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Detrended Correspondence Analysis (detrended + correspondence_analysis)
Selected AbstractsVegetation patterns and environmental gradients in tropical dry forests of the northern Yucatan PeninsulaJOURNAL OF VEGETATION SCIENCE, Issue 2 2004D.A. White Patterns of plant species composition and their relationships to soil and topographic variables were investigated in tropical dry forests across the north central Yucatan, Mexico. Seven sites were studied in the oldest accessible forests along a 200,km transect oriented northwest to southeast; an eighth site was located in a little-disturbed area located 75 km northeast of the transect. Two of the sites were on Mayan ruins. All sites were sampled using 9,24, 10m × 20m plots ( Polychaete Communities of Greece: An Ecological OverviewMARINE ECOLOGY, Issue 2 2000Nomiki Simboura Abstract. Benthic samples were collected from 188 stations distributed over the Aegean and Ionian Seas (Greece, Eastern Mediterranean). Sampled substrata represented a variety of biotopes in soft bottoms with depths ranging from 3 to 380 m. The samples yielded a total of 398 species of polychaetes. Detrended Correspondence Analysis was applied to the whole set of data as well as to three bathymetric groups into which the data was divided. The results showed that in each bathymetric group, different factors determine the spatial distribution of species. Over the whole data set the type of substrata proved to be the major factor, whereas depth is the second most important. Other controlling factors were the substratum type and exposure to hydrodynamism in the shallow group, depth and substratum in the intermediate, and sediment granulometry and depth in the deep one. Diversity, species number and density tended to decrease with depth, while diversity and species number are favoured by coarse material in the sediment. [source] The influence of stream invertebrate composition at neighbouring sites on local assemblage compositionFRESHWATER BIOLOGY, Issue 2 2005R. A. SANDERSON Summary 1. The composition of freshwater invertebrate assemblages at a location is determined by a range of physico-chemical and biotic factors in the local environment, as well as larger-scale spatial factors such as sources of recruits. We assessed the relative importance of the species composition of local neighbourhoods and proximal environmental factors on the composition of invertebrate assemblages. 2. Macroinvertebrate assemblages were sampled at 188 running-water sites in the catchment of the River Rede, north-east England. A total of 176 species were recorded. 3. Environmental data, in the form of 13 biotic and abiotic measurements that described stream physical structure, aquatic vegetation and water characteristics, were recorded for each site. Detrended correspondence analysis was then used to simplify nine of these stream environmental variables to create an index of stream structure. 4. The species composition of the invertebrate assemblages was related to the environmental variables, using an information theoretic approach. The impact of the species composition of neighbouring sites on each site was determined using Moran's I and autoregressive modelling techniques. 5. Species composition was primarily associated with water pH and stream structure. The importance of the species composition of neighbouring sites in determining local species assemblages differed markedly between taxa. The autoregressive component was low for Coleoptera, intermediate for Trichoptera and Plecoptera, and high for Ephemeroptera. 6. We hypothesise that the observed differences in the autoregressive component amongst these orders reflects variation in their dispersal abilities from neighbouring sites. [source] Anthropogenic and climatic impacts on surface pollen assemblages along a precipitation gradient in north-eastern ChinaGLOBAL ECOLOGY, Issue 5 2010Yun Zhang ABSTRACT Aim, To understand the scenarios of ,anthropogenic biomes' that integrate human and ecological systems, we need to explore the impacts of climate and human disturbance on vegetation in the past and present. Interactions among surface pollen, modern vegetation and human activities along climate and land-use gradients are tested to evaluate the natural and anthropogenic forces shaping the modern vegetation, and hence to aid the reconstruction of vegetation and climate in the past. This in turn will help with future predictions. Location, The North-east China Transect (NECT) in north-eastern China. Methods, We analysed 33 surface pollen samples and 213 quadrats across four vegetation zones along the moisture/land-use gradients of the NECT. Detrended correspondence analysis (DCA) and redundancy analysis (RDA) of 52 pollen taxa and three environmental variables were used to distinguish anthropogenic and climatic factors that affect surface pollen assemblages along the NECT. Results, The 33 surface samples are divided into four pollen zones (forest, meadow steppe, typical steppe and desert steppe) corresponding to major vegetation types in the NECT. Variations in pollen ratios of fern/herb (F/H), Artemisia/Chenopodiaceae (A/C) and arboreal pollen/non-arboreal pollen (AP/NAP) represent the vegetation and precipitation gradient along the NECT. DCA and RDA analyses suggest that surface pollen assemblages are significantly influenced by the precipitation gradient. Changes in the abundance of Chenopodiaceae pollen are related to both human activities and precipitation. Main conclusions, Surface pollen assemblages, fossil pollen records, archaeological evidence and historical documents in northern China show that a large increase of Chenopodiaceae pollen indicates human-caused vegetation degradation in sandy habitats. The A/C ratio is a good indicator of climatic aridity, but should be used in conjunction with multiple proxies of human activities and climate change in the pollen-based reconstruction of anthropogenic biomes. [source] Vegetation of the Stipa loess steppe in Ningxia (northern China) in relation to grazing intensityGRASSLAND SCIENCE, Issue 3 2007Yingzhong Xie Abstract Large areas of northern and western China are covered with steppe vegetation which is grazed with different intensities. Areas which are not or only slightly grazed are rare and mostly exist in nature reserves. We investigated floristic composition and species diversity of the steppe vegetation of the autonomous region Ningxia Hui with emphasis on the Yunwushan dry steppe nature reserve in relation to grazing intensity; all 77 plots were analyzed using ordination techniques, and the relationship between the variation in species composition and environmental conditions was analyzed. In Ningxia, two types of loess grass steppes prevail: in areas with lower altitudes from approximately 1650,1950 m a.s.l., the Stipa bungeana steppe occurs whereas the Stipa grandis steppe is typical for higher altitudes between 1900 and 2100 m a.s.l. For both vegetation types, three subtypes can be distinguished according to different levels of grazing intensity. With increasing grazing intensity, the number of plant species per plot strongly declines and the typical steppe vegetation types are dominated by Artemisia species (A. frigida in the Stipa grandis community and A. sacrorum in the Stipa bungeana community). In contrast to studies carried out in neighboring areas, in our study area the Artemisia steppes do not represent the final state of degradation. Instead, Convolvulus ammanii dominates in heavily grazed areas of both Stipa steppe types. Detrended correspondence analysis confirms the classification and shows that the heavily grazed subtypes of the Stipa grandis and the Stipa bungeana steppe with Convolvulus ammanii are more similar to each other than the other vegetation types. The first axis of the detrended correspondence analysis is strongly related to the grazing intensity (r = 0.93). Our results show that grazing intensity is an important factor for the differentiation of the steppe grasslands and a severe threat to species diversity. [source] Fish assemblages as influenced by environmental factors in streams in protected areas of the Czech RepublicECOLOGY OF FRESHWATER FISH, Issue 1 2006M. Humpl Abstract,,, Three streams of comparable size located in different landscape-protected areas were selected for studying the effect of environmental factors on fish assemblages using indirect (detrended correspondence analysis, DCA) and direct (canonical correspondence analysis, CCA) gradient analysis. DCA of species showed well a gradient of assemblage changes in the longitudinal profile. DCA of sites stressed the variability between the fish assemblages of the three streams. This pattern was then confirmed by the highly significant between-stream CCA. In the within-site CCA, environmental factors explained 50.7% variability for presence,absence data and 58.3% for the relative abundance data. The analysis revealed that number of ponds and land use are the most influential factors of the strongest environmental gradient. However, in the partial CCAs, factor substratum type explained the largest proportion of the variability affecting fish in their habitat choice. Generally, presence,absence and relative abundance data of fish gave similar results in both DCA and CCA analyses; the same environmental factors proved to be important in both data type analyses. The environmental factors explain more variability than the regional (between-stream) one. The total proportion of variability explained by the presence,absence data analysis was 71.9% and in the relative abundance analysis even 80.8%. The environmental factors measured during the field survey explain 2.1- and 3.4-times more assemblages' variability than factors measured from a hydrological map. Resumen 1. Tres ríos de tamaño comparable localizados en diferentes áreas de paisaje protegido de la República Checa fueron seleccionados para estudiar el efecto de factores ambientales sobre los ensamblajes de peces. Para ello, utilizando análisis de gradientes indirectos (DCA) y directos (CCA). 2. El DCA para las especies enfatizó la variabilidad entre los ensamblajes de peces de los tres ríos. Este patrón fue confirmado por un CCA altamente significativo. Para la variabilidad dentro de la localidad, un CCA reveló que los factores ambientales explicaron un 50.7% para datos de presencia-ausencia y un 58.3% para las abundancias relativas. 3. Los análisis revelaron que el número de pozas y el uso del suelo fueron los factores de mayor influencia en el gradiente ambiental. Sin embargo, en el CCA parcial, el tipo de sustrato explicó la mayor proporción de la variabilidad que afecta a los peces en la elección de hábitat. 4. Generalmente los datos de presencia-ausencia y abundancia relativa produjeron resultados similares tanto en los análisis DCA como en los CCA; los mismos factores ambientales probaron ser importantes en los análisis de ambos tipos de datos. Los factores ambientales explicaron mas variabilidad que los regionales (entre ríos). La proporción total de variabilidad explicada por el análisis de los datos de presencia-ausencia fue 71.9% mientras que para las abundancias relativas fue de 80.8%. Los factores ambientales medidos durante los muestreos de campo explicaron 2.1 y 3.4 veces mas variabilidad que los factores medidos sobre mapas hidrológicos. [source] Vegetation gradients in Atlantic Europe: the use of existing phytosociological data in preliminary investigations on the potential effects of climate change on British vegetationGLOBAL ECOLOGY, Issue 3 2000J. C. Duckworth Abstract 1This paper aims to demonstrate the use of available vegetation data from the phytosociological literature in preliminary analyses to generate hypotheses regarding vegetation and climate change. 2Data for over 3000 samples of calcareous grassland, mesotrophic grassland, heath and woodland vegetation were taken from the literature for a region in the west of Atlantic Europe and subjected to ordination by detrended correspondence analysis in order to identify the main gradients present. 3Climate data were obtained at a resolution of 0.5° from an existing database. The relationship between vegetation composition and climate was investigated by the correlation of the mean scores for the first two ordination axes for each 0.5° cell with the climate and location variables. 4The ordinations resulted in clear geographical gradients for calcareous grasslands, heaths and woodlands but not for mesotrophic grasslands. Significant correlations were shown between some of the vegetation gradients and the climate variables, with the strongest relationships occurring between the calcareous grassland gradients and July temperature, latitude and oceanicity. Some of the vegetation gradients were also inferred to reflect edaphic factors, management and vegetation history. 5Those gradients that were related to temperature were hypothesized to reflect the influence of a progressively warmer climate on species composition, providing a baseline for further studies on the influence of climate change on species composition. 6The validity of the literature data was assessed by the collection of an original set of field data for calcareous grasslands and the subsequent ordination of a dataset containing samples from both the literature and the field. The considerable overlap between the samples from the literature and the field suggest that literature data can be used, despite certain limitations. Such preliminary analyses, using readily available data, can thus achieve useful results, thereby saving lengthy and costly field visits. [source] Effect of soil and physiographic factors on ecological plant groups in the eastern Elborz mountain rangeland of IranGRASSLAND SCIENCE, Issue 2 2010Mohammadreza Tatian Abstract To investigate the cause of differences among ecological plant groups in the east of the Elborz mountain rangeland, the role of edaphical and topographical characteristics was considered. Two ordination techniques, detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA), were used. The values of slope, aspect, altitude and lithology information were provided by Geographic Information System (GIS), and geomorphological land units were determined by intersection of overlaid data layers. Plant sampling was undertaken within nine land units with similar lithology and altitude but which differed in slope and aspect, using 30 randomly selected 1 m2 plots per land unit. Soil samples were taken from two depths (0,20 and 20,50 cm) in each plot. Organic matter, bulk density, texture, calcium carbonate, total nitrogen and available phosphorus and potassium contents were determined. The results indicated that plant species have different responses to edaphical and topographical parameters. The invader species group had a balanced amount of influence from all soil components and topographic factors, whereas the native grasses were located in productive soils, which typically have a low grazing intensity, such as the north facing slopes. Coniferous bushy trees, cushion plants and some shrub plant groups were found on steep slopes with alkaline soils. The broad-leaved bushy trees plant group was abundant in fine texture soils on low and humid slopes. [source] Vegetation of the Stipa loess steppe in Ningxia (northern China) in relation to grazing intensityGRASSLAND SCIENCE, Issue 3 2007Yingzhong Xie Abstract Large areas of northern and western China are covered with steppe vegetation which is grazed with different intensities. Areas which are not or only slightly grazed are rare and mostly exist in nature reserves. We investigated floristic composition and species diversity of the steppe vegetation of the autonomous region Ningxia Hui with emphasis on the Yunwushan dry steppe nature reserve in relation to grazing intensity; all 77 plots were analyzed using ordination techniques, and the relationship between the variation in species composition and environmental conditions was analyzed. In Ningxia, two types of loess grass steppes prevail: in areas with lower altitudes from approximately 1650,1950 m a.s.l., the Stipa bungeana steppe occurs whereas the Stipa grandis steppe is typical for higher altitudes between 1900 and 2100 m a.s.l. For both vegetation types, three subtypes can be distinguished according to different levels of grazing intensity. With increasing grazing intensity, the number of plant species per plot strongly declines and the typical steppe vegetation types are dominated by Artemisia species (A. frigida in the Stipa grandis community and A. sacrorum in the Stipa bungeana community). In contrast to studies carried out in neighboring areas, in our study area the Artemisia steppes do not represent the final state of degradation. Instead, Convolvulus ammanii dominates in heavily grazed areas of both Stipa steppe types. Detrended correspondence analysis confirms the classification and shows that the heavily grazed subtypes of the Stipa grandis and the Stipa bungeana steppe with Convolvulus ammanii are more similar to each other than the other vegetation types. The first axis of the detrended correspondence analysis is strongly related to the grazing intensity (r = 0.93). Our results show that grazing intensity is an important factor for the differentiation of the steppe grasslands and a severe threat to species diversity. [source] The inselberg flora of Atlantic Central Africa.JOURNAL OF BIOGEOGRAPHY, Issue 4 2005Abstract Aims, To identify the relative contributions of environmental determinism, dispersal limitation and historical factors in the spatial structure of the floristic data of inselbergs at the local and regional scales, and to test if the extent of species spatial aggregation is related to dispersal abilities. Location, Rain forest inselbergs of Equatorial Guinea, northern Gabon and southern Cameroon (western central Africa). Methods, We use phytosociological relevés and herbarium collections obtained from 27 inselbergs using a stratified sampling scheme considering six plant formations. Data analysis focused on Rubiaceae, Orchidaceae, Melastomataceae, Poaceae, Commelinaceae, Acanthaceae, Begoniaceae and Pteridophytes. Data were investigated using ordination methods (detrended correspondence analysis, DCA; canonical correspondence analysis, CCA), Sørensen's coefficient of similarity and spatial autocorrelation statistics. Comparisons were made at the local and regional scales using ordinations of life-form spectra and ordinations of species data. Results, At the local scale, the forest-inselberg ecotone is the main gradient structuring the floristic data. At the regional scale, this is still the main gradient in the ordination of life-form spectra, but other factors become predominant in analyses of species assemblages. CCA identified three environmental variables explaining a significant part of the variation in floristic data. Spatial autocorrelation analyses showed that both the flora and the environmental factors are spatially autocorrelated: the similarity of species compositions within plant formations decreasing approximately linearly with the logarithm of the spatial distance. The extent of species distribution was correlated with their a priori dispersal abilities as assessed by their diaspore types. Main conclusions, At a local scale, species composition is best explained by a continuous cline of edaphic conditions along the forest-inselberg ecotone, generating a wide array of ecological niches. At a regional scale, these ecological niches are occupied by different species depending on the available local species pool. These subregional species pools probably result from varying environmental conditions, dispersal limitation and the history of past vegetation changes due to climatic fluctuations. [source] Representing species in reserves from patterns of assemblage diversityJOURNAL OF BIOGEOGRAPHY, Issue 7 2004M. B. Araújo Abstract Aim, A positive relationship between assemblage diversity (AD) , equivalent to the biotic version of the environment diversity, ED, method , and species diversity has been reported. This being true, reserve networks with many different assemblages would be expected to represent more species than reserve networks including fewer and less different assemblages. This idea was tested using European species atlas distributions of terrestrial vertebrates and plants. It is asked whether: (1) maximizing AD within one group would represent species diversity of this group better than expected by chance; and (2) maximizing AD within one group would represent species diversity of other groups better than expected by chance. Location, Europe. Methods, Three ordination techniques (non-metric multidimensional scaling, detrended correspondence analysis and correspondence analysis) are used to summarize patterns of compositional turnover within assemblages. p -Median location-allocation models are then calculated from ordination space to measure the degree of expected species representation within the group being sampled as well as the expected representation within other groups. Results are compared with near-optimal solutions obtained with complementarity-based algorithms and to a null model obtained by simulating selection of areas at random. Matrix correlation analysis was also performed to investigate broad patterns of covariation in compositional turnover of assemblages of species belonging to different taxonomic groups and these values were compared with correlation in species richness scores between groups. Results, The AD model did not always represent more species of the group being sampled than expected by chance (P < 0.05). Results were independent of the method and taxonomic group considered. Effectiveness of AD within one group to represent species of other groups varied, but in most cases it was worse than using complementarity-based algorithms as a surrogate strategy. Even when correlations indicated high coincidence between assemblages, taxonomic-based surrogates did not always recover more species than expected by chance (P < 0.05). Main conclusions, Results are discussed in the light of two possible explanations: (1) the AD model is based on unrealistic assumptions, namely that species have equal probability of having the centre of their distributions anywhere in ordination space and that species display unimodal, symmetrical, bell-shaped response curves to gradients; (2) particular implementation of methods may be inadequate to summarize useful complementarity among assemblages, especially for restricted-range species. We conclude that both arguments are likely to play a role in explaining results, but that opportunities exist to improve performance of existing surrogate strategies. [source] Community organization and species richness of ants (Hymenoptera/Formicidae) in Mongolia along an ecological gradient from steppe to Gobi desertJOURNAL OF BIOGEOGRAPHY, Issue 12 2003Martin Pfeiffer Abstract Aim, Ants (Hymenoptera/Formicidae) have strong influences on ecosystems especially in arid regions. However, little is known about ants of the vast steppe and desert regions of Central Asia. Here we provide the first comprehensive study of ant communities in Mongolia, conducted along a north-to-south gradient in climate. We examined ants' distribution patterns, assessed the impact of climatic parameters on community structure and species diversity and investigated the influence of the corresponding communities of plants. Location, Mongolia (Central Asia). Methods, We observed 31,956 ants at seed baits at 11 study sites along a transect from steppe to Gobi desert for which we attained meteorological data (mean yearly precipitation: 197 to 84 mm). Extra sampling was conducted at sugar and protein baits and by the inspection of different microhabitats. Vegetation patterns of each plot were recorded. Statistical evaluation comprised ordination and correlation. Results, We observed 15 species of ants at seed baits. Three faunal complexes of ants could be distinguished by detrended correspondence analysis (DCA): (1) in steppe baits were dominated by Formica - and Myrmica -species, (2) in semi desert we found mostly species of Tetramorium, Myrmica, Proformica, Plagiolepis, and Leptothorax, and (3) in desert Cataglyphis aenescens and Messor aciculatus dominated, and Lasius was exclusively found there. Another 11 rare ant species were sampled by hand and at sugar baits. Altogether five ant species were new to the Mongolian fauna: Cardiocondyla koshewnikovi, Myrmica koreana, Myrmica pisarskii, Polyergus nigerrimus, and Proformica kaszabi. Assignment of taxa to functional groups showed that in steppe cold climate specialists dominated, in semi desert we found mainly opportunists, and in desert hot climate specialists. Several functional groups know from arid zones in other parts of the world were missing. In desert certain species were highly dominant. First DCA scores of ant- and plant-communities were highly correlated with each other and with climatic parameters. While plant species diversity was positively correlated with increasing northern latitude, ant diversity and ant species richness were not correlated with latitude and responded neither to precipitation, nor to any other climatic parameter. Semi desert was a transition zone between steppe and desert, with high species richness. Ant genus composition of the ecotone overlapped with both other regions. However, beta diversity between pairs of plots within this zone was low, indicating a small-scale mosaic pattern. Main conclusions, The ant communities in the Mongolian steppe and desert zones were strongly influenced by low temperatures and differed in many aspects from the ant fauna in other arid ecosystems, especially in terms of species richness, diversity of feeding guilds, and richness of functional groups. [source] Spatial and temporal analysis of vegetation mosaics for conservation: poor fen communities in a Cornish valley mireJOURNAL OF BIOGEOGRAPHY, Issue 9 2003E. J. Southall Abstract Aim Biogeographers increasingly realize the importance of seeing plant communities as spatial mosaics and understanding the spatial and temporal heterogeneity of a site is often a key to successful conservation. The aim of this paper is to examine the approaches to the description and analysis of spatial and temporal variation in sub-communities within patch mosaics of vegetation in order to inform conservation management. The activities of the tin streaming industry in Cornwall over the last century have created a highly varied mosaic of poor fen vegetation on Goss Moor National Nature Reserve (NNR). The wetland mosaics comprise dry hummocks and different sized wet pools. The size and depth of the pools determines the rate and type of vegetation that develops, as does the nature of boundary or edge. The ergodic hypothesis is used to describe the various plant sub-communities and their boundaries to identify pathways of hydroseral succession. A further aim was to test the use of Ellenberg Indicator (EI) values as a tool for the rapid description of spatial and temporal environmental change on wetland sites with a view to their management. Location Goss Moor National Nature Reserve, Cornwall, UK. Methods An extensive survey of the whole wetland complex was undertaken to identify patches of poor fen vegetation containing Potentilla palustris (L.) Scop. and Menyanthes trifoliata L. At each patch, species abundance data were collected as well as associated environmental information such as depth of the organic layer and standing water depth, patch location, patch size and boundary type. The plant sub-communities present were defined using techniques of numerical classification [two-way indicator species analysis (twinspan)] and ordination [detrended correspondence analysis (DCA)] and these were ordered using the ergodic hypothesis in order to characterize the stages of the hydrosere. Floristic and environmental relationships were examined using canonical correspondence analysis (CCA). Further environmental differences between the poor fen sub-community types were characterized by weighted EI values for acidity (R), moisture (F), nitrogen (N) and light (L). Results and conclusions Twelve poor fen sub-community types were described and found to be distributed along a primary environmental gradient of organic matter depth, surface water height and bare substrate. Separation of the poor fen communities by a moisture gradient was considered as spatial evidence for hydroseral succession, which begins with the colonization of open-water pools created by tin excavations. High water levels were associated with the swamp communities, increased organic depth was associated with poor fen, and the type of boundary was shown to affect the resulting community composition. Weighted Community Ellenberg Indicator values for nitrogen, light, reaction and moisture are recommended as an effective tool for indicating differences between plant (sub-)communities. The importance of examining sub-community mosaics in the study of hydroseral development is stressed and the manner in which both sets of information may be used to underpin the conservation management of the site is demonstrated. [source] The forests of presettlement New England, USA: spatial and compositional patterns based on town proprietor surveysJOURNAL OF BIOGEOGRAPHY, Issue 10-11 2002Charles V. Cogbill Abstract Aim, This study uses the combination of presettlement tree surveys and spatial analysis to produce an empirical reconstruction of tree species abundance and vegetation units at different scales in the original landscape. Location, The New England study area extends across eight physiographic sections, from the Appalachian Mountains to the Atlantic Coastal Plain. The data are drawn from 389 original towns in what are now seven states in the north-eastern United States. These towns have early land division records which document the witness trees growing in the town before European settlement (c. seventeenth to eighteenth century ad). Methods, Records of witness trees from presettlement surveys were collated from towns throughout the study area (1.3 × 105 km2). Tree abundance was averaged over town-wide samples of multiple forest types, integrating proportions of taxa at a local scale (102 km2). These data were summarized into genus groups over the sample towns, which were then mapped [geographical information system (GIS)], classified (Cluster Analysis) and ordinated [detrended correspondence analysis (DCA)]. Modern climatic and topographic variables were also derived from GIS analyses for each town and all town attributes were quantitatively compared. Distributions of both individual species and vegetation units were analysed and displayed for spatial analysis of vegetation structure. Results, The tally of 153,932 individual tree citations show a dominant latitudinal trend in the vegetation. Spatial patterns are concisely displayed as pie charts of genus composition arrayed on sampled towns. Detailed interpolated frequency surfaces show spatial patterns of range and abundance of the dominant taxa. Oak, spruce, hickory and chestnut reach distinctive range limits within the study area. Eight vegetation clusters are distinguished. The northern vegetation is a continuous geographical sequence typified by beech while the southern vegetation is an amorphous group typified by oak. Main conclusions, The wealth of information recorded in the New England town presettlement surveys is an ideal data base to elucidate the natural patterns of vegetation over an extensive spatial area. The timing, town-wide scale, expansive coverage, quantitative enumeration and unbiased estimates are critical advantages of proprietor lotting surveys in determining original tree distributions. This historical,geographical approach produces a vivid reconstruction of the natural vegetation and species distributions as portrayed on maps. The spatial, vegetational and environmental patterns all demonstrate a distinct ,tension zone' separating ,northern hardwood' and ,central hardwood' towns. The presettlement northern hardwood forests, absolutely dominated by beech, forms a continuum responding to a complex climatic gradient of altitude and latitude. The oak forests to the south are distinguished by non-zonal units, probably affected by fire. Although at the continental scale, the forests seem to be a broad transition, at a finer scale they respond to topography such as the major valleys or the northern mountains. This study resets some preconceptions about the original forest, such as the overestimation of the role of pine, hemlock and chestnut and the underestimation of the distinctiveness of the tension zone. Most importantly, the forests of the past and their empirical description provide a basis for many ecological, educational and management applications today. [source] Spatial and temporal variability in seed dynamics of machair sand dune plant communities, the Outer Hebrides, ScotlandJOURNAL OF BIOGEOGRAPHY, Issue 5 2001N. W. Owen Aim The subjects of seed banks and seed rain represent comparatively neglected areas of biogeography, yet at the community scale, exhibit interesting patterns in both space and time. This paper describes the seed bank and seed rain characteristics of the machair sand dune communities of the Outer Hebrides. As well as looking at individual species distributions and variability, the seed banks and seed rain are examined in terms of their detailed subcommunity composition and its local spatial and temporal variation. The machair plant (sub)communities show extensive degrees of anthropogenic modification because of past and present agricultural management, including cultivation for cereals over wide areas and for potatoes in large numbers of ,lazy beds' or small patches. Thus over the historical period, large areas of machair have undergone regular ploughing and cultivation, which have provided the opportunity for a patchwork of secondary succession to occur. This pattern continues to the present day. Furthermore, most other non-cultivated plant (sub)communities are intensively grazed, primarily by cattle and also by sheep and rabbits. Location South Uist, the Outer Hebrides, north-west Scotland. Methods At two carefully selected locations, a range of these various successional subcommunities have been sampled for their seed banks, by taking cores and for their seed rain, by using specially designed traps located where each seed bank sample was removed. This paired sampling strategy allowed direct comparison of the seed bank and the seed rain. Both individual species distributions and the community assemblages of seed bank/seed rain species are examined in space and time using techniques of numerical classification [two-way indicator species analysis (TWINSPAN)] and ordination [detrended correspondence analysis (DCA)]. Results and conclusions There is considerable heterogeneity within and between machair subcommunities in terms of seed bank and seed rain characteristics. The soil seed banks and seed rain of the agriculturally disturbed machair subcommunities are consistently more dense and more species rich than non-cultivated areas of the machair. Overall, machair seed banks are small and stable with no discernible seasonal trends in either size or species composition. In contrast, seed rain on the machair is characterized by a distinct temporal trend. Both seed banks and seed rain are potentially very poor sources of propagules for recolonization following disturbance, indicating that the majority of revegetation following anthropogenic and/or environmental interference is through vegetative reproduction. [source] Fish assemblage changes relative to environmental factors and time in the Warta River, Poland, and its oxbow lakesJOURNAL OF FISH BIOLOGY, Issue 2 2004T. Penczak Four oxbow lakes and two neighbouring sections of their parent Warta River (Odra River system, Poland) were sampled to investigate differences in fish assemblages between habitats in 1999,2000. Additional comparisons were made with 12 other oxbow lakes in this section of the river that were sampled 30,40 years ago. Downstream of a man-made reservoir, higher species number, diversity and evenness were recorded in oxbow lakes than in the river channel. Upstream of the reservoir, differences in these variables from both habitats were insignificant. Fluvial and stagnant water samples were clearly separated in the multivariate space of a detrended correspondence analysis (DCA). For two oxbow lakes and two neighbouring sections of the Warta River, 12 abiotic and biotic environmental variables were available, and only velocity, water temperature and conductivity were significantly correlated with canonical correspondence analysis (CCA) axes. Fish assemblages of four recently investigated oxbow lakes were clearly separated in the multivariate space of DCA from other neighbouring oxbows sampled 30,40 years ago. Species previously subdominant were becoming rare. Oxbow lakes that are continuously or at least periodically connected with the channel are indispensable for maintaining high biodiversity and a sustainable fishery in the river system. [source] Relationships between soil hydrology and forest structure and composition in the southern Brazilian AmazonJOURNAL OF VEGETATION SCIENCE, Issue 2 2007Stefan Jirka Abstract Question: Is soil hydrology an important niche-based driver of biodiversity in tropical forests? More specifically, we asked whether seasonal dynamics in soil water regime contributed to vegetation partitioning into distinct forest types. Location: Tropical rain forest in northwestern Mato Grosso, Brazil. Methods: We investigated the distribution of trees and lianas , 1 cm DBH in ten transects that crossed distinct hydrological transitions. Soil water content and depth to water table were measured regularly over a 13-month period. Results: A detrended correspondence analysis (DCA) of 20 dominant species and structural attributes in 10 × 10 m subplots segregated three major forest types: (1) high-statured upland forest with intermediate stem density, (2) medium-statured forest dominated by palms, and (3) low-statured campinarana forest with high stem density. During the rainy season and transition into the dry season, distinct characteristics of the soil water regime (i.e. hydro-indicators) were closely associated with each vegetation community. Stand structural attributes and hydro-indicators were statistically different among forest types. Conclusions: Some upland species appeared intolerant of anaerobic conditions as they were not present in palm and campinarana sites, which experienced prolonged periods of saturation at the soil surface. A shallow impermeable layer restricted rooting depth in the campinarana community, which could heighten drought stress during the dry season. The only vegetation able to persist in campinarana sites were short-statured trees that appear to be well-adapted to the dual extremes of inundation and drought. [source] Does flooding of rice fields after cultivation contribute to wetland plant conservation in southern Brazil?APPLIED VEGETATION SCIENCE, Issue 1 2010Ana S. Rolon Abstract Question: Does flooding of rice fields after cultivation contribute to wetland plant conservation in southern Brazil? Location: Rice fields in the coastal plain of southern Brazil. Methods: Six rice fields with different management practices were randomly selected (three dry rice fields and three flooded rice fields). Six collections were carried out over the rice cultivation cycle. Richness and biomass were measured using the quadrat method. Results: A total of 88 macrophyte species was recorded. There was no statistical interaction between management practices and rice cultivation phases for macrophyte richness and biomass. Macrophyte species richness and biomass changed over time, but were similar between flooded and dry rice fields. The first three axes generated by detrended correspondence analysis explained 29% of the variation in species composition and the multivariate analysis of variance showed that there was a statistical interaction between management practices and agricultural periods. Conclusions: Rice fields may help to conserve an important fraction of the aquatic macrophyte diversity of wetlands of southern Brazil by providing the setting up of a greater number of species within the agricultural landscape. However, rice fields must not be viewed as surrogate systems for natural wetlands. The difference in species composition between flooded and dry rice fields is interesting in terms of biodiversity conservation. If rice producers could keep part of their agricultural land flooded during the fallow phase, this management practice could be an important strategy for the conservation of biodiversity in areas where natural wetlands have been converted to rice fields. [source] Recovery of sandy beach and maritime forest vegetation on Phuket Island (Thailand) after the major Indian Ocean tsunami of 2004APPLIED VEGETATION SCIENCE, Issue 2 2009D. Hayasaka Abstract Question: How rapidly has the sandy beach and maritime forest vegetation on Phuket recovered and regenerated after the impact of the major Indian Ocean tsunami of 2004? What are the characteristics of sandy beach species for regenerating their populations and the invasion patterns of originally non-sandy beach species or other newcomers after the tsunami? Location: Phuket Island, southern Thailand. Methods: Species composition of beaches was studied on the same research plots 6 months before and 9 months after the tsunami. The changes in individual species cover before and after the tsunami were determined by ,2 tests. Change in community composition was analysed by detrended correspondence analysis. The relationship between species and environmental factors was analysed by canonical correspondence analysis. Results: The sites disturbed by the tsunami were often invaded by annuals, especially grasses and asteraceous plants, rather than by perennials. In contrast, species with clonal growth by stolons decreased significantly. Factors determining the species habitat differences were soil hardness (penetration resistance of sandy soil), per cent silt content, soil water content and beach management. Habitat differences among originally non-sandy beach herbaceous species that expanded their population or moved to the coast after the disaster were defined by sand accretion or erosion caused by the tsunami. Many sandy beach herbaceous communities changed into Dactyloctenium aegyptium communities because of the tsunami were originally constituted by non-sandy beach D. aegyptium with Cenchrus echinatus. Although the forest floors of most maritime forests were invaded by originally non-sandy beach Tridax procumbens, Eleusine indica or D. aegyptium because of the tsunami, this did not result in a change in the vegetation unit, because species' loss was restricted to the understorey. In time, these forests will recover their previous community composition. Conclusions: Our results suggest that originally non-sandy beach native species invaded the disturbed beaches rapidly after the tsunami but their habitats differ. Sites where sand accumulated on a beach because of the tsunami were invaded by D. aegyptium and E. indica, whereas soil erosion permitted invasion by Digitania adscendens. Tridax procumbens establishes rapidly on wet sites with hard soil, high per cent silt content and low beach management pressure. Sandy beach species with subterranean long rhizomes are strongly tolerant of such disasters. We concluded that the species composition of the beaches disturbed by a temporary large disaster is determined by dormancy and growth forms, with radicoid form being influential. [source]
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