Article

Latitudinal Gradient of Floristic Condition Among Great Lakes Coastal Wetlands

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Abstract

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.

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... However, plant community distributions are not restricted to state boundaries, and are known to vary considerably across ecological gradients (Pearman et al., 2006;Muratet et al., 2008), even in relatively undisturbed landscapes (Pickett and Parker, 1994;Morgan and Short, 2002). FQA has been effective in evaluating wetland condition across many states, but a number of studies have reported variable and inconsistent performance of FQA across large geographic regions (Nichols, 1999;Reiss, 2006;Johnston et al., 2010). For example, Reiss (2006) found that FQI scores for reference depressional wetlands in Florida varied among locations, with higher FQI values occurring in the Panhandle and northern regions and lower values occurring in the southern and central regions. ...
... These results indicate that a single threshold to designate reference condition cannot be applied statewide, as western wetlands are unlikely to meet the criteria. Other studies have documented floristic quality patterns across regions, with FQI scores typically increasing latitudinally (Reiss, 2006;Johnston et al., 2010). For example, Johnston et al. (2010) found strong latitudinal variation in FQI scores from coastal emergent wetlands along the Great Lakes, with scores increasing to the north. ...
... Other studies have documented floristic quality patterns across regions, with FQI scores typically increasing latitudinally (Reiss, 2006;Johnston et al., 2010). For example, Johnston et al. (2010) found strong latitudinal variation in FQI scores from coastal emergent wetlands along the Great Lakes, with scores increasing to the north. Score variations were attributed to a combination of anthropogenic disturbance and natural variation based on latitudinal differences in mean annual temperature, length of growing season, and soil texture (Johnston et al., 2010). ...
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.
... Dobson et al. 2000;Heino & Toivonen 2008). The influence of climate and water quality, for example, has rarely been studied within the same work (see however Kosten et al. 2009Kosten et al. , 2011Johnson et al. 2010). Investigations executed with comprehensive empirical data are needed to enhance our understanding of the relationships between aquatic macrophytes and ecological gradients with respect to community composition and richness. ...
... In addition, the climate variables used represent air temperatures, but might well describe relative changes in water temperature (Pilgrim et al. 1998). Besides, Johnson et al. (2010) argued that a latitudinal gradient has probably always existed for wetland plant species around the Great Lakes, but human activities have steepened the gradient. My results support this reasoning that the latitudinal gradient is founded on climatic differences within the state, and land-use changes have strongly altered water quality in the southern part of the state. ...
... The development of bioassessment systems should acknowledge geographic variation of abiotic characteristics, as it may not be possible to prepare efficient assessment protocols at coarse scales (e.g. state or national scale) if environmental factors vary strongly at a regional or landscape scale (Johnson et al. 2010;). The ecoregion approach provides a sound basis for the development of assessment systems (e.g. ...
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.
... Harsh winter conditions are known to restrict macrophyte growth through thick ice cover limiting the availability of carbon, oxygen, and light, freezing bottom sediments, or increasing ice erosion (Lind et al. 2014). Alahuhta (2015) and Johnson et al. (2010) have described a similar gradient in species richness of all macrophyte taxa in the Midwest United States. ...
... Overall, these results provide support that the latitudinal gradient is partially based on climatic differences, whereas land-use changes along this gradient have further affected water quality in the southern parts of the states. A similar gradient that has been steepened by anthropogenic activities has been reported for wetland plant species in the Great Lakes region (Johnson et al. 2010). ...
Article
The diverse Potamogeton genus includes over 80 species of aquatic macrophytes that occur across a broad geographic range and have variable response to environmental conditions. This study evaluated how environmental and spatial variables structure assemblage composition and species richness of Potamogetons in the US states of Minnesota and Wisconsin. Variation partitioning analysis was used to study the relative contribution of local, climate and spatial variables in explaining assemblage composition and species richness. Models were also developed for sixteen Potamogeton species using partial linear regression. Assemblage composition and total species richness were better explained by the pure effects of spatial and local variables as compared to the pure effects of climate variables. However, geographical structuring of variables suggested that species followed a latitudinal gradient that was strongly related to eutrophication and partially related to climate. Models for individual species were similar although some were disproportionately described by specific categories of explanatory variables. For example, invasive Potamogeton crispus was more tolerant of eutrophication than most species and was also described by a strong spatial grouping of lakes near a large urban area. These results suggest that the distribution of Potamogetons is limited by species tolerances to lake variation in local and climate characteristics across spatial gradients, whereas specific species may be more limited by dispersal barriers between lakes with suitable habitat. This analysis is the first regional evaluation of factors related to the distribution of this ecologically important genus and the importance of landscape-level approaches to ecological conservation is emphasized.
... Further, because of the unitless property of both metrics (FQI and C ̅ ), several modified versions have been proposed. Examples include FQI and C ̅ calculated from all species present (i.e., native and non-native) (Rocchio 2007; Cariveau and Pavlacky 2009), FQI weighted by species abundance (e.g., Cretini et al. 2012;DeBerry and Perry 2015) similar to a prevalence index (see Tiner 1999), FQI as a percentage of a maximum attainable index score based on the species present , FQI and C ̅ expressed as ratios between different vegetation layers in forested wetlands (Nichols et al. 2006), and FQI adjusted to account for changes due to latitude (Johnston et al. 2010). Details on the relative merits of these approaches are discussed in the text. ...
... Others have advocated developing regional lists using ecoregions rather than state boundaries (Bourdaghs et al. 2006;Bried et al. 2013), an approach that has been undertaken in areas such as the Mid-Atlantic region (Chamberlain and Ingram 2012) and the Northeast region (Bried et al. 2012). Still others have evaluated the effect of latitude on FQA, suggesting that correction factors can be built into the method to account for natural variability across latitudinal gradients (Johnston et al. 2010;Spyreas 2014). Based on these observations, the regional specificity of existing and future C-value lists should be viewed as the modus operandi for FQA in wetland evaluation. ...
... One way forest integrity can be quantified using phytometers is with the Floristic Quality Index (FQI). This index was developed by Swink and Wilhelm (1979;1994) and has been widely used to assess site quality in wetlands (Bourdaghs et al., 2006;Matthews et al., 2009;Johnston et al., 2010), though its application in forested habitats has been limited (for an exception, see Andreas et al., 2004). The index ranges from 0 to 10 and reflects the degree of habitat faithfulness of the species present. ...
... One key aspect of our results was anticipated: the ranges of modified FQI values within parks were fairly limited. Use of the standard FQI tends to result in a wider range of values Most herbs, several trees and shrubs in the rose family Not applicable Ferns and allies Nativity Native Species whose presettlement distribution includes the park area Nonnative Species with presettlement distributions outside of the park area Native/nonnative Species identified only to genus with both native and nonnative species in the park within regions, even within the same general habitat type, such as wetlands (Johnston et al., 2010) or prairies (Taft et al., 1997). This is because the standard FQI is proportional to the number of species sampled and, therefore, indirectly related to the size of the study area (MacArthur and Wilson, 1967). ...
Article
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Measures of forest integrity often focus on only one or a small number of metrics (e.g., regeneration, soil organic layer depth). It is possible, however, to view forest integrity more holistically, using the species assemblages present as phytometers, or integrative measures of the complete set of drivers, stressors, and filters acting on the ecosystem. Thus, the species themselves express forest integrity. We collected extensive data on the overstory, understory, and groundlayer from 158 long-term vegetation monitoring plots in four U.S. national parks, within the Great Lakes basin. From these data, we calculated species richness and the modified Floristic Quality Index (mFQI), a measure of species' conservatism and habitat faithfulness. We also determined the proportion of species within categories of each of four separate ecological traits: growth form, life history, pollination mode, and nativity. In general we found lower mFQI values in parks with greater species richness. The proportions of species in categories within the life history and nativity ecological traits varied little among all four parks; proportions in categories for the growth form and pollination mode traits at Apostle Islands differed from the other parks, in having more woody species than any other growth form and more species pollinated abiotically than by other strategies. Across all four parks, our results are consistent with other assessments of species richness on islands and species richness in relation to habitat variability. Both the mFQI values and the taxa groupings in each of the four ecological traits are expected to be responsive to ongoing stressors of forest integrity. Because these techniques are both intuitive and relatively easily assessed, their application as effective gauges of change can apply not only in these four parks, but more broadly, throughout most natural areas.
... Hence, the thermal inertia, the 'memory' of the system, is controlled by the averaged depth: the larger the depth, the slower the adaptation to external forcing. On the other hand, the large geographic extent of the Great Lakes region encompasses a variety of local climate conditions, primarily depending on latitude [47]. As a first approximation, these conditions can be associated with AT (figure 3(a)) because air warms as a result of the combination of all climatic factors (e.g. ...
Article
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Studies on the impact of climate change in lakes have mainly focused on the average response of lake surface temperature during three summer months (July, August, September, usually termed JAS). Focusing on the Laurentian Great Lakes, we challenge this common assumption by showing that the thermal behaviour is diversified in time both among different lakes and within a single one. Deep regions experience a stronger warming concentrated in early summer, mainly due to anticipated stratification, while shallow parts respond more uniformly throughout the year. To perform such analysis, we use the difference between the five warmest and coldest years in a series of 20 years as a proxy of possible effects of climate alterations, and compare the warming of lake surface temperature with that of air temperature. In this way, based on past observations obtained from satellite images, we show how the warming is heterogeneously distributed in time and in space, and that the quantification of lakes’ thermal response to climate change is chiefly influenced by the time window used in the analysis. Should we be more careful when considering averaged indicators of lake thermal response to climate change?
... Thus pre-settlement plant communities and an FQI value of 19 may be unrealistic goals in this region. Johnston et al. (2010) found a positive relationship between total FQI and latitude in coastal wetlands throughout the Great Lakes, which they argue could be used to establish targets for restoration. Average total FQI in our managed sites was about 6 points higher than the average total FQI in Lake Erie wetlands used in that study and was similar to total FQI found in wetlands at higher latitudes, providing some measure of the success of herbicide management in our wetlands. ...
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Invasive plants, such as Phragmites australis, are a global threat to plant diversity and are commonly controlled using herbicide management. The purpose of this study was to evaluate the plant community response six to ten years after large‐scale herbicide management to remove Phragmites from Great Lakes coastal wetlands along the shores of Western Lake Erie. Vegetation surveys were conducted in nine wetlands undergoing herbicide management and four unmanaged Phragmites‐dominated wetlands. The relative percent cover of Phragmites was dramatically lower in the managed (1.3%) compared to unmanaged wetlands (93.0%; p < 0.001), although relative percent cover of other non‐natives following herbicide management averaged 39.2% (ranging from 6.4 to 67.6%). The cover‐weighted floristic quality index (wFQI) was significantly higher in managed wetlands (p < 0.01), with the highest indices (12.4–17.0) at sites that received prescribed fire after herbicide treatment (p < 0.05). Species richness and diversity were significantly higher in managed wetlands (p < 0.001); however, there was no significant difference between wetlands treated only with herbicide and those treated with herbicide and prescribed fire. Our results indicate that herbicide management is effective in reducing Phragmites and improving floristic quality over time scales of six to ten years. However, continued spot‐treatment and management of new invasive species may be required, and the return of high‐quality plant communities may be unrealistic in the study region. This article is protected by copyright. All rights reserved.
... At regional extents, macrophyte diversity may show conflicting patterns in relation with latitude depending on the study region. For example, macrophytes have followed the latitudinal gradient in the Fennoscandia , whereas a reversed pattern has been evidenced in the Midwestern USA (Johnston et al. 2010;Alahuhta 2015). Aquatic macrophytes may respond to climatic and elevational gradients at broad spatial scales, but these broad-scale characteristics are typically overcome by local environmental factors when accounting for variation in community structure Alahuhta 2015). ...
Article
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We studied community-environment relationships of lake macrophytes at two metacommunity scales using data from 16 regions across the world. More specifically, we examined (a) whether the lake macrophyte communities respond similar to key local environmental factors, major climate variables and lake spatial locations in each of the regions (i.e., within-region approach) and (b) how well can explained variability in the community-environment relationships across multiple lake macrophyte metacommunities be accounted for by elevation range, spatial extent, latitude, longitude, and age of the oldest lake within each metacommunity (i.e., across-region approach). In the within-region approach, we employed partial redundancy analyses together with variation partitioning to investigate the relative importance of local variables, climate variables, and spatial location on lake macrophytes among the study regions. In the across-region approach, we used adjusted R2 values of the variation partitioning to model the community-environment relationships across multiple metacommunities using linear regression and commonality analysis. We found that niche filtering related to local lake-level environmental conditions was the dominant force structuring macrophytes within metacommunities. However, our results also revealed that elevation range associated with climate (increasing temperature amplitude affecting macrophytes) and spatial location (likely due to dispersal limitation) was important for macrophytes based on the findings of the across-metacommunities analysis. These findings suggest that different determinants influence macrophyte metacommunities within different regions, thus showing context dependency. Moreover, our study emphasized that the use of a single metacommunity scale gives incomplete information on the environmental features explaining variation in macrophyte communities.
... In contrast to modelling, the conservatism values were assigned as static within regions, implicitly assuming species vary only according to anthropogenic factors and not the natural heterogeneity present at local and landscape scales ("within-region neutrality"). Just as conservatism is unlikely to hold across regions or broad latitudes due to climatic and environmental heterogeneity (Nichols, 1999;Johnston et al., 2010;Spyreas, 2014; but see Chamberlain and Ingram, 2012), within-region neutrality also seems untenable given strong local and landscape variation. Still, it is commendable that botanists attempted regional-based scores in this case (Forrest, 2010), as most conservatism assignments have occurred throughout large geopolitical boundaries and not with respect to ecologically meaningful regions or management units (Spyreas, 2014). ...
... Floristic condition also varies along this latitudinal gradient, with exotic or invasive plants substantially more prevalent in wetlands of the southern Great Lakes (i.e., Lakes Erie and Ontario) than those in the north (i.e. Lakes Superior and Huron) (Johnston et al., 2010). The forty-eight wetlands ("sites") in which both vegetation data and water chemistry data were collected are well-distributed across the region (Fig. 1). ...
Article
U.S. coastal wetlands of the Laurentian Great Lakes span a north-to-south gradient (latitude 47–41° N) of increasing human population and agricultural intensity that alters their water chemistry and vegetation. We related field-measured water chemistry to vegetation condition and composition using data from 48 freshwater coastal wetlands along this sub-continental gradient, building upon previous findings that GIS-derived landscape descriptors could adequately predict vegetation condition in Great Lakes coastal wetlands. Our aim was to determine (1) whether plant communities could be differentiated by their surface water chemistry, and (2) if water chemistry could better predict wetland vegetation condition than GIS-derived variables. Seven distinct plant communities were identified by agglomerative hierarchical clustering and non-metric multidimensional scaling of vegetation cover data: Sphagnum-carpeted poor fens, Sparganium eurycarpum marshes, Calamagrostis canadensis wetlands, Schoenoplectus pungens marshes, Phragmites australis marshes, and two floristically distinct Typha-dominated marshes. There were significant differences (ANOVA) among the seven plant assemblages identified for most water chemistry metrics (Cl−, chlorophyll a, conductivity, NO3-N, pH, total N, total P, total suspended solids), but dissolved oxygen, dissolved organic carbon, and NH4-N did not vary significantly across the assemblages. The two different Typha-dominated plant communities were chemically distinct from each other in chlorophyll a, conductivity, NO3-N, pH and total suspended solids concentrations, and we recommend that they be separated into distinct associations: Typha spp. – Thelypteris palustris – Hydrocharis morsus-ranae and Typha spp. – C. canadensis – Leersia oryzoides. Plant communities tended to be geographically clustered, but wetlands that were geographic outliers of their floristic type were chemically similar to other wetlands in their plant community grouping despite being on different lakes. When offered both GIS-derived and field-measured potential predictor variables, a regression tree model of wetland condition chose only GIS-derived variables. However, a classification tree model derived solely from field-measured water chemistry variables correctly classified 79% of the sites into four plant community groupings based on total N, conductivity, and pH. Grouping wetlands by plant communities could provide a scientifically-defensible basis for stricter water quality standards to protect sensitive wetland types.
... 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). For the four lower Great Lakes, latitude was a significant predictor of wetland condition and was correlated with both natural and anthropogenic stressors, making it often difficult to tease out degradation due to human activity alone (Johnston et al., 2010). Our geographically most distant Lake Superior sites were within one-half degree of latitude of each other, essentially eliminating latitude as a driving variable. ...
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A map of ecoregions of the conterminous United States has been compiled to assist managers of aquatic and terrestrial resources in understanding the regional patterns of the realistically attainable quality of these resources. The ecoregions are based on perceived patterns of a combination of causal and integrative factors including land use, land surface form, potential natural vegetation, and soils. A synoptic approach similar to that used to define these ecoregions is also useful for applications of the map. Initial efforts to use the framework are at the state level of resource management; they center on aquatic ecosystems — mainly attainable ranges in chemical quality, biotic assemblages, and lake trophic state.
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The six major hypotheses of the control of species diversity are restated, examined, and some possible tests suggested. Although several of these mechanisms could be operating simultaneously, it is instructive to consider them separately, as this can serve to clarify our thinking, as well as assist in the choice of the best test situations for future examination. 65 references.
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We use data from inundated-area surveys of 58 coastal wetlands spanning a gradient of anthropogenic impacts across all five Laurentian Great Lakes to describe the distribution of nine exotic and invasive taxa of aquatic plants. We found plants that were exotic or have invasive strains to be substantially more prevalent in wetlands in Lakes Erie and Ontario than in Lakes Superior and Huron, with Lake Michigan wetlands intermediate. Najas minor (slender naiad), Butomus umbellatus (flowering rush), and Hydrocharis morsus-ranae (European frogbit) were restricted to the lower lakes and rarely dominant. Myriophyllum spicatum (Eurasian milfoil), Potamogeton crispus (curly pondweed), Lythrum salicaria (purple loosestrife), Phalaris arundinacea (reed canary grass), Phragmites australis (common reed), and Typha sp. (cattail) were more widespread and except for P. crispus, often among the dominant taxa. None of the submerged or floating-leaf exotic taxa were associated with altered total plant cover or richness, although M. spicatum, P. crispus, and native Stuckenia pectinatus (sago pondweed) were positively associated with agricultural intensity in the watershed (a surrogate for nutrient loading). Emergent P. australis, L. salicaria, and Typha were more likely to be present and dominant as agricultural intensity increased, and were associated with elevated emergent cover and decreased emergent genera richness. Effects of dominant taxa on plant cover and richness were readily detected using ordinal data from 100 m inundated segments but were harder to discern with data aggregated to the wetland scale. The sum of shoreline-wide abundance scores for four easily identified taxa (S. pectinata, P. australis, Typha, and L. salicaria) is proposed as a rapidly-measured indicator of anthropogenic disturbance across the Great Lakes.
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The pace of Land Use/Land Cover (LULC) change in the Great Lakes, particularly in urban and suburban areas, far exceeds that predicted by population growth alone. Thus, quantification of LULC and change through time may be a key factor in understanding the near-shore ecology of this system. The work described in this paper is part of a larger effort called the Great Lakes Environmental Indicators Project (GLEI), whose goal was to develop and refine environmental state indicators for the U.S. near-shore zone of the Great Lakes. Here we describe methodologies for using existing Landsat-based LULC maps to assemble consistent LULC data for the U.S. portion of the Great Lakes basin for 1992 and 2001, as well as summarizing salient LULC results. Between 1992 and 2001, 2.5% (798,755 ha) of the U.S. portion of the Great Lakes watershed experienced change. Transitions due to new construction included a 33.5% (158,858 ha) increase in low-intensity development and a 7.5% (140,240 ha) increase in road area. Agricultural and forest land each experienced 2.3% (259,244 ha and 322,463 ha, respectively) decrease in area. Despite the large and enduring agricultural losses observed (2.23% of 1992 agricultural area), the rate of agricultural land decrease between 1992 and 2001 was less than that reported by the EPA (−9.8%) for the previous 10-year period. Areas of new development were largely concentrated near coastal areas of the Great Lakes. Over 38% (6,014 ha) of wetland losses to development between 1992 and 2001 occurred within 10 km of a coastal area, and most of that area was within the nearest 1 kilometer. Clearly, these land use change data will be especially useful as quantifiable indicators of landscape change over time and aid in future land use planning decisions for protection of the integrity of the Great Lakes ecosystem.
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We present water quality data from 58 coastal wetlands, sampled as part of a larger effort investigating effects of nutrient enrichment and habitat disruption in the Laurentian Great Lakes. Our sampling design selected sites from across a gradient of agricultural intensity within combinations of biogeographic ecoprovince and wetland hydromorphic type and captured a large range in water quality. Levels of total nutrients (N and P), and various measures of particulate concentration, water clarity, and ionic strength were strongly associated with agricultural intensity in the watershed, and could be effectively aggregated into an overall principal component-based water quality descriptor. Lake Erie wetlands had the highest nutrient levels and lowest water clarity, while wetlands in Lakes Superior and Huron had the lowest nutrient levels and clearest water. Lake Ontario wetlands had clearer water than would be expected from their nutrient levels and position on the agricultural intensity gradient. Dissolved oxygen, silica, pH, and dissolved organic carbon (DOC) were independent of agricultural intensity but DOC was responsible for low water clarity in some Lake Superior wetlands. Simple classification by hydromorphic type (riverine or protected) did not explain water quality differences among wetlands exposed to similar agricultural intensity levels, so finer hydrologic classification may be desirable. Results are used as a basis for discussing research and information needs underlying development of water quality criteria and monitoring programs for coastal wetlands of the Great Lakes.
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Water-level change is integral to the structure and function of Great Lakes coastal wetlands, and many studies document predictable relationships between vegetation and water level. However, anthropogenic stressors, such as invasive species, land-use change, and water-level stabilization, interact to shift the historical cycle (of native vegetation migration up- and down-slope) toward dominance by invasive Typha species. Knowing from earlier studies that water-level stabilization alters the historical vegetation cycle, we asked if similar shifts can occur where water levels are not stabilized. Using historical aerial photographs of three coastal wetlands (in Lake Michigan's Green Bay, Wisconsin), we determined that habitat dominated by Typha species has expanded to eliminate wet meadow habitat. Between 1974 and 1992, linear regressions showed strong, significant relationships of both meadow area (R2 ≥ 0.894; p < 0.02) and marsh area (R2 ≥ 0.784; p < 0.05) to water level in all three wetlands. In 2000, meadow area was below that predicted by the historical pattern due to the landward advance of marsh habitat during a year of decreasing water levels. In the same period, land use in the wetland watersheds converted from agriculture to urban. Urbanization and the replacement of native Typha latifolia by the invasive hybrid Typha xglauca may have overwhelmed the beneficial impact of water-level fluctuation. The documentation of vegetation shifts, as herein, is an essential step in the process of preserving and restoring ecological integrity.
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Developing indicators of ecosystem condition is a priority in the Great Lakes, but little is known about appropriate spatial scales to characterize disturbance or response for most indicators. We surveyed birds, fish, amphibians, aquatic macroinvertebrates, wetland vegetation, and diatoms at 276 coastal wetland locations throughout the U.S. Great Lakes coastal region during 2002–2004. We assessed the responsiveness of 66 candidate indicators to human disturbance (agriculture, urban development, and point source contaminants) characterized at multiple spatial scales (100, 500, 1,000, and 5,000 m buffers and whole watersheds) using classification and regression tree analysis (CART). Nonstressor covariables (lake, ecosection, watershed, and wetland area) accounted for a greater proportion of variance than disturbance variables. Row-crop agriculture and urban development, especially at larger spatial scales, were about equally influential and were more explanatory than a contaminant stress index (CSI). The CSI was an important predictor for diatom indicators only. Stephanodiscoid diatoms and nest-guarding fish were identified as two of the most promising indicators of row-crop agriculture, while Ambloplites rupestris (fish) and Aeshna (dragonflies) were two of the strongest indicators of urban development. Across all groups of taxa and spatial scales, fish indicators were most responsive to the combined influence of row-crop and urban development. Our results suggest it will be critical to account for the influence of potentially important non-stressor covariables before assessing the strength of indicator responses to disturbance. Moreover, identifying the appropriate scale to characterize disturbance will be necessary for many indicators, especially when urban development is the primary disturbance.
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Great Lakes coastal wetlands are subject to water level fluctuations that promote the maintenance of coastal wetlands. Point au Sauble, a Green Bay coastal wetland, was an open water lagoon as of 1999, but became entirely vegetated as Lake Michigan experienced a prolonged period of below-average water levels. Repeat visits in 2001 and 2004 documented a dramatic change in emergent wetland vegetation communities. In 2001 non-native Phragmites and Typha were present but their cover was sparse; in 2004 half of the transect was covered by a 3 m tall, invasive Phragmites and non-native Typha community. Percent similarity between plant species present in 2001 versus 2004 was approximately 19% (Jaccard's coefficient), indicating dramatic changes in species composition that took place in only 3 years. The height of the dominant herbaceous plants and coverage by invasive species were significantly higher in 2004 than they were in 2001. However, floristic quality index and coefficient of conservatism were greater in 2004 than 2001. Cover by plant litter did not differ between 2001 and 2004. The prolonged period of below-average water levels between 1999 and early 2004 exposed unvegetated lagoon bottoms as mud flats, which provided substrate for new plant colonization and created conditions conducive to colonization by invasive taxa. PCR/RFLP analysis revealed that Phragmites from Point au Sauble belongs to the more aggressive, introduced genotype. It displaces native vegetation and is tolerant of a wide range of water depth. Therefore it may disrupt the natural cycles of vegetation replacement that occur under native plant communities in healthy Great Lakes coastal wetlands.
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In wetlands, drought or managed late-summer drawdowns create exposed mudflats that provide an excellent substrate for germination of purple loosestrife seeds. If late-emerging purple loosestrife seedlings survive the winter, new or expanding populations of purple loosestrife will result. Spring survival was determined for overwintered purple loosestrife seedlings from seeds planted at weekly intervals in late summer or fall of the previous year. Seedlings of purple loosestrife that emerged from late July to early August had the greatest survival rates and the greatest shoot dry weight, and they were the tallest the following spring. However, 37% of purple loosestrife seedlings that emerged in late August, although stunted, generated a crown that was able to overwinter successfully and regrow the following spring. The number of growing degree days accumulated from planting date to October 6 (the average date of first frost for Minneapolis and St. Paul, MN) was 1,424 for seedlings from seeds planted on July 21 but only 219 for seedlings from seeds planted on September 15. Purple loosestrife seedlings that emerge during late summer through early September in Minnesota may survive the winter to create additional purple loosestrife weed problems in wetland mudflats caused by artificial drawdowns or droughts. Nomenclature: Purple loosestrife, Lythrum salicaria L. LYTSA.
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Recent expansion of Phragmites australis throughout many Great Lakes wetlands has caused concern among resource managers because it is thought to degrade waterfowl habitat and reduce biodiversity. Wetlands at Long Point, Lake Erie, have some of the most important habitats for staging waterfowl on the Great Lakes and anecdotal evidence suggests that Phragmites has been expanding rapidly in some of these wetlands. To make informed management decisions, a better understanding of historical changes in distribution and abundance of this species is needed, as well as the ability to iden-tify which plant species/communities Phragmites is replacing. Long Point's wetland communities were digitally mapped from aerial photographs from 1945 to 1999. The aerial extent of Phragmites stands was measured by digitizing vegetation boundaries, ground-truthing, and analyzing the data using a GIS. A geometric growth formula was used to determine the intrinsic rate of change of Phragmites over time. Phragmites abundance fluctuated throughout the period (1945: 4 ha; 1955: 7.7 ha; 1964: 69 ha; 1968: 3.6 ha; 1972: 15.1 ha; 1978: 17.7 ha; 1985: < 4 ha; 1995: 18 ha; 1999: 137 ha), but its abundance increased exponentially between 1995 and 1999 (137 ha; intrinsic rate of growth in area = +0.50/yr). The species/communities that were most often replaced by Phragmites between 1995 and 1999 were Typha spp. (33.8%), marsh meadow (31%), sedge/grass hummock (10.8%), and other mixed emergents (9.6%). Of 31 stands analyzed within the study area, 28 (90%) were of a non-native strain of Phragmites australis (haplotype M) that has been rapidly expanding throughout the Atlantic region of the United States. We suggest that the recent rapid expansion of Phragmites at Long Point is the direct result of this exotic invasion, and that it has been facilitated by both declines in Great Lakes water levels and increases in ambient air temperatures; anthropogenic and natural disturbances have possibly also con-tributed. Given the invasive nature of the exotic genotype, combined with future global warming predic-tions, Phragmites probably will continue to rapidly expand throughout lower Great Lakes coastal wet-lands.
Article
Invasive species are a major threat to global biodiversity and an important cause of biotic homogenization of ecosystems. Exotic plants have been identified as a particular concern because of the widely held belief that they competitively exclude native plant species. We examined the correlation between native and invasive species richness in 58 Ontario inland wetlands. The relationship between exotic and native species richness was positive even when we controlled for important covarying factors. In addition, we examined the relationship between the abundance of four native species ( Typha latifolia, T. angustifolia, Salix petiolaris, Nuphar variegatum) and four invasive species ( Lythrum salicaria, Hydrocharis morsus-ranae, Phalaris arundinacea, Rhamnus frangula) that often dominate temperate wetlands and native and rare native species richness. Exotic species were no more likely to dominate a wetland than native species, and the proportion of dominant exotic species that had a significant negative effect on the native plant community was the same as the proportion of native species with a significant negative effect. We conclude that the key to conservation of inland wetland biodiversity is to discourage the spread of community dominants, regardless of geographical origin.
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The Floristic Quality Index (FQI) has been proposed as a tool that can be used to identify areas of high conservation value, monitor sites over time, assess the anthropogenic impacts affecting an area, and measure the ecological condition of an area. FQI is based on the Coefficient of Conservatism (C), which is a numerical score assigned to each plant species in a local flora, primarily from best professional judgment, that reflects the likelihood that a species is found in natural habitats. FQI is computed by multiplying the mean Coefficient of Conservatism (C) by the square root of species richness for an observational unit. Great Lakes coastal wetlands were used to assess the properties and performance of various species richness, Coefficient of Conservatism, and Floristic Quality indices, as well as compare C-value assignments from two U.S. states (Wisconsin and Michigan). FQI and species richness increased with sampling area according to a power function, but C more or less remained constant. Sampling schemes should therefore focus on controlling sampling area and minimally sampling each community type at a site. In some cases, Wisconsin and Michigan assigned different values of C to the same species, highlighting possible effects due to the somewhat subjective nature of C-value assignment. Coefficient of Conservatism and Floristic Quality indices were better at discriminating differences between sites, independent of a condition gradient, than species richness alone, but neither index type outperformed the other. Both types of indices were also found to be acceptable ecological indicators of condition, although Floristic Quality indices consistently outperformed Coefficient of Conservatism indices in this capacity. Regardless of the subjectivity involved with the assignment of C-values and that ‘floristic quality’ is a human concept and not a true ecosystem property, both Coefficient of Conservatism and Floristic Quality indices seem to be effective indicators of condition in Great Lakes coastal wetland
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We studied a Great Lakes peatland protected by a barrier dune system to test the hypothesis that changes in the morphology of a barrier beach alter the wetland surface-water and ground-water hydrology such that the plant rooting zone in the wetland interior might be affected. Hydraulic head measured in observation wells located on transects perpendicular to a flow-through channel, uplands, and Lake Ontario were compared to lake-level changes, weather patterns, and the temporal conditions of the barrier beach. Water-table elevations within the wetland complex always remained 0.35 to 0.84 m above Lake Ontario's water level (mean difference = 0.62 m) and did not fluctuate in parallel with changes in the lake's water level. Flooding events occurred when breaches closed and isolated the wetland complex from Lake Ontario; daily average water levels rose between 0.06 m and 0.27 m. When the barrier beach was breached naturally or by human activity, daily average water-table elevations in the wetland receded between 0.16 m and 0.41 m. During the growing season, vertical ground-water-flow directions also changed as a function of changing hydraulics controlled by the barrier beach. Vertical recharge-discharge gradients ranged from -0.2 to 0.1 m.m(-1). Water-table elevation and hydraulic head gradients across the study area were controlled primarily by short-term (days to weeks) changes in shoreline geomorphology, whereas seasonal weather patterns and Lake Ontario water-level fluctuations imposed secondary controls on the ground-water-flow regime.
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Vegetation and soil indicators of nutrient condition were evaluated in 30 wetlands, 10 each in 3 Nutrient Ecoregions (NE) (VI-Corn Belt and Northern Great Plains, VII-Mostly Glaciated Dairy Region, IX-Temperate Forested Plains and Hills) of the Midwestern United States (U.S.) to identify robust indicators for assessment of wetland nutrient enrichment and eutrophication. Nutrient condition was characterized by surface water inorganic N (NH4-N, NO3-N) and P (PO4-P) concentrations measured seasonally for 1 year, plant available and total soil N and P, and aboveground biomass, leaf N and P and species composition of emergent vegetation measured at the end of the growing season. Aboveground biomass, nutrient uptake and species composition were positively related to surface water NH4-N (N) but not to PO4-P or NO3-N. Aboveground biomass and biomass of aggressive species, Typha spp. plus Phalaris arundinacea, increased asymptotically with surface water N whereas leaf P, senesced leaf N and senesced leaf P increased linearly with N. And, species richness declined with surface water N. Soil total P was positively related to surface water PO4-P but it was the only soil indicator related to wetland nutrient condition. Individual regressions for each NE generally were superior to a single regression for all NEs. In NE VI (Corn Belt), few indicators were related to surface water N because of the high degree of anthropogenic disturbance (85% of the landscape is cleared) as compared to NEs VII and IX (24–53% cleared). Of the indicators evaluated, stem height (r2 = 0.42 for all NEs, r2 = 0.56 for NE VII + IX) and percent biomass of aggressive species, Typha spp. plus Phalaris, (r2 = 0.46 for all NEs, r2 = 0.54 for NE VII + IX), were the best predictors of wetland nutrient enrichment. Vegetation-based indicators are a promising tool for assessment of wetland nutrient condition but they may not be effective in NEs where landscape disturbance is intense and widespread.
Article
Developing effective indicators of ecological condition requires calibration to determine the geographic range and ecosystem type appropriate for each indicator. Here, we demonstrate an approach for evaluating the relative influence of geography, geomorphology and human disturbance on patterns of variation in biotic indicators derived from multiple assemblages for ecosystems that span broad spatial scales. To accomplish this, we collected abundance information on six biotic assemblages (birds, fish, amphibians, aquatic macroinvertebrates, wetland vegetation, and diatoms) from over 450 locations along U.S. shorelines throughout each of the Great Lakes during 2002–2004. Sixty-six candidate taxon- and function-based indicators analyzed using hierarchical variance partitioning revealed that geographic (lake) rather than geomorphic factors (wetland type) had the greatest influence on the proportion of variance explained across all indicators, and that a significant portion of the variance was also related to response to human disturbance. Wetland vegetation, fish and bird indicators were the most, and macroinvertebrates the least, responsive to human disturbance. Proportion of rock bass, Carex lasiocarpa, and stephanodiscoid diatoms, as well as the presence of spring peepers and the number of insectivorous birds were among the indicators that responded most strongly to a human disturbance index, suggesting they have good potential as indicators of Great Lakes coastal wetland condition. Ecoprovince, wetland type, and indicator type (taxa vs function based) explained relatively little variance. Variance patterns for macroinvertebrates and birds were least concordant with those of other assemblages, while diatoms and amphibians, and fish and wetland vegetation were the most concordant assemblage pairs. Our results strongly suggest it will not be possible to develop effective indicators of Great Lakes coastal wetland condition without accounting for differences among lakes and their important interactions. This is one of the first attempts to show how ecological indicators of human disturbance vary over a broad spatial scale in wetlands.
Article
Many hypotheses have been proposed to explain the great variation among regions in species richness. These were tested by first examining patterns of species richness of birds, mammals, amphibians, and reptiles in 336 quadrats covering North America. These patterns were then compared with the regional variation of 21 descriptors of the environment suggested by the hypotheses. I found that, in the four vertebrate classes studied, 80%-93% of the variability in species richness could be statistically explained by a monotonically increasing function of a single variable: annual potential evapotranspiration (PET). In contrast, tree richness is more closely related to actual evapotranspiration (AET). Both AET and PET appear to be measures of available environmental energy. The relationships between tree and vertebrate richness are strikingly poor. Species richness in particular orders and families of the Vertebrata is also closely related to PET, but not always monotonically, often resembling a replacement s
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.
Article
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.
Floristic Quality Assessment with Wetland Categories and Examples of Computer Applications for the State of Michigan
  • K D Herman
  • L A Masters
  • M P Penskar
  • A A Reznicek
  • G S Wilhelm
  • W W Brodovich
Herman, K.D., Masters, L.A., Penskar, M.P., Reznicek, A.A., Wilhelm, G.S., Brodovich, W.W., et al., 2001. Floristic Quality Assessment with Wetland Categories and Examples of Computer Applications for the State of Michigan , 2nd edition. Michigan Department of Natural Resources , Lansing, MI , p. 19.
Significant Coastal Fish and Wildlife Habitats Coastal Resources Online, Division of Coastal Resources
  • Nysdos
NYSDOS, 2010. Significant Coastal Fish and Wildlife Habitats. Coastal Resources Online, Division of Coastal Resources , New York State Department of State , Albany.
Toward a New Conservation Vision for the Great Lakes Region: a Second Iteration. The Nature Conservancy, Great Lakes Program
  • Tnc
TNC, 2000. Toward a New Conservation Vision for the Great Lakes Region: a Second Iteration. The Nature Conservancy, Great Lakes Program , Chicago, IL , p. 45.