Article

Partitioning vegetation response to anthropogenic stress to develop multi-taxa wetland indicators

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Abstract

Emergent plants can be suitable indicators of anthropogenic stress in coastal wetlands if their responses to natural environmental variation can be parsed from their responses to human activities in and around wetlands. We used hierarchical partitioning to evaluate the independent influence of geomorphology, geography, and anthropogenic stress on common wetland plants of the U.S. Great Lakes coast and developed multi-taxa models indicating wetland condition. A seven-taxon model predicted condition relative to watershed-derived anthropogenic stress, and a four-taxon model predicted condition relative to within-wetland anthropogenic stressors that modified hydrology. The Great Lake on which the wetlands occurred explained an average of about half the variation in species cover, and subdividing the data by lake allowed us to remove that source of variation. We developed lake-specific multi-taxa models for all of the Great Lakes except Lake Ontario, which had no plant species with significant independent effects of anthropogenic stress. Plant responses were both positive (increasing cover with stress) and negative (decreasing cover with stress), and plant taxa incorporated into the lake-specific models differed by Great Lake. The resulting models require information on only a few taxa, rather than all plant species within a wetland, making them easier to implement than existing indicators.

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... Previous studies of vegetation responses to anthropogenic stress in Great Lakes coastal wetlands have typically focused on individual species rather than plant communities (Chow-Fraser 2005, Herrick and Wolf 2005, Stanley et al. 2005, Wei and Chow-Fraser 2006, Trebitz andTaylor 2007). This is a logical starting point for studying plant–environment relationships, and our own understanding of Great Lakes coastal wetlands has benefitted from analyzing individual plant species as indicators of wetland physical environment () and anthropogenic stress (Brazner et al. 2007a, Johnston et al. 2008). Most quantitative studies of plant community–environment relationships have considered only portions of the Great Lakes, rather than the entire region (Gathman et al. 2005, Stanley et al. 2005). ...
... Vegetation sampling was conducted from 2001 to 2003 and was restricted to the months of July and August to ensure that most of the vegetation could be identified and peak annual growth observed. Site characteristics and details of vegetation sampling methods are described by Johnston et al. (2007 Johnston et al. ( , 2008). ...
... Two environmental variables described hydrologic alterations within the wetlands studied. The hydrologic modification index (HMI) was computed as the length per unit wetland area of within-wetland features that likely disrupt the natural flow and fluctuation of water within wetlands, such as road beds, dikes, and ditches (Bourdaghs et al. 2006, Johnston et al. 2008). The presence or absence of dikes was also used as a separate categorical variable. ...
Article
Assessment of vegetation is an important part of evaluating wetland condition, but it is complicated by the variety of plant communities that are naturally present in freshwater wetlands. We present an approach to evaluate wetland condition consisting of: (1) a stratified random sample representing the entire range of anthropogenic stress, (2) field data representing a range of water depths within the wetlands sampled, (3) nonmetric multidimensional scaling (MDS) to determine a biological condition gradient across the wetlands sampled, (4) hierarchical clustering to interpret the condition results relative to recognizable plant communities, (5) classification and regression tree (CART) analysis to relate biological condition to natural and anthropogenic environmental drivers, and (6) mapping the results to display their geographic distribution. We applied this approach to plant species data collected at 90 wetlands of the U.S. Great Lakes coast that support a variety of plant communities, reflecting the diverse physical environment and anthropogenic stressors present within the region. Hierarchical cluster analysis yielded eight plant communities at a minimum similarity of 25%. Wetlands that clustered botanically were often geographically clustered as well, even though location was not an input variable in the analysis. The eight vegetation clusters corresponded well with the MDS configuration of the data, in which the first axis was strongly related (R2 = 0.787, P < 0.001) with floristic quality index (FQI) and the second axis was related to the Great Lake of occurrence. CART models using FQI and the first MDS axis as the response variables explained 75% and 82% of the variance in the data, resulting in 6-7 terminal groups spanning the condition gradient. Initial CART splits divided the region based on growing degree-days and cumulative anthropogenic stress; only after making these broad divisions were wetlands distinguished by more local characteristics. Agricultural and urban development variables were important correlates of wetland biological condition, generating optimal or surrogate splits at every split node of the MDS CART model. Our findings provide a means of using vegetation to evaluate a range of wetland condition across a broad and diverse geographic region.
... The resulting site-specific FQI values can be compared across space and time within and between sites to determine changes in the severity and/or spatial extent of impact from stressors such as elevated phosphorus levels from adjacent land use. Disadvantages of typical FQIs include the need for intensive and repeated plant surveys, as well as the significant potential for misidentification of species because of the requirement to identify all plants to the species level (Johnston et al. 2008). Typical FQIs used in FQAs include a site richness factor. ...
... However, earlier studies indicate that average CC values as an index score are a more reliable indicator of site condition and can be adequately calculated with minimal and controlled sampling effort (Rooney and Rogers 2002;Bourdaghs et al. 2006). Further, common and easy to identify species have been found to be the main drivers of typical FQI results, and limiting surveys to those species did not significantly change the interpretability of FQI scores (Lopez and Fennessey 2002;Johnston et al. 2008;Bourdaghs 2012;Chamberlain and Brooks 2016). Several studies concluded that including species richness in FQI calculations can bias the results because richness is strongly influenced by sampling effort (Francis et al. 2000;Matthews 2003;Rooney and Rogers 2002;Taft et al. 1997). ...
... (cattail) is a well-established indicator of stress (both nutrient enrichment and hydrology) within numerous ecosystems, including wetlands and lakes of the Everglades (Davis and Ogden 1994). Various species of both Typha and Polygonum (smartweed) were also found to be positively correlated with stress in the habitats of the Great Lakes (Johnston et al. 2008;Doherty et al. 2000;Lane et al. 2003). Typha spp. ...
Article
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Floristic quality assessments (FQA) using floristic quality indices (FQIs) are useful tools for assessing and comparing vegetation communities and related habitat condition. However, intensive vegetation surveys requiring significant time and technical expertise are necessary, which limits the use of FQIs in environmental monitoring programs. This study modified standard FQI methods to develop a rapid assessment method for characterizing and modeling change in wetland habitat condition in the northern Everglades. Method modifications include limiting vegetation surveys to a subset of taxa selected as indicators of impact and eliminating richness and/or abundance factors from the equation. These modifications reduce the amount of time required to complete surveys and minimizes misidentification of species, which can skew results. The habitat characterization and assessment tool (HCAT) developed here is a FQA that uses a modified FQI to detect and model changes in habitat condition based on vegetation communities, characterize levels of impact as high, moderate, or low, provide predictive capabilities for assessing natural resource management or water management operation alternatives, and uniquely links a FQI with readily accessible environmental data. For application in the northern Everglades, surface water phosphorus concentrations, specific conductivity, distance from canal, and days since dry (5-year average) explained 67% of the variability in the dataset with > 99.9% confidence. The HCAT approach can be used to monitor, assess, and evaluate habitats with the objective of informing management decisions (e.g., as a screening tool) to maximize conservation and restoration of protected areas and is transferable to other wetlands with additional modification.
... Previous studies of vegetation responses to anthropogenic stress in Great Lakes coastal wetlands have typically focused on individual species rather than plant communities (Chow-Fraser 2005, Herrick and Wolf 2005, Stanley et al. 2005, Wei and Chow-Fraser 2006, Trebitz andTaylor 2007). This is a logical starting point for studying plant–environment relationships, and our own understanding of Great Lakes coastal wetlands has benefitted from analyzing individual plant species as indicators of wetland physical environment () and anthropogenic stress (Brazner et al. 2007a, Johnston et al. 2008). Most quantitative studies of plant community–environment relationships have considered only portions of the Great Lakes, rather than the entire region (Gathman et al. 2005, Stanley et al. 2005). ...
... Vegetation sampling was conducted from 2001 to 2003 and was restricted to the months of July and August to ensure that most of the vegetation could be identified and peak annual growth observed. Site characteristics and details of vegetation sampling methods are described by Johnston et al. (2007 Johnston et al. ( , 2008). ...
... Two environmental variables described hydrologic alterations within the wetlands studied. The hydrologic modification index (HMI) was computed as the length per unit wetland area of within-wetland features that likely disrupt the natural flow and fluctuation of water within wetlands, such as road beds, dikes, and ditches (Bourdaghs et al. 2006, Johnston et al. 2008). The presence or absence of dikes was also used as a separate categorical variable. ...
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The wetland complex is the functional ecological unit of the prairie pothole region (PPR) of central North America. Diverse complexes of wetlands contribute high spatial and temporal environmental heterogeneity, productivity, and biodiversity to these glaciated prairie landscapes. Climate- warming simulations using the new model WETLANDSCAPE (WLS) project major reductions in water volume, shortening of hydroperiods, and less-dynamic vegetation for prairie wetland complexes. The WLS model portrays the future PPR as a much less resilient ecosystem: The western PPR will be too dry and the eastern PPR will have too few functional wetlands and nesting habitat to support historic levels of waterfowl and other wetland-dependent species. Maintaining ecosystem goods and services at current levels in a warmer climate will be a major challenge for the conservation community.
... Emergent vegetation was sampled in 26 Lake Superior coastal wetlands. Sampling was done by visual cover estimation in 1 × 1-m plots distributed along randomly placed transects, using a protocol described by Johnston et al. (2007Johnston et al. ( , 2008Johnston et al. ( , 2009b. A data matrix was constructed of taxa cover for each of the 26 sites; taxa found at a minimum of two sites were retained. ...
... Development (DEV) and forest cover (FOR) were summarized for buffer areas of different widths (100-metres, 500-metres, 1000-metres, 5000-metres) around each wetland Johnston et al., 2009b). The hydrologic modification index (HMI) was computed as the length per unit wetland area of within-wetland features that likely disrupt the natural flow and fluctuation of water within wetlands, such as road beds, dikes, and ditches (Bourdaghs et al., 2006;Johnston et al., 2008). In addition, each wetland was characterized by its area (WETL AREA), latitude (LAT), and growing degree days (GDD). ...
... FQI = floristic quality index, TN = total nitrogen, NO 3 -N = nitrite + nitrate nitrogen, NH 4 -N = ammonium nitrogen, TP = total phosphorus, TSS = total suspended solids, TURB = turbidity, DOC = dissolved organic carbon, Chl a = chlorophyll a, COND = specific conductance, Cl − = chloride, DO = dissolved oxygen, HMI = hydrologic modification index, WETL AREA = wetland area, LAT = latitude, GDD = growing degree days, SHED AREA = watershed area, CSI = cumulative stress index, STRAHLER = Strahler stream order, POPU = watershed human population, PC1 AG = agricultural principal component, PC1 URB = urban principal component, PC1 ATDEP = atmospheric deposition principal component, PC1 NPDES = point-source pollution principal component, PC1 SOIL = first soil principal component, PC2 SOIL = second soil principal component, EROS = watershed erosion, TP export = watershed total phosphorus export, TN export = watershed total nitrogen export, DEV 100 = urban development within 100 m buffer around wetland, FOR 100 = forest within 100 m buffer around wetland, † = data values were log-transformed prior to calculations and values reported for these are geometric means, * p < 0.05, * * p < 0.01, * * * p < 0.001. Johnston et al., 2009b, b Morrice et al., 2008, c Reavie et al., 2006, d Johnston et al., 2008, e Brazner et al., 2007b, f Danz et al., 2007, g Danz et al., 2005, h Smith et al., 1997 widely in the degree of human-related stress; generally, levels of stress decrease from south to north but with considerable variation, especially along the southern shore due to local agricultural activity and the presence of several population and industrial centers. With its east-west orientation, the U.S. Lake Superior coast is less subject to gradients of latitude and corresponding climatic and biogeographic factors that have had a significant influence on interlake variation in wetland quality compared with other Great Lakes (Niemi et al., 2009). ...
Article
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Biological indicators can be used both to estimate ecological condition and to suggest plausible causes of ecosystem degradation across the U.S. Great Lakes coastal region. Here we use data on breeding bird, diatom, fish, invertebrate, and wetland plant communities to develop robust indicators of ecological condition of the U.S. Lake Superior coastal zone. Sites were selected as part of a larger, stratified random design for the entire U.S. Great Lakes coastal region, covering gradients of anthropogenic stress defined by over 200 stressor variables (e.g. agriculture, altered land cover, human populations, and point source pollution). A total of 89 locations in Lake Superior were sampled between 2001 and 2004 including 31 sites for stable isotope analysis of benthic macroinvertebrates, 62 sites for birds, 35 for diatoms, 32 for fish and macroinvertebrates, and 26 for wetland vegetation. A relationship between watershed disturbance metrics and 15N levels in coastal macroinvertebrates confirmed that watershed-based stressor gradients are expressed across Lake Superior's coastal ecosystems, increasing confidence in ascribing causes of biological responses to some landscape activities. Several landscape metrics in particular—agriculture, urbanization, human population density, and road density—strongly influenced the responses of indicator species assemblages. Conditions were generally good in Lake Superior, but in some areas watershed stressors produced degraded conditions that were similar to those in the southern and eastern U.S. Great Lakes. The following indicators were developed based on biotic responses to stress in Lake Superior in the context of all the Great Lakes: (1) an index of ecological condition for breeding bird communities, (2) diatom-based nutrient and solids indicators, (3) fish and macroinvertebrate indicators for coastal wetlands, and (4) a non-metric multidimensional scaling for wetland plants corresponding to a cumulative stress index. These biotic measures serve as useful indicators of the ecological condition of the Lake Superior coast; collectively, they provide a baseline assessment of selected biological conditions for the U.S. Lake Superior coastal region and prescribe a means to detect change over time.
... Ecologists recognize that natural environmental gradients and human impacts structure coastal wetland biota, but wetland regulatory agencies are more interested in using biota to evaluate human-caused degradation of coastal environments. We and other authors have therefore attempted to distinguish natural from anthropogenicallyinduced variation in the biota of Great Lakes coastal wetlands (Brazner et al., 2007a,b; Johnston et al., 2008 Johnston et al., , 2009b Trebitz et al., 2009). In this paper we take an alternative approach, using latitude as a master predictor of Great Lakes coastal wetland vegetation condition. ...
... Land use in the Great Lakes basin becomes increasingly agricultural and urban (and less forested) with decreasing latitude (Lougheed et al., 2001; Wolter et al., 2006), which in turn degrades the water quality of coastal wetlands (Morrice et al., 2008;). Urban development also affects wetlands directly via roads and levees that restrict water movement (Johnston et al., 2008). In our previous classification and regression tree (CART) analysis using vegetation and stressor data collected from 90 wetlands distributed over all five Great Lakes, we found that environmental variables related to latitude (i.e., growing degree days, cumulative stress index) explained 60 to 68% of the variance in wetland vegetation condition, as measured by the Floristic Quality Index (FQI) and the first axis scores in a non-metric multidimensional scaling (MDS1) of wetland plant cover data (Johnston et al., 2009b). ...
... Data previously collected for U.S. Great Lakes coastal emergent wetlands, described by Johnston et al. (2008 Johnston et al. ( , 2009b), were used in this analysis. At each site, all vascular plants present within 1-m 2 quadrats distributed along randomly placed transects were identified to the lowest taxonomic division possible, and their percent cover was estimated visually by taxon using modified Braun Blanquet cover class ranges (Johnston et al., 2009b). ...
Article
Coastal wetland vegetation along the Great Lakes differs strongly with latitude, but most studies of Great Lakes wetland condition have attempted to exclude the effect of latitude to discern anthropogenic effects on condition. We developed an alternative approach that takes advantage of the strong relationship between latitude and coastal wetland floristic condition. Latitude was significantly correlated with 13 of 37 environmental variables tested, including growing degree days, agriculture, atmospheric deposition, nonpoint-source pollution, and soil texture, which suggests that latitude is a good proxy for several environmental drivers of vegetation. Using data from 64 wetlands along the U.S. coast of Lakes Huron, Michigan, Erie, and Ontario, we developed linear regressions between latitude and two measures of floristic condition, the Floristic Quality Index (FQI, adj. r2= 0.437, p<0.001) and the first axis scores from a non-metric multidimensional scaling of wetland plant cover (MDS1, adj. r2 = 0.501, p<0.001). Departures from the central tendency of these regression models represented wetlands of better or worse condition than expected for their latitude. This approach provides a means to identify wetlands worthy of preservation, to establish vegetation targets for wetland restoration, and to forecast changes in floristic quality associated with future climate change.
... Rooted plants are incapable of moving in response to stress, unlike other commonly monitored organisms such as fish and birds. Because of their sedentary nature, plants are often more responsive to and reflective of in situ stressors than other more mobile communities (Brazner et al., 2007;Johnston et al., 2008). Specific wetland plant genera and species have been correlated with a variety of different stressors, such as water-level regulation, nutrient enrichment, sedimentation, physical degradation, and land use/land cover (Lougheed et al., 2001;Albert and Minc, 2004;Boers et al., 2007;Brazner et al., 2007;Johnston and Brown, 2013). ...
... Overall cover by Carex species has also been suggested for use as an indicator and has been included in wetland indicators previously, albeit not specifically for lacustrine coastal wetlands (Mack, 2007;Rothrock and Simon, 2006). Regarding Great Lakes coastal wetlands specifically, Johnston et al. (2008) found that, while the species may differ by lake and geographic location, the presence of Carex was an important indicator of ecosystem health. Given this, and the prevalence of Carex species in the wet meadows of Great Lakes coastal wetlands, its inclusion as an indicator makes sense (Lemein et al., 2017). ...
... These impacts aid in understanding the relation between disturbance and the relative cover of turbidity/sedimentation-intolerant species within wet meadows. This category of turbidity/sedimentationintolerant species is composed of three specific species with a ubiquitous distribution throughout the Great Lakes, which have all been determined to be indicators of higher quality systems: Calamagrostis canadensis, Carex aquatilis, and C. stricta (Albert and Minc, 2004;Johnston et al., 2008;Wilcox et al., 2008). These species are prominent components of wet meadows; Lemein et al. (2017) identified C. canadensis-C. ...
Article
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Wetland plants, due to their sedentary nature, hold great potential for use as indicators of ecosystem condition in the Great Lakes. However, natural variations in lake levels have historically confounded efforts to create such indicators. Our goal was to use zone-level vegetation data collected over a seven-year period of low to high water levels to overcome these difficulties and identify metrics capable of accurately reflecting disturbance despite lake-level variation. Through a combination of multivariate statistical analyses and a review of the literature, we identified and tested a series of plant-based metrics for wet meadow, emergent, and submergent zones of lacustrine coastal wetlands of Western Lake Huron. These were combined into zone-specific indicators of ecosystem health, which were then applied to wetlands of the remaining Great Lakes to assess basin-wide viability. The resulting indicators were found to reflect disturbance without bias towards high or low water levels. While they must be assessed for use in riverine and barrier-beach coastal wetlands before full-scale implementation can occur, we suggest their use on a preliminary basis in monitoring and management efforts.
... Cover data for individual plant species were analyzed using hierarchical partitioning to identify taxa sensitive to anthropogenic stress, using methods described in Brazner et al. (2007a). These candidate taxa for Lake Huron wetlands were used in a stepwise multiple regression against the stress index developed for site selection by Danz et al. (2007) to create a multi-taxa vegetation indicator (Johnston et al., 2008). ...
... When FQI values were plotted against the GLEI segment-shed stress index (Danz et al., 2007), they were highly clumped into the two geographic groups (Figure 8a). The multi-taxa index developed for wetland vegetation in Lake Huron (Johnston et al., 2008) was strongly related (R 2 = 0.73) to the segment-shed stress index (Figure 8b). This multi-taxa index used mean percent cover of two plant species which are individually significantly related to the overall stress index: Schoenoplectus tabernaemontani (formerly Scirpus validus) and Populus deltoides seedlings. ...
Article
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Our overall goal was to develop indicators that both estimate ecological condition and suggest plausible causes of ecosystem degradation across the U.S. Great Lakes coastal region. Here we summarize data gathered along the U.S. Lake Huron coastline for breeding bird, diatom, fish, invertebrate, and wetland plant communities. We sampled these biotic communities on 88 sites in Lake Huron coastal wetlands, uplands, estuaries/bays, and high-energy shorelines. The sites were selected as part of a larger, stratified random design for the entire U.S. Great Lakes coastal region using gradients of anthropogenic stress that incorporated over 200 stressor variables (e.g. agriculture, land cover, human populations, and point source pollution). The U.S. Lake Huron coastal region exemplified wide variation in human-related stress relative to the entire U.S. Great Lakes coast. In general, levels of stress decreased from south to north partly reflecting the change in climate and physiography, but also due to the greater human influences in the southern region as compared with the north. The primary stressors in the southern region are due to agriculture and human development, while the northern region has substantially less agriculture and less human population. The biotic communities sampled were strongly related to the environmental stress gradients, especially agriculture and urbanization. The following indicators were developed based on responses to stress: 1) an index of biological condition for breeding bird communities corresponding to land use, 2) a diatom-inferred total phosphorus indicator corresponding to water quality, 3) exotic fish (carp [Cyprinus carpio] and goldfish [Carassius auratus]) corresponding to agriculture, and 4) a multi-taxa index for wetland plants corresponding to a cumulative stress index. These communities can all serve as useful indicators of the ecological condition of the Lake Huron coast. The ecological indicators provide a baseline on selected conditions for the U.S. Lake Huron coastal region and a means to detect change over time.
... Many assessment techniques have arisen from this need to monitor wetlands (Adamus andBrandt 1990, Rader et al. 2001). Some of the most successful assessment methods have utilized wetland plants as the main indicator of anthropogenic influence ( Balcombe et al. 2005b, Johnston et al. 2008, Johnston and Brown 2013. Since plants are sessile organisms that cannot uproot in order to move to a more ideal habitat, they must adapt to environmental changes and stressors, or they will not survive (Treshow 1970). ...
... The results of this study suggest that the vegetation community at EB is responding to a rise in anthropogenic stress with low richness, evenness, and diversity when compared to NWB ( Balcombe et al. 2005b, Johnston et al. 2008). This response is common in wetland ecosystems because human influence often results in niche modification and removal, which leads to noticeable decreases in these community assessment measures Lehman 2001, Johnston et al. 2008). ...
Thesis
Wetlands are some of the most important ecosystems on the planet, and are often referred to as "kidneys of the landscape" because of their remarkable ability to filter contaminants, especially those introduced by human activity. Some of the most important cleaning tools in wetlands are the plants that inhabit them. In this series of studies, wetland plant response to human impact in the Lake George watershed of the Adirondack Mountains was investigated. Measured differences in plant morphology and tissue chemistry indicated the importance of using such measures to assess short-term responses to human impact within wetland ecosystems. Additionally, a case-study depicting ecosystem establishment pre- and post- planting in a constructed stormwater treatment wetland was described. Results from these studies prompted specific phytoremediation experiments using the small duckweed, Lemna minor. Throughout these studies, it was determined that L. minor can acclimate morphologically and physiologically to human-related nutrient availability, which subsequently affects nutrient uptake potential. Attempts were made to induce this same natural acclimation response under laboratory conditions.
... Biological community metrics and indicator species have become very popular for classifying/estimating wetland quality. Among the many taxa proposed, vegetation may be the most widely used for wetland quality assessments and selecting reference sites (Rader et al. 2001; [U.S. EPA] U.S. Environmental Protection Agency 2002; Johnston et al. 2008Johnston et al. , 2009. ...
... Searching for a few indicator species may make it easier to designate new reference sites compared to sampling entire vegetation communities and buffer zones (Johnston et al. 2008). Reliable indicators were extracted for all final reference groups except the Depression category which had only eight sites; valid indicators may not be found if very few sites (<10) belong to the target group (De Cáceres et al. 2012). ...
Article
Reference criteria are needed for wetland monitoring and assessment programs. We used field-collected vege-tation data from non-forested wetland sites in the south-central United States to establish preliminary criteria for identifying reference-quality wetlands in future surveys. Our analysis included three parts: (1) preliminary reference verification and metric ranking using boxplots and standardized effect size, (2) updating the putative reference sample and metric selection using Test Site Analysis, and (3) establishing refer-ence criteria from best-metric confidence intervals and indicator species combinations. The Floristic Quality Assessment Index most clearly distinguished the reference wetlands; an index value of at least 20 is recommended for future reference designations in the study region. Other potential reference criteria include a maximum of 3–5 % bare ground in the 100 m buffer, a moderately sensitive species assemblage (mean conservatism>5.0), a small percentage (<10 %) of tolerant species (coefficient of conservatism≤2), and high native richness (>22 species). Five single species, four pairs, and one triplet combination were extracted as potential indi-cators of reference sites from 70,375 combinations of 75 candidate species, offering an efficient alternative to sampling entire vegetation communities. The analysis framework in this case study could be useful for similar projects in other regions.
... Variation partitioning untangles the relative importance of unique and shared effects of different explaining data sets (Borcard et al. 1992, Borcard and Legendre 1994, Legendre et al. 2005). The obtained ecological information is important for basic ecological knowledge of species or communities (Bo¨hning-Gaese 1997, Cushman andMcGarigal 2002), as well as for judging the effectiveness of (potential) conservation measures (Betts et al. 2006, Kivinen et al. 2007, Johnston et al. 2008. Variation partitioning lends itself to the study of complex ecosystems. ...
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Spatially organized distribution patterns of species and communities are shaped by both autogenic processes (neutral mechanism theory) and exogenous processes (niche theory). In the latter, environmental variables that are themselves spatially organized induce spatial structure in the response variables. The relative importance of these processes has not yet been investigated in urban habitats. We compared the variance explained by purely spatial, spatially structured environmental, and purely environmental components for the community composition of spiders (Araneae), bees (Apidae), and birds (Aves) at 96 locations in three Swiss cities. Environmental variables (topography, climate, land cover, urban green management) were measured on four different radii around sampling points (< 10 m, 50 m, 250 m, 1000 m), while Moran's eigenvector maps (MEMs) acted as spatial variables. All three taxonomic groups showed weak spatial structure. Spider communities reacted to very fine-scaled environmental changes of lawn and meadow management and climate. Bird community composition was determined by woody plants as well as solar radiation at all radii, the scale of the influence varying among species. Bee communities were weakly explained by isolated variables only. Our results suggest that the anthropogenic structuring of urban areas has disrupted the spatial organization of environmental variables and inhibited the development of biotic spatial processes. The near absence of spatial structure may therefore be a feature typical of urban species assemblages, resulting in urban community composition mainly influenced by local environmental variables. Urban environments represent a close-knit mosaic of habitats that are regularly disturbed. Species communities in urban areas are far from equilibrium. Our analysis also suggests that urban communities need to be considered as being in constant change to adapt to disturbances and changes imposed by human activities.
... Wetland values such as diversity, primary productivity, and habitat for wildlife and waterfowl will be affected if an increase in frequency and duration of low water levels results from future climate change (Mortsch 1998). A number of factors have been shown to facilitate Phragmites invasion, including land use changes in a wetland's watershed (King et al. 2007), increases in nitrate and the concentration of other nutrients (Marks et al. 1994; Bertness et al. 2002; Minchinton and Bertness 2003), the presence of exposed mineral soil (Tulbure et al. 2007), and alterations of the hydrologic regime by roads, dikes, and ditches ( McNabb and Batterson 1991; Hartman 2000, 2003;Herrick and Wolf 2005; Maheu-Giroux and de Blois 2007; Johnston et al. 2008). The use of dikes is a prevalent feature in coastal wetlands on the southwestern shore of Lake Erie (Kroll and Gottgens 1997; Gottgens et al. 1998). ...
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The invasion and expansion of the non-native Phragmites australis in Great Lakes coastal wetlands is of increasing concern, but quantitative studies of the extent, rate, and causes of invasion have been lacking. Here we revisited 307 plots in 14 wetlands along the Great Lakes coast in 2005 that had previously been sampled for vegetation in 2001–2003. During the 2–4years between sample events, Phragmites occurred in 101 plots. Genetic analysis revealed that none of the Phragmites samples collected at the 14 wetlands belonged to the native genotype. Decreases in water depth and bare soil area were associated with the greatest increases in Phragmites cover. Phragmites invasion was greater on Lakes Michigan, Huron, and Erie than it was on Lake Ontario, and occurred predominantly on sandy substrates. Soil water concentrations of NO3-N, NH3-N, and soluble reactive P did not differ significantly between plots with and without Phragmites. Monitoring coastal wetlands where water level has dropped and controlling Phragmites at early stages of invasion are essential for maintaining healthy Great Lakes coastal wetlands of high species diversity and wildlife habitat. This becomes important as water levels in the Great Lakes have reached extreme lows and are expected to decline with future climate change. KeywordsExotic species-Invasion-Invasive species-Nutrients-Soil-Water level
... We used D-frame nets to sample benthic macroinvertebrates and later identified them in the laboratory to the highest possible resolution (genus for most insects). We estimated vegetation cover for each taxon in randomly selected 1-m 2 quadrats (Johnston et al. 2010). We collected diatoms from natural substrates at 0.5-to 3-m depths with a push corer, Ponar sampler, or by rock scrubbing (see Reavie et al. 2006 for details). ...
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Biological attributes of ecosystems often change nonlinearly as a function of anthropogenic and natural stress. Plant and animal communities may exhibit zones of change along a stressor gradient that are disproportionate relative to the incremental change in the stressor. The ability to predict such transitions is essential for effective management intervention because they may indicate irreversible changes in ecological processes. Despite the importance of recognizing transition zones along a stressor gradient, few, if any, investigators have examined these responses across multiple taxa, and no community threshold studies have been reported at large geographic scales. We surveyed benthic macroinvertebrate, fish, bird, diatom, and plant communities in coastal wetlands across a geospatially referenced gradient of anthropogenic stress in the Laurentian Great Lakes. We used Threshold Indicator Taxon Analysis (Baker and King 2010) to analyze each community's response to identify potential zones of disproportionate change in community structure along gradients of major watershed-scale stress: agriculture and urban/suburban development. Our results show surprising congruence in community thresholds among different taxonomic groups, particularly with respect to % developed land in the watershed. We also analyzed uncertainty associated with the community-specific thresholds to understand the ability of different assemblages to predict stress. The high and congruent sensitivity of assemblages to development demonstrates that watershed-scale stress has discernible effects on all biological communities, with increasing potential for ecosystem-scale functional changes. These findings have important implications for identifying reference-condition boundaries and for informing management and policy decisions, in particular, for selecting freshwater protected areas.
... There has been some criticism of the use of hierarchical partitioning on correlated variables to determine causal influence (Kruskal 1987, Bring 1995. However, hierarchical partitioning is an accepted practice used widely within ecological literature (Radford and Bennett 2007, Barlow et al. 2008, Johnston et al. 2008, McGill 2008, Tautenhahn et al. 2008. We applied hierarchical partitioning on variables that are not highly correlated to determine independent explanatory power rather than infer causal influence, which is considered a valid approach (Bring 1995, MacNally 1997. ...
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Conceptualising landscapes as a mosaic of discrete habitat patches is fundamental to landscape ecology, metapopulation theory and conservation biology. An emerging question in ecology is: when is the discrete patch model more appropriate than alternative and conceptually appealing models such as the continuum model? There is limited empirical testing of the utility of alternative landscape models compared to the discrete patch model for a range of species. In this paper, we constructed three alternative sets of models for testing the effect of landscape structure on diversity and abundance of a suite of woodland birds in a savanna landscape of northern Australia: the null model (only site-scale habitat variables, landscape context not important), the continuum model, and the discrete patch model. We utilised high-spatial resolution satellite images to quantify spatial gradients in tree cover density (the continuum model), and to then aggregate the fine-scale heterogeneity in tree cover into discrete patches of trees, with grass cover forming the “matrix” (the discrete patch-model). We then evaluated the relative importance of the alternative models using generalised linear models and an information theoretic approach. We found that the importance of the models varied among species, with no single model dominant. Species that move between open grassy areas and woody shelter responded well to the continuum model, reflecting the importance of gradients in density of forage (grasses) and cover (trees), while the discrete model performed best for species that forage in all vegetation strata, and nest predominantly in dense woody vegetation. This finding supports a pluralistic approach, highlighting the need for adopting and testing more than one landscape model in savanna landscapes, and in other landscapes that do not have a well defined patch structure.
... In recent years, the nonnative Phragmites has proliferated in brackish and tidal freshwater wetlands on the Atlantic coast (McCormick et al. 2010), whereas the native Phragmites has declined in the same region (Saltonstall 2003; Vasquez et al. 2005). The recent expansion of Phragmites into brackish tidal wetlands on the US East Coast has been attributed to the introduction of the nonnative lineage, but factors such as disturbance ( Hartman 2000, 2003; Minchinton and Bertness 2003) and anthropogenic modifications within wetlands (Johnston et al. 2008; Maheu-Giroux and de Blois 2007; McNabb and Batterson 1991) or on adjacent upland areas (King et al. 2007; Minchinton and Bertness 2003; Tulbure 2008; Tulbure and Johnston 2010 ) facilitate Phragmites invasion. Once established, nonnative Phragmites forms large stands, with shoots up to 3–4 m tall. ...
Article
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Nonnative Phragmites is among the most invasive plants in the U.S. Atlantic coast tidal wetlands, whereas the native Phragmites has declined. Native and nonnative patches growing side by side provided an ideal setting for studying mechanisms that enable nonnative Phragmites to be a successful invader. We conducted an inventory followed by genetic analysis and compared differences in growth patterns and ventilation efficiency between adjacent native and nonnative Phragmites stands. Genetic analysis of 212 patches revealed that only 14 were native suggesting that very few native Phragmites populations existed in the study area. Shoot density decreased towards the periphery of native patches, but not in nonnative patches. Ventilation efficiency was 300 % higher per unit area for nonnative than native Phragmites, likely resulting in increased oxidation of the rhizosphere and invasive behavior of nonnative Phragmites. Management of nonnative Phragmites stands should include mechanisms that inhibit pressurized ventilation of shoots.
... Plant communities may be useful as indicators of restoration progress if they respond predictably to site conditions and age. The value of vascular plants as bioindicators has been discussed by several authors (e.g., Mack et al. 2000, Cronk and Fennessy 2001, U.S. Environmental Protection Agency 2002, Johnston et al. 2008), and vegetation-based indicators, especially FQI and multimetric indices that incorporate FQI, are now widely used in wetland assessment. Coefficients of conservatism have been developed for several U.S. and Canadian regions, and recent studies have evaluated the utility of FQI and ¯ C in naturally occurring wetlands. ...
Article
Temporal trends in attributes of restored ecosystems have been described conceptually as restoration trajectories. Measures describing the maturity or ecological integrity of a restoration site are often assumed to follow monotonically increasing trajectories over time and to eventually reach an asymptote representative of a reference ecosystem. This assumption of simple, predictable restoration trajectories underpins federal and state policies in the United States that mandate wetland restoration as compensation for wetlands damaged during development. We evaluated the validity of this assumption by tracking changes in 11 indicators of floristic integrity, often used to determine legal compliance, in 29 mitigation wetlands. Each indicator was expressed as a percentile relative to the distribution of that indicator among > 100 naturally occurring reference wetlands. Nonlinear regression was used to fit two alternative restoration trajectories to data from each site: an asymptotic (negative exponential) increase in the indicator over time and a peaked (double exponential) relationship. Depending on the particular indicator, between 48% and 76% of sites displayed trends that were at least moderately well described (R2 > 0.5) by one of the two models. Floristic indicators based on species richness, including native richness, number of native genera, and the floristic quality index, rapidly increased to asymptotes exceeding levels in a majority of reference wetlands. In contrast, indicators based on species composition, including mean coefficient of conservatism and relative importance of perennial species, increased very slowly. Thus, some indicators of restoration progress followed increasing trajectories and achieved or surpassed levels equivalent to high-quality reference sites within five years, whereas others appeared destined to either not reach equivalency or to take much longer than mitigation wetlands are typically monitored. Finally, some indicators of restoration progress, such as relative importance of native species, often increased over the first five to 10 years and then declined, which would result in a misleading assessment of progress if based on typical time scales of monitoring. Therefore, the assumption of simple, rapid, and predictable restoration trajectories that underlies wetland mitigation policy is unrealistic.
... Additionally, we identify environmental factors influencing patterns of species richness and distribution for the three taxa. We selected these particular taxa for study because they have high species richness, include an array of life history strategies, occupy diverse trophic positions, and each group shows potential as indicators of wetland condition (Lopez and Fennessey, 2002;Davis et al., 2003;Bilton et al., 2006;Johnston et al., 2008). Furthermore, these groups contain rare or endangered species; hence, identification of surrogate taxa could be useful in identifying critical habitat for conservation. ...
Article
Globally, there is a growing awareness that geographically isolated wetlands contribute to important landscape functions and ecological services. One of their most important functions is providing habitat to a diverse fauna and flora adapted to variable wet and dry environments. We focus on analysis of similarities among three distinct taxa, vascular plants, aquatic beetles, and amphibians, in isolated wetlands in the southeastern coastal plain of Georgia. Although species richness for these three taxa is quite high in isolated wetlands at a regional scale, we found a low degree of congruence in species richness and species composition among taxa. This finding demonstrates that none of these groups could be used as a surrogate for the overall biodiversity of these wetlands represented by the three taxa. We identified environmental factors influencing the complex patterns of species richness and distribution for the three groups that indicate biotic and abiotic processes operate at different scales for each taxonomic group and for individual species. Our study illustrates the importance of considering structural diversity, hydrologic variation and landscape position as key elements to understanding overall diversity represented by the three taxa in isolated wetlands and in developing assessment tools of wetland condition.
... The challenge for IBIs is to measure biological metrics that distinguish human-induced perturbation against a backdrop of natural climatic variability (Johnston et al., 2008;Euliss and Mushet, 2011). IBI assessments must be relatively insensitive to inter-annual variation in marsh plant communities since they are meant to inform environmental managers on the measured effects of human-induced disturbance. ...
Article
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ABSTRACT Plant-based assessments can contribute to wetland conservation and management by providing a standardized method to monitor biological communities in relation to human activity. One major challenge, however, is that their measurements must be fairly insensitive to temporal variation in community composition, which can be difficult since marsh plant communities are known to be influenced by natural climatic cycles. Variation in the scores for an index of biological integrity (IBI) was evaluated in relation to plant community changes that occurred between years with differing precipitation inputs throughout the growing season (dry: 240 mm in 2008, 198 mm in 2009; wet: 324 mm in 2010, 329 mm in 2011). Species composition and IBI scores were measured by sampling macrophytes in the centre of the wet meadow zone at 47 semi-permanent to permanent natural and constructed marshes. Non-metric multidimensional scaling (NMS) ordinations revealed that although plant community composition shifted between dry and wet years, IBI scores were sensitive to only 21% of the total inter-annual variation in species composition. The first NMS axis was positively correlated with IBI scores (r = 0.85) as well as several environmental parameters (r2 > 0.2), including dissolved organic carbon, total nitrogen, potassium, shoreline slope, and salinity. The wet meadow IBI also yielded consistent scores between dry and wet years (Spearman's rho = 0.82; Wilcoxon z-score = 0.53, P-value = 0.60) and was able to distinguish a change in biological condition among sites against a backdrop of natural variation (F-test = 3.0, P < 0.001). These findings provide support for the continued use of plants as indicators of wetland condition in permanent northern prairie marshes, providing that the range in water levels is moderate.
... Because riparian vegetation responds to climate, watershed disturbance, and geomorphic setting [9][10][11], it can be thought of as a composite variable that responds to multiple watershed processes as well as serving as an indicator of instream habitat potential [12,13]. Riparian vegetation is clearly tied to instream wood because riparian plant communities must grow sufficiently large trees and shrubs to contribute wood to the channel. ...
Article
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Instream wood is a driver of geomorphic change in low-order streams, frequently altering morphodynamic processes. Instream wood is a frequently measured component of streams, yet it is a complex metric, responding to ecological and geomorphic forcings at a variety of scales. Here we seek to disentangle the relative importance of physical and biological processes that drive wood growth and delivery to streams across broad spatial extents. In so doing, we ask two primary questions: (1) is riparian vegetation a composite variable that captures the indirect effects of climate and disturbance on instream wood dynamics? (2) What are the direct and indirect relationships between geomorphic setting, vegetation, climate, disturbance, and instream wood dynamics? We measured riparian vegetation composition and wood frequency and volume at 720 headwater reaches within the American interior Pacific Northwest. We used ordination to identify relationships between vegetation and environmental attributes, and subsequently built a structural equation model to identify how climate and disturbance directly affect vegetation composition and how vegetation and geomorphic setting directly affect instream wood volume and frequency. We found that large wood volume and frequency are directly driven by vegetation composition and positively correlated to wildfire, elevation, stream gradient, and channel bankfull width. Indicator species at reaches with high volumes of wood were generally long-lived, conifer trees that persist for extended durations once delivered to stream habitats. Wood dynamics were also indirectly mediated by factors that shape vegetation: wildfire, precipitation, elevation, and temperature. We conclude that wood volume and frequency are driven by multiple interrelated climatic, geomorphic, and ecological variables. Vegetation composition and geomorphic setting directly mediate indirect relationships between landscape environmental processes and instream large wood. Where climate or geomorphic setting preclude tree establishment, reaches may remain naturally depauperate of instream wood unless wood is transported from elsewhere in the stream network.
... Many invasive aquatic plants are restricted by extreme cold temperatures or ice cover (Rahel & Olden 2008). It is thus reasonable to assume that invasive species such as Lythrum salicaria, Myriophyllum salicaria and Potamogeton crispus favour southern latitudes, where warmer growing conditions allow them to outcompete native species (Johnson et al. 2008). On the other hand, invasive macrophytes are probably less vulnerable than native species to extreme water quality values found in the southern part of the state. ...
Article
Questions: Are community composition and species richness of aquatic macrophytes determined primarily by local (habitat heterogeneity and water quality) or regional patterns (climate) at regional scale? Do two macrophyte functional groups (i.e. emergent and submerged macrophytes) respond similarly to local and regional patterns? Are lake macrophytes and explanatory variables geographically structured? Location: The US state of Minnesota Material: The community composition and species richness of aquatic flora was studied using presence-absence data in 454 lakes, covering the entire US state of Minnesota. In addition, community composition and species richness of emergent and submerged macrophytes was investigated separately. Methods: Variation partitioning based on partial redundancy analysis and partial linear regression was used to study the relative roles of water quality, habitat heterogeneity, climate and sampling effort in explaining community composition and species richness of lake macrophytes, respectively. Results: Macrophyte community composition and species richness (all taxa and two functional groups) were explained by water quality and climate. Alkalinity and total phosphorus from water quality variables affected most community composition of aquatic flora and macrophytes species richness decreased with increasing concentrations of these two variables. Maximum temperature of the warmest month and mean annual temperature affect most plant community composition, whereas species richness had a negative relationship with minimum temperature of the coldest month. Most significant explanatory variables (e.g. alkalinity, total phosphorus and temperature) were geographically structured showing a latitudinal change. Conclusions: Community composition and species richness of macrophytes were congruently influenced by regional (climate) and local patterns (water quality) at regional scale. Community composition and species richness of helophytes and submerged macrophytes were explained by environmental gradient to equal degree. The latitudinal change in the most significant environmental variables was related to calcareous soils and intensive agriculture, which were situated in the southern part of the state. Macrophyte species richness showed a reversed latitudinal gradient, which was likely due to high nutrient concentrations found in southern latitude lakes. Water quality primarily filters species from regional species pool, allowing only species tolerating high nutrient concentration, like invasive plants, to survive in southern latitudes.
... Vascular plant species represent diverse adaptations, ecological tolerances, and life history strategies, and they integrate environmental factors, species interactions, and disturbance. Many disturbances are reflected in shifts in the presence or abundance of particular plant species (Magee and Kentula 2005;Johnston et al. 2008), plant functional or trait groups (Lopez and Fennessy 2002;Quétier et al. 2007), plant assemblages (Galatowitsch et al. 1999;Magee et al. 1999;DeKeyser et al. 2009;Johnston et al. 2009), or vegetation structural elements (Mack 2007), making vegetation a powerful indicator of wetland condition (Mack and Kentula 2010). Existing VMMIs or VIBIs have proven useful for monitoring condition and prioritizing conservation or management actions for specific wetland types at local or regional scales within the United States and elsewhere (e.g., DeKeyser et al. 2003;Reiss 2006;Mack 2007;Hargiss et al. 2008;Rothrock et al. 2008;Lemly and Rocchio 2009;Mack 2009;Veselka et al. 2010;Euliss and Mushet 2011;Genet 2012;Rooney and Bayley 2012;Deimeke et al. 2013;Wilson et al. 2013;Hernandez et al. 2015;Savage et al. 2015;Jones et al. 2016;Miller et al. 2016). ...
Article
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In 2011, the US Environmental Protection Agency and its partners conducted the first National Wetland Condition Assessment at the continental-scale of the conterminous United States. A probability design for site selection was used to allow an unbiased assessment of wetland condition. We developed a vegetation multimetric index (VMMI) as a parsimonious biological indicator of ecological condition applicable to diverse wetland types at national and regional scales. Vegetation data (species presence and cover) were collected from 1138 sites that represented seven broad estuarine intertidal and inland wetland types. Using field collected data and plant species trait information, we developed 405 candidate metrics with potential for distinguishing least disturbed (reference) from most disturbed sites. Thirty-five of the metrics passed range, repeatability, and responsiveness screens and were considered as potential component metrics for the VMMI. A permutation approach was used to calculate thousands of randomly constructed potential national-scale VMMIs with 4, 6, 8, or 10 metrics. The best performing VMMI was identified based on limited redundancy among constituent metrics, sensitivity, repeatability, and precision. This final VMMI had four broadly applicable metrics (floristic quality index, relative importance of native species, richness of disturbance-tolerant species, and relative cover of native monocots). VMMI values and weights from the survey design for probability sites (n = 967) were used to estimate wetland area in good, fair, and poor condition, nationally and for each of 10 ecoregion by wetland type reporting groups. Strengths and limitations of the national VMMI for describing ecological condition are highlighted.
... We infer that this difference was due in part to greater extent and variance in dispersal distances among macroinvertebrates (e.g., ranging from chironomids to large beetles) and the role of other habitats (e.g., ditches) and distances in that movement. The mix of local and regional processes at lesser land use intensity is consistent with theory (Chase, 2007) and the differences among taxa are intuitive; vegetation reflects local environmental conditions over time (Johnston et al., 2008), and is more likely to reflect local, niche-based assembly than mobile animals that annually recolonize seasonal wetlands. Also, different assemblages should best subscribe to different metacommunity paradigms in the same set of habitats. ...
... Beberapa metode penelitian bahkan dianggap paling berhasil dengan memanfaatkan lahan basah sebagai indikator utama dalam sistem antropogenik (Balcombe et al., 2005;C. A. Johnston et al., 2008;C. Johnston & Brown, 2013). Pada penelitian yang lain, metode ini dianggap cukup berhasil dalam mengolah air limbah domestik. Proses ini dapat dilakukan dengan metode fisika, kimia ataupun biologi (Brix & Arias, 2005). Sementara itu dalam beberapa penelitian telah menilai adanya perbedaan dalam komunitas atau kelompok mikroba dengan fung ...
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Penelitian ini bertujuan mengkaji efisiensi jenis tanaman dan waktu tinggal dalam menurunkan kandungan amoniak pada air limbah domestik menggunakan Bio-Rack Wetland. Bio-rack merupakan sistem baru dalam media pengolahan constructed wetland. Bio-rack wetland dijalankan dengan variasi waktu tinggal selama 15 jam dan 20 jam. Media bio-rack terbuat dari pipa PVC dengan ukuran diameter 22 mm. Tumbuhan yang ditanam pada media bio-rack adalah Typha latifolia dan Phragmites australis. Efisiensi penyisihan suhu, pH, dan amoniak pada reaktor bio-rack wetland dilakukan berdasarkan prosedur laboratorium. Efisiensi sistem bio-rack wetland yang terbaik dalam menyisihkan pencemar amoniak yaitu tanaman Typha latifolia dengan efisiensi penyisihan sebesar 35,2% pada waktu tinggal 20 jam. Sedangkan pada tanaman Phragmites australis mampu menyisihkan kadar amoniak sebesar 28,4% dengan waktu tinggal 20 jam. Efisiensi penyisihan parameter uji terbukti lebih baik pada bio-rack wetland dengan tanaman Typha latifolia pada waktu tinggal 20 jam. Kata Kunci: Amoniak, Bio-rack Wetland, Phragmites australis, Typha latifolia, Waktu Tinggal. This study aims to assess the efficiency of plant species and residence time in reducing ammonia content in domestic wastewater using Bio-Rack Wetland. Bio-rack is a new system in the constructed wetland processing media. Wetland bio-rack is run with a variation of the residence time of 15 hours and 20 hours. Bio-rack media is made of PVC pipes with a diameter of 22 mm. Plants grown on bio-rack media are Typha latifolia and Phragmites australis. The removal efficiency of temperature, pH, and ammonia in the wetland bio-rack reactor is carried out based on laboratory procedures. The best efficiency of the bio-rack wetland system in removing ammonia pollutants is Typha latifolia plants with a removal efficiency of 35.2% at a residence time of 20 hours. Whereas the Phragmites australis plant can set aside ammonia levels of 28.4% with a residence time of 20 hours. The removal efficiency of the test parameters was proven to be better in the wetland bio-rack with Typha latifolia plants at a residence time of 20 hours. Keywords: Ammonia, Bio-rack Wetland, Phragmites australis, Typha latifolia, the length of time.
... Finally, we wanted representation of most of the 11 categories of metric type (difficult choice, with a limit of seven). To introduce the ecological context for vegetation metrics, we briefly summarize the background of two classes of metrics, conservatism and degree of invasion-likely the two most important types of metrics we develop (Ervin et al. 2006, Johnston et al. 2008. ...
Technical Report
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Wetlands are important because they are biodiversity hotspots and support iconic wildlife. They also provide valuable “ecosystem services,” such as flood attenuation and storage, aquifer discharge and recharge, sediment stabilization and sequestration, carbon storage, water quality enhancement, and nutrient cycling. Wetlands also provide important aesthetic values and are highly valued by visitors. The National Park Service (NPS) Rocky Mountain Inventory and Monitoring Network (hereafter, network) conducts long-term monitoring at wetlands in Rocky Mountain National Park as part of its natural resources vital signs monitoring program. The purpose of this report is to describe and summarize wetland monitoring data and information collected under the network’s wetland ecological integrity monitoring protocol so that NPS resource managers and superintendents and scientific and technical staff will understand and be able to access the data and information. We summarize and provide descriptive statistics of the data but do no formal analysis, statistical testing, or modeling, and we do not interpret the data. For example, we do not compare the condition of park wetlands to other wetlands in Colorado or to desired conditions, and we do not analyze changes in wetland conditions over time. Our goal is to fully describe the dataset and provide access to the data and information collected. Therefore, this report has not undergone a formal peer review, though the data collection and analysis methods it contains have been independently peer-reviewed by outside scientific experts reviewing the Rocky Mountain Network Wetland Ecological Integrity Monitoring Protocol. Detailed syntheses can be found in a peer reviewed paper focused on models of structural relationships among human disturbance, ungulates, beavers, and wetland response (Schweiger et al. 2016) and in future status and trend reports. This report presents graphical and tabular summaries of data collected from wetlands at Rocky Mountain National Park (hereafter, the park) from 2007 to 2017. Monitoring included a sample of 154 fens, wet meadows and riparian wetlands conducted across the park from 2007 to 2009 and annual monitoring (2010–2017) at four “sentinel” wetlands. At each site, we collected data on vascular and nonvascular plant species composition, woody species (if present), stand structure (primarily cottonwood and willows), and damage and mortality of woody stems. We also collected field and laboratory soil chemistry samples, documented in-situ groundwater electrical conductivity and pH, and measured depth to water at a shallow groundwater well in the center of each plot. Finally, we documented human disturbance as well as beaver and ungulate use of habitat in and around each plot and in the wetland complex. This report documents fully quality assured and quality checked 2007–2017 data in the network’s Wetland Ecological Integrity (WEI) database. Results summarized here serve as important baselines for future modeling and assessment of status and trend in the condition of the park’s wetlands. These assessments will be reported in forthcoming publications.
... There has been an increasing emphasis on using ecological-trait analyses to determine which stressors are influencing the functioning of aquatic communities (Schäfer et al. 2011). Multi-taxa responses to human stressors (Johnston et al. 2008;Johnston et al. 2009) are required to assess the likely functional consequences of species loss. Future research may also reveal functional genes associated with suites of taxa, and thus directly assess ecosystem-functional consequences using molecular analysis of biomonitoring data. ...
Article
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Aquatic ecosystems are under threat from multiple stressors, which vary in distribution and intensity across temporal and spatial scales. Monitoring and assessment of these ecosystems have historically focussed on collection of physical and chemical information and increasingly include associated observations on biological condition. However, ecosystem assessment is often lacking because the scale and quality of biological observations frequently fail to match those available from physical and chemical measurements. The advent of high-performance computing, coupled with new earth observation platforms, has accelerated the adoption of molecular and remote sensing tools in ecosystem assessment. To assess how emerging science and tools can be applied to study multiple stressors on a large (ecosystem) scale and to facilitate greater integration of approaches among different scientific disciplines, a workshop was held on 10–12 September 2014 at the Sydney Institute of Marine Sciences, Australia. Here we introduce a conceptual framework for assessing multiple stressors across ecosystems using emerging sources of big data and critique a range of available big-data types that could support models for multiple stressors. We define big data as any set or series of data, which is either so large or complex, it becomes difficult to analyse using traditional data analysis methods.
... Furthermore, C-values are assigned at the species level, and at times at the variety and subspecies level, which requires that each plant species must be identified to its lowest taxonomic level (USEPA, 2002;Chamberlain and Brooks, 2016). Unfortunately, such botanical expertise is typically not available for applications for which condition assessments are often used (e.g., mitigation and restoration; Johnston et al., 2008). Plant-based indices are also limited by when sampling occurs because differences in phenology and growth of plants influence detection and identification of plant species (Andreas et al., 2004). ...
Article
Floristic Quality Assessment (FQA) has been recognized as a useful tool for evaluating wetland condition and guiding conservation and management efforts. However, FQA validation to confirm that results represent actual wetland condition is limited. Moreover, FQA has been applied across large regions without consideration for the high environmental variability (e.g., temperature, precipitation, and topography) within application areas, which may limit the effectiveness of FQA as an assessment tool. Because Oklahoma contains diverse ecoregions and extreme environmental gradients, this provides an opportunity to examine the influence of spatial and environmental variability on FQA results. We sampled 68 depressional wetlands dispersed across the state to (1) validate an FQA metric, Floristic Quality Index (FQI), with two established condition assessment methods (i.e., Landscape Development Intensity Index [LDI] and Oklahoma Rapid Assessment Method [OKRAM]) and (2) evaluate the influence of environmental variation (e.g., high and low precipitation) on FQI scores. In our validation analysis, we found a strong positive relationship between FQI and OKRAM, indicating the FQI was able to detect changes in wetland condition in depressional wetlands along a disturbance gradient. Additionally, strong negative relationships between FQI and LDI suggest that FQI is responsive to stressors within the surrounding landscape. When evaluating environmental influence on FQI scores, we found substantial variation between reference wetlands based on location, with higher scores occurring in eastern sites (high precipitation) and lower scores occurring in western sites (low precipitation). We used Canonical Correspondence Analysis (CCA) to assess the relationship between plant communities and environmental variables, and found that precipitation was more indicative of plant species distribution than wetland condition (i.e., disturbed or reference condition). Thus, C-values of plant species (i.e., predetermined values assigned to individual plant species) and corresponding FQI scores differed significantly across ecoregions based on high and low precipitation, regardless of wetland condition. This phenomenon highlights the importance of considering regional environmental differences when developing FQI thresholds for wetland assessments, especially across diverse states or ecoregions. To reduce the influence of regional differences on FQIs, as well as other vegetation-based methods, condition class thresholds and reference criteria should be established based on ecoregions to more accurately capture wetland condition using FQI.
... Collectively, these three aspects of wetland vegetation have strong management application, are relatively easy to measure, are ecologically distinct and independent, and often v www.esajournals.org appear in studies of wetland condition (Ervin et al. 2006, Johnston et al. 2008. The conservatism of a species is defined as its degree of fidelity to a specific habitat or range of environmental conditions (Wilhelm and Ladd 1988, Herman et al. 1997, Matthews et al. 2015. ...
Article
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The integrity of wetlands is of global concern. A common approach to evaluating ecological integrity involves bioassessment procedures that quantify the degree to which communities deviate from historical norms. While helpful, bioassessment provides little information about how altered conditions connect to community response. More detailed information is needed for conservation and restoration. We have illustrated an approach to addressing this challenge using structural equation modeling (SEM) and long-term monitoring data from Rocky Mountain National Park (RMNP). Wetlands in RMNP are threatened by a complex history of anthropogenic disturbance including direct alteration of hydrologic regimes; elimination of elk, wolves, and grizzly bears; reintroduction of elk (absent their primary predators); and the extirpation of beaver. More recently, nonnative moose were introduced to the region and have expanded into the park. Bioassessment suggests that up to half of the park's wetlands are not in reference condition. We developed and evaluated a general hypothesis about how human alterations influence wetland integrity and then develop a specific model using RMNP wetlands. Bioassessment revealed three bioindicators that appear to be highly sensitive to human disturbance (HD): (1) conservatism, (2) degree of invasion, and (3) cover of native forbs. SEM analyses suggest several ways human activities have impacted wetland integrity and the landscape of RMNP. First, degradation is highest where the combined effects of all types of direct HD have been the greatest (i.e., there is a general, overall effect). Second, specific HDs appear to create a " mixed-bag " of complex indirect effects, including reduced invasion and increased conservatism, but also reduced native forb cover. Some of these effects are associated with alterations to hydrologic regimes, while others are associated with altered shrub production. Third, landscape features created by historical beaver activity continue to influence wetland integrity years after beavers have abandoned sites via persistent landforms and reduced biomass of tall shrubs. Our model provides a system-level perspective on wetland integrity and provides a context for future evaluations and investigations. It also suggests scientifically supported natural resource management strategies that can assist in the National Park Service mission of maintaining or, when indicated, restoring ecological integrity " unimpaired for future generations. "
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Mat-forming “ground layers” of mosses and lichens often have functional impacts disproportionate to their biomass, and are responsible for sequestering one-third of the world's terrestrial carbon as they regulate water tables, cool soils and inhibit microbial decomposition. Without reliable assessment tools, the potential effects of climate and land use changes on these functions remain unclear; therefore, we implemented a novel “Ground Layer Indicator” method as part of the U.S.D.A. Forest Inventory and Analysis (FIA) program. Non-destructive depth and cover measurements were used to estimate biomass, carbon and nitrogen content for nine moss and lichen functional groups among eight contrasted habitat types in Pacific Northwest and subarctic U.S.A. (N = 81 sites). Ground layer cover, volume, standing biomass, carbon content and functional group richness were greater in boreal forest and tundra habitats of Alaska compared to Oregon forest and steppe. Biomass of up to 22769 ± 2707 kg ha−1 (mean ...
Article
Ecosystem water-use efficiency (WUE), a ratio between gross ecosystem production (GEP) and water loss through evapotranspiration (ET) can be helpful for the assessment of coupled peatland carbon and water cycles under anthropogenic changes in the Athabasca Oil Sands Region (AOSR) where extensive oil sands development has been occurring since the 1960’s. As such, this study assessed multiyear peak growing season variability of WUE at four fens (poor treed, poor open, treed moderate-rich, open saline) near Fort McMurray using the eddy covariance technique combined with a set of environmental variables. Freshwater fens were characterized by WUE values within the range reported from other boreal wetlands while a saline fen had significantly lower values of WUE. Negative correlation (Rs < −0.55, p < 0.05) between WUE and net radiation was observed. Moisture conditions were responsible for interannual differences in WUE, whereby increasing WUE under wetter conditions was observed. However, such a pattern was offset by decreased air temperature (Tair) resulting in moisture oversupply. This study also revealed a negative effect of wildfire on WUE due to a prominent decline in GEP and a moderate decrease in ET. WUE can be useful for monitoring the functioning of natural and constructed fens, but a better understanding of WUE variability under a wide range of climatic conditions with respect to differences in vegetation is required. This article is protected by copyright. All rights reserved.
Method
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This manual explains background and use of the spreadsheet posted separately here and which can be used to rapidly assess ecosystem services of an individual wetland.
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En muchas áreas de las Montañas Rocosas, el ciervo rojo (Cervus elaphus) migra durante la primavera de valles montañosos de baja elevación a áreas altas subalpinas y alpinas para el verano. Hasta ahora la investigación se ha enfocado en el impacto de la herbivoría del ciervo rojo sobre las comunidades de plantas en el invierno, particularmente en las especies leñosas como el sauce y el álamo; sin embargo, existe poca información disponible sobre el efecto de la herbivoría del ciervo rojo en los sauces alpinos. En la cordillera Sangre de Cristo al centro-sur de Colorado, ciertas áreas alpinas parecen tener altos niveles de herbivoría de verano por el ciervo rojo, en tanto que otras áreas quedan casi sin ramoneo. En 2005 y 2008 medimos la altura, cobertura y uso de los sauces en sitios en los que parecía haber sido abundante el ramoneo y los comparamos con sitios donde parecía haber sido más ligero, a fin de determinar las diferencias entre estas comunidades en el tiempo. Encontramos menos cobertura y altura de sauces en los sitios que recibían niveles más altos de ramoneo en comparación a los que tenían menos evidencia de ello. El uso humano recreativo era mayor en los sitios de ramoneo ligero que en donde era abundante. De 2005 a 2008, disminuyó el uso y aumentó la cobertura y la altura en sitios de ramoneo abundante, probablemente debido a que un valle adyacente cambió de propietario, lo cual provocó (1) la eliminación de la competencia por el pastoreo en ganado en el valle; y (2) un aumento del uso humano en áreas alpinas, desplazando al ciervo rojo. Discutimos las implicaciones del aumento del uso humano y el cambio climático en el uso por el ciervo rojo de estos habitats alpinos.
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We investigated the vegetation of beaver meadows and other beaver-flooded sites using a combination of field, greenhouse, model, and GIS studies. The beaver meadows were dominated by two graminoid plant species, Calamagrostis canadensis and Carex lacustris. Carex dominated in wetter sites along streams and the edges of residual beaver ponds which had lower nitrate availability (determined using in situ resin bags), whereas the ubiquitous Calamagrostis dominated in mesic to dry portions of beaver meadows that had higher nitrate availability. Greenhouse studies with these two species plus Scirpus cyperinus and Carex rostrata investigated the effects of fertilization and wetness: increased N supply increased plant height, biomass, leaf nitrogen, and the vertical distribution of photosynthetic machinery, effects that were accentuated at field moisture capacity (as opposed to saturation). In the field, light attenuation in various beaver meadow communities was primarily a function of canopy height. A model that combined the results of the greenhouse and light attenuation studies correctly predicted that Calamagrostis had a competitive advantage over Carex lacustris under high levels of nitrogen availability, whereas the reverse was true under low nitrogen, saturated conditions. Field observations of plant cover at 108 sample points in two Kabetogama beaver meadows were analyzed using agglomerative hierarchical clustering and non-metric multidimensional scaling to distinguish eight plant assemblages. The most diverse of these assemblages occurred along the upland edges of the beaver meadows, where forest species were beginning to encroach upon the meadows. The GIS analysis showed that “wet meadow/fen mosaic complex” was the most common beaver impoundment vegetation within the Kabetogama Peninsula, followed by deep marsh mosaic complex, speckled alder swamp, Canada bluejoint eastern meadow, and northern water lily aquatic wetland. Voles may affect the recolonization of beaver meadows by conifers due to their influence on ectomycorrhizae (symbiotic root-associated fungi).
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Land managers need reliable metrics for assessing the quality of restorations and natural areas and prioritizing management and conservation efforts. However, it can be difficult to select metrics that are robust to sampling methods and natural environmental differences among sites, while still providing relevant information regarding ecosystem changes or stressors. We collected herbaceous-layer vegetation data in wetlands and grasslands in four regions of the USA (the Midwest, subtropical Florida, arid southwest, and coastal New England) to determine if commonly used vegetation metrics (species richness, mean coefficient of conservatism [mean C], Floristic Quality Index [FQI], abundance-weighted mean C, and percent non-native species cover) were robust to environmental and methodological variables (region, site, observer, season, and year), and to determine adequate sample sizes for each metric. We constructed linear mixed effects models to determine the influence of these environmental and methodological variables on vegetation metrics and used metric accumulation curves to determine the effect of sample size on metric values. Species richness and FQI varied among regions, and year and observer effects were also highly supported in our models. Mean C was the metric most robust to sampling variables and stabilized at less sampling effort compared to other metrics. Assessment of mean C requires sampling a small number of quadrats (e.g. 20), but assessment of species richness or FQI requires more intensive sampling, particularly in species-rich sites. Based on our analysis, we recommend caution be used when comparing metric values among sites sampled in different regions, different years, or by different observers.
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AcknowledgmentsAlthoug h the research described in this article hasbeen funded wholly orin
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Ecosystem engineers impact other organisms through environmentally mediated indirect interactions, but the potential for the mechanisms and importance of engineering to vary predictably across environmental gradients has not been investigated. Previously, we investigated how hummock formation by Triglochin maritimum in physically stressful salt marsh pannes influences the plant community that grows only on hummock tops and found that species diversity was dependent on indirect positive effects of T. maritimum engineering. Here we examined how Carex stricta, the tussock sedge, drives superficially similar spatial patterning of plants in relatively benign tidal freshwater marshes at the opposite extreme of an estuarine salinity gradient. In C. stricta marshes, the entire vegetative community is located almost exclusively on top of tussocks while inter-tussock spaces are bare mud buried in C. stricta wrack. We manipulated tussock height, belowground substrate, and aboveground competition for light to investigate the mechanisms by which C. stricta influences the wetland plant community. We also conducted wrack-removal experiments and phytometer assays to examine the importance of wrack deposition in this community and to investigate the spatial distribution of herbivore pressure, respectively. Transplants of four common species performed well in all treatments, except natural inter-tussock spaces buried in wrack. Removal of wrack from inter-tussock spaces enabled substantial seedling emergence and vegetative cover within one growing season. C. stricta therefore drives plant distribution primarily through indirect negative impacts of wrack accumulation in inter-tussock spaces. Once tussocks are established, plants obtain a secondary benefit when growing on tussocks, as the inter-tussock spaces become runways for small mammalian herbivores that concentrate feeding in low protected areas. These results differ dramatically from nearby salt marshes where T. maritimum facilitates community diversity by alleviating physical stresses. The mechanisms and outcomes of hummock-forming engineers may thus vary predictably across estuarine salinity gradients where hummock formation has facilitative and important impacts in physically stressful environments, but negative and less essential impacts in physically benign environments.
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We collected water quality, land use, and aquatic macrophyte information from 62 coastal and inland wetlands in the Great Lakes basin and found that species richness and community structure of macrophytes were a function of geographic location and water quality. For inland wetlands, the primary source of water quality degradation was inputs of nutrients and sediment associated with altered land use, whereas for coastal wetlands, water quality was also influenced by exposure and mixing with the respective Great Lakes. Wetlands within the subbasins of the less developed, more exposed upper Great Lakes had unique physical and ecological characteristics compared with the more developed, less sheltered wetlands of the lower Great Lakes and those located inland. Turbid, nutrient-rich wetlands were characterized by a fringe of emergent vegetation, with a few sparsely distributed submergent plant species. High-quality wetlands had clearer water and lower nutrient levels and contained a mix of emergent and floating-leaf taxa with a diverse and dense submergent plant community. Certain macrophyte taxa were identified as intolerant of turbid, nutrient-rich conditions (e.g., Pontederia cordata, Najas flaxilis), while others were tolerant of a wide range of conditions (e.g., Typha spp., Potamogeton pectinatus) occurring in both degraded and pristine wetlands.
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. The vegetation succession in a floating mire was studied in relation to management and hydrological conditions in a former peat cutting area in the northern part of the Netherlands. An existing map showed that in 1956 the vegetation consisted mainly of meadows, reedbeds and rich fen vegetation while a recent survey revealed that this picture had completely changed in 1989. The area had mainly become woodland but part had remained open, due to the continuation of a mowing regime. The timing of the mowing appears to be critical, especially during the earlier phases of the succession. Winter-mowing favours the development of eutrophic reedbeds, while summer-mowing promotes mesotrophic sedge communities. In the course of time these succession lines converge increasingly towards acidic vegetation types. The development from open water to embryonic bog differed greatly between sites with a similar management regime. Mostly this took only a few decades but in a few sites the vegetation had hardly changed since 1956. Whereas the former sites were acid throughout the profile, the latter showed a high pH from top to bottom. It is obvious that acidification does not occur as long as alkaline surface water can move freely underneath the floating mat. As soon as a given site becomes disconnected from the surface water the depletion of bases by infiltrating rainwater is no longer compensated. A rough estimate of the acidification rate shows that in an infiltration area three decades are sufficient for a floating mat of 40 cm to become completely decalcified. This corresponds well to the observed succession from rich fens to embryonic bogs in the same period. It is suggested that the best way to preserve rich fen vegetation is to start the succession anew by digging turf ponds.
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The effect of high water on floristic composition and diversity was compared at a diked, managed marsh, and an undiked, unmanaged marsh. Species richness and alpha diversity were determined for Cells A through D at Pipe Creek Wetland (PCW), a restored, managed marsh, and MHD Wetland, an undiked, unmanaged marsh. Both wetlands are located on Sandusky Bay in the western basin in Lake Erie, Ohio. Water levels were unusually high during 1997 when this study was conducted. Thus, the flora of Cells C and D at PCW in 1997 were compared to results from a vegetation survey of these cells conducted in 1994, a low-water year. Values for species richness in 1997 ranged from 25 (Cell A) to 42 (Cell D). Pipe Creek Wetland, and Cell D in particular, had higher species richness than MHD Wetland. Average alpha diversity values in 1997 ranged from 0.95 to 1.34; Cell D had significantly higher alpha diversity than Cell C at PCW and MHD Wetland. Species richness of Cells C and D at PCW declined substantially between 1994 and 1997 and species composition changed considerably. These findings reflect the combined effects of the very different marsh surfaces, hydrologic regimes, and human influences at Pipe Creek and MHD Wetlands. It is suggested that species richness and alpha diversity at Pipe Creek Wetland would be even higher in a low-water year. However, MHD Wetland would not become more diverse if water levels dropped due to the extreme dominance of stress-tolerant, aggressive plant species at MHD.
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Undiked wetlands in Lake Erie experience fluctuating water levels, and diked wetlands are isolated from these natural hydrologic events. Growth and survival of vegetation within the two wetland types is influenced by different water level regimes. Our objective was to report the occurrence and abundance of flora in a 100 ha diked wetland (DW) and an adjacent 100 ha undiked wetland (UW) at Winous Point Shooting Club in southwestern Lake Erie (SWLE) during September 1991. Randomly sampled aquatic macrophytes were identified to species and number of stems was recorded. Water depth and land elevation readings were also made. Forty-six species of aquatic macrophytes were identified in the DW while no plants were found in the UW. The controlled water depth of the DW (28.40 ± 2.39 [SE] cm) was significantly lower (P <0.0001, t = 11.95) than the uncontrolled depth in the UW (95.41 ± 5.07 cm). Although the basin elevation of the DW was higher (P = 0.01) than the elevation of the UW, the mean difference in water depth between the two wetlands was much greater (P <0.0001) than the mean elevation differences. Thus, higher water levels were primarily responsible for floristic differences between the two wetlands. Because most ecological functions of wetlands are derived from processes requiring aquatic macrophytes, we suggest that unvegetated wetlands, such as undiked wetlands in SWLE, provide few of their potential ecological benefits. We propose that the relative ability of a SWLE wetland to advance landward is the most important factor in determining the need to construct dikes and control water levels for aquatic plant restoration. We generally recommend that dike systems should only be constructed on SWLE wetlands with restricted upland borders.
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Twelve wet meadows in Dane County, Wisconsin showed vegetation patterns that correlate with hydrologic disturbance and presence of a clonal invasive grass, Phalaris arundinacea L., at two scales, 4500-m 2 (0.45 ha) "sites" and 1-m 2 plots. Sites with indicators of hydrologic disturbance had lower species richness and diversity than reference sites, and species richness, diversity, and mean coefficients of conservatism (Mean C) were inversely related to the abundance of Phalaris on sites. Within 1-m 2 plots, 5.5 ± 0.4 (SE) species coexisted with Phalaris, while about twice as many coexisted with two widespread native graminoids: 11.5 ± 0.3 with Carex stricta Lam. and 10.6 ± 0.3 with Calamagrostis canadensis (Michx.) Beauv. Cover of Phalaris was approximately six times higher in plots on sites with disturbance indicators than on reference sites. Overall, plots with either Phalaris or hydrologic disturbance had 2/3 the species of plots lacking Phalaris on reference sites, as well as lower diversity and Mean C. These results suggest a strong negative effect of hydrologic disturbance or presence of Phalaris on the quantity and quality of species in a wetland. When Phalaris and disturbance indicators co-occurred, the difference was more severe. Plots with Phalaris on disturbed sites had 1/3 the species of reference plots and the lowest diversity and Mean C. Species were grouped into seven "response types" based on apparent sensitivity to the presence of Phalaris and hydrologic disturbance. Only the clonal grass Phragmites australis (Cav.) Trin. ex Steud. responded positively to the combination of Phalaris and hydrologic disturbance.
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Thousands of wetland restorations have been done in the glaciated midcontinent of the United States. Wetlands in this region revegetate by natural recolonization after hydrology is restored. The floristic composition of the vegetation and seed banks of 10 restored wetlands in northern Iowa were compared to those of 10 adjacent natural wetlands to test the hypothesis that communities rapidly develop through natural recolonization. Restoration programs in the prairie pothole region assume that the efficient-community hypothesis is true: all plant species that can become established and survive under the environmental conditions found at a site will eventually be found growing there and/or will be found in its seed bank. Three years after restoration, natural wetlands had a mean of 46 species compared to 27 species for restored wetlands. Some guilds of species have significantly fewer (e.g., sedge meadow) or more (e.g., submersed aquatics) species in restored than natural wetlands. The distribution and abundance of most species at different elevations were significantly different in natural and restored wetlands. The seed banks of restored wetlands contained fewer species and fewer seeds than those of natural wetlands. There were, however, some similarities between the vegetation of restored and natural wetlands. Emergent species richness in restored wetlands was generally similar to that in natural wetlands, although there were fewer shallow emergent species in restored wetlands. The seed banks of restored wetlands, however, were not similar to those of natural wetlands in composition, mean species richness, or mean total seed density. Submersed aquatic, wet prairie, and sedge meadow species were not present in the seed banks of restored wetlands. These patterns of recolonization seem related to dispersal ability, indicating the efficient-community hypothesis cannot be completely accepted as a basis for restorations in the prairie pothole region.
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Abstract A huge road network with vehicles ramifies across the land, representing a surprising frontier of ecology. Species-rich roadsides are conduits for few species. Roadkills are a premier mortality source, yet except for local spots, rates rarely limit population size. Road avoidance, especially due to traffic noise, has a greater ecological impact. The still-more-important barrier effect subdivides populations, with demographic and probably genetic consequences. Road networks crossing landscapes cause local hydrologic and erosion effects, whereas stream networks and distant valleys receive major peak-flow and sediment impacts. Chemical effects mainly occur near roads. Road networks interrupt horizontal ecological flows, alter landscape spatial pattern, and therefore inhibit important interior species. Thus, road density and network structure are informative landscape ecology assays. Australia has huge road-reserve networks of native vegetation, whereas the Dutch have tunnels and overpasses perforating road barriers to enhance ecological flows. Based on road-effect zones, an estimated 15–20% of the United States is ecologically impacted by roads.
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The question of how far different organisms may "indicate" environmental conditions is one of great interest to ecologists, although the fact that so many of the organic and environmental factors concerned may vary independently (cf. JENNY, 1941) suggests that close correlations of species to single habitat factors will be rather rare. However, where plant remains have accumulated to a point at which they constitute the major portion of the surface soil, as in the case of waterlogged peats, it might perhaps be expected that the relation between the soil character and the plant cover would be relatively clear. The present work was initiated in the course of some studies on the chemical stratigraphy of a mire, during which the problem arose of the extent to which chemical conditions at a given stage of mire development might be deduced from the vegetational composition of the peat laid down at that time. That there is some correlation of mire vegetation with chemical factors is clear from the highly interesting investigations on the chemistry of mire waters in various plant communities by KIVINEN (1935) and WITTING (1947, 1948, 1949). These two workers have used rather different methods of approach to the problem - the former determining the range and frequency of single species in relation to the acidity and total electrolyte content of mire waters; the latter studying the range of both these values and of the concentration of certain ions as well, but in relation to various phyto-sociological units of vegetation rather than to single species. For the present purpose it was felt that another mode of attack might be profitable -- a detailed study, in one locality, of the range of chemical conditions in a single clearly defined mire community, sufficiently abundant to constitute an important peat former.
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We studied disturbance in 15 palustrine wetland plant communities associated with commercial cranberry (Vaccinium macrocarpon) production in Wisconsin. The importance values (sum or relative frequency and relative cover) of species were correlated with distance from disturbance. Importance values of pteridophytes increased with distance from disturbance. Significant correlations of importance values with distance were detected for 26-31% of species in sedge meadows and 15% of species in bogs, where 10% was expected. Taxa which had high importance values close to the disturbance had affinity for sand and desiccated conditions. Further disturbance should be minimized by designing spatially compact cranberry bed complexes. Roads and dikes should be vegetated to prevent deposition of sand and biocides into the wetland.
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(1) Seedlings of Myrica gale, an actinorhizal dinitrogen-fixing shrub, were grown in two boxes with a gradient of water-table depth from 3-79 cm. The boxes were outdoors but sheltered from rain by translucent roofs. One box was filled with sand and the other with peat. The seedlings were harvested in autumn shortly before leaf-fall. (2) The plants produced maximum biomass at water-table depths between 10 cm and 35 cm on both substrata but the total amounts produced were substantially greater on peat than on sand. (3) Shoot-root quotients decreased with increasing water-table depth on both substrata but were much larger on sand. (4) The roots did not penetrate below the water table and the orientation of the major lateral roots changed from primarily horizontal to semi-vertical with increasing water-table depth. (5) Nodules formed 6-7% of the total seedling biomass in the wettest soils and decreased to 1% in the driest. (6) Nodule roots showed maximum development in the wettest soils where they were relatively long and thick, and emerged through the surface into the air above. This is consistent with a functional role in enhancing nodule oxygen uptake under oxygen-limiting conditions. (7) The considerable phenotypic plasticity in response to moisture and aeration exhibited by Myrica gale appears to be a valuable adaptation in its natural habitat where the water level often fluctuates.
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Differences among habitats in the relative availability of prey and inorganic nutrients suggest that carnivorous plants should vary their investment in prey capture. We tested this hypothesis using the carnivorous plant Utricularia macrorhiza, which is common in lakes exhibiting a broad range of nutrient conditions. We assessed U. macrorhiza investment in carnivory as the density of prey-capture bladders per leaf. Field surveys revealed that the number of prey-capture bladders per leaf varied significantly among lakes but was highly consistent within a habitat. Differences in the number of bladders reflects an increasing proportion of plant biomass in bladders. Contrary to our initial hypothesis, the number of bladders was positively, not negatively, correlated with the specific conductance of a plant's habitat water. Reciprocal transplant experiments of plants from lakes with many or few bladders per leaf revealed that the number of bladders per leaf is plastic, capable of changing on new leaves over a period of a few weeks. Experimental manipulations of animal prey indicated that a plant's bladder number per leaf is a direct response to water chemistry rather than to prey availability.
Article
1. Allocation of biomass and nitrogen were studied for 1 year in experimental populations of Carex diandra, C. rostrata and C. lasiocarpa (species from mesotrophic fens) and C. acutiformis (a species from eutrophic fens). These species were grown at two levels of N supply (3.3 and 20. 0 g N m-2 year-1, respectively). 2. At low N supply, total biomass did not differ between the species. At high N supply, the total biomass of C. lasiocarpa and C. acutiformis (`high-productive species') significantly exceeded that of C. diandra and C. rostrata (`low-productive species'). In all species, percentage nitrogen allocation to the leaves exceeded percentage biomass allocation to the leaves. 3. The high-productive species had a higher shoot: root ratio, a higher percentage biomass allocation to the leaves (leaf weight ratio, LWR), a higher total nitrogen content and a higher percentage nitrogen allocation to the leaves than the low-productive species. However, the low-productive species had higher leaf nitrogen concentrations (on a weight basis) than the high-productive species. 4. Parameters which are related to light interception, such as the specific leaf area (SLA: m2 of leaf per kg of leaf), the leaf area ratio (LAR: m2 of leaf per kg of plant), the leaf area index (LAI: m2 of leaf per m2 of soil) and the ratio between total leaf area and total root length, did not differ consistently between the high-productive and the low-productive species. 5. Compared with the high-productive species, the low-productive species invested relatively more biomass and nitrogen in plant parts which contribute to the acquisition of below-ground resources. 6. At low N supply, there was a decrease in all species of the shoot:root ratio, LWR, LAR, LAI, and the ratio between total leaf area and total root length. 7. The rank order of potential productivity of the species in this study did not match the rank order of nitrogen availability in their natural habitat. It is suggested that the distribution of these species is not only determined by their potential productivity, but also by specific demands on the water chemistry and by their competitive ability.
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Using a comparative approach, we tested the prediction that relative competitive performance of plant species is correlated with distribution along natural gradients of fertility and standing crop. The mean position of 40 species of herbaceous plants along standing crop, phosphorus, nitrate, magnesium, potassium pH, and percent organic content gradients was calculated based on data from 217 quadrats from lake and river shorelines in Nova Scotia, Quebec, and Ontario. Competitive performance was measured in an outdoor experiments in which species were grown together with a common phytometer, Lythrum salicaria (n = 5 replicated per species). The relative ability of each species to suppress the growth of the phytometer was used as a measure of relative competitive performance. This measure of competitive performance was significantly correlated with the mean position of species on the standing crop (r = 0.081; P < 0.0001), percent organic content (r = 0.71; P < 0.0001); phosphorous (r = 0.70; P < 0.0001), nitrate (r = 0.67; P< 0.0001), magnesium (r = 0.66; P < 0.0001), and potassium gradients (r = 0.61; P < 0.0001). When monocotyledons and dicotyledons were considered separately, the relationship between distribution along the macronutrient gradients and competitive performance was much stronger for monocotyledons. It is suggested that this may reflect a differential influence of disturbance on distribution.
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The seasonal contribution of living Typha components to the buoyancy of floating mats was investigated in a diked, freshwater impoundment near the head of the Bay of Fundy in New Brunswick, Canada. The objectives were (1) to examine the potential influence of a dominant, mat-building species on hydrologic conditions at the mat surface, and (2) to predict whether a complete killing of the dominant species could cause mats to sink. The Typha component contributing most to mat buoyancy was the rhizomes, which added a net buoyancy pressure of @?20 Pa throughout the growing season. The seasonal maximum buoyancy contribution of 28 Pa for all living Typha components combined was reached in spring, followed by a decline to 11 Pa in late summer as the aboveground shoots developed. This positive and seasonally variable contribution of Typha to mat buoyancy is expected to be most important during the early stages of mat development, when mats are thin and composed largely of living, belowground organs. However, on older and thicker mats the living Typha is less important because of the large volumes of gas bubbles from anaerobic decomposition that are trapped in the dead organic material. For the 50 cm thick floating mats under study, it is concluded that trapped gas is the main cause of buoyancy and would lead to the continued flotation of mats even if the living Typha were removed. Implications of the results are discussed in relation to the resiliency of floating mat systems.
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A Manual of Aquatic Plants can be said to be a classic; it made the identification of aquatic plants in sterile as well as in flowering or fruiting condition as simple as possible, and covers a region from Minnesota to Missouri and eastward to the Gulf of St. Lawrence and Virgina.
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We examined the effects of water level, surface water chemistry, and climatic parameters on aboveground primary plant production, and the tissue nutrient concentrations in the dominant herb species in a bog, three fens, and two marshes. In the fens, total NPP correlated best with NO 3- and total phosphorus surface water concentrations in 1993 and 1994. Total NPP in the marshes correlated best with alkalinity in 1993, and with soluble reactive phosphorus in 1994. Climatic parameters, such as mean annual growing season temperature, growing degree days, and precipitation, had the most notable effect on moss growth, whereas shrub and herb production correlated significantly with the water level relative to the moss surface. Herb production correlated positively and shrub production correlated negatively with the water level relative to the moss surface. Tissue nutrient concentrations of carbon (C), nitrogen (N), and total phosphorus (TP), and the C:N quotient in Carex lasiocarpa exhibited similar trends in the fens and the marshes. Carbon tissue concentrations in C. lasiocarpa remained unchanged, whereas N and TP tissue levels decreased throughout the growing season. In the site with the highest NPP and presumably the highest stand density, C. lasiocarpa exhibited the highest tissue N and TP levels. Furthermore, TP tissue concentrations in C. lasiocarpa were substantially higher in the marshes than in the fens. Tissue nutrient concentrations in Eriophorum vaginatum in the bog showed variable response patterns. N tissue levels increased, whereas tissue TP concentrations decreased from late June to late August. In the bog, E. vaginatum exhibited similar tissue TP levels to C. lasiocarpa in the fens; however, they were both substantially lower than those found in C. lasiocarpa from the marshes.
Article
Monotypic stands of reed canary grass, Phalaris arundinacea, replace native wetland vegetation where stormwater runoff alters hydrologic conditions, nutrient inflows, and sedimentation rates. We asked if different hydrologic conditions could explain the dominance of Phalaris and/or loss of the native grass, Spartina pectinata, and we compared the growth of each species alone and together under four hydroperiods (varying inundation frequency and duration) each at two water depths (surface saturation and flooding to 15 cm). When grown alone, aboveground biomass was similar for the two species, but Phalaris produced twice the stem length of Spartina via its low tissue density. Per unit biomass, Phalaris distributed its leaves over a larger canopy volume. Flooding reduced belowground biomass and increased total shoot length and shoot:root biomass of each species. Phalaris produced the most biomass, shoots, and total shoot length when wetter and drier conditions alternated weekly, while Spartina grew best with prolonged (4-week) inundation. When grown with Spartina, Phalaris changed its morphology by increasing its total shoot length:biomass ratio by 50%. However, ratios of Spartina:Phalaris aboveground biomass, shoot number, and total shoot length in two-species pots were not significantly affected by water depth or hydroperiod. We conclude that two plant attributes facilitate Phalaris' dominance of wetlands: its high ratio of total shoot length:biomass and its adaptable morphology (characterized herein as increased total shoot length:biomass when grown with Spartina).
Article
We examined the relationship between the richness of four different wetland taxa (birds, mammals, herptiles, and plants) in 30 southeastern Ontario, Canada wetlands and two anthropogenic factors: road construction and forest removal/conversion on adjacent lands. Data were obtained from two sources: road densities and forest cover from 1:50,000 Government of Canada topographic maps and species lists and wetland areas from Ontario Ministry of Natural Resources wetland evaluation reports. Multiple regression analysis was used to model the relationships between species richness and wetland area, road density, and forest cover. Our results show a strong positive relationship between wetland area and species richness for all taxa. The species richness of all taxa except mammals was negatively correlated with the density of paved roads on lands up to 2 km from the wetland. Furthermore, both herptile and mammal species richness showed a strong positive correlation with the proportion of forest cover on lands within 2 km. These results provide evidence that at the landscape level, road construction and forest removal on adjacent lands pose significant risks to wetland biodiversity. Furthermore, they suggest that most existing wetland policies, which focus almost exclusively on activities within the wetland itself and/or a narrow buffer zone around the wetland perimeter, are unlikely to provide adequate protection for wetland biodiversity.
Article
Aboveground net primary production (NPP) and surface water chemistry variables were monitored in a lacustrine sedge fen and a bog for four years. There were no significant differences in precipitation, mean growing season annual temperature, and number of growing degree days from 1991 to 1994. The mean annual water levels in the lacustrine sedge fen differed significantly, whereas they were similar in the bog during these four years. We measured 15 surface water variables in the lacustrine sedge fen and the bog, and found that only two correlated significantly with water level fluctuations. In the lacustrine sedge fen, calcium correlated positively (r^2= 0.56) and nitrate correlated negatively (r^2 =0.20) with water levels. In the bog, potassium correlated positively (r^2 = 0.88) and total dissolved phosphorus correlated negatively (r^2 = 0.62) with water levels. The remaining chemical variables showed no significant correlations with water level fluctuations. Net primary production of the different vegetation strata appeared to respond to different environmental variables. In the lacustrine sedge fen, graminoid production was explained to a significant degree by water levels (r^2 = 0.53), whereas shrub production was explained to a significant degree by surface water chemistry variables, such as nitrate (r^2 = 0.74) and total phosphorus (r^2 = 0.22). In the bog, temperature was the only variable that explained moss production to a significant degree (r^2 = 0.71), whereas ammonium explained graminoid production (r^2 = 0.66) and soluble reactive phosphorus explained shrub production to significant degrees (r^2 =0.71). There are few direct data on the impact of climatic warming in boreal wetlands, although paleoecological and 2×CO_2 model data have provided some indications of past and possibly future changes in vegetation composition, respectively. Our results suggest that the lacustrine sedge fen may succeed to a bog dominated by Sphagnum spp. and Picea mariana, whereas the bog may succeed to an upland-type forest ecosystem.
Article
Sedges (Cyperaceae) are the most important family of vascular plants in terms of species richness on Maine peatlands. Carex has more species than any other genus including Sphagnum in these peatlands. Optima (abundance weighted means) and tolerances (abundance weighted standard deviations) of pH, Ca, and shade are given for the 21 most frequently occurring sedge species. These species are also characterized in terms of habitat (vegetation type). Most of the species occur in the open, but a few (e.g., Carex trisperma) are most abundant in wooded habitats. Eriophorum species characterize bog and poor fen habitats. The rarest peatland sedges are all calciphiles. Canonical correspondence analysis with forward selection entered shade, pH, Al, a climate factor, K, Ca, Fe, and Mg as the minimum number of variables which best account for the species distributions. Sedge distributions within this region are determined primarily by gradients of shade and alkalinity/base cations. A comparison with other studies from boreal North American peatlands reveals that ecological requirements can differ across a sedge species' range.
Article
The influence of low (3 mM) and high (22 mM) nitrate or ammonium supply on biomass and nitrogen distribution of Urtica dioica L. was studied under controlled environmental conditions. With respect to biomass production growth on nitrate was more effective than on ammonium irrespective of the concentration of the nitrogen source. Low nitrogen supply favoured dry matter formation of the root plus rhizome fraction, whereas high nitrogen supply resulted in a preferential growth of the leaf plus stalk fraction. Growth on 22 mM nitrate or ammonium caused a significant higher content of total nitrogen, nitrate and free amino acids (particularly asparagine and arginine) in all plant parts as compared to that found in plants grown on the 3 mM nitrogen sources. The distribution of total nitrogen between the various plant parts was similarly affected by the concentration of the nitrogen supply as was that of biomass. The main nitrogen storage compounds were nitrate on the one hand and the free amino acids on the other when nitrate or ammonium were the nitrogen sources. Nitrate was preferentially accumulated in the leaves and the stalks, whereas the free amino acids were more equally distributed between leaves, stalks and roots; however, their concentrations were significantly highest in the stalks, if ammonium was the nitrogen source.
Article
The National List of Plant Species That Occur in Wetlands: 1988 (National List) represents the combined efforts of many biologists over the last decade to define the wetland flora of the United States. The National List has undergone a number of revisions resulting from intensive review by regional ecologists. National, regional and State lists are being distributed to provide users with the most current information. We welcome and encourage modification and improvement of the National List. Refinement of the National List will occur continually, reflecting increased knowledge in Indicator assignments, taxonomy, and geographic distribution. We anticipate that further refinement of the National List will lead to additional infra-specific and subregional Indicator assignments. Review documents and procedures are included with the National List to aid and encourage additional review. The U.S. Fish and Wildlife Service initially developed the National List in order to provide an appendix to the Classification of Wetlands and Deepwater Habitats of the United States (Cowardin et al. 1979) to assist in the field identification of wetlands. Plant species that occur in wetlands as used in the National List are defined as species that have demonstrated an ability (presumably because of morphological and/er physiological adaptations and/or reproductive strategies) to achieve maturity and reproduce in an environment where all or portions of the soil within the root zone become, periodically or continuously, saturated or inundated during the growing season (adapted from Huffman 1981). The development of the National List changed- significantly when a cooperative review effort was established by the major Federal agencies involved in wetland identification and management. The utility of the National List goes far beyond a simple catalog of wetland plants. The Fish and. Wildlife Service, in cooperation with North Carolina State University, has produced a weighted average procedure for using the wetland Indicator assignments of individual species to assist in determining the probability that a community is a wetland, (Wentworth and Johnson 1986). This procedure is used by the 'Soil Conservation Service to aid in the determination of wetlands included under the conservation provisions of the Food Security Act of 1985. The Fish and Wildlife Service, Army Corps of Engineers, Environmental Protection Agency, and Soil Conservation Service use the National List to aid in identifying wetlands falling under their various wetland program responsibilities.
Article
Dominant species play key roles in shaping community structure, but their behavior is far from uniform. We speculated that recognition of different behaviors (determined objectively) would be an indicator of the condition of plant communities. We developed a species dominance index (SDI) to identify dominant species and compare their behavior across multiple spatial scales. The SDI is based on three attributes (mean cover, mean species suppression, and tendency toward high cover), and it identifies up to 38 dominants within 74 Great Lakes coastal wetlands. Dichotomizing each of the attributes in a 2 × 2 × 2 matrix produced seven dominant behaviors, or forms, all of which occurred in Great Lakes wetlands. Species sho wed different dominant forms among locations and aggregation scales. Showing predominantly “monotype” form, invasive Typha was the taxon that was most often dominant in the samples. By quantitatively measuring dominance and describing dominance form, SDI can add insight into community change and is a useful addition to indicators of community condition.
Article
The effect of eight rates of N up to 672 kg/ha on the production of dry matter (DM) and crude protein (CP), and the levels of nine mineral elements in Frontier reed canarygrass (Phalaris arundinacea L.) was assessed in two experiments. All treatments received 25 kg P/ha. Two cuts were taken for yield estimations, and a third from more mature grass in mid-season for chemical analysis. Strongly linear relations (P = 0.01) were found for DM and CP with N. Recovery of N was highest where 224 kg N/ha was applied. All cuts were analyzed spectrographically for P, K, Ca, Mg, Mn, Fe, Cu, Zn, and Mo. Significantly positive correlations with N were found for K, Mn, Fe, Cu, and Zn in various cuts, whereas Mo showed a significantly negative correlation in one cut.
Article
Fertilizer trials were conducted on reed canary grass (Phalaris arundinaceae) and native sedge (Carex spp.) on meadowland at two sites in the Okanagan Valley of British Columbia. Rates of fertilizer were 112 kg/ha N, 49 kg/ha P, and 62 kg/ha K applied in several combinations; 112 kg/ha S was included at one site. Fertilizer treatments containing nitrogen produced about double the control yields on both reed canarygrass and sedge. At one site, there was a small yield reduction from omitting phosphorus. There was no response to sulfur at the one site where it was included.These data show that reed canarygrass and sedge meadows can have a large capacity to respond to nitrogen fertilizer, with a much smaller response to phosphorus.
Article
Water sedge (Carex aquatalis Wahl.), the main component of wet bogs, used for hay in central British Columbia responds under growth-room conditions to a complete fertilizer. Potted sedge-sod plugs were grown for five consecutive cuts (242 days) at temperatures of 70° and 40°F and at light intensities less than 1000 ft-c. Reducing the root temperature from 70° to 40°F, which simulated field conditions, lowered the average yield of all treatments by 45%. Phosphorus appeared to be the most limiting element at both temperatures. Nitrogen gave significant increases only at the lower temperature. The addition of soil nutrients more than doubled the recovery of the same nutrients in the forage from plants grown at both 40° and 70°F as compared with controls. On forage not supplied with P, the Ca/P ratio exceeded 3.
Article
A concerted research program discovers why reed canarygrass becomes established in degraded wetlands and suggests management options.
Article
Biological indicators of ecosystem integrity are increasingly being sought for use in ecosystem assessment and goal-setting for restoration projects. We tested the effectiveness of a plant community-based bioassessment tool, the floristic quality assessment index (FQAI) in 20 depressional wetlands in Ohio, USA. A priori, the 20 depressional wetlands were classified by type and ranked to form a disturbance gradient according to the local landscape condition. Ranks were based on surrounding land cover characteristics, vegetated buffer characteristics, and the extent of human-induced hydrologic alteration at the wetland site. The index was negatively correlated with the disturbance rank of a wetland and with the distance to neighboring wetlands (P = 0.01). Index values were lower for wetlands surrounded by agricultural or urban land use, wetlands with less vegetation on the wetland perimeter, and wetlands with more hydrologic modification, and at sites with greater distances to other wetlands. The wetlands with lower FQAI values tended to be dominated by plants that are typical of heavily cultivated landscapes or urban regions. Thus, the index is interpreted as a measure of environmental factors that maintain and control plant communities. The index was not correlated with differences in wetland surface water chemistry (alpha = 0.05) but was positively correlated with soil total organic carbon (P = 0.01), phosphorus (P = 0.05), and calcium (P = 0.05). Repeated wetland sampling in the summer and autumn revealed that the floristic quality assessment index could be useful for the assessment and monitoring of wetland ecosystems and for tracking wetland restoration projects over time.
Article
The study site was the transition zone between shrubs and herbaceous plants on the shore of Axe Lake, Ontario. To test for competitive release, shrubs (primarily Myrica gale) were removed from treatment plots paired with controls in 25 sections of shoreline and cover of herbaceous species was monitored for 4 yr. There were highly significant increases in cover, richness, and diversity in the removal plots, but < 1/4 of the individual species responded significantly. In general, these were small, partly evergreen species with high densities of buried seeds (eg Drosera intermedia, Hypericum boreale). On shores with frequent disturbance and low fertility there was no evidence for competitive release. The reduction in plant cover during a summer with high water levels suggests that lakeshores shift from abiotic to biotic structuring according to the water level in a particular year of series of years. Superimposed upon this is variation attributable to the type of shoreline and the type of species. -Author
Article
We examined the effect of changes in soil water table on the water relations, leaf gas exchange, and aboveground biomass of three riparian graminoids native to the semiarid western United States: Carex lanuginosa, Juncus balticus, and Carex nebrascensis. All three species co-occur at the wettest microhabitats within riparian corridors, but J. balticus and C. nebrascensis extend into drier areas. Lowering the water table to 1 m had little effect on the leaf gas exchange characteristics of the three graminoids. In the greenhouse, experimental reductions of the water table when plants had three fully mature leaves did not affect gas exchange rates or water potential in any of the three species. Lowering the water table when plants had one fully mature leaf resulted in limited differences between plants grown under high and low water table in J. balticus and C. lanuginosa. Further, these differences were only apparent after long periods of depressed water table (19 wk). In the field, rates of leaf gas exchange did not differ between plants growing near the creek from those occurring distant from the creek. Three factors contribute to the ability of these riparian graminoids to maintain favorable gas exchange and water relations across a range of water table depths. Each species appears to adjust rooting depth to, or just above, the shallow saturated zone. In the held, C. nebrascensis and J. balticus exhibited reductions of aboveground live biomass at locations far from the creek compared to those near the creek. Small adjustments of osmotic potential and the bulk modulus of elasticity help cells of C. nebrascensis and J. balticus maintain turgor as water table drops during the season. The limited distribution of C. lanuginosa near the creek may result, in part, from a higher biomass allocation to leaves and a less efficient water transport from roots to leaves, particularly when depressions of the water table occur during early growth stages.
Article
Natural disturbance related to fluctuating water levels governs the structure and composition of Saginaw Bay coastal wet meadow vegetation. European settlement introduced anthropogenic disturbance to the Saginaw Bay coastal zone, but the impact of anthropogenic disturbance on the vegetation is not known. We compared vegetation and abiotic data from six reference and six disturbed sites to examine anthropogenic impacts on Saginaw Bay coastal wet meadow vegetation. Reference sites were the least disturbed wet meadows available, whereas disturbed sites had suffered various anthropogenic impacts 10–30 years before the study started. We observed no significant difference in mean aboveground plot biomass, stem density, litter depth, hummock height and elevation, or mean site species richness, Shannon-Wiener diversity, coefficient of conservatism, and floristic quality between reference and disturbed sites. The importance values of only two of 15 major species differed significantly between reference and disturbed sites. Native wet meadow species re-vegetated previously disturbed sites, suggesting that Saginaw Bay coastal wet meadow vegetation is resilient once released from at least some forms of anthropogenic disturbance. Purple loosestrife (Lythrum salicaria L.) and several agricultural weeds occurred only in disturbed sites, suggesting a potentially useful metric for monitoring the health of Great Lakes coastal wet meadow vegetation. Additional studies are needed to gain insight into the probable revegetation trajectories of recently disturbed coastal wet meadows and to determine the form and utility of a “weedy plants” metric for classifying the condition of these wetlands.
Article
We compared the standing vegetation, seed banks, and substrate conditions in seven pairs of diked and undiked wetlands near the shores of Lake Michigan and Lake Huron, North America. Our analysis tested the null hypothesis that construction of artificial dikes has no effect on the vulnerability of Great Lakes coastal wetlands to non-native and native invasive species. Both the standing vegetation and seed banks in diked wetlands contained significantly more species and individuals of invasive plants. In addition, diked wetlands exhibited significantly higher levels of organic matter and nutrient levels, and significantly higher average pH. Two pervasive non-native invasive species in the Great Lakes region, Lythrum salicaria (purple loosestrife) and Phalaris arundinacea (reed canary grass) were significantly more abundant in diked wetlands. Typha spp. (cattail) also formed a much higher percent vegetation cover in the diked wetlands. Our results support the view that diking of shoreline wetlands modifies natural hydrologic regimes, leading to nutrient-rich aquatic environments that are vulnerable to invasion. The shallower, more variable water levels in non-diked wetlands, on the other hand, appear to favor another undesirable invasive species, Phragmites australis (common reed grass).
Article
We developed a spatial computer simulation model of the vascular plant community of a freshwater wetland in south-central Wisconsin. This model, based on the aggregation of an unwieldy collection of species into a manageable number of functional ''species-types'', is used to investigate the responses of wetland plant communities to anthropogenic disturbance that resulted in alterations in wetland hydrology. The results of the model are in general (rank-order) agreement with 7 yr of observed changes in vegetation structure of a sedge meadow and shallow marsh adjacent to a 1000-MW coal-fired power plant near Portage, Wisconsin. Sensitivity analysis of the model revealed that functional species' responses to disturbance depended most heavily on seed germination and dispersal characteristics, a result predicted qualitatively by the wetland succession model of van der Valk (1981). Although analyses of the model presented here appear to verify the model, validation of the model will depend on the collection of similar long-term data sets at disparate sites. This model may be of use in predicting the consequences of anthropogenic disturbance on other freshwater wetlands.
Article
Water, nitrogen, and water-plus-nitrogen at levels beyond the range normally experienced by shortgrass steppe communities were applied from 1971 through 1975, plant populations were sampled through 1977, and the results of the experiment were published. Upon revisiting the plots in 1982, we found it apparent that large changes had occurred since 1977. Sampling was re-established in 1982 to follow trajectories of recovery. Our purposes in this paper are to examine how conclusions from this study changed through time, and discuss implications of these changes for monitoring potentially stressed ecosystems. Although productivities increased, dissimilarities in plant species composition at the end of the 5 yr of nutrient treatments were not significantly different from controls. Two years after cessation of the treatments exotic ''weed'' species were increasing in water-plus-nitrogen treated communities, and community dissimilarities were diverging in water and water-plus-nitrogen treated communities. Seven years after cessation of treatments all communities were significantly different from controls. Exotics were more than ten times more abundant in water-plus-nitrogen and nitrogen treated communities than they had been 2 yr post-treatment. A consistent trend in recovery of all treated communities was evident over the next 5 yr. However, the trend towards recovery reversed over the next four consecutive years in the previously water-plus-nitrogen and water treated communities. The four-to-five year cycles in species composition and abundance of exotics towards, and then away from, conditions in undisturbed control communities were not related to weather but large accumulations of litter suggested biotic regulation. Inertia of existing plant populations, or the tendency to continue to occupy a site when conditions become unfavorable, can mask both future deterioration in ecosystem condition and unstable behavior resulting from environmental stressors. Time lags in initial response means that an ecosystem can pass a threshold leading to transitions to alternate states before it is evident in structural characteristics such as species composition. Global climate change and sulfur and nitrogen oxide pollutants also have the potential to act as enrichment-stressors with initial time lags and/or positive effects and cumulative, subsequent negative effects, rather than as disturbance forces with immediate negative impacts. Sociopolitical systems, however, often require change in biological variables or negative impacts before acting to ameliorate environmental problems. The manner in which conclusions changed at various periods in time, and the potential for time lags in responses of species populations, raises questions about which variables are most useful for detection of stress and how long studies must last to be useful.
Article
Land uses such as forestry and agriculture are presumed to degrade the biodiversity of riparian wetlands in the northern temperate regions of the United States. In order to improve land use decision making in this landscape, floral and faunal communities of 15 riparian wetlands associated with low-order streams were related to their surrounding land cover to establish which organismal groups are affected by anthropogenic disturbance and whether these impacts are scale-specific. Study sites were chosen to represent a gradient of disturbance. Vascular plants of wet meadow and shrub carr communities, aquatic macro-invertebrates, amphibians, fish and birds were surveyed, and total abundance, species richness and Shannon diversity were calculated. For each site, anthropogenic disturbances were evaluated at local and landscape scales (500, 1000, 2500 and 5000 m from the site and the site catchment) from field surveys and a geographic information system (GIS). Land use data were grouped into six general land use types: urban, cultivated, rangeland, forest, wetland and water. Shrub carr vegetation, bird and fish diversity and richness generally decrease with increasing cultivation in the landscape. Amphibian abundance decreases and fish abundance increases as the proportions of open water and rangeland increases; bird diversity and richness increase with forest and wetland extent in the landscape. Wet meadow vegetation, aquatic macro-invertebrates, amphibians and fish respond to local disturbances or environmental conditions. Shrub carr vegetation, amphibians and birds are influenced by land use at relatively small landscape scales (500 and 1000 m), and fish respond to land use at larger landscape scales (2500, 5000 m and the catchment). Effective conservation planning for these riparian wetlands requires assessment of multiple organismal groups, different types of disturbance and several spatial scales.1998 Academic Press
Article
The effects of five rates of nitrogen (N) fertilizer applied in the spring and four rates of N applied in the spring and after each harvest were determined on yield, percent N and nitrate accumulation in timothy (Phleum pratense L.), reed canarygrass (Phalaris arundinacea L.) and meadow foxtail (Alopecurus pratensis L.) for 4 yr. The three grass species were grown on a fine clay soil at Prince George, B.C. Meadow foxtail, reed canarygrass and timothy yields increased up to 5.0, 5.3 and 2.3 times, respectively, with spring-applied fertilizer. Yields of timothy were significantly higher than the other two species when no N was applied. Nitrogen content increased with increasing rates of applied N for the three grass species. Nitrate content measured as nitrate-nitrogen (NO3-N) increased with increasing N rates. Meadow foxtail accumulated the highest levels of NO3-N and reed canarygrass intermediate levels. The NO3-N content of timothy was always less than the minimum safe level of 0.15% NO3-N even at the highest N application rates. This minimum safe level was exceeded most often by meadow foxtail and sometimes by reed canarygrass.Key words: Yield, nitrogen, nitrate, reed canarygrass, meadow foxtail, timothy
Article
Understanding of the influence of groundwater depth on the physiology and growth of transplanted sedges is needed to improve revegetation efforts in degraded riparian meadows. In a greenhouse experiment, we exposed transplants of Carex lanuginosa, Carex nebrascensis, and Carex rostrata to three simulated groundwater depths (4, 19, and 35 cm). Groundwater depth was manipulated over two phases: (1) water depths were held constant for 16 wk and (2) water depths were then increased over the next 6 wk. Leaf gas exchange, water relations, and shoot growth were measured periodically during each phase, and aboveground and belowground biomass were measured at the end of each phase. All species adjusted rooting depth to groundwater depth in response to the constant groundwater treatments, and groundwater depth had no effect on net photosynthetic rate and stomatal conductance. Net photosynthetic rate and stomatal conductance of all species initially increased when groundwater levels dropped but decreased rapidly after 4 wk of lowering groundwater. This response indicates that anaerobic conditions hindered leaf gas exchange under shallow but constant groundwater depths and also indicates that transplants may be less tolerant of shallow groundwater than naturally established sedges because of their smaller root systems. Compared with the other species, net photosynthetic rate and stomatal conductance of C. rostrata were more sensitive to declines in leaf water potential, and this species allocated proportionately more root growth to saturated soil zones. Carex rostrata's growth and physiological characteristics indicate that its transplants have lower tolerance to dry soil and water stress than C. lanuginosa and C. nebrascensis.
Article
This study describes the present-day vascular flora of the marshes, woodlots, dikes, and drainage ditches of Winous Point, which is located approximately 3 1/2 miles southwest of Port Clinton, Ohio, near the mouth of Muddy Creek, at the western end of Sandusky Bay. Vascular plants found are recorded in a catalogue. Changes in the floristic composition of the marshes are discussed by comparing A. J. Pieters' observations (1901) of some marsh plants at the western end of Lake Erie with the present marsh flora. Plants reported by Pieters but not found at the present are predominantly submersed or partially emersed rooted aquatics, such as Elodea canadensis Michx., Nais flexilis Rost & Schmidt., Sagittaria graminea Michx., Vallisneria americana Michx., and some Potamogeton species. Zizania aquatica L. was common at the turn of the century, while at present it is uncommon. In 1901 Phragmites communis Trin. formed "extensive associations," while now it is common only in small scattered patches. Pieters reported Typha latifolia L. as everywhere and T. angustifolia L. as rare. Now T. angustifolia is very common, whereas T. latifolia is found only sporadically. Sagittaria rigida Pursh and S. latifolia Willd. are also reversed in frequency, with S. rigida rare today and S. latifolia now common. Factors that probably have contributed to these floristic changes, as exemplified by the above species, are construction of drainage ditches in the Black Swamp, marsh management practices at Winous Point, and pronounced physiographic changes that have occurred over the past 150 years (based on maps) at the mouths of Muddy Creek and the Sandusky River.