Wetland Vegetation Dynamics Research Articles

Global environmental change mediated response of wetland plants: Evidence from past decades.

Wetland ecosystems are critically affected by global environmental changes, yet understanding the impact of these changes on wetland plants remains a challenge. This review article employs a comprehensive approach, including bibliographic analysis, utilization of various climate models for historical data retrieval, and extensive literature survey, to investigate the response of wetland plants to environmental shifts over the past decades. The analysis conducted in this study uncovers a multitude of climatic parameters that exhibit an influence on the dynamics of wetland vegetation. Results indicated a significant positive trend in atmospheric CO2 concentration, leading to increased water use efficiency in some plant species, particularly C3 plants. However, C4 plants did not show the same positive response. Nitrous oxide growth rate showed a weaker, less consistent trend than CO2, highlighting the need for further investigation into the complex factors influencing Nitrous oxide emissions from wetlands. Methane growth rate and global mean sea level demonstrated a strong positive linear trend. Ocean pH exhibited a statistically significant downward trend (acidification), while sea surface temperature showed a moderate but statistically significant upward trend. Glacier mass balance revealed a significant negative trend. Although some plants may benefit from increased CO2 initially, but the combined effects of rising sea levels, ocean acidification, and temperature changes pose substantial threats to the overall health and diversity of wetland plant life.

Recovery dynamics of wetland vegetation along a hydrological gradient in an agriculturally used inland valley in Uganda

Wetlands in East Africa are important for providing ecosystem services and for conserving biodiversity. They are also suitable and increasingly used for agriculture. Between cropping cycles, spontaneous vegetation regrows on fallow plots. We hypothesize that recovery is affected by hydro-edaphic conditions and the duration of the fallow period. Land use intensification reduces fallow durations. A multi-year field study investigated the dynamics, biodiversity, and potential uses of fallow vegetation species after a disturbance event in an inland valley wetland in Central Uganda. The wetland was stratified into three hydrological positions along a gradient comprising the valley fringe, the mid-valley, and the riparian zone. In each zone, biomass was removed, and the soil was tilled, simulating a common disturbance event. Subsequently, four plots of 4 × 4 m size were delineated in each zone. Vegetation regrowth was subsequently monitored over a period of two years. We recorded and analyzed changes in aboveground live biomass, abundance of selected plant species, taxonomic and functional composition, and evenness during a 27-months recovery phase. While annual species dominated the vegetation initially, these were gradually replaced by herbaceous perennials, and eventually by tall reeds and woody plants, constituting three successional stages. The dynamics were similar, but species composition differed across the positions. At all successional stages, we observed the presence of useful wild plants, but also invasive species such as Mimosa pigra were recorded. While temporary fallows are important for biodiversity in tropical wetlands, such successions cannot substitute for the functions and services provided by natural vegetation and may promote invasive species.

Soil water conditions together with plant nitrogen acquisition strategies control vegetation dynamics in semi-arid wetlands undergoing land management changes

Land management changes can significantly alter wetland soil environment, vegetation, and their interactions. Although the relationships between plant communities and environmental factors have been widely studied, the intrinsic driving mechanisms of vegetation dynamics are poorly understood because nutrient acquisition strategies play an important role in plant community assembly. This study compared the plant community characteristics of wetlands under different land management practices in the semi-arid western Songnen Plain, Northeast China, and investigated soil properties and plant community nutrient contents. Results showed compared with those in natural wetlands, the values of growth characteristics of plant communities were generally lower, whereas species diversity was higher in grazed or mowed wetlands. Furthermore, soil carbon (C), nitrogen (N), phosphorus (P) contents, their stoichiometric ratios, and soil water content were lower, and N contents in leaves and stems, soil bulk density, and pH were higher compared with those in natural wetlands. The plant community characteristics were significantly correlated with soil properties and plant nutrient contents. A redundancy analysis showed that soil water content, bulk density, and organic carbon, accounted for 59.3%, 15.6%, and 2.9%, respectively, the N in leaves, stems, and roots accounted for 62.8%, and the P in leaves and roots accounted for 12.2% of the variation in the plant community. Variation partitioning analysis further demonstrated that soil properties, plant nutrient contents, and their interactions explained 19.1 %, 11.8%, and 59.4% of the variation in the plant community, respectively. Therefore, the wetland vegetation dynamics are combinedly controlled by soil properties (especially soil water conditions) and plant nutrient acquisition strategies (especially plant nitrogen acquisition) under different land management practices. This study provides the theoretical basis for maintaining the stability of wetland ecosystems by designing plant resources-related managements in semi-arid regions.

Monitoring spatial and temporal dynamics of wetland vegetation and their response to hydrological conditions in a large seasonal lake with time series Landsat data

Periodic hydrological processes of seasonal lakes are the dominant factors leading to the development of vegetation communities and ecological processes. Dongting Lake is a typical seasonal lake in the middle and lower reaches of the Yangtze River and its hydrological conditions have changed significantly due to the construction of the Three Gorges Dam (TGD). However, there are knowledge gaps in the responses of wetland vegetation dynamics to the changes of hydrological conditions, especially in cloudy and rainy regions, where continuous large-scale monitoring is still challenging. In this study, by using time series of Landsat data on Google Earth Engine, a long-term cloudless remote sensing images dataset of Dongting Lake during the dry season was constructed. The multi-year wetland vegetation from 2003 to 2020 was mapped using the random forest model. Relationships between wetland vegetation dynamics and hydrological conditions (e.g., water level and inundation character) were examined using correlation and linear analysis. Results revealed that wetland vegetation in the Dongting Lake experienced significant inter-annual spatial heterogeneity and temporal dynamic equilibrium with a slight increase during the post-TGD period. Only Carex communities at elevations above 28 m and below 26 m displayed apparent changes. Reed communities have relatively high selectivity to inundation frequency, and are affected mainly by changes in water levels during the dry season of the current year. Hydrological conditions during the rising period have an important impact on the first growth and reproduction stage of Carex, while higher water levels or more rapid surface submergence lead to a decrease in seed density in the soil of low-elevation floodplains. This study deepens our knowledge of changes of wetland vegetation and their response to hydrological conditions, and is of great significance to the ecological protection and restoration of Dongting Lake.

Deltaic floodplain wetland vegetation dynamics along the sediment surface elevation gradient and in response to disturbance from river flooding and hurricanes in Wax Lake Delta, Louisiana, USA

Herbaceous wetland vegetation species percent cover data collected over five growing seasons (2007–2011) was used to define unique species assemblages along the elevation gradient of deltaic islands in the actively prograding deltaic floodplain wetlands in the Wax Lake Delta, a major distributary of the Mississippi River. The passage of Hurricanes Gustav and Ike in September 2008 as well as a major river flood in spring of 2011 provided an opportunity to quantify the response and recovery of the vegetation community following disturbances of varying intensities. Two significant persistent species assemblages were observed from 2007 through 2011. The higher elevation species assemblage occurred above mean low water (MLW; –0.04 m NAVD88). While the lower elevation species assemblage occurred at elevations ranging from –0.47 to 0.30 m NAVD88. These unique lower and higher elevation species assemblages overlap at intertidal elevations. Hurricanes Gustav and Ike drastically reduced aboveground vegetation and percent cover immediately following the storms particularly for lower elevation species. No aboveground cover was observed for Sagittaria latifolia, Nelumbo lutea, Potamogeton nodosus, or Submerged Aquatic Vegetation (SAV) in any of the sampling stations following the hurricanes, compared to pre-hurricane aboveground cover mean ranging from 2 to 5%. Sagittaria platyphylla aboveground cover decreased from a pre-hurricane mean of 12.5% to <1% following the hurricanes. In subsequent years the community composition for all species returned to pre-disturbance cover, with the significant species assemblages returning within two years. In 2011 the major river flood resulted in disturbance that reduced species richness within both assemblages, likely related to differences in flood tolerance of vegetation species, with Nelumbo lutea cover expanding from a mean of 10% cover in the year prior to the flood to 22.5% following the flood. Vegetation community composition was shown to be robust to major river floods and hurricane storm surge passage.

Non-monotonic vegetation activity trends in the Lower Delta of the Paraná River: Masking evidence of wetland degradation?

To understand the consequences of unsustainable management practices and global change, analyzing the patterns of ecosystem functioning and land degradation is as important as quantifying the spatio-temporal patterns of land cover loss. This is particularly important for wetlands where loss and degradation are globally intensifying. In the Lower Delta of the Paraná River, Argentina, land use change has occurred in the context of cattle raising intensification, which involves water management infrastructure. However, when those changes specifically occurred and whether they permanently influenced the functional component of wetland ecosystems remain unanswered. We used a long-term (2001–2015) fused satellite-derived Normalized Difference Vegetation Index dataset to identify major shifts in vegetation activity trends using the Breaks for Additive Seasons and Trend algorithm. We assembled a set of hydro-climatic, environmental, and anthropogenic variables to study their association with the spatio-temporal patterns of vegetation activity trends. Our results show that browning-to-greening trends dominated throughout the study area. Concomitantly, the magnitude of breakpoints was mainly negative, which points towards rapid land degradation and biomass submersion or removal events. Breakpoints primarily occurred between 2007 and 2009 and were partially coincident with an extraordinary flood event and intentional fire outbreaks. Paranacito river flooding, precipitation, the synchronicity with temperature patterns, water management infrastructure and the occurrence of local land cover conversions were determining factors in the differentiation and characteristics of vegetation activity trends, shifts and breakpoints. Our results provide evidence that even though regional hydro-climatic patterns remain as main drivers of wetland vegetation dynamics, human influence and its negative effects increase in the context of adverse hydro-climatic scenarios. In this matter, we observed that the decouplement from the flood pulse promoted a post-disturbance recolonization of herbaceous vegetation. Consistently, the widespread browning-to-greening trend reversal does not necessarily relate to wetland vegetation recovery but instead, might have masked its extensive conversion to grasslands.

A U.S.‐China EcoPartnership study of disturbed wetland vegetation in West Dongting Lake, China

AbstractWest Dongting Lake in China is important for human livelihoods and habitat of migratory waterfowl and other wildlife. The waterway re‐engineering and agriculture intensification have contributed to changes in hydrology, sediment, and vegetation on the floodplain. This paper describes an EcoPartnership program conducted by the U.S. Geological Survey, Wetland and Aquatic Research Center, and Beijing Forestry University. It focused on the development of a wetland ecosystem network in West Dongting Lake with technical support from the U.S. partner using a number of related studies to examine wetland vegetation dynamics from upstream to downstream along the tributaries. The results of U.S. studies showed that the regeneration potential of species might be altered by changes in climate and local environment, and seed bank depletion by germination may be a major conservation threat in a future with recurring droughts in swamps of the southeastern United States. In the monsoonal wetlands of West Dongting Lake, the soil seed bank could be used as a seed source for revegetation after hydrologic restoration with the introduction of certain foundational species and the removal of poplar plantations. Also, West Dongting Lake is at high ecological risk of mercury pollution. Wetland ecosystem monitoring may allow managers to use the information to predict effects of climate change, water level and flow changes on sedimentation, and to manage for desired vegetation to support waterfowl and ecosystem services. The cooperation of two countries through the EcoPartnership program is now well established and poised for extensive research projects in the future.

Spatial heterogeneity of vegetation extent and the response to water level fluctuations and micro-topography in Poyang Lake, China

Wetland vegetation dynamics are vital but difficult to understand due to complex impact factors and their spatial heterogeneities. Poyang Lake, the largest freshwater lake in China, is well-known for its ecological importance as a floodplain wetland. However, heterogeneity in vegetation extent and its response to water regimes across different geomorphic units of Poyang Lake remain unclear to date. To address this gap, Landsat images acquired during dry seasons from 1987 to 2018 were selected to explore vegetation extent and its response to water level fluctuations across multiple elevation bands and four wetland types, namely Riparian Wetland (RW), Delta Wetland (DW), Dish-shaped Wetland (DSW), and Fan-shaped wetland (FSW). Results show that vegetation extent in lower elevation bands of the four wetland types increased remarkably with an average increase rate of 0.53 km2/year between 2003 and 2018 compared to −0.17 km2/year−1 during 1987 to 2002. Hydrological variables indicating high-flow events negatively affected vegetation extent in DSW while variables indicating low-flow events appear to be positive for vegetation extent in RW, DW, and FSW. Over-long floods as happened in 2016 has caused fatal damage to vegetation extent in DSW. In addition, extreme droughts in recent years caused by the Three Gorges Dam promoted significant (p < 0.05) vegetation expansion in lower elevation bands of RW, DW, and FSW, but a deterioration of vegetation extent in higher elevation bands, making Poyang Lake at risk of shrinkage and degradation. Human impacts on the evolution Poyang Lake system have caused wide concern, which also contribute to the proposal of Poyang Lake water control structure. Heterogeneity in vegetation extent and their response to water regimes across Poyang Lake provide precise spatial information for restoration efforts of the wetland ecosystem.

Disentangling the effects of hydro-climatic factors and land use intensification on wetland vegetation dynamics in the Lower Delta of the Paraná River

The non-insular portion of the Lower Delta of the Paraná River is part of the largest mosaic of wetlands in Argentina. However, it is being altered by intensification of cattle grazing and the increasingly rapid implementation of water management infrastructure. In this context, studying the relationship between hydro-climatic variables and vegetation growth is urgent to ensure sound management and conservation. To overcome the limitation of high cloud cover in the area which has hampered the construction of regularly spaced high-resolution time series, we implemented the recently developed spatio-temporal vegetation index image fusion model (STVIFM). In order to understand the relationship between vegetation growth and hydro-climatic factors, we performed pixel-wise correlation analyses between the newly synthesized monthly (30m) NDVI time series and hydro-climatic variables. Then, we tested whether water control infrastructure alters these relationships. Based on the accurate performance of STVIFM, we provide quantitative and spatially accurate evidence on the positive, complementary and heterogeneous relationships between vegetation growth, temperature, rainfall and the flood pulse. Our results show that water management infrastructure decouples certain areas from its natural hydrological regime, decreasing water availability and altering vegetation growth dynamics. In this context, urgent action is needed aimed towards implementing land planning measures that consider the natural variability and hydrologic regime of the system while balancing production and conservation.

Wetland vegetation response to record-high Lake Ontario water levels

Lake Ontario water levels were the highest in recorded history in 2017 and 2019, resulting in significant impacts to shoreline properties and observable (but not previously quantified) changes in coastal wetland vegetation. In this study, we assessed differences in coverage of five plant community guilds (submerged aquatic vegetation, Typha, meadow marsh, shrub, and upland) along the shoreline elevation gradient from 12 Lake Ontario coastal wetlands surveyed from 2009 to 2019. This time period included a span of relatively stable water levels (2009–2016), followed by the two high-water years. In general, we found that extreme high water levels led to a decrease in vegetation coverage, most notably at the lower extent of the elevation ranges for the meadow marsh, shrub, and upland vegetation guilds. We also found a modest increase in Typha coverage at the upper extent of its elevation range in 2019, indicating that Typha advanced into the meadow marsh zone during the study period. These findings can be used to calibrate and validate predictive models that inform adaptive management of the new outflow regulation plan for Lake Ontario and can aid in modelling the dynamics of wetland vegetation in relation to predicted changes in Great Lakes water levels due to climate change.

Patch organization and resilience of dryland wetlands

Dryland wetlands are ecosystems of high ecological importance as they serve as habitat sanctuaries for aquatic and terrestrial biota in areas with very few resources; therefore, the study of such environments is of major importance for the conservation of biodiversity in arid and semi-arid areas. The vegetation organization in these ecosystems is driven by the water regime as the main driver, but local processes like seed banks and soil resources redistribution also play a crucial role in determining the spatial distribution of the vegetation. Assessment of vegetation dynamics and long-term resilience requires the use of realistic models that can integrate the water regime and that can continuously simulate vegetation extent and conditions under flood-drought cycles. Here we study the influence of the water regime as the main driver of the vegetation. We apply a vegetation-modelling framework to compare the performance of a simplified model at the cell scale and a model integrated at a patch scale. Our results show that aggregating the analysis of vegetation dynamics at the patch scale allows for the incorporation of the effects of both local drivers (acting within the patch) as well as the global drivers (acting over the patch as a whole). The water regime acts as a global driver for the vegetation and indirectly affects the local drivers. Our patch scale model successfully captures wetland vegetation dynamics using the water regime as the main driver for representing changes in the vegetation and assessment of the wetland resilience under flood-drought periods.

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.

Non-linear dynamics of wetland vegetation induced by groundwater table

Non-linear dynamics of wetland vegetation induced by groundwater table

Dynamics of the wetland vegetation in large lakes of the Yangtze Plain in response to both fertilizer consumption and climatic changes

Using moderate-resolution imaging spectroradiometer (MODIS) data that cover the 15-year period from 2000 to 2014 and a phenology-based classification method, the long-term changes in the wetland vegetation of 25 large lakes on the Yangtze Plain were obtained. The classification method was developed based on the phenological information extracted from time series of MODIS observations, which demonstrated mean user’s/producer’s accuracies of 76.17% and 84.58%, respectively. The first comprehensive record of the spatial distribution and temporal dynamics of wetland vegetation in the large lakes on the Yangtze Plain was created. Of the 25 lakes examined, 17 showed a decreasing trend of vegetation area percentages (VAPs) during the study period, and 7 were statistically significant (p < 0.05). The same number of lakes was found to display decreasing trends in vegetation greenness over this 15-year period, and these decreasing trends were statistically significant (p < 0.05) for 11 of the lakes. Substantially fewer lakes showed increases in either their VAPs or their vegetation greenness values. Analysis using a multiple general linear model revealed that the amounts of chemical fertilizer used for farmlands surrounding the lakes, precipitation, daily sunshine hours, temperature and water turbidity played the most important roles in regulating the interannual changes in vegetation greenness in 40% (10/25), 12% (3/25), 4% (1/25), 20% (5/25) and 12% (3/25) of the lake wetlands, respectively. On average, the combined effects of these five driving factors above explained 89.08 ± 7.89% of the variation in greenness over this 15-year period for the 25 lakes. This wetland vegetation environmental data record (EDR) of large lakes in Yangtze Plain demonstration will provide a crucial baseline information for the wetland environment conservation and restoration.

Effects of flooding regime on wetland plant growth and species dominance in a mesocosm experiment

Flooding regimes are a primary influence on the wetland plant community. Human-induced disturbance often changes the duration and frequency of flooding in wetlands, and has a marked influence on wetland plant composition and viability. Comprehensive studies of the environmental thresholds of wetland plants are required for the development of proper practices for wetland management and restoration after hydrological disturbance. This study provides a quantitative assessment of the establishment, growth, and community shifts in dominance of three emergent plant species (Scirpus tabernaemontani, Typha orientalis, and Zizania latifolia) typical of South Korean wetlands, under five hydrological regimes (waterlogged, low-level standing water, high-level standing water, intensive periodic flooding, and intermittent flooding) over four growing seasons. A mesocosm experiment was conducted in the campus of Seoul National University, South Korea. The number and biomass of shoots of Z. latifolia responded positively to increased water level and flooding frequency, while that of the other plants did not. Zizania latifolia outcompeted S. tabernaemontani and T. orientalis irrespective of hydrological regime. This study suggests that Z. latifolia can outcompete the other two macrophytes in the field. This study will improve our ability to predict the dynamics of wetland vegetation and so facilitate the formulation of wetland management and restoration strategies.

Spatial–Temporal Dynamics of Wetland Vegetation Related to Water Level Fluctuations in Poyang Lake, China

Hydrological properties are driving forces of wetland systems. The influence of water level fluctuations on vegetation distribution is of growing interest as wetlands are increasingly disturbed by climate change and intensive human activity. Based on time series MODIS (Moderate Resolution Imaging Spectroradiometer) imagery from 2000 to 2012, we investigated the spatial–temporal dynamics of wetland vegetation in Poyang Lake using a combined Sen’s slope and Mann–Kendall (MK) test approach, and explored their correlations with water level fluctuations in different hydrological periods. The results showed that more than 34% of wetlands at lower elevations of Poyang Lake had experienced an increasing trend in the enhanced vegetation index (EVI), whereas EVI in about 11% of the wetlands at higher elevations decreased significantly. Responses of grassland area extracted from MODIS EVI were found to be more sensitive to water level fluctuations in the southern lakes. The change rate of grassland area decreased with the rising water level during the rising period, but increased with the rising water level during the retreating period. Correlations between grassland area and water level were much weaker in the dry period. In addition, we found fluctuations of the main water body had negligible effect on grassland area since the water level at Xingzi station was below 14 m. These results provide new insights for predicting future changes of wetland vegetation influenced by the ongoing threats from climate change and human activity, and form a foundation for ecosystem management of Poyang Lake.

Multivariate analysis of modern and fossil pollen data from the central Tianshan Mountains, Xinjiang, NW China

To interpret past vegetation and climate changes from pollen data, we need to reveal the degree of similarity between modern analogues and fossil pollen spectra, which would help us predict the future climate and vegetation. Ninety surface pollen samples across six vegetation zones along an altitudinal gradient from 460 to 3510 m and 44 fossil samples at Caotan Lake were collected in the central Tianshan Mountains, northern Xinjiang, China. Discriminant analyses results, fossil pollen and phytolith assemblages were then used to reconstruct palaeovegetation and palaeoclimate in the area. The 90 surface samples were divided into six pollen zones (alpine cushion, alpine and subalpine meadow, montane Tianshan spruce forest, forest-steppe ecotone, Artemisia desert, typical desert), corresponding to the major vegetation types in the area. These zones follow a climatic gradient of increasing precipitation with increasing elevation. Paleovegetation reconstructed from 44 fossil pollen assemblages through discriminant analysis reflects the regional vegetation shifted from typical desert to Artemisia desert since 4640 cal. year BP in the Caotan Lake wetland. The fossil pollen and phytolith record also reveal the arid climate has not fundamentally changed in the period. But a dry-wet-dry local climate oscillation since 2700 cal. year BP has a fundamental influence on local wetland vegetation dynamics and peat accumulation of the Caotan wetland. Modern wetland landscape and surface pollen assemblages from the Ebinur Lake Wetland Nature Reserve provide further evidence for ferns and Betula growing in the Caotan Lake wetland during the historical period.

Analysis of the relationship between inundation frequency and wetland vegetation in Dongting Lake using remote sensing data

ABSTRACTHydrological characteristics significantly drive the formation of and variations in wetland vegetation. Given increasing impact from human activities and climate change, the hydrological regime has become exceedingly unstable, thereby heavily affecting the distribution and dynamics of wetland vegetation. The relationship between inundation frequency – an important hydrological factor – and vegetation community distribution in Dongting Lake was analysed to depict how the hydrological regime determines the distribution of wetland vegetation cover. Wide tempo‐spatial scales were used to calculate the inundation frequency in the lake and to compare the distribution patterns of the communities. For the implementation of the aforementioned tasks, this study provides remote sensing‐ and geographical information system‐based methods. The responses of individual vegetation communities to inundation frequency differ depending on their specific physiological characteristics. Wood and reed communities are more suitable for regions with low inundation frequency, whereas grass and lake‐grass communities are more adaptable to areas of high inundation frequency. The variations in inundation frequency may explain the succession of vegetation communities, which occurs when inundation frequency decreases with increasing wood and reed communities. These results can serve as support for evaluating the impact of hydrological changes on the community structures and distributions of wetland vegetation. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Monitoring temporal dynamics of Great Artesian Basin wetland vegetation, Australia, using MODIS NDVI

The Great Artesian Basin springs (Australia) are unique groundwater dependent wetland ecosystems of great significance, but are endangered by anthropogenic water extraction from the underlying aquifers. Relationships have been established between the wetland area associated with individual springs and their discharge, providing a potential means of monitoring groundwater flow using measurements of vegetated wetland area. Previous attempts to use this relationship to monitor GAB springs have used aerial photography or high resolution satellite images and gave sporadic temporal information. These “snapshot” studies need to be placed within a longer and more regular context to better assess changes in response to aquifer draw-downs. In this study we test the potential of 8 years of Moderate Resolution Imaging Spectroradiometer Normalised Difference Vegetation Index data as a long-term tracer of the temporal dynamics of wetland vegetation at the Dalhousie Springs Complex of the Great Artesian Basin. NDVI time series were extracted from MODIS images and phenologies of the main wetland vegetation species defined. Photosynthetic activity within wetlands could be discriminated from surrounding land responses in this medium resolution imagery. The study showed good correlation between wetland vegetated area and groundwater flow over the 2002–2010 period, but also the important influence of natural species phenologies, rainfall, and anthropogenic activity on the observed seasonal and inter-annual vegetation dynamics. Declining trends in the extent (km2) of vegetated wetland areas were observed between 2002 and 2009 followed by a return of wetland vegetation since 2010. This study underlines the need to continue long-term medium resolution satellite studies of the GAB to fully understand variability and trends in the spring-fed wetlands. The MODIS record allows a good understanding of variability within the wetlands, and gives a high temporal-frequency context for less frequent higher spatial resolution studies, therefore providing a strong baseline for assessment of future changes.

Wetland vegetation dynamics in response to beaver (Castor canadensis) activity at multiple scales

Beaver activity is often considered a hydrologic disturbance that “resets” succession. We determined how beaver impoundment and wetland size and water chemistry affected the vegetation and succession of 25 beaver meadows and ponds using the space-for-time substitution. We used aerial photography to investigate whether a large 1947 fire in one region of Mount Desert Island, Maine, led to differences in regional temporal fluctuations in beaver pond occupancy over 60 y and determined whether these fluctuations led to different regional distributions of beaver wetland plant community types. Cluster analysis segregated 4 wetland groups: sedge meadows, sedge fens, shrub fens, and forested fens, which segregated along gradients of time since dam collapse, water chemistry, and wetland size. Beaver did not affect water chemistry or wetland size. Pond vegetation was a function of community type prior to flooding, water chemistry, and geomorphic setting. The successional model consisted of 2 separate cycles, corresponding to differences in pH and peat accumulations. Beaver pond creation rates differed in burned and unburned regions over time. Due to increased activity in the burned region, there was a different distribution of plant communities between the regions. Wetlands abandoned at the peak of beaver pond creation in 1979 were flooded for shorter durations, resulting in forested fen vegetation. Beaver activity created different successional cycles within different water chemistry and geomorphic contexts. Water chemistry, wetland size, and initial wetland state, which primarily determined non-forested wetland type, were not influenced by beaver.