Detrended Correspondence Analysis Scores Research Articles

Environmental filtering is the primary driver of community assembly in forest–grassland mosaics: A case study based on CSR strategies

AbstractAimsEcological strategies can provide information about plant community assembly and its main drivers. Our aim was to reveal the dominant strategies of the vegetation types of forest–grassland mosaics and to deduce the assembly processes responsible for their species composition.LocationHungary.MethodsWe investigated eight vegetation types of Hungarian forest–steppes. The trade‐off between three key traits related to leaf size and economics was used to calculate Grime's competitive–stress tolerance–ruderal (CSR) value for each species, based on which the mean value for each vegetation type was determined. Detrended correspondence analysis (DCA) ordination was used to reveal the compositional differences among the vegetation types under study. To analyze how ecological strategies correlate with the compositional gradient, we used linear regression between plot ordination scores (the first DCA scores) and each strategy (C, S, and R). Linear mixed‐effect models were used to evaluate the differences between the vegetation types regarding each strategy (C, S, and R).ResultsEach vegetation type was dominated by the stress‐tolerator strategy, indicating the prominent role of environmental filtering in community assembly. However, ecological strategies differed significantly among the communities. The importance of the stress‐tolerator strategy decreased toward the less harsh end of the gradient (i.e., from grasslands to forests), while the competitor strategy showed a reverse pattern. The ruderal strategy was weakly correlated with the gradient, although its proportion increased toward the harsh end of the gradient.ConclusionsWith ongoing climate change, an increasing importance of environmental filtering is expected in the assembly of the vegetation types in the studied forest–grassland mosaics. We suggest that CSR strategies offer a useful tool for studying plant‐community assembly rules along environmental gradients.

Use of remote sensing to track postindustrial vegetation development

AbstractThe effects of natural processes on deposited mineral material of postindustrial sites is underestimated. Natural vegetation development on mineral material substratum is an unappreciated way of site management. Due to the classification‐based approach to assembly of plant community diversity, remote sensing methods have limited application. We aimed to assess whether remotely sensed data allow for building predictive models, able to recognise vegetation variability along the main gradients of species composition. We assessed vegetation in 321 study plots on four coal‐mine spoil heaps in Silesia (S Poland). We determined the main gradients of species composition using detrended correspondence analysis (DCA), and we identified how DCA scores describe vegetation variability. DCA axes explained 38.5%, 35.4%, 31.4%, and 20.1% of species composition variability. We built machine learning models of DCA scores using multispectral satellite images and airborne laser scanning data as predictors. We obtained good predictive power of models for the first two DCA axes (R2 = 0.393 and 0.443, root mean square errors, RMSE = 0.571 and 0.526) and low power for the third and fourth DCA axes (R2 = 0.216 and 0.064, RMSE = 0.513 and 0.361). These scores allowed us to prepare a vegetation map based on DCA scores, and distinguish meadow‐like from forest‐edge‐like vegetation, and to identify thermophilous and highly productive vegetation patches. Our approach allowed us to account for species composition gradients, which improved remote sensing‐based vegetation surveys. This method may be used for planning future management.

Mapping of arthropod alpha and beta diversity in heterogeneous arctic-alpine ecosystems

Assessing biodiversity in arctic-alpine ecosystems is a costly task. We test in the current study whether we can map the spatial patterns of spider alpha and beta diversity using remotely-sensed surface reflectance and topography in a heterogeneous alpine environment in Central Norway. This proof-of-concept study may provide a tool for an assessment of arthropod communities in remote study areas. Data on arthropod species distribution and richness were collected through pitfall trapping and subjected to a detrended correspondence analysis (DCA) to extract the main species composition gradients. The DCA axis scores as indicators of species composition as well as trap species richness were regressed against a combined data set of surface reflectance as measured by the Sentinel-2 satellite and topographical parameters extracted from a digital elevation model. The models were subsequently applied to the spatial data set to achieve a pixel-wise prediction of both species richness and position in the DCA space. The spatial variation in the modelled DCA scores was used to draw conclusions regarding spider beta-diversity. The species composition was described with two DCA axes that were characterized by post hoc-defined indicator species, which showed a typical annidation in the arctic-alpine environment under study. The fits of the regression models for the DCA axes and species richness ranged from R2 = 0.25 up to R2 = 0.62. The resulting maps show strong gradients in alpha and beta diversity across the study area. Our results indicate that the diversity patterns of spiders can at least partially be explained by means of remotely sensed data. Our approach would likely benefit from the additional use of high resolution aerial photography and LiDAR data and may help to improve conservation strategies in arctic-alpine ecosystems.

Fish habitat associations along a longitudinal gradient in a preserved coastal Atlantic stream, Brazil

Habitat conditions at multiple scales are one of the major factors structuring ichthyofauna. Thus, we analyzed the fish habitat associations along the headwater-mouth gradient of a coastal Atlantic stream. We categorized the sampling sites into habitat units, so that in the middle reach these categories were statistically differentiated into riffles, runs and pools. Samplings were carried out quarterly from May 2009 to February 2010 using electrofishing. Principal component analysis (PCA) indicated an environmental gradient from higher water velocity and rocky bottom to deeper and sandy areas in the headwater-mouth direction. A total of 1,495 individuals belonging to 27 species were captured, being 13, 18 and 22 from headwater, middle and mouth reaches, respectively. Shannon diversity was slightly higher in the middle reach, while beta diversity showed higher rates of addition than turnover in species along the longitudinal gradient. Fish structure, evaluated by DCA (detrended correspondence analysis) scores, showed significant differences between upper reaches and mouth reach, but the middle riffles did not differ from headwater habitats. In the middle reach, mesohabitat analysis distinguished riffles, with higher abundance of fast-water crenuchids, from pools, with a higher abundance of lentic-water characids. These results suggest that environmental differences along the stream determine the wider structural patterns. However, the middle reach amassed species from upper areas and lowlands in structured fish mesohabitat associations, possibly implying distinct local ecological interactions. These findings contribute to the assessment of stream conservation status and to recognize eventual direct impacts on fish structures along longitudinal gradients.

Long‐term changes in marsh vegetation in Sanjiang Plain, northeast China

AbstractQuestionsIs there a consistent change in species composition and species richness across the communities along the wetness zonation? Which species are sensitive to environmental changes? Has species richness increased or decreased? What are the relative effects of climate, geographical position and local environmental factors on the inland marsh community?LocationSanjiang Plain, northeast China (130–133° E, 45–48° N).MethodsA total of 94 plots were re‐surveyed in 2012 and compared with data from 1973. Detrended correspondence analysis (DCA) and indicator species analysis were used to analyse the direction and nature of change in community composition between 1973 and 2012. Paired t‐test was used to test for change in species richness, water level and soil variables between the two surveys. Correlation and step‐wise regression analyses were used to test the relationship between vegetation change (species richness and DCA scores), environmental variables and geographic position.ResultsVegetation has changed towards a drier state, with the greatest changes in the wettest Carex lasiocarpa community and the smallest changes in the driest Calamagrostis angustifolia community. The frequency and cover of hygrophilous species and species typical of oligotrophic wetlands decreased, while grasses and other non‐marsh species increased. Species richness per community and per plot increased over time. The dynamics within each community was only weakly correlated with biogeographic predictors: longitude, latitude, elevation and annual precipitation.ConclusionsHydrology was the main factor controlling changes along the marsh zonation, and was most likely in response to climate warming and land‐use changes. The different responses among the marsh communities along the zonation and between hydrophytes and other species imply that future protection and management need to be based on community type and plant functional types.

Geomorphic Determinants of Species Composition of Alpine Tundra, Glacier National Park, U.S.A.

Because the distribution of alpine tundra is associated with spatially limited cold climates, global warming may threaten its local extent or existence. This notion has been challenged, however, based on observations of the diversity of alpine tundra in small areas primarily due to topographic variation. The importance of diversity in temperature or moisture conditions caused by topographic variation is an open question, and we extend this to geomorphology more generally. The extent to which geomorphic variation per se, based on relatively easily assessed indicators, can account for the variation in alpine tundra community composition is analyzed versus the inclusion of broad indicators of regional climate variation. Visual assessments of topography are quantified and reduced using principal components analysis (PCA). Observations of species cover are reduced using detrended correspondence analysis (DCA). A “best subsets” regression approach using the Akaike Information Criterion for selection of variables is compared to a simple stepwise regression with DCA scores as the dependent variable and scores on significant PCA axes plus more direct measures of topography as independent variables. Models with geographic coordinates (representing regional climate gradients) excluded explain almost as much variation in community composition as models with them included, although they are important contributors to the latter. The geomorphic variables in the model are those associated with local moisture differences such as snowbeds. The potential local variability of alpine tundra can be a buffer against climate change, but change in precipitation may be as important as change in temperature.

Climate of the Little Ice Age and the past 2000 years in northeast Iceland inferred from chironomids and other lake sediment proxies

A sedimentary record from lake Stora Viðarvatn in northeast Iceland records environmental changes over the past 2000 years. Downcore data include chironomid (Diptera: Chironomidae) assemblage data and total organic carbon, nitrogen, and biogenic silica content. Sample scores from detrended correspondence analysis (DCA) of chironomid assemblage data are well correlated with measured temperatures at Stykkisholmur over the 170 year instrumental record, indicating that chironomid assemblages at Stora Viðarvatn have responded sensitively to past temperature changes. DCA scores appear to be useful for quantitatively inferring past temperatures at this site. In contrast, a quantitative chironomid-temperature transfer function developed for northwestern Iceland does a relatively poor job of reconstructing temperature shifts, possibly due to the lake’s large size and depth relative to the calibration sites or to the limited resolution of the subfossil taxonomy. The pre-instrumental climate history inferred from chironomids and other paleolimnological proxies is supported by prior inferences from historical documents, glacier reconstructions, and paleoceanographic studies. Much of the first millennium AD was relatively warm, with temperatures comparable to warm decades of the twentieth century. Temperatures during parts of the tenth and eleventh centuries AD may have been comparably warm. Biogenic silica concentrations declined, carbon:nitrogen ratios increased, and some chironomid taxa disappeared from the lake between the thirteenth and nineteenth centuries, recording the decline of temperatures into the Little Ice Age, increasing soil erosion, and declining lake productivity. All the proxy reconstructions indicate that the most severe Little Ice Age conditions occurred during the eighteenth and nineteenth centuries, a period historically associated with maximum sea-ice and glacier extent around Iceland.

Arthropod Diversity in Lama Forest Reserve (South Benin), a Mosaic of Natural, Degraded and Plantation Forests

Arthropod assemblages were examined in Lama forest reserve, a protected area situated in the Dahomey gap, southern Benin, composed of plantations, degraded forest and remnants of natural forest. The objectives were to compare assemblages in relation to forest type and use, to elucidate the value of forest plantations for biodiversity conservation and to identify indicator species for specific forest habitats. Arthropods were collected over an 11-month period, using standardized sets of traps (pitfall, emergence, Malaise and flight intercept traps). Nine different habitats were studied, including natural and degraded forest, forest plantations (Tectona grandis and Senna siamea) of different age, and isolated forest fragments. Our analysis focused on detritivorous and xylophagous arthropods but also included ground beetles and heteropterans, totalling 393 species. We found no differences in species richness among natural and degraded forest habitats in the centre of the reserve (Noyau central). Outside of the Noyau central, species richness was highest in old teak plantations and isolated forest fragments and lowest in young teak and fuelwood plantations. Detrended correspondence analysis (DCA) separated three main groups: (1) natural forest, (2) degraded forest and young plantations, and (3) old plantations and isolated forest fragments. Multiple regression of DCA scores of the first two axes on environmental variables identified one natural and three disturbance-related predictors of arthropod assemblages in Lama forest: soil type (texture), canopy height, naturalness (proportion of Guineo-Congolian plant species) and understorey vegetation cover. We identified 15 indicator species for six different forest habitats. The highest numbers were found in abandoned settlements and old teak plantations. β-diversity was similar among the three DCA ordination groups (degraded forest excluded). Values for β-diversity were relatively high, suggesting that all major forest habitats contribute significantly to regional species pools and should therefore be protected. To enhance arthropod diversity, we propose that management practices in Lama forest should aim to encourage the development of species-rich understorey vegetation of the Guineo-Congolian phytogeographical region.

Stratigraphic paleoecology: Bathymetric signatures and sequence overprint of mollusk associations from upper Quaternary sequences of the Po Plain, Italy

Upper Quaternary sequences of the Po Plain (Italy) were used to assess the informative strength and sequence-stratigraphic overprint of quantitative paleoecological patterns. Three densely sampled cores (89 samples, 98 genera, 23,280 specimens), dominated by extant mollusk species with known environmental distributions, were analyzed with detrended correspondence analysis (DCA). The DCA scores, calibrated using extant genera, provided outstanding estimates of bathymetry (±3 m) and related environmental parameters. Depth-related successions of mollusk associations delineated by using DCA were consistent with independent sequence-stratigraphic interpretations and yielded insights inaccessible via routine techniques (e.g., depth estimates for maximum flooding surfaces). The DCA ordination demonstrates the severity of the sequence-stratigraphic overprint: samples are highly uniform taxonomically during late transgressive systems tracts and highly variable during the following highstand systems tracts. When analyzed across comparable systems tracts, similar species associations repeat during the last and current interglacial cycles, suggesting that Po Plain mollusk associations have remained remarkably stable over the past 125 k.y. The results are consistent with the bathymetric interpretation of the DC axis 1 postulated previously for the Paleozoic fossil record, demonstrate the sequence-stratigraphic overprint of paleoecological patterns predicted by computer modeling, and illustrate the utility of quantitative paleoecological patterns in augmenting sequence-stratigraphic interpretations.

Community organization and species richness of ants (Hymenoptera/Formicidae) in Mongolia along an ecological gradient from steppe to Gobi desert

AbstractAim 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 byFormica‐ andMyrmica‐species, (2) in semi desert we found mostly species ofTetramorium,Myrmica,Proformica,Plagiolepis, andLeptothorax, and (3) in desertCataglyphis aenescensandMessor aciculatusdominated, andLasiuswas 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, andProformica 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.

Mapping alpine vegetation using vegetation observations and topographic attributes

Local planning in mountain areas requires spatial information on site factors such as vegetation that is commonly lacking in rugged terrain. This study demonstrates a procedure for the efficient acquisition of a vegetation map using topographic attributes and nominal vegetation data sampled in the field. Topographic attributes were derived from a digital elevation model (DEM) and nominal vegetation data were reduced to normalised scores by detrended correspondence analysis (DCA). The procedure for mapping vegetation types addressed the relations between DCA scores and topographic attributes, spatial correlation of DCA scores and classification of predicted DCA scores based on a cluster analysis of DCA scores at observation locations. The modelled vegetation classes corresponded with the impression obtained in the field. We also showed that the final result is rather sensitive to which samples are included in the analysis.

Patterns of forest use and endemism in resident bird communities of north-central Michoacán, Mexico

We compared breeding avian communities among 11 habitat types in north-central Michoacán, Mexico, to determine patterns of forest use by endemic and nonendemic resident species. Point counts of birds and vegetation measurements were conducted at 124 sampling localities from May through July, in 1994 and 1995. Six native forest types sampled were pine, pine–oak, oak–pine, oak, fir, and cloud forests; three habitat types were plantations of Eucalyptus, pine, and mixed species; and the remaining two habitats were shrublands and pastures. Pastures had lower bird-species richness and abundance than pine, oak–pine, and mixed-species plantations. Pine forests had greater bird abundance and species richness than oak forests and shrublands. Species richness and abundance of endemics were greatest in fir forests, followed by cloud forests. Bird abundance and richness significantly increased with greater tree-layer complexity, although sites with intermediate tree complexity also supported high abundances. When detrended correspondence-analysis scores were plotted for each site, bird species composition did not differ substantially among the four native oak-and-pine forest types, but cloud and fir forests, Eucalyptus plantations, and mixed-species plantations formed relatively distinct groups. Plantations supported a mixture of species found in native forests, shrublands, and pastures. Pastures and shrublands shared many species in common, varied greatly among sites in bird-species composition, and contained more species specific to these habitats than did forest types.

Diversity Patterns of Woody Species on a Latitudinal Transect From the Monsoon Tropics to Desert in the Northern Territory, Australia

A belt transect, made up of 15 contiguous cells (width, 3.5° of longitude; length, 1° of latitude), was established from the monsoon tropics on the central north coast of the Northern Temtory (11°S) to the central Australian desert on the South Australian border (26°S). On this transect, mean annual rainfall was found to have a negative exponential decay with latitude, with arid conditions commencing at around 18"s-the limit of the monsoonal rains. The mean elevation of each cell steadily increased from the north coast to reach a maximum average elevation of 700 m at around 23°S. The mean alphadiversity (quadrat species richness), and mean beta-diversity (turnover of species along an environmental gradient) was determined for each of the 15 cells by sub-sampling a large 20 × 20 m quadrat data set (N > 2000) collected during the course of the Northern Territory 1:106 vegetation mapping program. It was found that there was little within-cell variation of beta-diversity of woody species which occurred in at least five quadrats, as approximated by the first axis of a detrended correspondence analysis (DCA) of these data. The mean first axis DCA scores were strongly correlated with latitude (r = 0.99); thus, there is no evidence for a floristic disjunction in the composition of common woody species between the monsoon tropics and desert. Mean alpha-diversity had a bimodal distribution on the latitudinal transect, with the maximum mean quadrat richness in the monsoon tropics and a second smaller peak occurred in central Australia, with the lowest levels of alpha-diversity to the south of the limit of the monsoon rains. This pattern was mirrored by the mean number and mean Shannon-Wiener diversity of 1:106 vegetation map units on the transect. It was found that 81% of the variance of mean alpha-diversity was explained by mean annual rainfall and mean elevation for the 15 cells. The increase in mean alpha-diversity in central Australia appears to be related to environmental heterogeneity associated with mountainous terrain. It is possible that the central Australian mountains are a refuge for plants that were more widespread during the last ice-age. It is unknown whether the woody species diversity patterns are in equilibrium with the prevailing climate. More data on the palaeo-environments of the Northern Territory are required to answer this question.

Vegetation variation among mesic successional forest stands in northern lower Michigan

Vegetation composition of the shrub–tree and herb layers was sampled in 70 successional aspen (Populus tremuloides and Populus grandidentata) stands of different ages (1–90 years) on a variety of sites in northern lower Michigan. Physical and chemical characteristics of soil profiles were also measured at each site. Three stand groupings were identified based on site conditions and detrended correspondence analysis (DCA) ordination of the vegetation. Sandy dry-mesic soils support forests of Acer rubrum, Quercus rubra, Pinus resinosa, and Pinus strobus. On lowland sandy soils with a fluctuating water table, Pinus strobus, Abies balsamea, Viburnum lentago, and Viburnum cassinoides are important. Mesic soils with stratified calcareous layers or clay till substrates support Acer saccharum, Fagus grandifolia, Tilia americana, Fraxinus americana, Ostrya virginiana, and Acer pensylvanicum. Canonical correlation analysis (CCA) was used to compare DCA scores with soil variables; first-axis DCA scores were correlated with a suite of soil variables and stand age was correlated with second or third DCA axis scores. Separate DCA ordinations of the dry-mesic and mesic groups revealed successional relations on these sites. On dry-mesic sites, Pinus resinosa and Pinus strobus increase in importance with stand age, while Prunus serotina, Prunus virginiana, Prunus pensylvanica, and the aspens decrease. On mesic sites, early successional species include the aspens, Corylus cornuta, Prunus serotina, and Prunus pensylvanica. Fagus grandifolia, Acer pensylvanicum, Quercus rubra, Viburnum acerifolium, Betula papyrifera, Acer rubrum, and Tilia americana are more abundant in mature mesic-site stands. Ordinations of the herb data were remarkably similar to those for trees and shrubs except on dry-mesic sites. Much of the residual variability in vegetation not accounted for by site conditions and stand age is probably related to historical factors such as the nature of disturbance and variations in seed rain.

Ordination and classification of operational geographic units in Southwest Sweden

The vascular plant distributions of Dalsland and northern Bohuslan (Southwest Sweden) were subjected to multivariate analyses in order to delimit geographically coherent floristic zones. 271 squares of 5×5 km were the Operational Geographic Units; the data matrix comprises presence/absence species records for each OGU. Different ordination and classification methods were tested and detailed results are presented for detrended correspondence analysis (DCA), UPGMA and ordination space partitioning (OSP). A weighting procedure, neighbour-weighting, which gives pseudo-frequency scores along the nominal scale 0–9 depending on the species' distribution patterns, is introduced. The superior method for delimiting geographically coherent floristic zones was judged to be ordination space partitioning, using DCA and neighbour-weighted species scores.