ENVIRONMENTAL CORRELATES OF PLANT SPECIES DISTRIBUTION ON THE NYL RIVER FLOODPLAIN

Summary

The envisaged construction of a dam on a major tributary of the Nyl River will alter the hydrological regime with consequent effects on the structure and functioning of the downstream floodplain ecosystem (Nylsvley). Attempts to minimise this impact will be facilitated by knowledge of relationships between vegetation structure and key environmental variables. Historically flooding regime, and its co-variables, have been assumed to be the most important environmental factors controlling the distribution of floodplain plant species. Canonical correspondence analysis of selected soil characteristics (soil texture, electrical conductivity, pH and bulk density), elevation and plant abundance was carried out on the Nylsvley Floodplain in order to critically examine the assumption that flooding regime, measured as elevation, is the primary correlate of floodplain plant species distribution. Results indicate that, although flooding regime is the primary correlate of plant species distribution, other edaphic factors, not correlated with elevation, may play a more substantial role than earlier considered.     

Multivariate analysis of the vegetation of the volcanoes Tláloc and Pelado,Mexico

Abstract. Multivariate analysis was used to describe the composition and distribution of vegetation types on the slopes of the volcanoes Tláloc and Pelado, Mexico. These volcanoes are situated in the transitional zone between the Holarctic and Neotropical floristic regions, which offers a partial explanation for the relatively high α and β diversities. Previous research argued that human activities, i.e. burning and grazing, rather than abiotic factors, play a major role in determining the distribution and floristic composition of the vegetation. TWINSPAN, Detrended Correspondence Analysis and Canonical Correspondence Analysis were used to test this hypothesis. Floristic and environmental data from 138 relevés and seven explanatory environmental variables were included: elevation, soil depth, soil moisture, percentage litter cover, percentage cover of bare ground, burning and grazing were included in the analysis. Soil moisture and elevation accounted for ca. 63% of the residual inertia and none of the remaining explanatory variables proved to be correlated significantly with the first two axes. The present results suggest that burning and grazing operate on a finer scale. In conclusion, soil moisture and elevation are the most relevant variables to explain the distribution of the vegetation under study.     

黄土丘陵小流域土壤水分时空分异与环境关系的数量分析

采用ＤＣＣＡ排序,研究了流域尺谍上土壤水分的时空分异类型及环境因子的关系。研究结果表明,丰水年土壤水分垂直的分布呈降低型、波动型和增长型３种类型,主要影响因子为土地利用与地形（地貌类型、坡度、坡位与海拔高度）;土壤水分的季节变化表现为三峰型、四峰同步型与四峰滞后型３种类型,主要影响因子为降雨与地形（坡度、海拔高度、坡向与坡位）。分析得出,降低型与波动型的土壤水分利用率较高;从丰水年到欠水年,降低型     

Groundwater Macrocrustaceans as Natural Indicators of the Ariège Alluvial Aquifer

The macrocrustacean fauna from an alluvial aquifer in the French Pyrénées was investigated using 15 wells scattered over the floodplain. Wells were sampled at three contrasting periods for faunal, phy‐sical and chemical variables to investigate relationships between amphipod, isopod distributions and environmental factors. The assemblages, dominated by stygobite amphipod species, showed an overall persistence between the sampling dates. Groundwater quality exhibited between‐site variations related to agriculturally‐induced pollution. Low correlations existed between water quality and fauna distribution patterns. At the scale of the aquifer, groundwater contamination did not influence the macrocrustacean distribution. The spatial distribution of amphipods and isopods was clearly related to hydrogeology and hydrodynamics: strong relationships were found between the assemblages composition and the hydrological context of the stations (wells from the alluvial plain and from the alluvial terrace). With respect to spatial and temporal scales and providing adequate sampling methods, macrocrustaceans then constitute natural indicators of groundwater hydrodynamics in the Ariège aquifer.     

Patterns in groundwater nitrogen concentration in the floodplain of a subtropical stream (Wollombi Brook,New South Wales)

The sources of groundwater and the patterns in groundwater dissolved N and DOC concentration in the floodplain of a subtropical stream (Wollombi Brook, New South Wales) were studied over a 2-year period using three piezometer transects. While the stream was generally a discharge area for regional groundwater, this source represented only a small contribution to either the water or N budget of the alluvial aquifer. Groundwater–surface water interactions appeared mostly driven by cycles of bank recharge and discharge between the stream and the alluvial aquifer. DON and NH₄⁺ were the principal forms of dissolved N in groundwater, consistent with the primarily suboxic to anoxic conditions in the alluvial aquifer. A plume of groundwater NO₃⁻ was found at one transect where oxic conditions persisted within the riparian zone. The origin of the NO₃⁻ plume was hypothesized to be soil NO₃⁻ from the riparian zone flushed to the water table during recharge events. When present, NO₃⁻ did not reach surface water because conditions in the alluvial aquifer in the vicinity of the stream were always reduced. The concentration of groundwater DOC was variable across the floodplain and may be related to the extent of the vegetation cover. Overall, transformation and recycling of N during lateral exchange processes, as opposed to discharge of new N inputs from regional groundwater, appears to primarily control N cycling during groundwater–surface water interactions in this subtropical floodplain.     

Linking vegetation pattern to hydrology and hydrochemistry in a montane river floodplain, the Šumava National Park, Central Europe

Cover of higher plants (in 4 × 4 m plots), groundwater table height, and water chemistry in boreholes were sampled at 43 sites along three cross-sectional transects in a flat floodplain of the Upper Vltava River in the Šumava Mountains (Šumava National Park, Czech Republic). The goal was to describe the relationships between vegetation and alluvial environment. Correlations between hydrochemical and plant community characteristics were calculated, and Canonical Correspondence Analysis (CCA) was used to express relationships between the abiotic factors and vegetation. The following characteristics were significantly correlated with the vegetation pattern: mean height of the water table, distance from the river, pH, and concentration of NH₄ and humic acids in the groundwater. Two distinct zones were distinguished in the floodplain: Zone I was under direct influence of the river, and exhibited higher pH and ammonium content in a fluctuating groundwater table. Zone II, covering more than half of the floodplain extent, was under the prevailing influence of water coming from the adjacent upland, and exhibited lower pH, higher content of humic acids, and a higher and relatively stable groundwater table. A diverse mosaic of the riparian communities, especially of tall-sedge and tall-grass marshes and alluvial meadows, was typical for the former zone, while peatland vegetation characterised the latter one. The floodplain exhibited a rather oligo- to mesotrophic status with only very local eutrophication, and harboured diverse and valuable plant communities. The protection of this floodplain should be among the priorities of the National Park authorities.     

Effects of ecological factors on plant communities of Ziwuling Mountain, Shaanxi Province, China

This paper explores the relationships between environmental factors and community patterns. In 60 plots in the Malan Forest Region of the Loess Plateau, 17 variables were used as indicators of spatial position, soil and topography characteristics. Plant community types were analyzed by TWINSPAN (Two-way Indicator Species Analysis). Significant environmental factors were selected by forward selection and Monte Carlo tests. The relationship between communities and environmental factors was identified by DCCA (Detrended Canonical Correspondence Analysis). Partial CCA (Canonical Correspondence Analysis) partitioned observed compositional variation into components explained by environment, locality and covariation between them. The results showed that: (1) the plant communities can be divided into 13 types including 4 different successional stages. (2) Salt and alkali-hydrolyzable nitrogen are the significant factors related to plant community distribution at early stage. Elevation and humus thickness are the significant factors in the transitional stage. Elevation, slope, aspect, thickness of forest floor, humus thickness and pH are the significant factors for the sub-climax stage. Elevation, slope, aspect, pH and available phosphorus are the significant factors for the climax stage. (3) The ecological characters and the distribution patterns of plant communities in different successional stages are consistent with environmental gradients. (4) As succession proceeds, the impact of environmental conditions on plant communities increases, while the total influence of spatial location, and the interaction between the spatial location and environmental factors decrease.     

Effects of ecological factors on plant communities of Ziwuling Mountain, Shaanxi Province, China

This paper explores the relationships between environmental factors and community patterns. In 60 plots in the Malan Forest Region of the Loess Plateau, 17 variables were used as indicators of spatial position, soil and topography characteristics. Plant community types were analyzed by TWINSPAN (Two-way Indicator Species Analysis). Significant environmental factors were selected by forward selection and Monte Carlo tests. The relationship between communities and environmental factors was identified by DCCA (Detrended Canonical Correspondence Analysis). Partial CCA (Canonical Correspondence Analysis) partitioned observed compositional variation into components explained by environment, locality and covariation between them. The results showed that: (1) the plant communities can be divided into 13 types including 4 different successional stages. (2) Salt and alkali-hydrolyzable nitrogen are the significant factors related to plant community distribution at early stage. Elevation and humus thickness are the significant factors in the transitional stage. Elevation, slope, aspect, thickness of forest floor, humus thickness and pH are the significant factors for the sub-climax stage. Elevation, slope, aspect, pH and available phosphorus are the significant factors for the climax stage. (3) The ecological characters and the distribution patterns of plant communities in different successional stages are consistent with environmental gradients. (4) As succession proceeds, the impact of environmental conditions on plant communities increases, while the total influence of spatial location, and the interaction between the spatial location and environmental factors decrease.     

Vegetation response after restoring the connectivity between a river channel and its floodplain

Questions: How is restored inundation affecting the ground‐water composition in a floodplain? To what extent has the floodplain plant community composition changed? What are the effects of flooding frequency and intensity and water quality on the floodplain vegetation changes? Location: Demer river, Flanders, Belgium. Methods: 75 10 m x 10 m plots were surveyed in 1997 and in 2003. Vegetation changes were quantified using a Detrended Correspondence Analysis on the combined 1997–2003 data‐set. Groundwater quality in the floodplain was analysed on macro‐ions. Inundation intensity and frequency were related to vegetation changes. Results: The inundation water was rich in nutrients, although only for NH₄ and ortho‐PO₄, and a significant increase was recorded in the groundwater. Plant species characteristic of very nutrient‐rich herb vegetation disappeared or decreased while the cover and species richness of species from wet, moderately productive habitats increased. Very few new species colonized the floodplain. Conclusion: Nutrient‐rich flooding water does not necessarily result in increased abundance of species from nutrient‐rich habitats, very likely because N becomes less available by deni‐trification and is transformed into biomass by tall herbs. Either micro‐site limitation or dispersal limitation could explain the colonization problems of new species. The data do not allow distinction between these two mechanisms.     

黄土高原归一化植被指数与自然环境因子的空间关联性——基于地理探测器

植被对改善黄土高原脆弱的生态环境有着关键作用,系统研究黄土高原归一化植被指数(NDVI)空间分布和环境因子的空间关联性,可为新时代黄土高原植被高质量建设提供科学依据。以黄土高原2000-2017年年均植被NDVI为研究对象,选取气候要素、地形因素、土壤类型和植被类型等自然环境因子,运用GIS和地理探测器技术手段,在剔除土地利用类型发生变化栅格的基础上,研究黄土高原年均NDVI与环境因子的空间关联性,结果表明:2000-2017年黄土高原年均NDVI值在0.016-0.72之间,呈地带性分布,由西北部向东南部逐渐升高,大于0.3的区域占50.23%;2000-2017年黄土高原年均植被NDVI分布具有空间异质性,且在不同植被区、地貌区、土壤区和气候区中,NDVI空间分布的主要环境驱动因子具有差异性。年均降雨量对NDVI空间分布具有强解释力,是黄土高原85.20%的区域植被生长的主要制约因子;约12.01%的区域主要受土壤类型影响,为中等解释力,其余区域的植被生长主要受年均气温,日照时数或海拔影响。建议综合考虑不同环境条件下植被NDVI的空间分布与环境影响因子的空间关联性,明确不同区域中植被NDVI的环境制约因子,以制约因子定植,在防止土壤干燥化、贫瘠化的前提下,提高植被覆盖率和生物多样性,以期促进黄土高原植被建设高质量发展。     

Vegetation composition of Lolium perenne-dominated grasslands under organic and conventional farming

Agricultural intensification has caused a decline of semi-natural grasslands and loss of botanical diversity, making agricultural fields dominated by Lolium perenne the main grassland system in large areas of Europe. Increased insight into the factors determining their vegetation composition and plant species richness is needed to improve the effectiveness of agri-environment schemes and to substantiate the benefits of organic over conventional agriculture. Our aims were (1) to determine the difference in vegetation composition (including species richness) between Lolium perenne-dominated fields of conventional and organic farms in a case study region in The Netherlands, and (2) to identify the soil and management related drivers behind this difference.We collected vegetation, soil and management data in grasslands of dairy farms under conventional or organic management (45 fields in total), and used multivariate statistics to determine the effect of fertilisation rates, grazing and cutting regime, and soil properties on plant species composition. In a next step we determined to what extent these abiotic drivers differ between organic and conventional farms.On average the organic fields appeared to have a c. 30% higher plant species richness compared to the conventional ones. Vegetation composition was most strongly influenced by groundwater level and nitrogen and phosphorus fertilisation rates, and to a lesser extent by plant-available soil potassium, mowing date, total soil nitrogen, potassium fertilisation rate, age of each field, and livestock (cow or sheep). In general, a low fertilisation rate, high groundwater level, late mowing, low level of plant-available potassium, high level of total soil nitrogen, old fields and the presence of sheep promote a high species richness. However, of these variables only nitrogen fertilisation rate and groundwater level differ significantly between the organic and conventional farms and are therefore likely to be the abiotic drivers of the difference in species richness and vegetation composition between the farm types. Of these two, the difference in nitrogen fertilisation rate is a direct result of a difference in management philosophy, but the difference in groundwater level is not. We hypothesize that the latter difference is caused by economic drivers, whereby a less productive soil is an incentive for a changeover to organic farming. If this is the case indeed, the application of agri-environment schemes would be most effective in less productive (and naturally more species-rich) sites.     

Patchiness of River–Groundwater Interactions within Two Floodplain Landscapes and Diversity of Aquatic Invertebrate Communities

In fluvial systems, the interactions between rivers and groundwater significantly affect various ecological structures (for example, riparian vegetation) and functions. To examine the effects of hydrological exchange between groundwater and surface water on the distribution of aquatic invertebrates within a riverine landscape, we investigated the main stem, tributaries, and various surface and subsurface waters of two floodplains of a southern Alpine river (Brenno, Switzerland) in terms of their physicochemical, hydraulic, substratum, and faunal characteristics. The origins of the water were investigated by analyzing geomorphic settings and physicochemical variables. The two floodplains had different hydrological regimes. The middle floodplain was dominated by lateral inputs and exfiltration of hillslope groundwater from two different subcatchments. Bank filtration of river water sustained subsurface water only close to the channel. The aquatic habitats of the middle floodplain formed a rather homogeneous group with high taxon richness and intrahabitat diversities. These aquatic habitats resembled mountain springbrooks in their physicochemical characteristics and faunal compositions. In the lower floodplain, the exchange between river water and groundwater was more extensive. The aquatic floodplain habitats of the lower floodplain were fed mainly by deep and shallow alluvial groundwater, hyporheic exfiltration, and partly by surface water. In contrast to aquatic habitats of the middle floodplain, habitats of the lower floodplain showed a low intrahabitat and a high interhabitat diversity in terms of both substrate characteristics and faunal compositions. For both floodplains, ordination analyses showed a high concordance between the structure of the invertebrate community and the characteristics of the environmental habitat, including chemical, geomorphic, and hydraulic variables. Ordinations grouped aquatic habitats according to the origins of the waters. Taxon richness was related to local structural diversity, but species turnover was related to differential vertical and lateral connectivity. Exfiltration of groundwaters provided aquatic floodplain habitats for several specialized species. The results of this study show the significance of the river–groundwater connectivity for the creation of the habitat mosaic that sustains biodiversity in floodplains and thus have important implications for managing the ecological integrity of floodplains.     

三峡库区消涨带植物群落的数量分析

运用双向指示种分析法(TWINSPAN)和除趋势对应分析法(DCA)对三峡库区消涨带植物群落进行了数量分类和排序分析。TWINSPAN将122个样方分成19类,可归为4个植被型,分类结果反映了植物群落与环境梯度间的关系,并在DCA分布图上得到较好的验证。DCA分布图的对角线基本反映了水淹时间长短和土壤湿度高低,表明水淹时间和土壤湿度是该区域植物群落组成和空间分布的主要限制性影响因子。对消涨带不同部位植物群落的物种组成和分布规律的分析为筛选耐水淹物种、进行三峡水库消涨带的植被恢复提供了物种参考。     

Do faunal assemblages reflect the exchange intensity in groundwater zones?

The exchange of water with groundwater is a key determinant of water quality and faunal assemblage. Water exchange not only occurs with running waters, but also through percolation, interception (soil, porous alluvium), and evaporation. The aim of this study was to identify how different types of exchange were related to the groundwater faunal assemblage of an alluvial aquifer. Hydrological exchange is largely governed by pore space and thus ultimately by geological formation. In the Marbling Brook catchment of Western Australia the different geological formations did not eventuate in hydrochemically distinct groundwater zones. The cluster analysis of faunal assemblages revealed five groups within the faunal samples which did not reflect spatial patterns such as geological, chemical or topographic features. Discriminant analysis showed that these five groups were best characterized by a range of abiotic features including dissolved oxygen, land-use, and temperature. These variables signal different types and intensities of exchange with the surface. Handling editor: K. Martens     

Vegetation ecology of phytogenic hillocks (nabkhas) in coastal habitats of Jal Az-Zor National Park,Kuwait: Role of patches and edaphic factors

Phytogenic sandy hillocks (Arab. ‘nabkha’) are very frequently occurring aeolian deposits along the coastal plain of Kuwait. We investigated the vegetation of 42 nabkhas in a coastal habitat of Jal Az-Zor National Park, Kuwait. Sixty-two species were recorded (47 annuals and 15 perennials) in the studied nabkhas. Four vegetation types were recognized after classifying the vegetation of the nabkhas by TWINSPAN. They were named after their dominating host species which are Nitraria retusa, Zygophyllum qatarense, Haloxylon salicornicum and Panicum turgidum. Using Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA), we assessed the relationships between environmental gradients, floristic composition, species diversity, and geomorphology aspects of the studied habitats. Notable environmental variables affecting the distribution of the vegetation types in the study area were: geomorphological aspect, size of plants forming the core of the nabkha, moisture and nutrients contents, salinity, sand and silt components, and pH.     

The distribution of ecological species groups in Fagetum communities of Caspian forests: Determination of effective environmental factors

Aim of the research was the recognition of ecological species groups in beech forests south of the Caspian Sea (Northern Iran) and the determination of the main effective environmental factors explaining the distribution of plant ecological groups. Selective stratification sampling was used to locate samples. A total of 120 samples (400 m² each) were selected in Fagetum communities within the study area. At each sample, a floristic list of the plot and an estimate of percent cover and abundance of all vascular plants were recorded in separate strata using the Braun-Blanquet scale. At the center of each vegetation plot, two soil samples were taken of 0–10 and 10–30 cm depth levels for physico-chemical analyses. Cluster analysis was used for the classification of vegetation samples and Multi-response Permutation Procedure (MRPP) was used to test the hypothesis of no difference between ecological groups in the species space. Indicator species analysis was used to identify indicator species for each group. A Tukey test was used to compare environmental variables among groups. Detrended Correspondence Analysis (DCA) was used to analyze the relationships between the ecological groups and environmental variables.     

Classification and ordination of plant communities in Abune Yosef mountain range,Ethiopia

Understanding how topography-soil-disturbance drives spatial distribution of vegetation is the interest of ecologists. This study was, conducted to investigate the topography-soil-disturbance and vegetation relationships in Abune Yosef mountain range, Ethiopia. A total of 85 nested sample plots measuring 400 m², 25 m² and 1 m² were established for trees, shrubs and herbs respectively. Topographic, soil and disturbance variables were also assessed from each plot. Plant community classification was described and identified by agglomerative hierarchical clustering using Ward's minimum variance clustering methods. Shannon diversity index was employed to determine community diversity. After detecting the length of the first Detrended Correspondence Analysis (DCA) axis, Canonical Correspondence Analysis (CCA) forward and backward stepwise selection of environmental variables was performed based on their p-value by running permutation tests. The first axis explained 43.63% of the overall inertia and is correlated with Elevation, pH, slope aspect, total Nitrogen, soil organic Carbon & Clay. On the other hand, the second axis explained 32.06% of the total inertia and is correlated with bulk density, slope, logging, & available Phosphorus. The present study revealed that topographic variables have a profound influence on vegetation spatial distribution than soil and disturbance factors.     

The steppes of Tierra del Fuego: floristic and growthform patterns controlled by soil fertility and moisture

Northern Tierra del Fuego is the insular extreme of the Magellanic steppe, a unique example of a cold-temperate oceanic grassland in South America. We surveyed this poorly known region with a landscape-based procedure to classify plant communities and investigate environmental gradients. Sampling sites were selected with the aid of aerial photos, and floristic composition, soil, topography and landform type were recorded in each site. Classification was achieved with Two-Way Indicator Species Analysis and gradients were analyzed with Detrended Canonical Correspondence Analysis. Two broad groups of communities were separated by the presence of typical acidophilous dwarf shrubs: acidophilous/mesotrophic and neutrophilous vegetation. Along the main floristic gradient, ericoid dwarf shrubs were replaced by forbs and grasses as soil acidity decreased. The acidic habitats were on Pleistocene glacial and alluvial deposits, and had coarse texture, poorly decomposed organic matter, and low base status. The eutrophic habitats were on Tertiary rocks of medium to fine texture and had well-decomposed organic matter and high base status. A second axis of variation was associated to latitudinal position and slope aspect, revealing a precipitation/evaporation gradient. Scrubs dominated by midheight shrubs, with species from the southern forests, were at the humid extreme (higher latitudes/south aspects); and short grass steppes, with taxa commonly found further North in the continent, at the xeric end (lower latitudes/north aspects). Although fertility and moisture seem to control the overall floristic gradient, the extreme vegetation types of the fertility gradient, both having a very simple structure, could be attributed to grazing disturbance. Floristics and ecology of the Fuegian steppe resemble to a certain degree some boreal oceanic systems.     

丹江口水库水滨带植物群落空间分布及环境解释

探讨了环境因素对丹江口水库(南水北调中线水源地)水滨带植物群落空间分布的影响。通过对水滨带植物群落和环境因素的实地调查,用双向指示种分析(TWINSPAN)对201个水滨带植物群落进行分类;结合地形、土壤和水文因素用除趋势典范对应分析法(DCCA)分析环境因素对水滨带植物群落的影响;并对环境因素的解释能力进行定量分离。结果表明:(1)水滨带植物群落包括7种类型,分别是萹蓄群落、苘麻群落、细叶水芹+狗牙根群落、狗牙根群落、响叶杨-狗牙根群落、杜梨-白刺花-狗牙根群落和侧柏-牡荆-三穗苔草群落;(2)海拔和水淹影响对水滨带植物群落空间分布具有主导作用。海拔升高,水淹影响减弱,植物群落呈现由草本植物群落向木本植物群落变化的格局;(3)土壤因素的解释能力大于地形因素,水文因素的解释能力最小。各类环境因素之间存在交互作用,地形、水文和土壤因素三者间的交互作用最大,地形和土壤因素之间的交互作用最小。环境因素共解释水滨带植物群落空间分布的21.99%,未解释部分为78.01%。结果证明环境对植被的解释能力是由植被的复杂程度决定的,植被越复杂,环境的解释能力越低。     

Do we really need phytosociological classes to calibrate Ellenberg indicator values?

Abstract. Wamelink et al. (2002) calibrated Ellenberg indicator values for acidity and water availability against measured soil pH and measured mean spring groundwater level (MSL), respectively. Linear regression between indicator value and measured value of all the observations gave a poor fit. Regression lines per phytosociological vegetation class, on the other hand, generally described the observations well. In this article we demonstrate that this result is, at least partly, an artefact. First, because the data utilized are likely to contain systematic errors, and second, because a wrong regression model was applied. A sigmoid function for the relation between the indicator value for water availability and MSL gives a far better fit than a linear function does.‘Vegetation class’ is not an obvious choice as an extra explanatory variable for the regression, as it is only a convenient label for vegetation and should not be used as if it were a real independent environmental variable. In general, indicator values of plant species should be calibrated against environmental variables with great care. This implies that researchers should have knowledge about the ecological demands plants make on their environment, as well as about the spatial and temporal variability of this environment.