Vegetation Physiognomy Research Articles

Composição e estrutura de comunidades arbóreas de cerrado stricto sensu no norte do Tocantins e sul do Maranhão

Este trabalho teve por objetivo avaliar a composição e a estrutura da comunidade arbórea de cerrado stricto sensu (s.s.) no município de Filadélfia (norte do Tocantins) e compará-la com a mesma fitofisionomia em uma área adjacente na bacia do rio Tocantins, no município de Carolina (MA), na província norte-nordeste do Cerrado. Em Filadélfia foram alocadas aleatoriamente 10 parcelas de 20 × 50m, totalizando um ha. Todos os indivíduos lenhosos com diâmetro de caule > 5 cm, medidos a 30 cm do solo, foram incluídos. Os dados de composição e estrutura da vegetação em Carolina foram obtidos em literatura. Dois métodos de análise foram empregados: UPGMA, adotando-se o índice de Sørensen, e TWINSPAN, agrupando parcelas e espécies. Em Filadélfia foram encontrados 789 indivíduos, 53 espécies e 44 gêneros; H' foi igual a 3,32 nats. ind-1 e J'=0,83. Nove espécies (Qualea parviflora, Pouteria ramiflora, Curatella americana, Hirtella ciliata, Qualea grandiflora, Parkia platycephala, Diospyros sericea, Stryphnodendron sp. e Stryphnodendron rotundifolium) representaram 49,9% do VI total. Das 69 espécies encontradas nas duas áreas, 36 foram comuns. O índice de Sørensen mostrou baixa similaridade florística entre Carolina e Filadélfia. A análise por TWINSPAN também mostrou similaridade qualitativa e quantitativa reduzidas entre as áreas. Os resultados revelaram que as comunidades de cerrado s.s. são diferenciadas entre e dentre as áreas, com provável influência das diferenças de solo. Não obstante, a fitossociologia foi similar a de outros estudos na região e a composição é característica da província fitogeográfica norte/nordeste do bioma Cerrado, contendo elementos típicos como Hirtella ciliata, Platonia insignis e Caryocar coriaceum.

Angiosperms from the Araripe National Forest, Ceará, Brazil

This study provides a species list of the angiosperms from the Araripe National Forest (ANF) in the south part of Ceará state, northeastern Brazil. The floristic survey recorded 188 species from 55 Angiosperm families. The most species-rich families were Fabaceae (31), Rubiaceae (17), Asteraceae (14), Bignoniaceae (10), Myrtaceae (9), Euphorbiaceae (7), Apocynaceae and Malpighiaceae (7) and Annonaceae and Solanaceae (5). The flora of the ANF is composed of typical species from the vegetation physiognomies of Cerrado sensu lato such as cerradão and cerrado sensu stricto and it is influenced by the northeastern phytogeographic Cerrado province. Furthermore, there are influences of ecotones between these physiognomies, seasonal forests and carrascos within the Caatinga biome. In addition to four threatened species that were recorded, the ANF also harbors species that represent important incomes for local communities because of the non-timber forest products, such as Dimorphandra gardneriana Tul. and Caryocar coriaceum Wittm.

Hydrological impacts of mesquite encroachment in the upper San Pedro watershed

Over the past century, mesquite trees (Prosopis spp.) have exhibited substantial increase in abundance throughout areas in the American Southwest that were once dominated by desert grassland. To assess hydrological consequences of mesquite encroachment, the Soil and Water Assessment Tool (SWAT) was applied to simulate progressive mesquite encroachments in the upper San Pedro watershed (U.S./Mexico). The simulated average annual basin evapotranspiration (ET) increases with mesquite encroachment, leading to the decrease of annual water yield and percolation by 9.8% and 9.7%, respectively. Substantial increase of ET (up to 19.19mm) and decrease of percolation, and surface runoff (to −12.90 and −3.20mm, respectively) were observed in the southeast, middle-west, and northern subwatersheds of the basin and the most significant decrease of surface runoff (around −35.8%) was simulated during the wet period. In addition, a non-linear hydrological response relative to mesquite encroachment was observed, i.e. hydrological processes changed markedly until a certain amount (approximately 40%) of grassland was removed, indicating that the strongest increase of ET occurred in the earliest stages of encroachment. Consequently, changes in vegetation physiognomy, such as mesquite encroachment, have broad implications for landuse management especially in regard to reliable water supplies in arid and semi-arid environments.

Environment, vegetation and greenness (NDVI) along the North America and Eurasia Arctic transects

Satellite-based measurements of the normalized difference vegetation index (NDVI; an index of vegetation greenness and photosynthetic capacity) indicate that tundra environments are generally greening and becoming more productive as climates warm in the Arctic. The greening, however, varies and is even negative in some parts of the Arctic. To help interpret the space-based observations, the International Polar Year (IPY) Greening of the Arctic project conducted ground-based surveys along two >1500 km transects that span all five Arctic bioclimate subzones. Here we summarize the climate, soil, vegetation, biomass, and spectral information collected from the North America Arctic transect (NAAT), which has a more continental climate, and the Eurasia Arctic transect (EAT), which has a more oceanic climate. The transects have broadly similar summer temperature regimes and overall vegetation physiognomy, but strong differences in precipitation, especially winter precipitation, soil texture and pH, disturbance regimes, and plant species composition and structure. The results indicate that summer warmth and NDVI increased more strongly along the more continental transect.

Mapping and monitoring riparian vegetation distribution, structure and composition with regression tree models and post-classification change metrics

Riparian systems have become increasingly susceptible to both natural and human disturbances as cumulative pressures from changing land use and climate alter the hydrological regimes. This article introduces a landscape dynamics monitoring protocol that incorporates riparian structural classes into the land-cover classification scheme and examines riparian change within the context of surrounding land-cover change. We tested whether Landsat Thematic Mapper (TM) imagery could be used to document a riparian tree die-off through the classification of multi-date Landsat images using classification and regression tree (CART) models trained with physiognomic vegetation data. We developed a post-classification change map and used patch metrics to examine the magnitude and trajectories of riparian class change relative to mapped disturbance parameters. Results show that catchments where riparian change occurred can be identified from land-cover change maps; however, the main change resulting from the die-off disturbance was compositional rather than structural, making accurate post-classification change detection difficult.

Produire des savoirs environnementaux face aux changements d’usage du sol : les enseignements du conflit pour la définition du Plan de Zonage de la Sylviculture du Rio Grande do Sul (Brésil)

This paper investigates emerging logics in the production of environmental knowledge in Southern Brazil through the case study of a complex process launched in 2004 that led the state of Rio Grande do Sul to adopt a management tool known as “Environmental Zoning for Silvicultural Activity” (ZAS). In order to regulate the implantation of Eucalyptus, Pine, and Acacia tree-farms on its territory, the State Environmental Administration decided to regulate silvicultural activities by establishing a set of restrictions based on the ecological vulnerability of landscape units. A conflict between public administration, silvicultural companies, and environmentalist groups, led to a thorough reformulation of this zoning plan between 2007 and 2010. The companies succeeded in reducing the restrictions placed on their activity, however, environmentalist groups later successfully imposed the need to conserve biodiversity, most notably natural grasslands. The ZAS is innovative on a regional scale because it is the first attempt to regulate agrarian activities that underpin the advancement of the agricultural frontier over the natural grasslands of the Campos. It also represents the first legal definition of the physiognomy of this herbaceous vegetation, allowing conservation measures to be taken. We explore in this paper some salient aspects of this case study, representative of the current processes of environmental knowledge production in the neo-developmentist context of South America: The contribution of natural resource conflicts in the emergence and legitimation of new environmental categories; The greater capacity of multinational companies to reshape the legislation about environment management; The intensive use of free-access environmental geographical databases (public open data) during the zoning conflict, and the general consensus about the legitimacy of their use. We highlight how this use creates new ways of measuring environmental vulnerability and allows actors to implement new environmental strategies. In spite of being generally conceived as a factor of democratization of information and empowerment, environmental open data may reinforce asymmetries between actors in environmental controversies and the processes of knowledge production.

Depth of water uptake in woody plants relates to groundwater level and vegetation structure along a topographic gradient in a neotropical savanna

Vegetation structure of the savannas is variable across the landscape, ranging from open grassland to savanna woodland within topographic gradients of a few hundred meters in length. Here we investigated whether patterns of soil water extraction by the woody layer and vegetation structure changed in response to groundwater depth. We determined depth of plant water uptake, groundwater level and vegetation structure on five different locations along a topographic gradient in the highlands of Central Brazil. The elevation gradient of about 110 m covered all vegetation physiognomies generally associated with topographic gradients in savannas of Central Brazil. To estimate the depth of plant water uptake in the different slope positions we relied on comparisons of hydrogen and oxygen isotope ratios of plant stem water, water from different soil depths, from groundwater and from rainfall. We subsequently used a stable isotope mixing model to estimate vertical partitioning of soil water by woody plants along the elevation gradient. We were able to show that groundwater level affected plant water uptake patterns and soil water partitioning among savanna woody species. Vegetation at higher elevation extracted water from deeper unsaturated soils and had greater variability in water uptake strategies, which was coupled to a denser and more complex woody layer. Plants on these soils used stored water from both shallow (<0.6 m) and deep (0.6–2.00 m) soil layers. At lower elevation sites, however, the presence of a water table near the soil surface restricted water uptake to the shallower wet season unsaturated zone of the soil profile. The sparser woody vegetation is probably composed of species that only rely in superficial water uptake, or are plastic in relation to root characteristics.

Recognition and proposal on the vegetation classification system of China

An encyclopedia of Chinese vegetation is going to be compiled as a series of books, and comments are sought to revise the "Vegetation Classification System of China"(VCSC).These require several key decisions. First,the principle of VCSC proposed by Vegetation of China (1980) that "the higher rank of classification unit would be based on the physiognomy of vegetation, while the middle and lower rank emphasized on species composition and community structure" should be maintained because it is corresponding with the current trends of international vegetation classifications. Second, VCSC should classify Chinese vegetation to be compatible with global vegetation classification, so that the terms and concepts will be widely accepted internationally.Third,"Associa-tion", a fundamental classification unit described by the series of books of Chinese vegetation, should be defined and used consistently,so that misunderstandings between northern and southern associations can be avoided. Fourth, the hierarchy in the classification of vegetation generally should be rigid, but different ranks remain open and flexible, i.e.,upper-level units can be supplemented to meet future needs. A draft of the VCSC (from class to vegetation type) is proposed in this paper.

Áreas de endemismo: as espécies vivem em qualquer lugar, onde podem ou onde historicamente evoluíram?

. Areas of endemism are coincidences between species ranges and hypotheses of common restriction events for part of a biota. Several historical processes can be the causes of this restriction, such as orogenetic events, climatic fluctuation, changes in vegetation physiognomies, or the appearing of any geographic barrier. To objectively delimitate an area of endemism, one needs numerical analyses instead of simply relying on congruences in distribution ranges. As historical hypothesis, the phylogenetic relationship between the endemic species in question, the geographical evidence, and the identification of transition zones must also be taken into account. Although these areas are important for biogeographical regionalization and conservation plans, they have been poorly studied, and we still face the increasing necessity for a more interdisciplinary approach in Biogeography

Richness preservation in a fragmented landscape: a study of epiphytic bryophytes in an Atlantic forest remnant in Northeast Brazil

Fragmentation and loss of habitat are considered to be the main causes for the decrease in biological diversity in tropical forests. This study aims to evaluate the size and edge effects on tree physiognomy and on the bryophyte community structure in relation to richness, composition, and distribution of ecological groups. Ten forest fragments from the Murici Ecological Station, in the state of Alagoas (Brazil) were studied. In each fragment 10 evenly spaced plots were delimited along four 100 m transects located perpendicularly to the border. One hundred and six species were found, of which 56 were liverworts and 50 were mosses. Results showed that flora impoverishment and other variations in the bryophyte community structure are related to fragment size. Shade epiphytes were the most affected. An ‘edge effect’ was not detected in this study. Vegetation physiognomy parameters contributed partially to the bryophytes’ responses. Diameter at breast height, height, and the density of trees were both positively correlated with bryophyte richness, while canopy openness was not. Our results suggest that the larger fragments are better structured physiognomically, i.e. the trees are taller and have larger diameters, which are probably important factors in enabling them to retain a rich bryophyte flora.

Development of an IKONOS image classification rule-set for multi-scale mapping of Mediterranean rural landscapes

In this research, a rule-set of object-based classification of IKONOS imagery for fine-scale mapping of Mediterranean rural landscapes was developed. This study was conducted on the Mediterranean island of Crete (Greece). A three-level classification hierarchy was designed in a bottom-up approach containing a total number of 22 classes. The first level was associated with vegetation physiognomy (6 classes), the second level with linear features (6 classes) and the third level with land uses existing in the area (10 classes). Image objects were created with multiresolution segmentation, an algorithm supplied by eCognition software. The segmentation parameters were selected through a trial-and-error approach after visual evaluation of the resulting image objects. The rule-set comprised 100 classification rules described with the ‘Membership Function’ classifier. The classification stability was found to lie between 0.59 and 0.77, inversely proportional to the complexity of each level's classification. For an accuracy assessment, the error matrix method was used in a set of 250 randomly selected points. The overall classification accuracy achieved at the first level was 74%, at the second level 50% and at the third level 64%. The geometric accuracy of the classification was beyond the scope of this research; and moreover, consistent reference data sets were not available. The conclusion is that the use of rules in an object-based image analysis (OBIA) process has the potential to produce accurate landscape maps even in the case of complex environments, in which ancillary data are not available. Future work should focus on testing the transferability of the rule-set in different Mediterranean study sites, in order to draw a conclusion in relation to its potential operational use.

Road Verges: Potential Refuges for Declining Grassland Species Despite Remnant Vegetation Dynamics

Whether road verge vegetation can be manipulated to resemble traditionally managed grassland has been much debated. This short-term study compared management effects on road verge and pasture vegetation in western Norway. We quantified vegetation change and explored whether it occurred along underlying environmental gradients. We found management-related variation in species richness and vegetation physiognomy, but high resistance in species composition prevented directional changes in vegetation dynamics. Initial differences between the habitats indicated historical management effects on traditionally managed pastures and road verges. Given proper management, road verges may have a nature conservation potential. Moreover, their linear structure may enable fine-scale mosaic management that allows the coexistence of a wide range of grassland species.

Combining Isomap ordination and imaging spectroscopy to map continuous floristic gradients in a heterogeneous landscape

Mapping requires a meaningful generalization of information. For vegetation maps, classification is frequently used to generalize the species composition of (semi-)natural plant assemblages. As an alternative to classification, ordination methods aim to extract major floristic gradients describing the prevailing compositional variation in a floristic data set as metric variables. This ability has been used previously to derive gradient maps of homogeneous landscapes that show plant species composition in continuous fields. In the present study, gradient mapping was used in a more heterogeneous landscape with intricate environmental gradients and higher variation in vegetation physiognomy. Since established ordination methods may have difficulties to cope with the highly variable plant species composition, we tested the novel method Isometric Feature Mapping (Isomap) against conventional methods (Detrended Correspondence Analysis and Nonmetric Multidimensional Scaling). The resulting floristic gradients were related to hyperspectral imagery (HyMap) using partial least squares regression (PLSR) and subsequently mapped. Prediction uncertainties are provided as additional map. Isomap was able to preserve 74% of the original variation inherent to the floristic data set in a three-dimensional solution. This was considerably more than the established techniques achieved. The PLSR models for the floristic gradients extracted with Isomap showed model fits ranging from R² = 0.59 to R² = 0.73 in calibration and from R² = 0.55 to R² = 0.69 in tenfold cross-validation. The resulting gradient map provides detailed information on compositional vegetation patterns.

Common ground between two British Pennsylvanian wetland floras: Using large, first-hand datasets to assess utility of historical museum collections

Studies on the macrofloral record of the Pennsylvanian palaeotropical peat-forming wetlands (‘coal swamps’) depend heavily on historical collections in museums. This paper examines the robustness of such collections for macrofloral studies. 110,000 individually recorded specimens from South Wales, field collected by David Davies during the early 20th century, were compared with the 6500 museum voucher specimens derived from them, eventually intended for a representative teaching collection. This showed that the voucher collections accurately reflect the order of abundances of the plant groups as documented in the field records, but not their actual numerical abundances. These Welsh data were then compared with the available museum collections for similar-aged macrofloras in the nearby Bristol–Somerset Coalfield. Cluster analyses and Detrended Correspondence Analyses were performed (1) on the raw data recorded on the museum labels, (2) on standardised data that were updated to reflect the currently accepted taxonomy for these fossils, and (3) on standardised data in which single occurrences of taxa have been removed. The results suggest that unstandardised museum collection data can reveal meaningful biostratigraphical and biogeographical patterns, but that these become clearer with the standardised data. The effect of removing the singleton taxa was less clear, although it did provide a slightly enhanced resolution with cluster analysis. Whilst previous studies have considered these to be separate basins, with the Bristol–Somerset coalfield being proximal to South Wales on the mid-Pennsylvanian Variscan Front, results show an overall consistency between the two basins and suggest a common gene pool and vegetational physiognomy as well as a general stasis through time based on relatively stable environmental and growth conditions. The study confirms that even unrevised historical collections can provide some data to help understand the dynamics of these systems. However, it also underlines the importance of taxonomy in such studies as it helps improve both the biostratigraphical and biogeographical resolution.

Characterizing vegetation cover in global savannas with an annual foliage clumping index derived from the MODIS BRDF product

The global savanna biome is characterized by enormous diversity in the physiognomy and spatial structure of the vegetation. The foliage clumping index can be calculated from bidirectional reflectance distribution function (BRDF) data. It measures the response of the darkspot reflectance to increased shadow associated with clumped vegetation and is related to leaf area index. Clumping index theoretically declines with increasing woody cover until the tree canopy begins to become uniform. In this study, clumping index is calculated for Moderate Resolution Imaging Spectroradiometer BRDF data for the Australian tropical savanna, the tropical savannas of South America, and the tropical savannas of east, west and southern Africa and compared with site-based measurements of tree canopy cover, and with area-based classifications of land cover. There were differences in sensitivity of clumping index between red and near-infrared reflectance channels, and between savanna systems with markedly different woody vegetation physiognomy. Clumping index was broadly related to foliage cover from historical site data in Australia and in West Africa and Kenya, but not in Southern Africa nor with detailed site-based demographic data in the cerrado of Brazil. However, clumping index decreased with proportion of woody cover in land cover datasets for east Africa, Australia and the Colombian Llanos. There was overlap in the range of clumping index values for forest, cerrado and campo land covers in Brazil. Clumping index was generally negatively correlated with percentage tree cover from the MODIS Vegetation Continuous Fields product, but regional differences in the relationship were evident. There were large differences in the frequency distributions of clumping index from savanna, woody savanna and grassland land cover classes between global ecoregions. The clumping index shows differing sensitivity to savanna woody cover for red and NIR reflectance, and requires regional calibration for application as a universal indicator.

Determinants of plant community composition of remnant biancane badlands: a hierarchical approach to quantify species-environment relationships

Question: Which environmental variables best explain patterns in the vegetation of biancane badlands? What is the role of spatial scales in structuring the vegetation of biancane badlands within the agricultural matrix? Location: Five biancane badlands in Central Italy (Tuscany). Methods: An object-oriented approach on high-resolution multispectral images was used to classify physiognomic vegetation types in five biancane badlands. Within each badland, data on vascular plant species abundance were collected using a stratified random design. Variation partitioning based on partial redundancy analysis was used to evaluate the contribution of three sets of environmental predictors, recorded at the spatial scales of plot, patch and biancane badland in explaining patterns in plant community composition. Results: Environmental variables included in the final model ‐ electrical conductivity and carbon/nitrogen ratio (plot scale), shape index (patch scale) and area (biancane badland scale) ‐ accounted for 15.5% of the total variation in plant community composition. Soil characteristics measured at the plot level explained the majority of variation. In the smallest badlands, Bromus erectus perennial grasslands were absent, while annual grasslands, linked with harsh soil conditions (i.e. high soil salinity), were not affected by either the surface area of biancane badlands or by the soil nitrogen availability. Conclusions: The identification of the major predictors of patterns in remnant vegetation requires conducting investigations at multiple spatial scale. Management strategies should operate at different spatial scale, preventing any further reduction in the size of existing badlands and relying on habitat- instead of area-focused conservation practices.

Fraction images for monitoring intra-annual phenology of different vegetation physiognomies in Amazonia

In this study we investigate the potential of fraction images derived from a linear spectral mixture model to detect vegetation phenology in Amazonia, and evaluate their relationships with the Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices. Time series of MODIS 250-m data over three contrasting land cover types in the Amazon were used in conjunction with rainfall data, a land cover map and a forest inventory survey to support the interpretation of our findings. Each vegetation physiognomy was characterized by a particular intra-annual variability detected by a combination of the fraction images. Both vegetation and shade fractions were important to evaluate the seasonality of the open tropical forest (OTF). The association of these results with forest inventory data and the literature suggests that Enhanced Vegetation Index (EVI) and vegetation fraction images are sensitive to structural changes in the canopy of OTF. In cerrado grassland (CG) the phenology was better characterized by combined soil and vegetation fractions. Soybean (SB) areas were characterized by the highest ranges in the vegetation and soil fraction images. Vegetation fraction and vegetation indices for the OTF showed a significant positive relationship with EVI but not with Normalized Difference Vegetation Index (NDVI). Significant relationships for vegetation fraction and vegetation indices were also found for the CG and soybean areas. In contrast to vegetation index approaches to monitoring phenology, fraction images provide additional information that allows a more comprehensive exploration of the spectral and structural changes in vegetation formations.

Pedological and isotopic relations of a highland tropical peatland, Mountain Range of the Espinhaço Meridional (Brazil)

The evolution of organic matter sources in soil is related to climate and vegetation dynamics in the past recorded in paleoenvironmental Quaternary deposits such as peatlands. For this reason, a Histosol of the mineralotrophic peatland from the Pau-de-Fruta Special Protection Area - SPA, Espinhaço Meridional, State of Minas Gerais, was described and characterized to evidence the soil constituent materials and properties as related to changes in environmental conditions, supported by the isotopic and elementary characterization of soil C and N and 14C ages. Samples were collected in a depression at 1,350 m asl, where Histosols are possibly more developed due to the great thickness (505 cm). Nowadays, the area is colonized by vegetation physiognomies of the Cerrado Biome, mainly rocky and wet fields (Campo Rupestre and Campo Úmido), aside from fragments of Semidecidual Seasonal Forest, called Capões forests. The results this study showed that early the genesis of the analyzed soil profile showed a high initial contribution of mostly herbaceous organic matter before 8,090 ± 30 years BP (14C age). In the lower-mid Holocene, between 8,090 ± 30 years AP (14C age) to ± 4,100 years BP (interpolated age), the vegetation gradually became more woody, with forest expansion, possibly due to increased humidity, suggesting the existence of a more woody Cerrado in the past than at present. Drier climate conditions than the current were concluded ± 2,500 years BP (interpolated age) and that after 430 years BP (14C age) the forest gave way to grassland, predominantly. After the dry season, humidity increased to the current conditions. Due to these climate fluctuations during the Holocene, three decomposition stages of organic matter were observed in the Histosols of this study, with prevalence of the most advanced (sapric), typical of a deposit in a highly advanced stage of pedogenetic evolution.

The role of climate and plant functional trade-offs in shaping global biome and biodiversity patterns

Aim: Two of the oldest observations in plant geography are the increase in plant diversity from the poles towards the tropics and the global geographic distribution of vegetation physiognomy (biomes). The objective of this paper is to use a process-based vegetation model to evaluate the relationship between modelled and observed global patterns of plant diversity and the geographic distribution of biomes. Location: The global terrestrial biosphere. Methods: We implemented and tested a novel vegetation model aimed at identifying strategies that enable plants to grow and reproduce within particular climatic conditions across the globe. Our model simulates plant survival according to the fundamental ecophysiological processes of water uptake, photosynthesis, reproduction and phenology. We evaluated the survival of an ensemble of 10,000 plant growth strategies across the range of global climatic conditions. For the simulated regional plant assemblages we quantified functional richness, functional diversity and functional identity. Results: A strong relationship was found (correlation coefficient of 0.75) between the modelled and the observed plant diversity. Our approach demonstrates that plant functional dissimilarity increases and then saturates with increasing plant diversity. Six of the major Earth biomes were reproduced by clustering grid cells according to their functional identity (mean functional traits of a regional plant assemblage). These biome clusters were in fair agreement with two other global vegetation schemes: a satellite image classification and a biogeography model (kappa statistics around 0.4). Main conclusions: Our model reproduces the observed global patterns of plant diversity and vegetation physiognomy from the number and identity of simulated plant growth strategies. These plant growth strategies emerge from the first principles of climatic constraints and plant functional trade-offs. Our study makes important contributions to furthering the understanding of how climate affects patterns of plant diversity and vegetation physiognomy from a process-based rather than a phenomenological perspective.

Relationship between anthropogenic sewage discharge, marsh structure and bird assemblages in an SW Atlantic saltmarsh

One of the main effects of urbanization on coastal areas is through the discharge of sewage, which increases nutrient concentrations in the receiving environment. Salt marshes, like other coastal marine environments, are limited by nutrients, mainly nitrogen, and thus increasing nutrient loadings to a marsh may have consequences on marsh characteristics. We evaluated how the effects of nutrient enrichment in the form of sewage input, affected the vegetation structure and bird assemblages in a Spartina alterniflora salt marsh system near Bahía Blanca, Argentina (39° 01′ S – 56° 25′ W). Surveys of nutrient concentration, vegetation and birds were made at three different distances from the sewage discharge source. The concentration of ammonium, phosphate, and nitrate and the percent organic matter was higher in marshes nearest to the sewage discharge source. Bird composition and abundance, and vegetation physiognomy changed along a gradient of nutrient concentration. The increased habitat complexity found near the areas of higher nutrient concentration was exploited by birds that use neighboring interior and coastal habitats, including Spartina densiflora marshes, freshwater marshes and upland shrubby habitats. Our results show that local increases of nutrient inputs directly changed the vegetation physiognomy, and indirectly the composition and abundance of bird assemblages.