Detrended Correspondence Analysis Axis Research Articles

The epiphytic bryophyte succession of Buxus sempervirens forests in the Fırtına Valley, Rize (North Türkiye)

In this study, the epiphytic bryophyte succession of the Buxus sempervirens L. forests in Fırtına Valley (Çamlıhemşin-Rize, North Türkiye), one of the nine biodiversity hotspots in Türkiye, were investigated. For this purpose, a total of 60 sampling plots were taken from the live trunks of the B. sempervirens trees of different ages. Twenty-nine epiphytic bryophyte species were determined (24 mosses and 5 liverworts) within the sample plots. Also, six different life form types and four different habitat affinity categories were determined. The mat type life form is in the first place with 34.4% whereas the and cortico-saxicolous species are the most common with 51.7%. Two-Way Indicator Species Analysis (TWINSPAN) classified the epiphytic bryophyte communities on the trunks of the B. sempervirens at the second level into two main clusters (A and B) and three sub-clusters (A1, B1 and, B2). Detrended Correspondence Analysis (DCA) axis 1 was interpreted as gradient along the height of the epiphytic habitat (from the lower base to the upper zone) on trunks and the DCA axis 2 was interpreted as gradient of moisture (from mesic to xeric). Exsertotheca crispa (Hedw.) S.Olsson, Enroth & D.Quandt was the species with the highest Index of Ecological Significance (IES) value on the lower bases of the aged trees. Species diversity and epiphytic cover in the upper zones were lower than in the basal and middle zones in the study area. While Metzgeria furcata, (L.) Corda, Oxyrrhynchium hians (Hedw.) Loeske, Plagiothecium nemorale (Mitt.) A.Jaeger, and Radula lindenbergiana Gottsche ex C.Hartm were only found on old trees, Ctenidium molluscum (Hedw.) Mitt. and Pseudoleskeella nervosa (Brid.) Nyholm were only found on middle-aged trees.

Measurements of the Cognitive Level of Ecotourists for the Tourism Environment in the Mountain Resorts

Tourists are the main body of tourism activities, and studying the environmental cognition of tourists is beneficial for the environmental management of scenic spots. In this article, data obtained by questionnaire were used to compose a data matrix of 169×10 dimensions, and the cognitive level of ecotourists for the tourism environment was measured by two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA) in Luya Mountain Nature Reserve. This analysis revealed three main points. (1) TWINSPAN divided all the samples into the strict environment protection type, the ordinary environment protection type, the occasional environment protection type, and the natural enjoyment type. Both the strict and ordinary environment protection types agreed with biocentrism and had a consciousness regarding the protection of nature, but the former advocated that tourism activities should be restricted in nature reserves, while the latter did not agree with restrictions on tourism activities. The occasional environment protection types denied biocentrism; on the one hand, they thought that nature should serve human beings, but on the other hand, they showed a tendency toward environmental protection. The natural enjoyment type argued that natural resources should be maximized to meet human needs. (2) There were significant correlations between the first axis of the DCA and gender, age, education, number of trips, and cognition of nature reserve function, and the second axis of DCA was significantly correlated with gender, age, and education level. Under the impact of all the factors in the DCA figure, ecotourist types transitioned gradually from the first type to the second, the third, and the fourth types along the diagonal line, and accordingly, their cognitive level for the tourism environment was reduced slowly. (3) For nature reserves, the strict environment protection type had 74 people, who was the most popular. The ordinary and occasional environment protection types had 43 people and 31 people, respectively, who should be strived to raise environmental awareness. The natural enjoyment type had 21 people, who must be systematically educated.

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.

Assessment of tree diversity and above-ground biomass in coffee agroforest dominated tropical landscape of India’s Central Western Ghats

The purpose of this study was to quantify the changes in tree diversity and above-ground biomass associated with six land-use types in Kodagu district of India’s Western Ghats. We collected data on species richness, composition and above-ground biomass (AGB) of trees, shrubs and herbs from 96 sample plots of 0.1 ha. Totals of 83 species from 26 families were recorded across the land-uses. Tree species richness, diversity and composition were significantly higher in evergreen forest (EGF) than in other land-uses. Similarly, stem density and basal area were greater in EGF compared to other land-uses. Detrended correspondence analysis (DCA) yielded three distinct groups along the land-use intensities and rainfall gradient on the first and second axes, respectively. The first DCA axis accounted for 45% and second axis for 35% of the total variation in species composition. Together the first two axes accounted for over 2/3 of the variation in species composition across land-use types. Across the land-uses, AGB ranged from 58.6 Mg ha−1 in rubber plantation to 327.3 Mg ha−1 in evergreen forest. Our results showed that species diversity and AGB were negatively impacted by the land-use changes. We found that coffee agroforests resembled natural forest and mixed species plantation in terms of tree diversity and biomass production, suggesting that traditional coffee farms can help to protect tree species, sustain smallholder production and offer opportunities for conservation of biodiversity and climate change mitigation.

Late-Quaternary spatiotemporal dynamics of vegetation in Central Mexico

Central Mexico exhibits a complex environment with wide topographic, climatic, and biological gradients. Lacustrine basins distributed along the region have been the source for numerous paleoenvironmental reconstructions, representing an exceptional opportunity for studying vegetation turnover dynamics across time and space. A total of 1397 fossil and modern pollen samples were ordinated through a Detrended Correspondence Analysis (DCA) to characterize the regional ecological space. Resulting DCA Axis 1 scores were related to a forest cover gradient. Aiming to generalize the interpretation of the analyzed records and given the clear altitudinal pattern shown by modern samples, paleoenvironmental interpretations were performed grouping fossil records according to their elevation. Euclidean distances among sites scores were used as estimators of ecological distance and summarized from two different approaches to observe turnover dynamics at different spatial scales: i) local turnover through time, and ii) ecological versus geographic distance. The regional late Quaternary vegetation dynamics were found mostly driven by global climatic events, whereas the Holocene was marked by more local factors such as precipitation regime and human occupation patterns. Strong local modulation in turnover dynamics was observed in the region. Additionally, we conclude that a palynological record produces results that are repeatable within 50km, considering a maximum compositional turnover of 50%.

Elucidating woody vegetation patterns in relation to soil and topography in tropical Africa: the case of Nech Sar National Park (Ethiopia)

Background and aims - Although soils and topography are reported to be key factors determining vegetation patterns, there are very few studies on this topic in tropical Africa. Given the young nature of the soils of Nech Sar National park, we hypothesised that the woody vegetation would be related to both topsoil and subsoil characteristics. As topography also determines soil characteristics, we investigated whether soil and topography could be considered independently. Methods - Abundance of woody plant species was measured in 19 stratified randomly selected plots of 20 m x 20 m. At the centre of each plot a soil profile pit was dug and samples were taken from each horizon. Topographic characteristics were derived from a 30 m x 30 m digital elevation model. TWINSPAN and Detrended Correspondence Analysis (DCA) were used to identify major patterns in species composition. Factor Analysis was used to assess the variability of, and correlation between, the soil characteristics. Differences between the vegetation groups in-terms of stand and environmental characteristics was tested with the Maim-Whitney U test. DCA axes describing the major variation in vegetation patterns were correlated with soil and topographic characteristics. Results - Forest vegetation was found on Fluvisols and Gleyic Cambisols while bushland was found on Andosols and Vertic Cambisols. The vegetation gradient from forest to bushland (DCA-1) was correlated with both topsoil and subsoil characteristics reflecting parent material and alkalinity; these could however not be dissociated from topography. In contrast, variation both within the forest and the bushland (DCA-2) was not correlated with environmental characteristics. We attribute this variation to disturbances such as collection of firewood or logging, and to the absence of large browser or scarcity of wildfires. Conclusions - This study calls for giving equal attention to topsoil and subsoil for elucidating woody vegetation patterns. Though vegetation patterns vary with topography, a comprehensive understanding requires insights into soils.

The Application of Benthic Diatoms in Water Quality Assessment (Mlava River, Serbia)

AbstractThe main objective of this study was to assess the ecological status of the Mlava River based on epilithic diatoms and to test the use of diatom indices as a tool for estimating the quality of flowing waters in Serbia. Quantitative analysis showed that in AprilAchnanthidium minutissimumwas dominant at each site, except at the fifth site, whereAmphora pediculuswas dominant. In July and September,Achnanthidium minutissimum, Achnanthidium pyrenaicum,Amphora pediculus,Denticula tenuis,Diatoma vulgaris,Gomphonema elegantissimum,Cocconeis pseudolineataandCocconeis placentulavar.lineatadominated. Detrended correspondence analysis (DCA) was used to detect the major patterns of variation in species composition. The first DCA axis summarizes the distribution of the diatom community, mainly through temperature, conductivity, oxygen and water hardness gradient. The second DCA axis was weakly correlated with few variables. Based on the average values of the pollution sensitivity index (IPS), commission for economical community metric (CEE) and biological diatom index (IBD), the water of the Mlava River belonged to water class I during all three seasons. Values of the diatom-based eutrophication/pollution index (EPI-D) indicated class II water quality. According to calculated trophic diatom index (TDI) values, water of the Mlava River was characterized by intermediate nutrient concentrations during three seasons. Principal components analysis was used to represent the correlation between diatom indices, and the highest correlation among the selected diatom indices is seen between EPI-D, IPS and IBD.

The environmental heterogeneity of sediment determines Chironomidae (Insecta: Diptera) distribution in lotic and lentic habitats in a tropical floodplain

Abstract Several limnological variables including sediments affect community structure in lotic and lentic environments. In general, Chironomidae larvae are dominant in macroinvertebrate communities both in abundance and in species richness in floodplains. Using granulometric texture as a surrogate for heterogeneity, we hypothesised that the diversity and distribution of Chironomidae larvae is higher in more heterogeneous environments. For this study, samples were collected quarterly from February to December 2008 at 12 stations in a tropical floodplain including both lotic and lentic stations in the Paraná River. We recorded 66 morphospecies belonging to three subfamilies. Density, species richness and alpha diversity were greater in lotic versus lentic environments. Granulometric data were more diverse in lotic environments according to the Shannon–Wiener index. Different species dominated each environment, and these taxonomic differences were demonstrated by detrended correspondence analysis (DCA). The link between granulometric characteristics and chironomid assemblages were further established by a significant correlation between granulometric variables and one or both of the DCA axes. Thus, the results support our hypothesis and suggest that the diversity and distribution pattern of Chironomidae larvae can be related to sediment heterogeneity due to the higher values of the assemblage attributes found in the lotic environments.

Effects of grazing and precipitation variability on vegetation dynamics in a Mongolian dry steppe

Grazing and water availability are the primary drivers of vegetation dynamics in grazing-dominated regions of Mongolia with a semi-arid climate and frequent droughts. Nomadic animal husbandry still plays a large part in the economy of Mongolia, but more variable precipitation regime and increase in livestock number have severely affected grassland ecosystems through overgrazing, leading to pasture degradation. This study aimed to examine the effects of grazing exclusion, interannual variation of plant-available precipitation (PAP) and their interaction on the aboveground biomass (AGB) of each dominant species, the AGB of annual species and the total AGB in a Mongolian dry steppe, using long-term field data. To detect the effect of grazing on vegetation dynamics, vegetation surveys were conducted in a non-grazed exclosure zone and a fully grazed area outside the exclosure. We assessed the effects of grazing, PAP and their interaction on AGB parameters using a generalized linear model. A detrended correspondence analysis (DCA) was used to visualize the effects of grazing and PAP on the AGB of each species. Grazing, PAP and their interaction had significant effects on AGB. The effect of grazing on AGB was larger with higher precipitation and higher amounts of AGB (i.e. forage) while AGB was strongly limited in drought years, which resulted in a smaller grazing effect. The current year PAP had the highest impact (r = 0.88, P < 0.01) on AGB. The dominance of annual species was characterized by the amount of PAP in the current and preceding years: annuals dominated in wet years that followed consecutive dry years. The DCA Axis 1 reflected the variation of AGB with interannual variation of PAP while the DCA Axis 2 differentiated the grazing effect. The DCA scatter diagram based on species score illustrated that Artemisia adamsii (an unpalatable herb) was clearly linked to grazing disturbance whereas palatable perennials such as Agropyron cristatum, Stipa krylovii and Cleistogenes squarrosa were related to grazing abandonment and wetter conditions. In brief, number of livestock, hence the grazing impacts on vegetation dynamic in this region could have driven by forage availability, which is mainly controlled by current-year PAP.

The influence of environmental factors on the distribution and composition of plant communities in Kizilirmak valley-Black Sea region, Turkey

The aim of this study is to explore the influence of environmental factors on the distribution of plant associations in Kizilirmak Valley, in northern Turkey. This paper provides a quantitative analysis of the vegetation – environment relationships for a study site in this valley. 130 vegetation plots were sampled and analysed using two-way indicator species analysis (TWINSPAN) and Detrended Correspondence Analysis (DCA) in order to identify the principal vegetation communities and determine the environmental gradients associated with these. Eleven associations and six sub-associations were found by using TWINSPAN. There were three main vegetation groups, namely sclerophyllous, xerophyllous and mesophyllous according to TWINSPAN dendrogram, in Kizilirmak valley. The principal DCA axes represent gradients of elevation, relative humidity and soil pH. Shannon diversity index and species richness were also calculated for studied plant associations.

Vegetation development and water level changes in Shenjiadian peatland in Sanjiang Plain, Northeast China

This paper documents a 7800-year proxy record from the Shenjiadian peatland on the Sanjiang Plain in Northeast China. High-resolution plant macrofossil and colorimetric humification methods were used to reconstruct the vegetation and hydrologic history from a 193 cm-long sedimentary profile. Detrended correspondence analysis (DCA) was applied to transform the raw plant macrofossil data into latent indices of peatland water level. The vegetation community transited from an Equisetum fluviatile community to a Carex lasiocarpa community at approximately 3800 cal yr BP and was followed by a Carex-shrub community at approximately 480 cal yr BP. Based on the plant macrofossil DCA axis 1 scores and humification values, we distinguished four hydrologic periods: a wet period from 7800 cal yr BP to 4500 cal yr BP, dry periods up to 1600 cal yr BP, drier periods until 300 cal yr BP, and the driest period from 300 cal yr BP until the present. Through a comparison with other climate records, we suggest that the East Asian summer monsoon (EAM) was the main driving force for vegetation and water level changes to the Shenjiadian peatland through its impacts on precipitation.

VARIAÇÃO DA ESTRUTURA DA FLORESTA ESTACIONAL DECIDUAL NO ESTADO DE SANTA CATARINA E SUA RELAÇÃO COM A ALTITUDE E CLIMA

http://dx.doi.org/10.5902/1980509817465O objetivo deste trabalho foi identificar as possíveis similaridades estruturais entre remanescentes da Floresta Estacional Decidual (FED) em Santa Catarina e associar os grupos à influência de condicionantes ambientais. Associado a este objetivo primário, também se buscou a identificação das zonas de contato entre esta tipologia florestal e a Floresta Ombrófila Mista (FOM). Foram analisados os dados de 78 unidades amostrais (UA) instaladas em remanescentes da FED entre 2008 e 2009 pelo Inventário Florístico Florestal de Santa Catarina (IFFSC). Os dados foram tratados através da Análise de Correspondência Corrigida (DCA) e da Análise de Correspondência Canônica (ACC), valendo-se de uma matriz de densidade de espécies e uma matriz de variáveis ambientais, esta constituída por altitude e parâmetros climáticos. A proporção da variância explicada pelos três primeiros eixos da DCA foi baixa, somando aproximadamente 21% do total de informação contida no conjunto original de dados. Este resultado ofereceu baixo poder de interpretação para os resultados. No entanto, quando a DCA foi aplicada sobre os dados de densidade média das espécies em cada bacia hidrográfica, os resultados apontaram para autovetores muito explicativos do conjunto (58,1% da variação). Observada somente a ordenação provocada pelo primeiro eixo da DCA, vê-se a disposição das bacias de leste, em um extremo, e das bacias de oeste, no outro extremo deste eixo. Na extremidade direita do primeiro eixo estão dispostas as bacias do rio Canoas, Pelotas e do Peixe, as quais são caracterizadas pela presença de espécies como Ocotea pulchella, Zanthoxylum fagara, Lithrea brasiliensis, Matayba elaeagnoides, Cinnamodendron dinisii, comumente associadas com a Floresta Ombrófila Mista. Na extremidade esquerda estão distribuídas as bacias de oeste, grupo que inclui as bacias dos rios Jacutinga, Irani, Chapecó, Antas e Peperi-Guaçu. Dentre as espécies que mais fortemente influenciaram os resultados na análise, cabe destacar Apuleia leiocarpa, Rauvolfia sellowii, Bastardiopsis densiflora, Chrysophyllum gonocarpum, Cordia trichotoma, Holocalyx balansae, Myrocarpus frondosus e Pisonia zapallo, as quais são frequentes em florestas estacionais do interior meridional do Brasil. A análise através da ACC apontou para resultados similares e a interpretação conjunta dos dados ambientais indicou que as UA situadas nas bacias de leste estão associadas a climas mais frios, em que as geadas são mais frequentes, como consequência de altitudes mais elevadas. Considerando que as altitudes tendem a declinar das porções lestes para oeste e, diante do resultados apresentados, os autores propõem a existência de uma zona de transição entre as duas regiões fitoecológicas (FOM e FED) na faixa dos 600 m s.n.m., onde ocorre a interdigitação de elementos da flora estacional e aqueles da Floresta Ombrófila Mista, resultando na delimitação de uma área core da FED abaixo deste patamar altimétrico.

Grazing and Grazing Exclusion Along a Resource Gradient in Magellanic Meadows of Tierra del Fuego

Although Magellanic meadows have been subject to ungulate herbivory for a long time; they have suffered severe grazing by domestic sheep since the end of the 19th century. We hypothesized that, if protected from grazing, the present dominant dwarf forms would be replaced by taller competitive forms, mainly grasses. We then monitored floristic composition along a gradient of soils over periods of 5 to 16 on seven meadow sites under grazing and, in five, also on exclosures. Initial and final floristic samples were classified with TWINSPAN and ordinated with Detrended Correspondence Analysis (DCA). We also tracked cover changes in life-forms (grasses, dwarf sedges/rushes, rhizomatous helophytes, and cushion shrubs). At the end of the study, we assessed floristic similarity between paired grazed and exclosed treatments, and compared their life-form cover, diversity, biomass, and soil compaction with Student's t and Mann-Whitney's tests. Temporal displacements of composition in ordination space showed the effect of a long drought (DCA axis 1) and of grazing removal (DCA axis 2). Grazing exclusion had a much greater impact in wet meadows–where grasses became the dominant life-form–than in dry meadows. The effect of drought was shown in 1) the expansion of the cushion shrub Azorella trifurcata (Gaertn.) Pers. in both grazed and nongrazed treatments of the drier wetlands; 2) the decrease in Caltha sagittata Cav. in riparian meadows, and its encroachment under grazing in the wettest spring meadow; and 3) the large increase in Poa pratensis L. in exclosed wet meadows. Despite this strong response to environmental conditions, overall results supported the idea that these wetlands are equilibrium systems. Although the drier meadows have crossed an irreversible threshold, the Caltha-encroached wet meadows returned to a grass state in about 4 when protected from grazing. Their resilience suggests that they could be partly restored with rest-rotation grazing.

Fungal diversity of saprotrophic litter fungi in a Mediterranean maquis environment

Monospecific and mixed-leaf litters from plant species of Mediterranean maquis (Quercus ilex, Phillyrea angustifolia, Pistacia lentiscus, Cistus spp.) in an undisturbed area in southern Italy were studied with respect to the structure and composition of their decomposer fungal community over an incubation period of 403 d. The data matrix structure was analyzed by means of detrended correspondence analysis (DCA), while indicator species analysis (ISA) was used to determine the preferential association of species with a substrate, a succession phase and monospecific/mixed experimental conditions. The ecological nature of the gradient expressed by the DCA axes was investigated by means of experimental and main chemical leaf-litter variables. The litter mixture had non-additive effects on the decomposition process even though the fungal species richness of the mixed litter was considerably higher than that of the monospecific litter. Our findings highlight the occurrence of shifts in the fungal community during decomposition in response to changes in the substrate, such as those related to the cellulose content and lignin/N ratio.

Tree species composition and stand structure of woody savanna in Dahomey Gap

The Dahomey gap is a savanna region separating the West African rainforests to two regions. We set two sites in this woody savanna, at north and south regions in purpose to examine the differences in tree community properties between sites and among canopy-closure types, and to reveal the factors affecting the differences. Two sites are ca. 225 km distant from each other and have different rainfall patterns. Six 1-ha plots in each site were studied, which cover three types of canopy-closure (closed, semi-open and open). We recorded 3,720 trees that are equal to or more than 5 cm diameter at the breast height, consisted of 70 species belonging to 34 families. Most abundant three species, Isoberlinia doka, Vitellaria paradoxa and Pericopsis laxiflora appeared in both sites. The detrended correspondence analysis (DCA) based on species abundance divided 12 plots into groups of north and south sites along the first axis, whereas canopy-closure types were not associated with DCA axes. At any given total tree height, trees in the north site had slenderer stems with narrower crowns than those in the south site. The specific leaf area was smaller in the north site. Between-site differences in species abundance and allometry are possibly driven by rainfall variation.

Composition and diversity of weed communities in Al-Jouf province, northern Saudi Arabia

The aim of this study was to identify the main weed communities in Al-Jouf province in northern Saudi Arabia. Moreover, the composition and diversity of these communities were studied in relation to soil variables and crop type. Some 54 stands representing olive orchards, date palm orchards, wheat crop and watermelon crop were studied, using ten quadrats (1×1m) per stand. A total of 71 species belonging to 22 families and 61 genera were observed. The classification of vegetation using the Two Way Indicator Species Analysis (TWINSPAN) resulted in the recognition of four vegetation groups representing wheat crop, orchards in winter season, orchards in summer season and watermelon crop. These results suggested the importance of both crop and season for the formation of weed community. Detrended Correspondence Analysis (DCA) showed that these groups are clearly distinguished by the first two DCA axes. The species richness was higher in both olive and date palm orchards than in wheat and watermelon crops. This pattern of species richness could be related to farm management practices and habitat micro-heterogeneity. Soil electrical conductivity, organic carbon and soil texture showed significant correlations with species richness and the cover values of some dominant species, suggesting the significant role of soil characteristics in weed community structure and diversity.

Response of plant species to abandonment of subalpine fields, Manang, Nepal

Spatial dimension of abandoned fields has been expanding more in rural subalpine zones of Nepal leading to various patterns of secondary succession. The secondary succession in the subalpine Himalayas has not yet been evaluated. Here, I describe a study initiated in Manang district, Central Nepal where enough abandoned fields of different chronosequences were located. A definitive successional pattern was predicted from the data obtained from sampling 256 plots of 1 × 1 m2 each systematically in a total of 43 abandoned fields from 1 to 55 years after abandonment. Change in composition pattern of 11 most important plant species was analyzed through the Detrended Correspondence Analysis (DCA). The first two axes of DCA explained 19.1 % of the total variation in the species composition. Early, mid and late successions were three stages distinguished each by their abundance scores and life-forms composition. Malva neglecta, Phleum alpinum and Fagopyrum esculentum were dominant at the recently abandoned fields. Cynoglossum zeylanicum, Malaxis muscifera, Medicago falcata and Pennisetum flaccidum were mid succession species, and Thymus linearis, Tanacetum gossypinum, Pinus wallichiana and Poa annua represented the late succession species.doi: http://dx.doi.org/10.3126/botor.v8i0.5553 Botanica Orientalis – Journal of Plant Science (2011) 8: 10-15

Diatom ecological response to altered hydrological forcing of a shallow lake on the Yangtze floodplain, SE China

ABSTRACTThe Yangtze floodplain is characterized by numerous large (surface area &gt; 1 km2; ∼25% are &gt; 10 km2) and shallow lakes (maximum depth mainly &lt; 5 m). Floodplain lakes are inherently dynamic and important sites for biogeochemical cycling, biodiversity as well as human resources. Importantly, the degree of hydrological connectivity between lakes and river channels is affected by climate, geomorphic processes as well as cultural disturbance of the catchment. This study investigated the long‐term (∼200 years) interaction between a shallow floodplain lake (Taibai Lake; area 25 km2, mean depth 3·2 m) and the Yangtze River using high‐resolution multi‐proxy analysis (diatoms, geochemistry, and grain size) of a 210Pb‐dated sediment core. Diatom assemblages in Taibai Lake exhibited a strong temporal succession and were successively dominated by Aulacoseira granulata (planktonic), Gyrosigma acuminatum (periphytic), and the facultatively planktonic Nitzschia palea over the past 200 years. Eutrophication as inferred by diatom inferred‐total phosphorous (DI‐TP), however, only started around 1990 with TP concentration increasing from 65 to 95 µg L−1. Prior to 1950 DI‐TP was constant and detrended correspondence analysis axis 1 sample scores (of the diatom assemblages) were not correlated with DI‐TP concentration suggesting that there were other stressors driving changes in the diatom assemblage besides nutrients. We used sediment grain size as a proxy for hydrological connectivity; median grain size is strongly correlated with the abundance of A. granulata (R2 = 0·67). A comparison of the diatom stratigraphy with physical and geochemical proxies suggested that Taibai Lake shifted from a riverine‐influenced, turbid algae‐macrophyte mixed state to a clearwater macrophyte‐dominated state around 1950 AD, primarily due to the changes in the hydrological regime of the floodplain resulting from land reclamation and building of reservoirs. After 1990 AD, the lake ecosystem deteriorated following continuous input of nutrients from agriculture and aquaculture, shifting to a hyper‐eutrophic algae‐dominated state. These results indicate the dynamic nature of floodplain ecosystems and the complexity of multiple stressors affecting them over decadal timescales and the long‐term interaction between anthropogenic and natural forcing processes. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Environmental gradients across wetland vegetation groups in the arid slopes of Western Alborz Mountains, N. Iran

Mountain wetlands are unique ecosystems in the arid southern slopes of Alborz range, the second largest range in Iran. The spatial distribution characteristics of wetland vegetation in the arid region of the Alborz and the main factors affecting their distributional patterns were studied. A classification of vegetation and ecological characteristics were carried out using data extracted from 430 relevés in 90 wetland sites. The data were analyzed using Two Way Indicator Species Analysis (TWINSPAN) and detrended correspondence analysis (DCA). The wetland vegetation of Alborz Mountain was classified into four large groups. The first vegetation group was calcareous rich vegetation, mainly distributed in the river banks and characterized by helophytes such as &lt;em&gt;Bolboschoenus affinis&lt;/em&gt; as indicator species. The second group was saline transitional vegetation, distributed in the ecotone areas and dominated by &lt;em&gt;Phragmites australis&lt;/em&gt;. The third vegetation group is wet meadow vegetation which mainly consists of geophytes, endemic and Irano-Turanian species, distributed in the higher altitudes. This vegetation is mainly characterized by indicator species such as &lt;em&gt;Carex orbicularis&lt;/em&gt;, high level concentration of Fe&lt;sup&gt;2+&lt;/sup&gt; and percentage of organic matter in the soil. The fourth vegetation group is aquatic vegetation, distributed in the lakeshores. The aquatic group species are mainly hydrophytic such as &lt;em&gt;Batrachium trichophyllum&lt;/em&gt;. The TWINSPAN vegetation groups could be also recognized in the DCA graphs and ecologically differentiated by ANOVA of studied variables. Four vegetation groups can be differentiated on two first axes of indirect ordination. There is a gradient of pH, EC and organic matter associated with altitude on the DCA diagram. Correlation analysis between the axes of DCA and environmental factors shows that altitude, soil texture and other dependant environmental variables (e.g. pH) are the main environmental factors affecting the distribution of wetland vegetation groups.