Management intensity affects the relationship between non‐native and native species in subtropical wetlands

Question: Does management intensity affect the association between non‐native and native species and between non‐native species and soil nutrients in wetlands? Location: MacArthur Agro‐Ecology Research Center, Florida, USA. Methods: We evaluated native and non‐native plant richness and relative frequency in 15 1‐m² plots in 40 wetlands across two types of pastures, highly managed (fertilized, ditched, planted, heavily grazed by cattle) and semi‐natural (unfertilized, lightly seasonally grazed). Plant biomass was collected in five 0.25‐m² plots per wetland and sorted to species. Soil cores were collected to analyse soil total nitrogen (N) and phosphorus (P). An information‐theoretic approach was used to compare mixed effects models considering the association of non‐native richness, relative frequency, and biomass with native richness, relative frequency, biomass, C₃ grass relative frequency (a dominant native group), N, P and wetland‐type. Results: Non‐native richness was negatively correlated with native richness in semi‐natural wetlands, but there was no evidence of an association between these variables in highly managed wetlands. Non‐native richness increased with increasing soil N in semi‐natural wetlands, but not in the highly managed wetlands. Soil P was positively related to non‐native frequency in semi‐natural wetlands but negatively related in highly managed wetlands. Non‐native frequency and biomass were negatively related to relative frequency of C₃ grasses in both management types. Conclusions: Our results indicate that management intensity influences relationships between native and non‐native richness. Management intensity interacts with abiotic or biotic factors, such as soil nutrients and composition, in predicting where non‐native species will most likely need control.     

Mollusc diversity patterns in Central European fens: hotspots and conservation priorities

Aim To assess mollusc species composition and diversity patterns of treeless fen sites and to find simple environmental parameters that characterize diversity hotspots and priority sites for conservation. Location Western Carpathian Mountains, Europe. Methods Mollusc communities were sampled quantitatively from a homogeneous area of 16 m² in the central part of each of 145 treeless fen sites. Water conductivity and pH, geographical coordinates, altitude and habitat size of the sites studied, mean annual rainfall, mean annual temperature and mean January temperature were compiled for each plot. Nestedness in species composition was tested using the binmatnest program to confirm the ‘nested habitat‐quality hypothesis’. Patterns in species diversity were analysed using the regression trees method to isolate the main predictors of species diversity. Results Nested subset patterns of species composition were found along the gradient of mineral richness. Species distribution was highly nested (T_obs = 11.21, P << 0.001) in mineral‐poor sites (with water conductivity < 300 μS cm^?1, n = 42) and was highly correlated with the site’s mineral richness (r_s = 0.76, P << 0.001). By contrast, species distribution and richness of mineral‐rich sites (c.≥ 300 μS cm^?1, n = 103) were not controlled by mineral richness. Variation in species richness was further explained by January temperature, landscape geomorphology, and total habitat area. The southern mineral‐rich low altitude fens were the most species rich, especially those of larger total area (23 species on average). These 24 sites (17% of all sites) harboured 90% of all recorded species, including all highly endangered ones. Mineral‐rich fens in montane valleys were the second most important group because they hosted the majority of populations of two rare glacial relict species (Vertigo geyeri and Pupilla alpicola). Main conclusions The significant nestedness raises the possibility of conserving the whole fen‐mollusc species pool within the most species‐rich sites. Thus, to select the conservation priority sites, easily available site characteristics for the prediction of species richness are needed. This knowledge can help us maintain fen biodiversity, which has become closely dependent on conservation management practices after the cessation of traditional mowing of fens for haymaking.     

Abandonment alters community composition and canopy structure of Swiss calcareous fens

Abstract. We compared the plant species composition, productivity and canopy structure of seven mown sites to a chronosequence of 20 abandoned calcareous fens in northeastern Switzerland. Cessation of mowing led to an 18% decline in overall plant species richness and the diversity of most functional groups. Abandonment did not lead to marked increases of above‐ground productivity, but rather selectively favoured certain functional groups. On abandoned fens biomass of grasses increased nearly threefold, at the expense of biomass of Cyperaceae and Juncaceae, which declined by 30% compared to mown fens, while forb biomass remained unaffected. Litter mass increased more than 15‐fold in fallows, while canopy height increased by 50%. The foliage in abandoned fens was oriented more horizontally and had a lower overall cover. However, these successional changes were never dependent upon the age of the fallow. Furthermore, nearly all traits differed significantly on regional and local spatial scales, suggesting that floristic and (meso‐)climatic differences obscure or override successional trajectories in these species‐rich wetlands.     

BIODIVERSITY RESEARCH: Native‐exotic species richness relationships across spatial scales and biotic homogenization in wetland plant communities of Illinois,USA

Aim To examine native‐exotic species richness relationships across spatial scales and corresponding biotic homogenization in wetland plant communities. Location Illinois, USA. Methods We analysed the native‐exotic species richness relationship for vascular plants at three spatial scales (small, 0.25 m² of sample area; medium, 1 m² of sample area; large, 5 m² of sample area) in 103 wetlands across Illinois. At each scale, Spearman’s correlation coefficient between native and exotic richness was calculated. We also investigated the potential for biotic homogenization by comparing all species surveyed in a wetland community (from the large sample area) with the species composition in all other wetlands using paired comparisons of their Jaccard’s and Simpson’s similarity indices. Results At large and medium scales, native richness was positively correlated with exotic richness, with the strength of the correlation decreasing from the large to the medium scale; at the smallest scale, the native‐exotic richness correlation was negative. The average value for homogenization indices was 0.096 and 0.168, using Jaccard’s and Simpson’s indices, respectively, indicating that these wetland plant communities have been homogenized because of invasion by exotic species. Main Conclusions Our study demonstrated a clear shift from a positive to a negative native‐exotic species richness relationship from larger to smaller spatial scales. The negative native‐exotic richness relationship that we found is suggested to result from direct biotic interactions (competitive exclusion) between native and exotic species, whereas positive correlations likely reflect the more prominent influence of habitat heterogeneity on richness at larger scales. Our finding of homogenization at the community level extends conclusions from previous studies having found this pattern at much larger spatial scales. Furthermore, these results suggest that even while exhibiting a positive native‐exotic richness relationship, community level biotas can/are still being homogenized because of exotic species invasion.     

Macrophyte species diversity in formerly cultivated wetlands in Uganda

The diversity of major macrophytes was assessed in cultivated areas in Bukasa and Kinawataka wetlands in Central Uganda. One thousand and seventy‐two plots of 1 × 1 m were established in 69 cultivated areas. Data were collected on species richness and abundance. Two‐way analysis of covariance (ANCOVA) showed how cropping regimes affected macrophyte species richness and abundance. There were 127 plant species belonging to 37 families in cultivated areas. Of the 127 species, 42 were macrophytes and of the 37 families, fourteen contained macrophyte species. Plant species diversity was higher in the short‐term cropping regime areas (11.3 species per 1 m²) than in the long‐term cropping regime areas (9.3 species per 1 m²). However, macrophyte species richness was similar in the short‐term (3.2 species per 1 m²) and the long‐term (3.3 species per 1 m²) cropping regimes. The dominant families were Poaceae, Asteraceae and Cyperaceae with more than ten species each. The higher plant species diversity in cultivated areas than in uncultivated was because of nonmacrophyte species, thus cropping regime does not influence macrophyte species diversity. Increase in diversity of nonmacrophyte species in short‐term cropping regime implies that the use of wetlands for agricultural crop growing may alter plant species composition and diversity during secondary succession.     

Microtopographic heterogeneity constrains alpine plant diversity, Glacier National Park, MT

Theoretical and empirical evidence exists for a positive relationship between environmental heterogeneity and species diversity. Alpine plant communities can exhibit exceptional diversity at a fine scale, which niche theory would suggest is the result of fine scale spatial heterogeneity of the environment. To test if species diversity of alpine plants is driven by environmental heterogeneity, we sampled vascular plant species composition, microtopography, and ground cover within 1?m² plots with and without solifluction forms in Glacier National Park, MT. We analyzed the relationship between microtopographic heterogeneity and species richness at the plot and sub-plot scale with linear and quantile regression, respectively. Species richness does not differ between the plots varying in cover type. Species richness is negatively related to the fractal dimension (D) of the ground surface and non-vegetated ground cover within 1?m² plots. At a finer scale, the standard deviation of elevation and slope appear to impose a limit on species richness such that more variable sub-plots have lower species richness. Contrary to our expectations, microtopographic heterogeneity does not promote the diversity of alpine plants. The negative relationship between topographic heterogeneity and species richness is contrary to the theoretical prediction that environmental heterogeneity generally results in greater species diversity. It is possible that microtopographic variability represents a measure of soil disturbance, which would be expected to have a negative effect on species diversity in alpine tundra due to its low productivity.     

Changes in aquatic vegetation and fish communities following 5 years of sustained low water levels in coastal marshes of eastern Georgian Bay,Lake Huron

Aquatic vegetation in the relatively pristine coastal wetlands of eastern Georgian Bay provides critical habitat for a diverse fish community. Declining water levels in Lake Huron over the past decade, however, have altered the wetland plant assemblages in favour of terrestrial (emergent and meadow) taxa and have thus reduced or eliminated this important ecosystem service. In this study, we compared IKONOS satellite images for two regions of eastern Georgian Bay (acquired in 2002 and 2008) to determine significant changes in cover of four distinct wetland vegetation groups [meadow (M), emergent (E), high‐density floating (HD) and low‐density floating (LD)] over the 6 years. While LD decreased significantly (mean ?2995.4 m²), M and HD increased significantly (mean +2020.9 m² and +2312.6 m², respectively) between 2002 and 2008. Small patches of LD had been replaced by larger patches of HD. These results show that sustained low water levels have led to an increasingly homogeneous habitat and an overall net loss of fish habitat. A comparison of the fish communities sampled between 2003 and 2005 with those sampled in 2009 revealed that there was a significant decline in species richness. The remaining fish communities were also more homogeneous. We suggest that the observed changes in the wetland plant community due to prolonged low water levels may have resulted in significant changes in the fish communities of coastal wetlands in eastern Georgian Bay.     

Vegetation and soil properties in restored wetlands near Lake Taihu,China

Riparian wetlands are important components of the lake ecosystem, and they play essential roles in maintaining system health. Remediation of degraded lakeshore wetlands is an essential component of lake restoration. A study was conducted to investigate the restoration of lakeshore wetlands, which were converted to rice fields and then abandoned for 2, 5, 10 and 15 years, near Lake Taihu. Soil samples (0–20 cm and 20–40 cm) were taken and plant species were investigated. The carbon content in the soil had increased significantly, rising from 0.71% to 1.85% between 2 and 15 years. Organic matter accumulation improved soil texture, and water stable aggregate content (>0.25 mm) and soil porosity increased. Total nitrogen in the soil increased from 0.06% to 0.13%, and total Kjeldahl nitrogen increased from 124.4 mg kg⁻¹ to 351.5 mg kg⁻¹. Total phosphorus in the soil increased from 0.045% to 0.071%, and the Olsen-P value increased from 5.13 mg kg⁻¹ to 16.0 mg kg⁻¹. Results showed that phosphorous did not increase as much as nitrogen. In the vegetation restoration process, plant species composition moved towards a natural wetland community, and spatial heterogeneity and landscape diversity increased. The richness of plant biodiversity increased rapidly in the first 2 years, then more slowly in later restoration stages. The wetlands recovery process may be complicated by interactions of biota and soil and hydrological conditions.     

Mollusc community patterns and species response curves along a mineral richness gradient: a case study in fens

Aim The goals of this study were to: (1) compare water conductivity and pH as proxy measures of mineral richness in relation to mollusc assemblages in fens, (2) examine the patterns of mollusc species richness along the gradient of mineral richness based on these factors, (3) model species–response curves and analyse calcicole–calcifuge behaviour of molluscs, and (4) compare the results with those from other studies concerning non‐marine mollusc ecology. Location Altogether, 135 treeless spring fen sites were sampled within the area of the Western Carpathians (east Czech Republic, north‐west Slovakia and south Poland; overall extent of study area was 12,000 km²). Methods Mollusc communities were recorded quantitatively from a homogeneous area of 16 m². Water conductivity and pH were measured in the field. The patterns of local species diversity along selected gradients, and species–response curves, were modelled using generalized linear models (GLM) and generalized additive models (GAM), both using the Poisson distribution. Results When the most acid sites (practically free of molluscs) were excluded, conductivity expressed the sites’ mineral richness and base saturation within the entire gradient, in contrast to pH. In the base‐rich sites, pH did not correlate with mineral richness. A unimodal response of local species diversity to mineral richness (expressed as conductivity) was found. In the extremely mineral‐rich, tufa‐forming sites (conductivity > 600 μS cm^?1) a decrease in species diversity was encountered. Response curves of the most common species showed clear differentiation of their niches. Significant models of either unimodal or monotonic form were fitted for 18 of the 30 species analysed. Species showed five types of calcicole–calcifuge behaviour: (1) a decreasing monotonic response curve and a preference for the really acid sites; (2) a skewed unimodal response curve with the optimum shifted towards the slightly acid sites; (3) a symmetrical unimodal model response curve with the optimum in the base‐rich sites, with no or slight tufa precipitation; (4) a skewed unimodal response curve but with the optimum shifted to the more mineral‐rich sites; and (5) an increasingly monotonic response curve, the optimum in the extremely base‐rich sites with strong tufa precipitation. Main conclusions Conductivity is the only reliable proxy measure of mineral richness across the entire gradient, within the confines of this study. This information is of great ecological significance in studies of fen mollusc communities. Species richness does not increase with increasing mineral richness along the entire gradient: only a few species are able to dwell in the extremely base‐rich sites. The five types of calcicole–calcifuge behaviour seen in species living in fens have a wider application: data published so far suggest they are also applicable to mollusc communities in other habitats.     

Calcium and iron as key drivers of brown moss composition through differential effects on phosphorus availability

Brown moss-dominated rich fens are characterized by minerotrophic conditions, in which calcium (Ca) and iron (Fe) concentrations show large variations. We examined the relative importance of Ca and Fe in relation to the occurrence of three typical brown moss species: Scorpidium scorpioides, Scorpidium cossonii, and Hamatocaulis vernicosus. Peat chemistry was examined in 24 stands of brown moss-dominated rich fens: 12 in the Netherlands and 12 in central Sweden. Ca and Fe turned out to be important drivers of brown moss composition. Fens dominated by Scorpidium scorpioides or Scorpidium cossonii were characterized by high pore water Ca-concentrations and total soil Ca-contents, but low P-availability. In these Ca-rich, but Fe-poor fens, foliar N:P ratios of vascular vegetation exceeded 20?g?g^?1, indicating phosphorus (P)-limitation due to Ca-P precipitation or low P-sorption capacity due to low Fe-levels. In contrast, fens dominated by Hamatocaulis vernicosus were characterized by high pore water Fe-concentrations and total soil Fe-contents, but also relatively high P-availability. N:P ratios in these fens were below 13.5?g?g^?1, indicating potential nitrogen (N)-limitation. We conclude that the relative roles of Ca and Fe, as related to the geohydrological conditions present, strongly determine the brown moss composition in rich fens through their differential effects on plant P-availability.     

Species richness and composition patterns of clitellate (Annelida) assemblages in the treeless spring fens: the effect of water chemistry and substrate

Spring fens are isolated treeless wetlands of a high conservation value. Their environmental conditions are strongly related to their groundwater chemistry, which controls species distribution within various groups of organisms. Clitellates, a dominant group of non-insect aquatic fauna, however, have never been studied in these habitats. It is unclear from previous studies to what extent the distribution of aquatic non-insect taxa reflects water chemistry rather than the substrate structure. We studied 34 spring fens sampled in 17 isolated sites in the Western Carpathian Mountains to determine mainly the effects of water chemistry and substrate structure on variation in species richness and composition of clitellate assemblages as examples of the non-insect fauna. A total of 34 taxa were found, with 3–15 taxa collected per sample. Species richness was negatively correlated with water mineral concentration measured as water electric conductivity (r = −0.57, P < 0.001) and positively with TOC (r = 0.60, P < 0.001). Surprisingly, the lowest number of taxa was found in calcareous fens and richness increased towards Sphagnum-fens. There was a species turnover related to changes in mineral richness and substrate characters. The main change of species composition was promoted by changes in substrate structure. The second gradient of species composition was linked with the amount of nutrients, moisture, and dominance of sphagna, and was associated with an increase of eurytopic species in fens with high nutrient availability. It was difficult to separate the effects of water chemistry and substrate on clitellate species distributions owing to the fact that variation in tufa precipitation and vegetation was driven by water chemistry changes. This study presented the first quantitative data on fen clitellate assemblages, which appear to have an unusual pattern of species richness. In contrast to plants and molluscs, calcareous fens appeared to be a harsh environment for clitellate species. Only few specialized species, mainly Trichodrilus strandi, were able to establish viable populations. The significant effect of water chemistry on clitellate distribution patterns raises questions about the direct influence of water chemistry on non-insect aquatic taxa, which have previously been considered to be mostly determined by substrate characteristics.     

Canopy-borne seed store in three Western Australian plant communities

The canopy-borne store of seed in the kwongan plant communities at Kulin and Eneabba, and in the forest understorey stratum at Jarrahdale, Western Australia was found to average 1121, 305 and 7 seeds m^-2, respectively. The bradysporous seed reserve of the plant communities increased with decreasing average annual rainfall. In comparisons between species of the same genus, obligatory reseeding bradysporous species tended to have greater numbers of seed per plant than resprouting species. The bradysporous species richness and the average seed content per plant within a species did not vary significantly with soil type, although the bradysporous species composition changed.     

Environmental gradients,plant distribution,and species richness in arctic salt marsh near Prudhoe Bay,Alaska

Spatial patterns of plant cover and species composition in arctic salt marsh and salt affected tundra near Prudhoe Bay, Alaska reflect gradients in elevation, soil conductivity, and soil concentrations of the ions prevalent in seawater. Soil conductivity and soil concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ⁼ and Cl^– were significantly related to site elevation, decreasing as elevation increased. Vascular plant species richness increased significantly as soil conductivity and soil ion concentrations decreased, and site elevation increased. Puccinellia phryganodes was the only species present in low elevation sites with low plant cover, high soil conductivity and high soil concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ⁼ and Cl^–. Mid-gradient sites were dominated by Carex subspathaceae. Plant cover at these sites was greater than at lower elevation sites, but bare ground was still present. Higher elevation sites had the lowest concentrations of soil ions and the lowest soil conductivities. These sites had little bare ground, contained as many as 16 species, and were dominated by Dupontia fischeri and Eriophorum angustifolium. Ordinations indicated that a complex topographic gradient related most closely to elevation and site distance from the coast best explains variation in the vegetation cover. Irregular deposition along the coastline partially or completely buried three sites in peat or sand up to 20 cm deep. Such rapid changes in plant cover and species composition contributes to the community patch mosaic typical of these marshes. Results suggest an individualistic response of plant species to the environmental gradients in salt marsh and salt affected tundra and are indicative of successional models developed in other marginal arctic environments.     

Plant responses to nutrient addition and predictive ability of vegetation N:P ratio in an austral fen

1. Previous studies of the N:P ratio in wetland plants have been carried out in northern hemisphere wetlands where atmospheric nitrogen deposition is higher. There is little research on foliar N:P ratio as a potential indicator of nutrient limitation in vegetation communities in southern hemisphere wetlands. This study aimed to redress this knowledge gap and answer the following questions: how well does the plant tissue nitrogen to phosphorus (N:P) ratio predict wetland plant community nutrient limitation, as indicated by vegetation standing stocks and below-ground biomass, in southern hemisphere fens? Secondly, what are the impacts of realistic upper levels of farm nutrient run-off on natural montane fen vegetation?
2. Low (35 kg ha⁻¹ year⁻¹) and high (70 kg ha⁻¹ year⁻¹) levels of nitrate-N or ammonium-N with and without P (20 kg ha⁻¹ year⁻¹) were added to 81 vegetation plots over a period of 2.75 years. Species composition, plant nutrient status, and above-ground live vegetation standing stocks were assessed after 3 years, and below-ground biomass after 2 years.
3. Plant tissue analysis suggested the community was N limited or N and P co-limited; we found greater standing stocks of vegetation in plots treated with 70 kg ha⁻¹ year⁻¹ ammonium-N, indicating N limitation. No difference between other treatments was found in above-ground standing stocks or below-ground biomass. Plant species cover increased in both high N treatments, consistent with N limitation. These changes in plant species cover were accompanied by significant decreases in species richness in both high N treatments. Native species dominated the vegetation and this was unaffected by nutrient addition (90% cover).
4. This is one of the first studies to test and find support for the N:P ratio in southern hemisphere wetlands. Observed declines in species richness after N fertilisation in an N-limited fen suggests increased N may pose risks to austral wetlands. Responses by plant communities (changes in composition, biomass) to lower levels of nutrient addition may require longer periods of fertilisation to be apparent in slow growing ecosystems.

     

Multi-scale analysis of plant species richness in Serengeti grasslands

Aim To assess scale dependence between environmental factors and plant species richness. Additionally, we aimed to identify the scales at which niche relations and habitat heterogeneity, as hypothesized by A. Shmida & M.V. Wilson (1985) Journal of Biogeography, 12 , 1–20, operate in the savanna grasslands that were the focus of this study. Location Savanna grassland plant communities of Serengeti National Park, Tanzania. Methods Plant species richness was sampled in 102 modified Whittaker plots and tested for associations with two climate factors, mean annual rainfall (MAP) and potential evapotranspiration (PET), and two landscape variables, plot aspect (ASP) and topographic variation (TOPO), using multiple regressions. Scale dependence was assessed by conducting regressions after altering three aspects of spatial scale: grain, extent and focus. Grain was altered by analysing plant richness at 1, 10, 10² and 10³ m²; extent was investigated by restricting the maximum distance between samples to 75, 100, 125 and 150 km; and focus was manipulated by averaging samples spatially according to geographical land regions. Within the context of our data, we assumed that niche relations were represented by climate factors and habitat heterogeneity by landscape factors. Results Across all 102 plots, plant species richness between 1 and 10² m² had a negative relation to PET and a weak positive relation to MAP. Plant species richness at 10³ m² had a positive association with TOPO and weaker associations with climate factors. ASP stayed in the model between grains of 10 and 10³ m², but had a very weak positive association with richness. When the focus was changed to land regions, associations between plant species richness and explanatory variables strengthened, but were not qualitatively different. At spatial extents of 75 and 100 km, PET was the strongest correlate of plant species richness across all spatial grains. At spatial extents ≥ 125 km, PET explained the majority of the model variance at spatial grains ≤ 10² m², whereas TOPO explained equal amounts or more of the model variance at spatial grains of 10³ m². Main conclusions Both climate and topographic variation explained plant species richness in Serengeti grasslands, but specific patterns depended on grain, extent and, to a lesser degree, focus. Consistent with the ideas of Shmida & Wilson (1985) , determinants of plant species richness shifted from niche relations to habitat heterogeneity between spatial grains of 1 and 10³ m², although this occurred only at relatively large spatial extents (≥ 150 km). Finally, the signs, strength and shape of plant species richness relationships in Serengeti closely match those that describe macro‐scale patterns of woody plant species richness across the entire African continent.     

Plant species richness and diversity along an altitudinal gradient in the Sierra Nevada, Mexico

This article presents an analysis of plant species richness and diversity and its association with climatic and soil variables along a 1300‐m elevation gradient on the Cerro Tláloc Mountain in the northern Sierra Nevada in Mexico. Two 1000‐m² tree sampling plots were created at each of 21 selected sampling sites, as well as two 250‐m² plots for shrubs and six 9‐m² plots for herbaceous plants. Species richness and diversity were estimated for each plant life form, and beta diversity between sites was estimated along the gradient. The relationship between species richness and diversity and environmental variables was modelled using simple linear correlation and regression trees. Species richness and diversity showed a unimodal pattern with a bias towards high values in the lower half of the elevation gradient under study. This response was consistent for all three life forms. Beta diversity increased steadily along the elevation gradient, being lower between contiguous sites at intermediate elevations and high – the species replacement rate was nearly 100%– between sites at the extremes of the gradient. Few species were adapted to the full spectrum of environmental variation along the elevation gradient studied. The regression tree suggests that differences in species richness are mainly influenced by elevation (temperature and humidity) and soil variables, namely A₂ permanent wilting point, organic matter and horizon field capacity and A₁ horizon Mg²⁺.     

Seed Banks in Arid Wetlands with Contrasting Flooding,Salinity and Turbidity Regimes

Aquatic plant communities in arid zone wetlands underpin diverse fauna populations and ecosystem functions yet are relatively poorly known. Erratic flooding, drying, salinity and turbidity regimes contribute to habitat complexity, creating high spatial and temporal variability that supports high biodiversity. We compared seed bank density, species richness and community composition of aquatic plants (submergent, floating-leaved and emergent) among nine Australian arid zone wetlands. Germinable seed banks from wetlands within the Paroo and Bulloo River catchments were examined at nested scales (site, wetland, wetland type) using natural flooding and salinity regimes as factors with nondormant seed density and species richness as response variables. Salinity explained most of the variance in seed density (95%) and species richness (68%), with flooding accounting for 5% of variance in seed density and 32% in species richness. Salinity-flooding interactions were significant but explained only a trivial portion of the variance (<1%). Mean seed densities in wetlands ranged from 40 to 18,760 m⁻² and were highest in wetlands with intermediate levels of salinity and flooding. Variability of densities was high (CVs 0.61–2.66), particularly in saline temporary and fresh permanent wetlands. Below salinities of c. 30 g l⁻¹ TDS, seed density was negatively correlated to turbidity and connectivity. Total species richness of wetlands (6–27) was negatively correlated to salinity, pH and riverine connectivity. A total of 40 species germinated, comprising submergent (15 species), floating-leaved or amphibious (17 species), emergent (6 species) and terrestrial (6 species) groups. Charophytes were particularly important with 10 species (five Chara spp., four Nitella spp. and Lamprothamnium macropogon), accounting for 68% of total abundance. Saline temporary wetlands were dominated by Ruppia tuberosa, Lamprothamnium macropogon and Lepilaena preissii. Variable flooding and drying regimes profoundly altered water quality including salinity and turbidity, producing distinctive aquatic plant communities as reflected by their seed banks. This reinforces the importance of hydrology in shaping aquatic biological communities in arid systems.     

Vascular plant diversity and climate change in the upper zone of Sierra Nevada,Spain

Abstract

This study examines the effects of altitudinal, temperature and aspect gradients on vascular plant species richness on mountain tops in Sierra Nevada (Spain) at different spatial scales (1 m² quadrats, plot clusters of 4 m², upper summit area down to the 5-m contour line, entire summit down to the 10-m contour line). The methodology follows the Global Observation Research Initiative in Alpine Environments (GLORIA) programme. Floristic and soil temperature data of eight summits sites in two neighbouring regions of the high part of Sierra Nevada (from 2668 m to 3327 m a.s.l.) were used in this study. In total, 102 taxa were recorded (84 genera; 29 families). The species richness decreased, whereas the proportion of endemic taxa increased with elevation. There were significant linear relationships between species richness and altitude and average soil temperature at each spatial scale. However, there was no significant relationship between species richness and aspect variables. Facing continued climate change, the high-altitude flora of Sierra Nevada is expected to be particularly vulnerable and prone to warming-induced biodiversity losses due to the high proportion of endemic taxa, ranging from 23% at lower elevations up to 67% at higher ones.     

黄龙钙化滩流地物种-面积关系

黄龙沟钙化滩流地由于溪流的作用,在滩流地之间形成面积大小不一的植物群落斑块。这些小尺度斑块面积的大小对植物物种数量的影响尚不清楚。应用回归分析法和幂函数方程对黄龙沟钙化滩流地内的物种-面积关系进行了研究。结果表明黄龙沟钙化滩流地中斑块的大小对物种数(含兰科植物)具有强烈的影响,而调查的其他因子对总的植物物种数量的影响不显著。在所调查的环境因子中,斑块面积对物种数量的影响达到79.5%,即斑块越大,所包含的物种数量越多。兰科植物种类数量除了受斑块面积的影响外,还与距离林缘的距离有关(负相关)。物种-面积关系符合幂函数方程S=cA^Z的规律。不同的尺度下,z值略有差异,在中等尺度下 (1-10 m²)最大,为0.2616,较大尺度下(10-100 m²)的最小,z值为0.2050,小尺度下(<1 m²),z值为0.2382。表明中等尺度的斑块(1-10 m²)包含的物种数(含兰科植物)的增长速度最快,而在斑块面积大于10 m²时,物种数增长速度最小。     

农田开垦对三江平原湿地土壤种子库影响及湿地恢复潜力

种子库是湿地植被恢复的重要途径之一,不同时期的耕作土壤中残留的种子对开垦湿地恢复具有重要的作用.本文采用温室萌发法在两种水分条件下对三江平原天然湿地、不同开垦年限湿地种子库结构和规模进行了研究,以了解不同开垦年限湿地种子库特征及其在湿地植被恢复中的潜力.本次实验共萌发物种50种,随着开垦年限增加,萌发物种逐渐减少,天然湿地、开垦1年、3年、10年、20年的湿地分别为34种、31种、21种、21种和8种,萌发物种数与种子库规模均表现出极显著差异(F1=8.32,F2=5.946,P＜0.001).种子库密度以天然湿地和开垦1年湿地最大,分别为7624粒/m2,9836粒/m2.随着开垦年限增加,种子库规模逐渐减小,开垦3年、10年种子库密度为4336粒/m2,4872粒/m2.开垦20 a后,显著减少为432粒/m2.湿润条件下萌发物种数及种子密度显著高于淹水处理,种子库具有明显的分层现象,0-5 cm土层种子库规模显著高于5-10 cm.小叶章(Calamagrostis angustifolia)作为该地区优势物种,由最初的1192粒/m2,经过20 a开垦后在种子库中消失.研究表明,在一定的开垦年限范围内,开垦湿地土壤中仍然保留大量的湿地物种种子,在湿地恢复中具有重要的作用.