservoir/river major species over 1 year to newly created ponds, from a massive inoculum of added river water, studied in relation to the novel and changing physical and chemical environment. Periods of predominant decomposition were there linked with the abundance of other species not observed in the original river water. Reservoir species can be carried to extend abundance far downstream, as observed in the Blue Nile where normal succession was altered by a new reservoir upstream; also in Egypt below the former Aswan Reservoir and the later High Dam Lake. The different and distinctive compositions of the phytoplankton communities in headwater lakes reflect large environmental differences that, with high downstream turbulence, probably make them insignificant for recruitment of most species typical of the downstream waters. There is evidence from hydrology and floristic similarities for recruitment from lateral standing waters along the river, especially those of one major swamp area.     

Fine‐scale patterns of species and phylogenetic turnover in a global biodiversity hotspot: Implications for climate change vulnerability

Question: What is the relative importance of environmental and spatial factors for species compositional and phylogenetic turnover? Location: High‐rainfall zone of the Southwest Australian Floristic Region (SWAFR). Methods: Correlates of species compositional turnover were assessed using quadrat‐based floristic data, and establishing relationships with environmental and spatial factors using canonical correspondence analyses and Mantel tests. Between‐quadrat phylogenetic distance measures were computed and examined for correlations with environmental and spatial attributes. Processes structuring pa2t2terns of beta diversity were also evaluated within four broad floristic assemblages defined a priori. Results: Floristic diversity was strongly related to environmental attributes. A low significance of spatial variables on assemblage patterns suggested no evident effect of dispersal limitations. Species compositional turnover was especially high within the swamp and outcrop assemblage. Phylogenetic turnover was closely coupled to species compositional turnover, implying the occurrence of many locally endemic and phylogenetically relict taxa. Beta diversity patterns within assemblages were also significantly correlated with the local environment, and relevant correlates differed between floristic assemblage types. Conclusion: Phylogenetic diversity in the SWAFR high‐rainfall zone is clustered within edaphic microhabitats in a generally subdued landscape. A clustered rather than dispersed distribution of phylogenetic diversity increases the probability of significant plant diversity loss during periods of climate change. Climate change susceptibility of the region's flora is accordingly estimated to be high. We highlight the conservation significance of swamp and outcrops that are characterized by distinct hydrological properties and may provide refugial habitat for plant diversity during periods of moderate climate change.     

Diversity and habitat relationships of hypogeous fungi. I. Study design, sampling techniques and general survey results

Hypogeous fungi are a large yet unknown component of biodiversity in forests of south-eastern mainland Australia. To better define their diversity and habitat relationships, we identified and counted fruit-bodies at 136 study sites sampling the climatic, geological and topographic features of the region. In one year 7451 fruit-bodies representing 209 species were collected in an autumn and spring sampling period. Only 57 of these species were previously described. Within genera, the number of species ranged from 1 to 21. Sites sampled in autumn averaged higher diversity of species and greater number of fruit-bodies than the same sites sampled in spring. Most major taxa occurred at more sites in autumn than in spring, whereas a few occurred more frequently in spring than in autumn. These patterns are consistent with those identified in previous smaller studies and likely reflect seasonal changes in soil moisture and temperature levels. Subsequent papers will explore factors influencing the occurrence, relative abundance and numbers of species of hypogeous fungi at the study sites and their community structure and possible host–plant relationships.     

Soil and Geographic Distance as Determinants of Floristic Composition in the Azuero Peninsula (Panama)

Many studies analyzing the relative contribution of soil properties versus distance‐related processes on plant species composition have focused on lowland tropical forests. Very few have investigated two forest types simultaneously, to contrast ecological processes that assemble the communities. This study analyses—at the landscape scale—the relative contribution of soil and distance on lowland and submontane tropical forests, which co‐occur in two reserves of the Azuero peninsula (Panama). Floristic inventories and soil sampling were conducted in 81 0.1‐ha plots clustered in 27 sites, and data were analyzed using Mantel tests, variance partitioning and non‐metric multidimensional scaling. The largest differences in floristic composition occurred between reserves in both forest types. Soil variation and geographic distance were important determinants of floristic composition, but their effects were highly correlated; together they explained 7–25 percent and 46–50 percent of the variation in lowland and submontane forests, respectively. Soil variables that had the best correlations with floristic composition were iron, zinc, and silt content in lowland, and calcium, copper, iron, potassium, magnesium, phosphorus, zinc, and sand content in submontane forests. The studied forests showed a high beta diversity that seems to be related primarily with soils and, secondarily, with dispersal limitation and stochastic events. The results reveal a response of tree assemblages to environmental gradients, which are particularly conspicuous in Panama. The effects of limited dispersal seem to be more important in submontane than in lowland forests, probably as a result of higher isolation.     

Temporal and spatial partitioning of water resources among eight woody species in a Hawaiian dry forest

Lowland dry forests are unique in Hawaii for their high diversity of tree species compared with wet forests. We characterized spatial and temporal partitioning of soil water resources among seven indigenous and one invasive dry forest species to determine whether the degree of partitioning was consistent with the relatively high species richness in these forests. Patterns of water utilization were inferred from stable hydrogen isotope ratios (δD) of soil and xylem water, zones of soil water depletion, plant water status, leaf phenology, and spatial patterns of species distribution. Soil water δD values ranged from –20‰ near the surface to –48‰ at 130 cm depth. Metrosideros polymorpha, an evergreen species, and Reynoldsia sandwicensis, a drought-deciduous species, had xylem sap δD values of about –52‰, and appeared to obtain their water largely from deeper soil layers. The remaining six species had xylem δD values ranging from –33 to –42‰, and apparently obtained water from shallower soil layers. Xylem water δD values were negatively correlated with minimum annual leaf water potential and positively correlated with leaf solute content, an integrated measure of leaf water deficit. Seasonal patterns of leaf production ranged from dry season deciduous at one extreme to evergreen with near constant leaf expansion rates at the other. Species tapping water more actively from deeper soil layers tended to exhibit larger seasonality of leaf production than species relying on shallower soil water sources. Individuals of Myoporum sandwicense were more spatially isolated than would be expected by chance. Even though this species apparently extracted water primarily from shallow soil layers, as indicated by its xylem δD values, its nearly constant growth rates across all seasons may have been the result of a larger volume of soil water available per individual. The two dominant species, Diospyros sandwicensis and Nestegis sandwicensis, exhibited low leaf water potentials during the dry season and apparently drew water mostly from the upper portion of the soil profile, which may have allowed them to exploit light precipitation events more effectively than the more deeply rooted species. Character displacement in spatial and temporal patterns of soil water uptake was consistent with the relatively high diversity of woody species in Hawaiian dry forests. Received: 20 May 1999 / Accepted: 2 March 2000