Indirect Gradient Research Articles

Discovering the ecological structure of different macrophyte groups in rivers using non-parametric and parametric multivariate ordination techniques

This paper analyses various methods of ecological ordering that are often used in modelling the relationship between vegetation and habitat. The results of direct gradient ordination by Canonical correspondence analysis (CCA), which is based on correlation, were compared with Non-metric multidimensional scaling (NMDS), which is based on rank analyses. Both tools were also compared with Detrended correspondence analysis (DCA), which is a popular indirect gradient analysis method. The macrophyte assessment was conducted at 98 river locations in the lowland regions of Poland. Each of the surveyed locations falls within a consistent abiotic category: small to medium-sized lowland rivers with a sandy bottom. Habitat elements analysed included limnological variables and geographic parameters, and the botanical survey focused on submerged macrophytes, including vascular plants, as well as bryophytes and algae. Firstly, it was shown that various analytical tools for determining the importance of ecological factors (Monte Carlo test, BIOENV) identify slightly different significant factors responsible for the development of macrophytes in rivers. Secondly, considerable similarity was found in the structure of macrophyte communities generated on NMDS and DCA biplots, while macrophyte communities were presented very differently based on CCA. Thirdly, the ecological preferences of aquatic plants based on one-dimensional analyses primarily reflected the results of CCA, whereas they did not always follow the ecological pattern revealed by NMDS. Finally, by conducting separate studies for non-vascular plants and vascular macrophytes, it was confirmed that different ecological drivers are responsible for the development of particular groups of macrophytes

The relation of alpine vegetation cover and geomorphic processes in the Belianske Tatra Mts. (Slovakia)

Abstract The geomorphic processes in high-mountain environments are crucial and often limiting factors of vegetation development. Studies based on the long-term field monitoring are still scarce, however, thus limiting our understandng to vegetation dynamics and the knowledge needed for effective conservation management. In this paper we interpret results of a 20 years long observation considering the relationship between alpine vegetation and intensity of geomorphic processes in the territory of seven permanent plots in the Belianske Tatra Mts. (Slovakia, Central Europe). In principle, these sites represent a “battle field” for ongoing geomorphic processes and vegetation. They are either gradually occupied by initial stages of ecological succession of vegetation or were occupied in the past with the vegetation being more or less destructed. The field research was combined with data collection for standard phytosociological relèves. Spatial distribution of particular tussocks or individuals on each field was drawn in detail. We observed the share of species and their spatial arrangement in relation to the control sites with uncovered substrate. Special attention was paid to measuring the intensity of geomorphic processes using various methods and carried out three times a year. The CANOCO software was used for quantitative evaluation of the phytosociological relèves data. We applied indirect gradient analysis of principal components (PCA) to find out the variability of vegetation and sites, and the direct gradient analysis (RDA) to explain the diversity of species ad the habitat characteristicsThe geomorphic processes affecting the extreme high-mountain environment were evaluated as the most crucial elements that determine the spatial distribution of vegetation, its particular species or overall nature of coppice fragmentation. The relief and mainly its spatial geomorphic attributes are therefore relevant phenomena of landscape that enable scientists to understand, for example the scale and hierarchy of vegetation arrangement. The relationship of vegetation and the intensity of geomorphic processes can be only considered and generalized on the basis of longtermed research.

Comparative insight into the effects of different carbon source supplement on antibiotic resistance genes during whole-run and short-cut nitrification-denitrification processes.

Mature landfill leachate is known for nitrogen-removal challenging and meantime was considered as an important sink of antibiotic resistance genes (ARGs). The added external carbon sources, enabling the short-cut nitrification and denitrification, may facilitate the proliferation of bacteria that possibly carry ARGs. However, this speculation has yet to be studied. Here, we explored the effects of glucose, sodium acetate, and methanol supplements on ARGs during whole-run and short-cut treatment processes. The results showed that sodium acetate supplement during short-cut process efficiently reduced the abundances of total ARGs (0.84-1.99 copies/16S rRNA) and integrons (0.59-1.20 copies/16S rRNA), which were highly enhanced by methanol addition during whole-run treatment process (total ARGs: 3.60-11.01 copies/16S rRNA, integrons: 1.20-4.69 copies/16S rRNA). Indirect gradient analysis showed that the variation of ARGs was not correlated with the supplement of different external carbon source. Correlation analysis indicated that dominant intl1 (55.99 ± 17.61% of integrons) showed positively significant correlations with all detected ARGs expect for sul2 and ermB (p < 0.05), suggesting the significant role on ARGs dissemination. Redundancy analysis illustrated that the potential hosts of intl1, intl2, sul1, tetQ, tetM, mefA, and mexF were dominant Bacteroidetes and Actinobacteria. Interestingly, the numbers and significant extent of correlations under the supplement of sodium acetate during short-cut denitrification process were obviously declined, and it was in accordance with ARGs reduced by sodium acetate supplement, suggesting sodium acetate displayed the efficient ARGs reduction during short-cut process. In summary, this study provides a comparative understanding of the effects on ARGs by different carbon source supplements during nitrification-denitrification processes of leachate; sodium acetate is the optimal carbon source.

Plant-soil interactions in the communities dominated by alien and native plants

It has been established by research on plant invasions that soil biota and availability of nutrients affect the processes of alien species establishment and spread. So far, attention was mainly on alien invaders, although some native species (expansive), vigorously spread in human-influenced landscapes and also transform the habitats they colonize. Based on indirect gradient ordination analysis of vegetation relevés dominated by five native (Calamagrostis epigejos, Filipendula ulmaria, Phalaris arundinacea, Rubus idaeus, Urtica dioica) and five alien taxa (Impatiens glandulifera, Lupinus polyphyllus, Telekia speciosa, Reynoutria sp., Solidago canadensis agg.) in the Czech Republic, Central Europe, we identified pairs of species differing by origin (native vs alien) and growing in similar habitats. In the resulting 10 pairs, we tested the net effect of species origin on the following soil characteristics: (i) physical properties, (ii) nutrient availability, and (iii) biological activity. We found that the impact of alien invasive and native expansive species on soil cannot be explained simply by species’ origin as a factor. Regardless of the origin, a statistically significant effect was recorded only for factors expressing nitrogen supply at the peak of the vegetation season and soil biological activity. Differences in impacts attributable to origin were only verified for individual pairs, being most pronounced between the alien Lupinus and its native counterparts Calamagrostis and Filipendula, and least between Solidago vs Calamagrostis, and Telekia vs Rubus. Both invasive alien and expansive native dominant plants can alter the rate of decomposition by changing the litter quality and availability of nutrients, mainly inorganic nitrogen. Therefore, management actions to preserve or restore diversity and mitigate the negative impacts of dominant species should be focused both on native and alien species.

A Generic Indirect Deep Learning Approach for Multisensor Degradation Modeling

To monitor the degradation status of units and prevent unexpected failures in engineering systems, health index (HI)-based data fusion technologies have been rapidly developed by combining multiple sensor signals, which are helpful to understand the degradation processes of units and predict their remaining useful lifetime (RUL). Although promising, existing HI-based data fusion models for degradation modeling are still limited due to the restrictive assumptions made during the fusion or the degradation modeling processes, e.g., assuming the fusion model as a linear or kernel-based function from multiple sensor signals, or modeling the degradation process by a preselected basis function. Such assumptions are often invalid in industrial practice and may fail to accurately characterize the complicated relationships between multiple sensor signals and the underlying degradation process. To address the issue, this article proposes a generic indirect deep learning method that constructs an HI by combining multiple sensor signals to better characterize the degradation process. In particular, our innovative idea is to seamlessly integrate a deep neural network (DNN) and a long short term memory (LSTM) model to construct the HI by fusing multiple sensor signals and characterize the degradation process, which can be applied to the degradation modeling of various engineering systems. Domain knowledge including the concept of failure threshold and monotonicity of the degradation process is also considered to enhance the interpretability of the proposed method. For parameter estimation, we develop an indirect gradient descent (IGD) algorithm to train the proposed method. Simulation studies and a case study on the degradation of aircraft gas turbine engines are presented to validate the performance of the proposed method. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —The article aims to develop a generic health index (HI)-based data fusion method for degradation modeling when multiple sensors are available to monitor the degradation status of a unit. Specifically, the developed method addresses two challenging questions in practice: 1) how to effectively combine multiple sensor signals to construct an HI that accurately characterizes the underlying degradation status and 2) how to flexibly model the degradation evolution based on the constructed HI. To implement this method in practice, four steps are included as follows: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">First</i> , collecting multiple sensor signals and failure time of historical units. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Second</i> , constructing the HI and describing the underlying degradation process by training a deep neural network (DNN) model and a long short term memory (LSTM) model, respectively. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Third</i> , estimating model parameters using the proposed IGD algorithm. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Fourth</i> , constructing the HI of in-service units and predicting their remaining useful lifetime (RUL) using the constructed HI. The proposed method is expected to be able to characterize various degradation processes and be applied to the degradation modeling of different engineering systems.

Weed communities in the irrigated rice paddies of northern Iran

Dedicated insights into the diversity, spatial and temporal distribution of rice weed communities, as well as underlying ecological factors, are critical for developing effective ecological weed management strategies in these agroecosystems, leading to the preservation of biodiversity and ecosystem services in a sustainable agriculture framework. To fulfill this aim, 108 vegetation relevés were conducted at 23 sites of rice paddies throughout 9 counties in the north of Iran at various altitudes, during three different phenological stages of rice. Data from vegetation relevés was analyzed using TWINSPAN, resulting in the identification of four main plant community types related to the different stages of rice growth: Echinochloa crus-galli–Paspalum distichum, Spirodela polyrrhiza–Lemna minor, Monochoria vaginalis s.l.–Marsilea quadrifolia, and Cyperus difformis–Ammannia baccifera. Complementary direct (canonical correspondence analysis) and indirect gradient analyses (detrended correspondence analysis) confirmed these communities’ separation and indicated that the most significant environmental factors affecting plant community distribution were soil water content and soil pH. Moreover, out of 72 segetal species of investigated rice paddies, 12 species were alien to Iran, indicating that this agroecosystem provides an important source for the introduction, distribution, and possible spread of alien species into other adjacent ecosystems. Our findings contribute to the knowledge of detecting patterns of weed composition and distribution in rice paddy ecosystems, as well as their interpretation in relation to environmental gradients. They can support the establishment of ecological weed management practices in northern Iran's paddy fields.

Classification and ordination analysis of herbaceous flora in district Tor Ghar, western Himalaya

District Tor Ghar is phytosocilogically unexplored region in the western Himalaya. Present study was conducted in district Tor Ghar during the summers of 2012 and 2013 to study floristic diversity of herbaceous flora in the region. The district Tor Ghar is located on 34° 32′ - 34° 50′ N, and 72° 48′ - 72°58′ E. A total of 229 herb species belonging to 168 genera and 66 families were identified. Herbaceous vegetation was sampled from 1 × 1 m quadrats. For vegetation classification into plant communities, presence, absence (1,0) data on 229 herbaceous species and 64 locations were analyzed in PCORD version 5 via Cluster and Two Way Cluster Analyses. Six plant communities were established. Plant abundance data were treated in CANOCO version 4.5 to measure the ecological gradient of plant species and communities of the region. Detrended Correspondence Analysis (DCA) a type of indirect gradient analysis reconfirmed the results of Cluster and Two way Cluster Analysis. Moreover the study furnishes useful information for improvement, protection and management of present vegetation status for future generation. A comprehensive conservation measure with practical implementation is utmost necessary for conservation of rapidly depleting plant resources of the area.

Impact of invasive and native dominants on species richness and diversity of plant communities

Invasive alien plants are known to reduce the diversity of recipient communities. However, there is an ongoing debate on whether or not native dominant species have similar effects. To answer this question, we compared herbaceous dominant species of plant communities in central Europe, 10 of which were native and nine alien to this region. We sampled 5–16 populations per species, selected to reflect a gradient from a low to a high cover of the dominant species studied and include a range of typical habitats. To reveal the possible effect of scale, we sampled the vegetation in 4 × 4 m (large scale) and 1 × 1 m (small scale) plots. All vascular plant species and their percentage covers were recorded in each plot. LMM regressions models were used to relate the dominant species’ cover to the richness and diversity of the plant community and ANCOVAs to test for differences between the impacts of native vs. invasive dominants. On the large scale, 17 dominants (nine native and eight invasive) significantly reduced community species richness, and seven (four native and three alien) decreased species diversity measured using the Shannon H’ index. Reynoutria ×bohemica, Calamagrostis epigejos and Phalaris arundinacea had the strongest negative impact on species richness, while Reynoutria ×bohemica, Phalaris arundinacea and Urtica dioica had the strongest impact on species diversity H’; the results at the small scale were very similar. No significant differences in impacts were detected with regard to the origin of the dominant species when all 19 dominants were included in one model. Further, we used indirect gradient ordination analysis (DCA) to identify pairs of native and invasive dominants that grow in similar habitats and, thus, their impacts can be compared and tested for the effect of origin (native vs. alien). This procedure yielded 27 pairs in total, as some dominants occur in more than one type of habitat and could, therefore, be coupled with more than one species from the other group. At the large scale, native dominants had stronger impacts on species richness in three cases (Calamagrostis epigejos, Cirsium oleraceum and Phalaris arundinacea) and invasive dominants in two (Aster novi-belgii agg. and Rumex alpinus), making up 11.1% and 7.4% of the total number of pairs examined, respectively. Only the invasive dominants (Reynoutria ×bohemica, Rumex alpinus) had stronger impacts on species diversity H’, in four pairwise comparisons (14.8%). The differences were not significant at the small scale in all but one comparison. The results show that both native and invasive dominants can reduce the diversity of vegetation. To conserve biodiversity, measures should be adopted to mitigate not only the impacts of invasive species but also those of native dominants, spreading in the current landscape; this would be best achieved by promoting traditional management and land-use.

Identifying the anthropogenic influence on the spatial distribution of plant diversity in an estuarine island through multiple gradients

Identifying the anthropogenic influence on the spatial distribution of plant diversity can provide reference for ecological conservation. In this study, an identification method for the anthropogenic influence was proposed by observing multiple gradients in estuarine areas. The multiple gradients included soil, vegetation, heat and aridity, distance, and landscape gradients; the former three are direct gradients and the latter two are indirect ones. The single and comprehensive effects of the multiple gradients on plant diversity were analyzed. Anthropogenic influence was then identified by combining the influence degrees of human activity through different gradients and the effect weights of different gradient factors on the plant diversity. A new index, namely, anthropogenic influence index (AII) was established to quantify and spatially express the influence. Chongming Island, the largest estuarine alluvial island in the world, was selected to demonstrate the method. Results validated the effectiveness of our method. The multiple gradients determined the spatial distribution of plant diversity. The direct gradient factors exhibited significant gross and net effects, whereas the indirect gradient factors showed significant gross but insignificant net effects. Of all the gradient factors, the normalized difference vegetation index contributed the most to the spatial distribution of plant diversity. The AII was 53.38% over the entire study area, which indicated that anthropogenic influence has been the main driving factor of the spatial variation of plant diversity. The differences of AII across different plant communities and nature reserves revealed that human activity generally increased the plant diversity on Chongming Island.

Pollution indicandum and marble waste polluted ecosystem; role of selected indicator plants in phytoremediation and determination of pollution zones

Abstract The absence or presence of particular plant species indicates specific level of pollution. It was hypothesized that the marble waste polluted ecosystem also host specific plant indicators that can grow, survive and tolerate more successfully than others and can be utilized in better managements of such systems. The current research work was therefore, conducted to determine the indicators of marble polluted region of Buner, Pakistan. Ecological techniques using varying sized quadrats i.e., 1 × 1 m2, 5 × 2 m2 and 10 × 2 m2 for herbs, shrubs and tree species were used respectively. Standard protocols were used to prepare soil samples and plant parts (root, leaf and shoot) for Atomic Absorption Spectrophotometry. Indicator i.e., Populus alba L., Arundo donax L., Erigeron canadensis L and Morus alba L. were identified via Indicator Species Analyses (ISA) in various polluted zones. All the collected data were put in MS Excel for analyses in PCORD through Cluster Analysis (CA), Two Way Cluster Analysis (TWCA) and ISA. CANOCO software was used to examine the impact of miscellaneous environmental variables in zonation via both direct and indirect gradient techniques i.e., Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA). A total of 102 plant species belonging to 95 genera and 48 families were recorded in the marble waste polluted ecosystem. CA and TWCA through Jaccard Distance measurements and Wards Linkage methods gave rise to 3 major polluted zones. These zones were i) Heavily Polluted Zone (HPZ), ii) Moderate Polluted Zone (MPZ) and iii) Less Polluted Zone (LPZ). The recorded values of Biological Concentration Factor (BCF), Translocation Factor (TF) and Bioaccumulation Coefficient (BAC) for analyzed heavy metals i.e. Fe, Mg, Ca, Na and Cu in root and shoot of P. alba L., A. donax L., and M. alba L. showed that these species were significant phytostabilizers and E. canadensis L. was phytoextracters and hence best indicandum of marble waste polluted ecosystems. It was concluded that among all the measured environmental variables, higher phosphorus level, higher pH, moderate potassium and lower electrical conductivity (EC) had significant effects (p 0.05 ) on the functions of these indicators as phytoremediaters. It is recommended to develop green belts of these indicators around the marble industrial areas for the better management and hazardous free environment.

Vulnerability of diatom communities in the Peace-Athabasca Delta to environmental change.

Habitat degradation associated with resource development is a major ecological concern, particularly in Canada’s boreal zone where limited information on biodiversity is available. Habitat degradation can lead to reductions in biodiversity and ecosystem function, especially when drivers of variability and diversity patterns have not been identified for a region of interest. In this study, the distribution of diatom genera in the Peace–Athabasca Delta in northeastern Alberta was examined in relation to seasonal, geographic, and alkalinity gradients. Grab samples of six abiotic variables (total dissolved nitrogen, total dissolved phosphorus, dissolved iron, turbidity, pH, and specific conductance (SPC)) were taken from 12 remote wetlands over three sampling periods, and regressed against an ordination of diatom community composition to identify key environmental drivers of diatom community variation. Indirect gradient analysis identified two major gradients among sites. First, separation of sites among sampling periods showed successional seasonal changes in diatom community composition. Second, separation of sites from the Peace sub-delta and Birch sub-delta showed a gradient of geographic separation. Direct gradient analysis failed to explain the underlying drivers of these two gradients, but did show that alkalinity is a key driver of diatom community composition in the Embarras sub-delta, and that these sites could be particularly vulnerable to community changes associated with acidification.

Local patterns of diversity in California northern coastal scrub.

Within global biodiversity hotspots such as the California Floristic Province, local patterns of diversity must be better understood to prioritize conservation for the greatest number of species. This study investigates patterns of vascular plant diversity in relation to coast–inland environmental gradients in the shrublands of Central California known as northern coastal scrub. We sampled coastal shrublands of the San Francisco Bay Area at coastal and inland locations, modeled fine‐scale climatic variables, and developed an index for local exposure to maritime salts. We compared diversity, composition, and structure of the coastal and inland plots using indirect gradient analysis and estimated species accumulation using rarefaction curves. Coastal plots were significantly higher in alpha, beta, and gamma diversity than inland plots. Plant diversity (effective species number) in coastal plots was 2.1 times greater than inland plots, and beta diversity was 1.9 times greater. Estimated richness by rarefaction was 2.05 times greater in coastal sites than inland sites. Salt deposition and water availability were the abiotic process most strongly correlated with increased maritime plant diversity and compositional differences. Stands of northern coastal scrub on the immediate coast with higher maritime influence exhibit markedly higher plant diversity than most interior stands, paralleling previous work in other vegetation types in this region. These studies suggest that the California coastline deserves special consideration for botanical conservation. Fine‐scale climatic models of cloud frequency, water availability, and the salt deposition index presented here can be used to define priority areas for plant conservation in California and other coastal regions worldwide.

Plant communities of the uMlalazi Nature Reserve and their contribution to conservation in KwaZulu-Natal

Vegetation research is an important tool for the simplified and effective identification, management and conservation of the very complex ecosystems underlying them. Plant community descriptions offer scientists a summary and surrogate of all the biotic and abiotic factors shaping and driving ecosystems. The aim of this study was to identify, describe and map the plant communities within the uMlalazi Nature Reserve. A total of 149 vegetation plots were sampled using the Braun-Blanquet technique. Thirteen plant communities were identified using a combination of numeric classification (modified Two-way-Indicator Species Analysis) and ordination (non-metric multidimensional scaling). These communities were described in terms of their structure, floristic composition and distribution. An indirect gradient analysis of the ordination results was conducted to investigate the relationship between plant communities and their potentially important underlying environmental drivers. Based on the results, the floristic conservation importance of each plant community was discussed to provide some means to evaluate the relative contribution of the reserve to regional ecosystem conservation targets.Conservation implications: The uMlalazi Nature Reserve represents numerous ecosystems that are disappearing from a rapidly transforming landscape outside of formally protected areas in Zululand. The descriptions of the plant communities of these relatively pristine ecosystems provide conservation authorities with inventories and benchmarks with which the ecological health of similar ecosystems in the region can be measured.

Online appendix 2:Plant communities of the uMlalazi Nature Reserve and their contribution to conservation in KwaZulu-Natal

Vegetation research is an important tool for the simplified and effective identification, management and conservation of the very complex ecosystems underlying them. Plant community descriptions offer scientists a summary and surrogate of all the biotic and abiotic factors shaping and driving ecosystems. The aim of this study was to identify, describe and map the plant communities within the uMlalazi Nature Reserve. A total of 149 vegetation plots were sampled using the Braun-Blanquet technique. Thirteen plant communities were identified using a combination of numeric classification (modified Two-way-Indicator Species Analysis) and ordination (non-metric multidimensional scaling). These communities were described in terms of their structure, floristic composition and distribution. An indirect gradient analysis of the ordination results was conducted to investigate the relationship between plant communities and their potentially important underlying environmental drivers. Based on the results, the floristic conservation importance of each plant community was discussed to provide some means to evaluate the relative contribution of the reserve to regional ecosystem conservation targets.Conservation implications: The uMlalazi Nature Reserve represents numerous ecosystems that are disappearing from a rapidly transforming landscape outside of formally protected areas in Zululand. The descriptions of the plant communities of these relatively pristine ecosystems provide conservation authorities with inventories and benchmarks with which the ecological health of similar ecosystems in the region can be measured.

Online appendix 1:Plant communities of the uMlalazi Nature Reserve and their contribution to conservation in KwaZulu-Natal

Vegetation research is an important tool for the simplified and effective identification, management and conservation of the very complex ecosystems underlying them. Plant community descriptions offer scientists a summary and surrogate of all the biotic and abiotic factors shaping and driving ecosystems. The aim of this study was to identify, describe and map the plant communities within the uMlalazi Nature Reserve. A total of 149 vegetation plots were sampled using the Braun-Blanquet technique. Thirteen plant communities were identified using a combination of numeric classification (modified Two-way-Indicator Species Analysis) and ordination (non-metric multidimensional scaling). These communities were described in terms of their structure, floristic composition and distribution. An indirect gradient analysis of the ordination results was conducted to investigate the relationship between plant communities and their potentially important underlying environmental drivers. Based on the results, the floristic conservation importance of each plant community was discussed to provide some means to evaluate the relative contribution of the reserve to regional ecosystem conservation targets.Conservation implications: The uMlalazi Nature Reserve represents numerous ecosystems that are disappearing from a rapidly transforming landscape outside of formally protected areas in Zululand. The descriptions of the plant communities of these relatively pristine ecosystems provide conservation authorities with inventories and benchmarks with which the ecological health of similar ecosystems in the region can be measured.

Comparing assembly processes for multimetric indices of biotic integrity

Anthropogenic alterations to global ecosystems necessitate management action to conserve or restore biodiversity and ecosystem services. A major advancement in ecosystem management was the development of multimetric indices of biotic integrity (MMIBI) used to guide development of, and measure progress towards, restoration goals. Despite considerable refinement of MMIBI applications over the past three decades, a central challenge remains concerning the method of selecting ecological indicators for inclusion in MMIBI. We quantitatively compared MMIBI metric assembly processes across four sub-regions for fish assemblages in western Tennessee, USA to assess relative performance of three metric selection approaches. Metric selection methods we assessed included “filter gradient” using a multi-step approach to filter candidate metrics down to only the most reproducible and responsive, “indirect gradient” using a correlative unconstrained ordination approach, and “direct gradient” involving an automated constrained ordination approach. For each method, we calculated MMIBI using the selected metrics and compared their precision (i.e., stability across multiple samples), responsiveness (i.e., discrimination between most- and least-altered sites), and sensitivity (i.e., ability to detect landscape alterations). We found metric selection using the filter gradient approach produced MMIBI that were most responsive across all four sub-regions, while the indirect gradient approach produced the most sensitive and precise MMIBI for three of four sub-regions. The direct gradient metric selection approach produced the most sensitive MMIBI only for a single sub-region with a relatively short gradient in landscape alterations. These results reveal a tradeoff between filter and indirect gradient selection methods in which filter gradient metric selection provides high MMIBI responsiveness, but at the cost of increased number of steps and reduced precision and sensitivity. The “middle of the road”, indirect gradient metric selection approach produced precise and sensitive MMIBI, but at the cost of reduced responsiveness. These findings highlight the necessity to pair well-developed ecosystem management goals with MMIBI application, and provide a road map for the most appropriate assembly process for managers developing MMIBI. For example, identification of least- and most-altered sites might best be accomplished with MMIBI developed using the filter gradient approach, but assessing the factors contributing to alteration and precisely measuring progress towards restoration endpoints might best be accomplished with MMIBI developed using the indirect gradient approach. Restoration and management actions guided by MMIBI will become increasingly prevalent with increased future alteration to global ecosystems, and this work provides important insight into how technological and quantitative advances will improve application of ecological indicators.

Flora and vegetation of rocky outcrops/cliffs near the Hyrcanian forest timberline in the Mazandaran mountains, northern Iran

Due to their numerous endemic/sub‐endemic and rare plant species, rocky outcrops and cliffs, particularly those occurring at the timberline and forest/steppe ecotones of the Hyrcanian area, are considered as among the most important and fragile ecosystems in Iran. As a representative of such ecosystems, one of the last remnants of relatively undisturbed timberline and ecotone areas of the central Hyrcanian region was selected for phytogeographical, floristic and vegetation analyses. The flora and vegetation of rocky outcrops and crevices at altitudes of 2500–3000 m a.s.l. was surveyed by 40 relevés of 25 m2 surface area. A total of 215 vascular plants belonging to 55 families and 150 genera were identified in the different vegetation types. Hemicrytophytes (55.8%) were the dominant life form and Euro–Siberian/Irano–Turanian biregional plants (28.2%) were the most common chorotype at the study sites. A phytogeographical analysis indicated that Euro–Siberian elements (including Hyrcanian endemics) precede other uniregional chorotypes in the timberline and upper‐mountain parts of the central Hyrcanian area. The Caucasus, an important biodiversity hotspot close to Iran, has a considerable number of taxa in common with the Irano–Turanian floristic regions. Five vegetation types were identified using a modified TWINSPAN procedure and subsequently analysed by indirect gradient analysis applying both species‐related (species richness, life form and phytogeographical elements) and topographic/bedrocks features of the studied relevés. The analysis revealed that the vegetation of the area is mainly affected by altitude, heat index, northness, slope inclination and bedrock features.

Decomposing the land-use specific response of plant functional traits along environmental gradients

Environmental conditions affect functional trait variability within communities and thus shape ecosystem properties. With the ability of plants to adapt morphologically and physiologically to changing abiotic conditions, gradient analysis was shown to be a suitable tool to identify the drivers which determine trait values. Apart from direct environmental drivers and indirect gradients such as elevation, also anthropogenic effects (e.g. irrigation, grazing) can influence trait variability. Our aim was to assess the interactive effects of different environmental drivers on major plant traits and to investigate how these are modulated within two different land-use types (hay meadow vs. pasture). An elevational gradient spanning 1000m was decomposed into its underlying direct components (temperature, water input, length of growing season) for the investigation of gradual responses of five prominent functional traits (aboveground dry weight (AGDW), vegetative height (VegHt), specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen concentration (LNC)) for key species from two functional groups (grasses, forbs) in the two land-use/management regimes. The present study revealed that the detailed analysis of single direct gradients provides substantial additional information on trait response which remains hidden or is even reversed if only indirect gradients such as elevation are analysed. However, trait response to the combination of the three direct gradients aligned surprisingly well with trait response to the indirect gradient underpinning the adequate representation of temperature, water input and length of growing season by elevation. The response of traits significantly depended on the management regime and corresponding intensity which was shown to play an overriding role and constrained and attenuated response ranges of traits to climatic gradients.

Influence of instream habitat and water chemistry on amphibians in channelized agricultural headwater streams

The widespread use of stream channelization and subsurface tile drainage for removing water from agricultural fields has led to the development of numerous channelized agricultural headwater streams within agricultural watersheds of the Midwestern United States, Canada, and Europe. Channelized agricultural headwater streams have been documented to serve as habitat for amphibians, but information on amphibian habitat relationships within these streams is lacking and needed for developing effective conservation strategies. We quantified instream habitat, water chemistry, and sampled amphibians from seven sites in three channelized streams in Cedar Creek, Indiana in 2008 and 2009 and five sites in five channelized streams in Upper Big Walnut Creek, Ohio in 2009. We conducted an indirect gradient analysis involving the use of principal component analysis and generalized linear mixed effect model analysis to determine which variables had the greatest influence on amphibian community and population structure. Overall, amphibian community and population structure was most strongly correlated with water chemistry rather than instream habitat within channelized agricultural headwater streams in Indiana and Ohio. Eleven of 12 amphibian response variables were most strongly correlated with either a water chemistry gradient of nitrate+nitrite and acetochlor, a gradient of total nitrogen and ammonia, or a gradient of simazine and total phosphorus. Only one amphibian response variable was most strongly correlated with an instream habitat gradient of dissolved oxygen and water depth. Our results suggest that conservation strategies that target reductions of nutrients and herbicides will provide the greatest benefits for amphibians within channelized agricultural headwater streams.

Flora and ecology of a neotropical savanna, Utila, Bay Islands, Honduras

Neotropical savannas exhibit unique patterns of diversity of plant and animal life that are poorly understood. Effective conservation of these often imperiled ecosystems requires a basic understanding of species occurrence as well as the site-specific factors that influence plant community composition. This study focuses on the savanna flora of the island of Utila, Bay Islands, Honduras. Compositional trends were assessed across multiple environmental gradients including surface hydrology, microtopography, nutrient levels and pH using Braun-Blanquet cover abundance in a stratified systematic sampling design. Non-metric multidimensional scaling and non-parametric multiplicative regression were applied to identify community types and to model species’ responses to environmental gradients. We separated habitats into three basic types: sedge meadow, Blechnum-Cladium parkland and woody hammock. Compositional gradients along ordination axes were highly correlated with depth of the water table, pH and conductivity. Disturbance history, especially time since fire, was also linked to an indirect gradient. Some species – notably Acoelorrhaphe wrightii and Chrysobalanus icaco – are generalists, and their distributions may reflect past disturbance. Microtopography was critical in determining distribution for a suite of species that occurred only on mound formations in areas subject to prolonged inundation during the rainy season. Disturbance, particularly by hurricanes and fire, may promote within-habitat diversity; for example, the exposed lignotubers and rhizomes of trees killed by saline inundation provide habitat for less flood-tolerant species in wet areas, while burned clones of A. wrightii and surrounding peat areas permit colonization by many herbaceous species. Pair-wise floristic comparisons between Utila and eight other neotropical savannas revealed fewer than half of the 40 savanna species found on Utila were present in any other site. Two species of Cyperaceae, Fuirena scirpoidea and Rhynchospora tracyi, are new records for Honduras.