Wetland Plant Community Composition Research Articles

Hydrologic flushing rates drive nitrogen cycling and plant invasion in a freshwater coastal wetland model.

Coastal wetlands intercept significant amounts of nitrogen (N) from watersheds, especially when surrounding land cover is dominated by agriculture and urban development. Through plant uptake, soil immobilization, and denitrification, wetlands can remove excess N from flow-through water sources and mitigate eutrophication of connected aquatic ecosystems. Excess N can also change plant community composition in wetlands, including communities threatened by invasive species. Understanding how variable hydrology and N loading impact wetland N removal and community composition can help attain desired management outcomes, including optimizing N removal and/or preventing invasion by nonnatives. By using a dynamic, process-based ecosystem simulation model, we are able to simulate various levels of hydrology and N loading that would otherwise be difficult to manipulate. We investigate in silico the effects of hydroperiod, hydrologic residence time, N loading, and the : ratio on both N removal and the invasion success of two nonnative species (Typha×glauca or Phragmites australis) in temperate freshwater coastal wetlands. We found that, when residence time increased, annual N removal increased up to 10-fold while longer hydroperiods also increased N removal, but only when residence time was >10d and N loading was >30gN·m-2 ·yr-1 . N removal efficiency also increased with increasing residence time and hydroperiod, but was less affected by N loading. However, longer hydrologic residence time increased vulnerability of wetlands to invasion by both invasive plants at low to medium N loading rates where native communities are typically more resistant to invasion. This suggests a potential trade-off between ecosystem services related to nitrogen removal and wetland invasibility. These results help elucidate complex interactions of community composition, N loading and hydrology on N removal, helping managers to prioritize N removal when N loading is high or controlling plant invasion in more vulnerable wetlands.

Projected climate and land use changes drive plant community composition in agricultural wetlands

ABSTRACT Playa wetlands in the Great Plains, USA support a wide variety of plant species not found elsewhere in this agriculturally-dominated region due to the ephemeral presence of standing water and hydric soils within playas. If longer dry periods occur due to climate change or if changes in surrounding land use alter sediment accumulation rates and water storage capacity in playas, plant communities could experience decreased diversity, with lasting effects on ecosystem services provided by playas in the Great Plains and at a continental-level in North America. We quantified potential changes in playa wetland plant community composition associated with predicted changes in precipitation and land use in the Great Plains through the end of the 21st century. We conducted two six-month greenhouse experiments mimicking field conditions using intact mesocosms collected from playas in Nebraska and Texas. In the precipitation experiment, treatments derived from historical precipitation observations and three future moderate emissions (CMIP5 RCP4.5) downscaled climate projections were applied to mesocosms. For the land use experiment, treatments were simulated by nitrogen (N) applications to soil ranging from 0 to 100 mg-N L-1 with each precipitation event under historical rainfall patterns, representing increasing and decreasing area in agricultural use in playa watersheds. Plant communities tended to shift toward more native species under projected future climate conditions, but as N runoff increased, native species richness decreased. Agricultural land-use surrounding playas may have a greater effect on wetland plant communities than future alterations to hydrology based on climate change in the Great Plains; thus, efforts to reduce nutrient runoff into playas would likely mitigate loss in ecosystem function in the coming decades.

Seed germination traits shape community assembly along a hydroperiod gradient.

Hydroperiod drives plant community composition in wetlands, resulting in distinct zonation patterns. Here, we explored the role of seed germination traits in shaping wetland community assembly along a hydroperiod gradient. Specifically, we tested the hypothesis that seeds of reed, mudflat, swamp, shallow- and deep-water communities only germinate under a specific set of environmental factors characterized by the community-specific optimal conditions for seedling survival and growth. In a three-factorial experiment, we tested the seed germination response of 50 species typical for temperate wetlands of Europe to temperature fluctuations (constant vs. fluctuating temperature), illumination (light vs. darkness) and oxygen availability (aerobic vs. hypoxia). Phylogenetic principal component analysis, cluster analysis and phylogenetic linear regressions were used to confirm the community-specific seed germination niches. Our study revealed the presence of five distinct, community-specific seed germination niches that reflect adaptations made by the study communities to decreasing light intensity, temperature fluctuations and oxygen availability along the hydroperiod gradient. Light as a germination trigger was found to be important in mudflats, swamps and shallow water, whereas the seeds of reed and deep-water species were able to germinate in darkness. A fluctuating temperature is only required for seed germination in mudflat species. Germination of species in the communities at the higher end of the hydroperiod gradient (reed and mudflat) demonstrated a strict requirement for oxygen, whereas swamp, shallow- and deep-water species also germinated under hypoxia. Our study supports the recent argument that the inclusion of seed germination traits in community ecology adds significant insights to community response to the abiotic and biotic environment. Furthermore, the close relationship between seed germination adaptations and community assembly could help reach a better understanding of the existing patterns of wetland plant distribution at local scales and wetland vegetation dynamics, as well as facilitate nature conservation measures and aquatic habitat restoration.

Low extent but high impact of human land use on wetland flora across the boreal oil sands region

Boreal wetlands are at risk of degradation from anthropogenic activities including oil sands energy extraction. Despite efforts to monitor the impacts of oil sands energy extraction-related activities on wetland ecology, few studies examine the impacts of diverse human development types on wetland plant communities. Here, we sought to quantify the effects of human development in the Athabasca, Peace River, and Cold Lake Oil Sands Regions in Alberta, Canada, and to examine its impact on wetland plant community composition. Across the region, we found that total development and development related to energy and mining were both low; ~80% of the study area was undeveloped. Despite the low spatial extent, total anthropogenic development was negatively correlated with site-level conservatism (a metric of plant tolerance to environmental perturbation) in all five wetland classes examined. This suggests that wetlands surrounded by human development are inhabited by generalist species that are tolerant of environmental disturbance. Moreover, distinct floristic groups within each wetland class could be distinguished based on their total developed area, providing additional evidence that human development affects plant composition and diversity, despite its limited extent in the study area. In contrast to total development, energy and mining development had an inconsistent or no detectable impact on wetland plant community composition at the regional level, likely because although oils sands surface mining is intensive, it is spatially restricted to a small area within the oil sands region. Our findings show that wetland plant communities in the oil sands region are impacted by multiple types of human land use concurrently; further research should aim to evaluate both the distinct impacts of different land use types using gradients of development intensity, as well as the cumulative impacts of multiple land use types happening concurrently.

Human land use as a driver of plant community composition in wetlands of the Chicago metropolitan region

Anthropogenic alteration of the landscape has facilitated plant community change and non-native species invasion in urban areas. We used species occurrence data from over 2000 wetlands within the Chicago metropolitan region to classify urban wetlands into community types and examined non-native species composition across community types. Non-native species were widespread across the region, occurring in over 99% of wetlands. On average, 35% of the plant species in individual wetlands were non-native. A single non-native species, Phalaris arundinacea, was present in 74% of wetlands. Six wetland community types were identified (wet meadows, marshes, forested wetlands, farmed wetlands/mudflats, roadside marshes, and an undetermined wetland type), with each having aggressively spreading non-natives amongst the most common plant species. We conducted canonical correspondence analysis to evaluate the contribution of surrounding land cover, roads, and location of wetlands to plant community composition in these wetlands, and found that similar changes to the landscape have resulted in similar combinations of native and non-native species. Differences in species composition reflected spatial gradients in land use from urban to rural areas across the region, as well as proximity to major roads. Anthropogenic drivers have resulted in profound and pervasive changes to wetland communities across the region, creating novel habitats and ultimately novel community types.

Timing of white-tailed deer browsing affects wetland plant communities

White-tailed deer (Odocoileus virginianus Zimm.) have the potential to alter plant community composition and successional trajectory by browsing differentially on forb, graminoid, and woody species. The objective of this study was to determine if seasonal elimination of deer browsing changed wetland plant community composition and structure. We established 66 deer exclosure plots in two wetland vegetation communities in Canaan Valley, West Virginia, USA. Plots were established in April 2005 and monitoring was conducted in June and October, 2005–2007 to obtain data on both early and late species. Composition differed between control and treatment plots in Solidago spp.–Rubus hispidus L. communities in late-protected plots (enclosed July–October) when data were gathered in October. Community composition also varied in early-protected plots (enclosed April–July) when data were gathered in June. Forb cover increased in treatment plots in Solidago spp.–Rubus hispidus communities. Composition differed in Populus tremuloides Michx. communities in late-protected and continuously protected plots. There was no increase in cover by any wetland indicator status categories after 2 years of protection. Timing of browse played an influential role in the effect that white-tailed deer have on wetland plant communities. Our results suggest that reducing browsing pressure seasonally can increase forb species cover.

Transformation of methane in peatland environments

Abstract Wetlands and particularly peatlands are the main natural source of methane. Data indicate that 10-45% of methane emission comes from these sources. Methane emission from wetlands is the result of the balance between methanogenesis and methanotrophic processes and is actively affected by the wetland plant community composition. There are many factors affecting the balance of CH4: for instance, vegetation has a strong effect on CH4 emissions from wetland ecosystems by influencing methane production, consumption and transport in the soil. The effects of plants on methane fluxes may be mediated by: molecular diffusion, internal transport through plant aerenchyma tissues and ebullition. Methane is formed in the process of methanogenesis under anaerobic conditions. It may then be emitted into the atmosphere directly from the soil or by internal transport through the plant. Alternatively, it may undergo methane oxidation by methanotrophic bacteria, both free-living in the root zone and associated with the host plant in symbiosis. Sphagnum moss is of particular importance for this processes as it contains methanotrophic bacteria in its endophytic system. Methanotrophic bacteria live inside the dead hyaline cells or on the surface of Sphagnum leaves and are able to oxidise methane produced in the soil during methanogenesis, making peatlands a natural biofilter for methane, one of the main greenhouse gases

Remote sensing of plant communities as a tool for assessing the condition of semiarid Mediterranean saline wetlands in agricultural catchments

Semiarid Mediterranean saline wetlands are unique ecosystems sheltering high biodiversity. In the last decades, the expansion of irrigated lands has led to hydrological imbalances in Mediterranean catchments, causing wetland degradation. Vegetation composition assessment is considered an important tool for evaluating wetland ecological condition and can be mapped using remote sensing. This study aims to develop a condition index based on plant community composition suitable for semiarid Mediterranean saline wetlands, as well as to test the applicability of airborne multispectral remote sensors for discriminating plant communities. Characteristic plant communities of 12 wetlands were identified by means of ordination and classification analysis of plant taxa cover percentages obtained through fieldwork sampling. An index for assessing wetland ecological condition was developed based on the relationship between wetland plant community composition and watershed hydrological condition. Selected wetland plant communities were then mapped by means of remote sensing techniques using random forest algorithm for supervised classification of airborne images. Following this methodology, remote sensing served as a tool for wetland condition assessment at a regional scale.

Plant community, environment, and land-use data from oil sands reclamation and reference wetlands, Alberta, 2007–2009

Our goal was to evaluate the success of wetland reclamation efforts on oil sands mining company lease-holdings in Alberta, Canada. Already, 60 200 ha of land have been disturbed by mining, and an additional 419 800 ha will be mined in the future. Wetland reclamation efforts have been underway for 35 years, and current mine closure plans call for the construction of 15 840 ha of wetland habitat. There are, however, no accepted criteria by which the Alberta Government can evaluate constructed wetlands. We employed the reference condition approach, comparing reclamation wetlands to appropriate natural analogues with plants as bioindicators of wetland condition. The data set includes 74 wetlands, spanning a range in salinity, nutrient levels, size, and degree of human disturbance. Reclamation wetlands include those contaminated with oil sands tailings (oil sands process affected, OSPA, n = 13) and those free from tailings (oil sands reference, OSREF, n = 12). In contrast, some natural wetlands are exposed to agricultural impacts (AG, n = 12), but the majority represent our least-disturbed condition (reference wetlands, REF, n = 37). The data set includes species relative abundance from plant communities in the wet meadow, emergent, and open-water vegetation zones. In addition, we measured water and sediment chemistry variables and physical variables to quantify local environmental conditions. We also quantified land use surrounding 45 of the wetlands in a series of nested buffers ranging from 300 m to 2000 m from the edge of each wetland's open-water zone. This data set represents the most comprehensive, publicly available data on reclamation wetlands from the lease areas of the two largest oil sands mining companies. It may be used to investigate changes in wetland plant community composition along both natural and human-caused environmental gradients, including contamination by oil sands mine tails. The data could also inform studies into the effects of surrounding land use on wetland plants and local-level environmental conditions. Information about reclamation wetlands could serve as a basis for tracking reclamation trajectories over time, whereas information about reference wetlands could be used to characterize natural variability in plant communities in shallow open-water wetlands from the Boreal Plains ecoregion.

Vegetation along hydrologic, edaphic, and geochemical gradients in a high-elevation poor fen in Canaan Valley, West Virginia

Wetland plant community composition and pattern are regulated by a host of abiotic/environmental gradients and biotic factors. We used multivariate analyses to classify wetland plant communities and determine the relation of hydrologic, edaphic, and geochemical gradients on community composition and spatial distribution among 18 vegetation, hydrology, and soil sampling points in Abe Run, a botanically unique poor fen in northeastern West Virginia. We also examined the interactions of disturbance with the physical environment and species composition. A total of 179 vascular plant species were identified from sample plots. Vegetative composition and structure, dominant soil texture, and hydrology lacked the distinct concentric zonation of northern peatlands; instead, all were patchy and varied considerably over short distances. Graminoid-forb meadows with primarily silt-loam mineral horizons, greater depth to groundwater, and fewer days of inundation characterized the lower reaches of the wetland. These plots were more acidic, with absent or shallow O horizons, and lower concentrations of soil base cations (Ca, Mg, K). In the upper reaches of the wetland, mixed herb-shrub-tree dominated communities were structurally and compositionally more complex; here, organic horizons were much more prominent, peat depth ranged from 80 to 100 cm, and the average depth to water table was 10 cm less than for wells in the lower reaches of the wetland. Plots from upper transects (3–6) tended to have more shrub and tree cover, and higher concentrations of soil base cations. Much of the variability among plots in the upper and lower reaches of the wetland are consistent with beaver inundation of a large portion of the wetland during the 1980s. Multiple-response permutation procedures verified the difference (P < 0.0001) between vegetation of plots in the lower and upper reaches of the watershed. Because fens are connected to groundwater, these habitats are particularly vulnerable to disturbances, particularly those that alter existing land use and land cover. Minimization of disturbances in the surrounding watershed, controls on an excessive deer population, removal of exotic, non-native species, and control on foot traffic are all integral to maintaining the integrity of this high-value wetland.

Effect of nitrogen and phosphorus on tissue nutrition and biomass of freshwater wetland plant in Sanjiang Plain, Northeast China

Nitrogen (4, 10, 20 and 40g/m2) and phosphorus (1.2, 4.8 and 9.6g/m2) were applied to tanks to evaluating the effects of N and P additions on plant tissue nutrition and the biomass of two freshwater wetland plants in the Sanjiang Plain of Northeast China, namely Carex lasiocarpa and Carex meyeriana. For C. lasiocarpa, the total N concentration (TN) of plant tissues under the treatment of 10g/m2 was lower compared with the other N treatments. Initially, C. lasiocarpa exhibited a significant increase of biomass as compared with the control value, reaching the maximum of 31.20±4.01g/tank under the treatment of 10g/m2, and then dropped to 18.02±1.53g/tank under the treatment of 40g/m2. For C. meyeriana, TN generally increased with increasing amount of N applied. High N applied produced more aboveground biomass than low N applied. C. meyeriana, as the accompanying species, can adapt itself to the wetland enriched by N, and it may replace C. lasiocarpa as the dominant species of wetland. The total P concentration (TP) in tissues of C. lasiocarpa increased with P addition. The aboveground biomass of C. lasiocarpa increased with P addition, and it changed from 18.77±3.29g/tank to 46.03±3.95g/tank. However, TP of tissue may accelerate the C. meyeriana development under the treatment of 1.2g/m2. P accumulation contributes to the dominance of C. lasiocarpa but limits the production of C. meyeriana, and the latter may disappear gradually from the wetland enriched by P. Increased input of N and P might have an influence on wetland plant community composition and structure, so the effects of nutrient inputs and accumulation should be considered to protect the freshwater wetland.

Arbuscular mycorrhizal fungi and water table affect wetland plant community composition

Summary Most studies of the community‐level effects of arbuscular mycorrhizal fungi (AMF) have been conducted in upland grassland plant communities where a majority of the plant species are colonized by AMF. Here, we examine the effects of AMF on plant community composition in experimental wetland plant communities, where the dominant plant species are non‐mycorrhizal and subordinate plant species are colonized by AMF. We also assess how an important abiotic soil variable, depth to water table (soil saturation), might mediate the community‐level effects of AMF. In the low water table (un‐saturated) treatment, above‐ground plant biomass increased in the presence of AMF relative to the controls, while in the high water table treatment, biomass decreased with the presence of AMF. Contrary to predictions, plant diversity was unaffected by the presence of AMF in the low water table treatment, but significantly decreased in the presence of AMF in the high water table treatment. Changes in biomass and composition were driven by the interactions between the dominant non‐mycorrhizal species Carex hystercina, and the remaining mycorrhizal plant species. Our results indicate that AMF have the potential to influence plant community composition in calcareous fens and that these effects can be mediated by soil saturation. This study has implications for understanding how established principles of above‐ground/below‐ground interactions from upland communities translate to wetland plant communities and for understanding how AMF function can be mediated by abiotic soil properties. Contrary to previous thought, AMF may be important drivers of plant community composition in wetland plant communities.

Impacts of stressors on the emergence and growth of wetland plant species in Pennsylvania, USA

Agriculture and urbanization in the upland landscape often generate stressors, such as sedimentation and eutrophication, that may negatively impact wetland plant communities. Individual plant species responses to stressors are also likely influenced by the hydrologic and geomorphologic characteristics of different wetland hydrogeomorphic (HGM) subclasses. The goal of this study was to determine to what extent the two stressors listed above influence the growth and development of wetland plant species and how these responses vary across HGM subclasses. The impacts of the two stressors on wetland plant species emergence and growth were examined in a 2 × 2 factorial greenhouse experiment, using soil moisture and organic matter content to simulate three HGM subclasses. Both stressors elicited significant responses in species establishment and growth, but overall trends in stressor responses differed by wetland type. For instance, sedimentation reduced the emergence of four species in simulated riparian depressions but only affected one species in simulated slope wetlands and none in simulated headwater floodplains. Sedimentation had little impact on any species establishment or growth in headwater floodplains. Approximately half of the species showed an increase in at least one growth variable in response to nitrogen enrichment. Additionally, the conditions used to simulate HGM subclasses appeared to impact a species performance and sensitivity to stressors. Therefore, further investigation of the impacts of HGM subclass conditions on species performance is needed. We expected differences in species responses to be related to their natural distribution across pristine and impacted wetlands; however, no obvious relationships were found. Our results suggest that it will be difficult to make generalizations about species responses to stressors because responses varied by stressor type, stressor interactions, and HGM subclass. Therefore, perhaps the next step in formulating broad generalizations and predictions about wetland plant community composition will require a shift from species-based approaches to a trait-based approach for examining how species composition may change in response to future disturbances.

Community Assembly Rules, Morphological Dispersion, and the Coexistence of Plant Species

In order to find and define any assembly rules for communities, we must first investigate the patterns among species assemblages. We used a series of null models to test for patterns in wetland plant composition at the level of species, functional guilds, and traits. At the species level, we found significant checkerboard and nestedness patterns. Three functional guilds had some tendency to contribute a constant percentage to species richness, but after Bonferroni correction there was no significant pattern. Coexisting plant species showed no consistent overall pattern of morphological dispersion. However, when we considered each of 11 traits in turn, we found that 4 traits were overdispersed and 3 were underdispersed. Thus there are morphological assembly rules that constrain wetland plant community composition. These results reconcile contrasting views of community assembly. Communities can be simultaneously structured by a tension between two forces: abiotic external forces that constrain certain traits within limits and biotic internal forces that tend to keep coexisting species from being too similar. Because our sites vary along a fertility/disturbance gradient, we also investigated how trait dispersion varies in space. Trait dispersion increases with soil fertility; soil phosphorus explains about 36% of the variance in mean nearest neighbor distance. Species richness tends to decline with mean nearest neighbor distance, which contrasts with the general pattern for animal assemblages.

Hydrology and nutrient gradients in North Carolina peatlands

Soil chemistry and hydrology gradients are closely associated with and have often been cited as the causative agents for changes in wetland plant community composition. We analyzed the biogeochemistry and hydrology of three freshwater peatland communities on the North Carolina Coastal Plain—short pocosins, tall pocosins, and gum swamps. We compare this community gradient to the classical bog-fen gradient of northern peatlands. Short pocosins, in the ombrotrophic center of the raised bog complex, have the highest summer water table, with a large part of the peat profile remaining anaerobic throughout the year. They are highly nutrient-deficient with low levels of total and extractable P, N, and basic cations. They additionally have the greatest peat depth, with an organic matter content of ca. 95%. Tall pocosins have a highly seasonal water table, shallower peat depth, low soil nutrient levels, and an average soil organic matter content from 76 to 93% in the top 30 cm. Gum swamp forests have a highly seasonal water table and the shallowest peat depth. They are the most minerotrophic community, based on low organic matter and high N and P content of the soil, but have low levels of exchangeable Ca and Mg and low percent base saturation. All communities had low soil pH (<4). Short pocosins and tall pocosins were effectively differentiated by seasonal hydrology and peat depth but not by soil characteristics, while the pocosins and swamp forest had large differences in seasonal hydrology, peat depth, percent organic matter, and soil nutrients.

Water depth and biotic insulation: Major determinants of back-swamp plant community composition

Based on phytosociological data, a polythetic divisive classification technique resulted in the delineation of eight broad vegetation types in the back-swamp areas of the Maunachira River System of the Okavango Delta, Botswana. A detrended correspondence analysis indicated that water depth was the major environmental factor influencing the distribution of submerged, floating-leaved and tall, emergent species dominated communities. The remaining communities, with relatively distinct boundaries between each of them, were of short emergent species assemblages rooted in peat deposits with a water depth of less than 0.7 m. Their species composition was not related to water depth, conductivity, pH, redox potential, water temperature or total nitrogen or phosphorus concentrations in the water. The relationship between the present day wetland plant community composition and its environment may be masked by long term, biotic, ‘insulating’ processes such as the accumulation of resources during peat formation and clonal plant growth. This insulation process does not lead necessarily to long term community stability as has been previously suggested (Mitsch and Gosselink 1986).