Herbaceous Wetland Research Articles

Improved Automated Detection of Subpixel-Scale Inundation—Revised Dynamic Surface Water Extent (DSWE) Partial Surface Water Tests

In order to produce useful hydrologic and aquatic habitat data from the Landsat system, the U.S. Geological Survey has developed the “Dynamic Surface Water Extent” (DSWE) Landsat Science Product. DSWE will provide long-term, high-temporal resolution data on variations in inundation extent. The model used to generate DSWE is composed of five decision-rule based tests that do not require scene-based training. To allow its general application, required inputs are limited to the Landsat at-surface reflectance product and a digital elevation model. Unlike other Landsat-based water products, DSWE includes pixels that are only partially covered by water to increase inundation dynamics information content. Previously published DSWE model development included one wetland-focused test developed through visual inspection of field-collected Everglades spectra. A comparison of that test’s output against Everglades Depth Estimation Network (EDEN) in situ data confirmed the expectation that omission errors were a prime source of inaccuracy in vegetated environments. Further evaluation exposed a tendency toward commission error in coniferous forests. Improvements to the subpixel level “partial surface water” (PSW) component of DSWE was the focus of this research. Spectral mixture models were created from a variety of laboratory and image-derived endmembers. Based on the mixture modeling, a more “aggressive” PSW rule improved accuracy in herbaceous wetlands and reduced errors of commission elsewhere, while a second “conservative” test provides an alternative when commission errors must be minimized. Replication of the EDEN-based experiments using the revised PSW tests yielded a statistically significant increase in mean overall agreement (4%, p = 0.01, n = 50) and a statistically significant decrease (11%, p = 0.009, n = 50) in mean errors of omission. Because the developed spectral mixture models included image-derived vegetation endmembers and laboratory spectra for soil groups found across the US, simulations suggest where the revised DSWE PSW tests perform as they do in the Everglades and where they may prove problematic. Visual comparison of DSWE outputs with an unusual variety of coincidently collected images for locations spread throughout the US support conclusions drawn from Everglades quantitative analyses and highlight DSWE PSW component strengths and weaknesses.

Grassland Dynamics and the Driving Factors Based on Net Primary Productivity in Qinghai Province, China

Qinghai province is an important part of the Tibetan Plateau, and is characterized by extremely fragile ecosystems. In the last few decades, grasslands in this province have been influenced profoundly by climate change, as well as human activities. Here, we use the Carnegie-Ames-Stanford Approach (CASA) model to assess the dynamics of temperate steppe, alpine steppe, temperate meadow, alpine meadow, sparse grassland and herbaceous wetland via actual net primary productivity (NPPa). Our findings showed that: (1) From 2001 to 2016, the average NPPa in Qinghai province showed a fluctuation presented a generally increasing trend. The mean value of NPPa was 114.27 g C m−2 year−1, and the increase rate was 0.47 g C cm−2 year−1. (2) There were NPPa increase rate discrepancies among the six typical grassland biomes. Herbaceous wetland had the highest change rate, closely followed by alpine steppe, temperate steppe, alpine meadow, temperate meadow and sparse grassland. (3) The largest area of restoration mainly impacted by climate change reached 47.08% of the total grassland area, with human activities accounting for 21.74%. By contrast, the deteriorated area induced by human activities accounted for 9.78% of the total grassland. (4) Temperature may have been a greater factor than precipitation in driving grassland change during the study period. Decreasing grazing intensity and implementing effective protection measures were favorable to grassland restoration.

Wet Agriculture in the Lowlands: Maize Marceña

Core Ideas The milpa marceña is an ancient maize agrosystem on herbaceous wetlands “popals” in the dry season. Three improved maize cultivars and the traditional cultivar mején were evaluated. The mején cultivar showed the highest performance. The milpa marceña is compatible with the hydrological dynamics of wetlands and without the use of industrial inputs. Although herbaceous wetlands are one of the most productive ecosystems and their functions provide benefits to humankind, they have been subjected to a number of disturbances over the past 65 yr. Wetlands have been drained to convert them into permanent agricultural land and urban areas, or used by the oil industry or for construction of hydroelectric dams. Moreover, little has been done to innovate the milpa marceña, an ancient maize (Zea mays L.) agrosystem on herbaceous wetlands dominated by hojilla (Thalia geniculata f. rheumoides) named popals in the dry season (March–June). From an agroecological perspective for improving milpa marceña, in a popal soil (Eutric Molic Gleysol), three improved maize cultivars (CP‐560, CP‐561, and CP‐562) and the traditional cultivar mején were evaluated under three planting densities (50,000, 53,000, and 60,000 plants ha–1) with no use of mineral fertilizers, herbicides, or pesticides. The results show that precipitation during the milpa marceña growth cycle was 50% lower than the amount required for a successful maize crop (>1 Mg ha–1), hence avoiding the risk of flooding. Maize cultivars take groundwater and nutrients from popal soil; however, these results suggest that cultivars were subject to N deficiency and water stress in the flowering stage. We concluded that the mején cultivar showed the highest performance, with 3.3 Mg ha–1, i.e., it has attributes not previously considered (e.g., plant × microbe interactions) in plant breeding programs for drought‐tolerant or flood‐tolerant cultivars. There is a need for further research and conservation on the use of popals.

Coastal wetland resilience to climate variability: A hydrologic perspective

Climate-induced disturbances are expected to increase in frequency and intensity and affect wetland ecology by altering its hydrology. Investigating how wetland hydrology responds to climate disturbances is an important first step to understand the ecological response of coastal wetlands to these disturbances. Wetland hydrologic resilience, the ability of wetland in absorbing disturbances and restoring to pre-disturbance conditions in hydrological function, is a critical measure of wetland hydrological response to climate disturbances. However, a practical methodology for quantifying wetland hydrologic resilience (HR) is still lacking. This study aimed to improve the approach for quantifying the hydrologic resilience of wetland ecosystems to climate variability and climate change. A set of quantitative metrics was developed including the variations of groundwater table, overland flow, and saltwater table. This approach was then applied to a coastal landscape that includes coastal-forested and herbaceous wetlands in North Carolina, USA. We investigated the threshold behaviors of groundwater table, overland flow, and saltwater table for a 20-year period (1995–2014) by applying a regional scale wetland hydrological model, Penn State Integrated Hydrological Model for wetland hydrology (PIHM-Wetland). We found that the multiscale variations of groundwater table under dry climatic conditions is a good indicator of wetland HR to drought. The variation of overland flow during rainfall events effectively quantified HR to wet periods. We also found that the variation of the water level of saltwater is an important metric of wetland HR to sea level rise. This study improves the methodology of quantifying wetland hydrologic resilience at a regional scale, representing an important first step towards understanding the wetland hydrological and ecological resilience to future intensified climate disturbances in coastal regions and beyond.

Response of herbaceous wetland plant species to changing precipitation regimes

AbstractThe structure of wetland plant communities is sensitive to patterns of precipitation. In some regions, climate change is expected to result in more large‐magnitude, infrequent precipitation events. Typically, the response of wetland plants to changing precipitation regimes is studied under alterations in the amount of precipitation (drought), rather than event frequency. Here, we seek to understand how changes in rainfall frequency affect (a) soil moisture variability, (b) plant performance, and (c) plant C and N concentrations. We conducted a greenhouse study using eight herbaceous plant species (three eudicots, five monocots) subject to three precipitation treatments: (a) 80 mm per month distributed in equal volumes every 3 days (control treatment), (b) 80 mm per month distributed every 15 days (infrequent treatment), and (c) 110 mm per month distributed every 15 days (large magnitude‐infrequent treatment). Infrequent treatments decreased soil moisture by >60% compared with the control. Rainfall frequency affected soil moisture losses to evapotranspiration, which differed between early‐ and late‐growing seasons. This soil moisture stress in the infrequent treatments contributed to a 10–49% decrease in biomass among all eudicot species and a 25–54% decrease in two monocots. In contrast, changes in C and N concentration were limited to two forb species. Our results show that changes in precipitation frequency can strongly impact some wetland species. For some impacted species increased magnitude can alleviate the negative effects of infrequent rainfall. These results provide insight into how forecasted changes in the frequency and magnitude of precipitation may affect wetland plant species.

Understanding coastal wetland hydrology with a new regional‐scale, process‐based hydrological model

AbstractCoastal wetlands represent an ecotone between ocean and terrestrial ecosystems, providing important services, including flood mitigation, fresh water supply, erosion control, carbon sequestration, and wildlife habitat. The environmental setting of a wetland and the hydrological connectivity between a wetland and adjacent terrestrial and aquatic systems together determine wetland hydrology. Yet little is known about regional‐scale hydrological interactions among uplands, coastal wetlands, and coastal processes, such as tides, sea level rise, and saltwater intrusion, which together control the dynamics of wetland hydrology. This study presents a new regional‐scale, physically based, distributed wetland hydrological model, PIHM‐Wetland, which integrates the surface and subsurface hydrology with coastal processes and accounts for the influence of wetland inundation on energy budgets and evapotranspiration (ET). The model was validated using in situ hydro‐meteorological measurements and Moderate Resolution Imaging Spectroradiometer (MODIS) ET data for a forested and herbaceous wetland in North Carolina, USA, which confirmed that the model accurately represents the major wetland hydrological behaviours. Modelling results indicate that topographic gradient is a primary control of groundwater flow direction in adjacent uplands. However, seasonal climate patterns become the dominant control of groundwater flow at lower coastal plain and land–ocean interface. We found that coastal processes largely influence groundwater table (GWT) dynamics in the coastal zone, 300 to 800 m from the coastline in our study area. Among all the coastal processes, tides are the dominant control on GWT variation. Because of inundation, forested and herbaceous wetlands absorb an additional 6% and 10%, respectively, of shortwave radiation annually, resulting in a significant increase in ET. Inundation alters ET partitioning through canopy evaporation, transpiration, and soil evaporation, the effect of which is stronger in cool seasons than in warm seasons. The PIHM‐Wetland model provides a new tool that improves the understanding of wetland hydrological processes on a regional scale. Insights from this modelling study provide benchmarks for future research on the effects of sea level rise and climate change on coastal wetland functions and services.

Performance of rapid floristic quality assessment indices for increasing cost-effectiveness of wetland condition evaluation

This project tested whether rapid floristic quality indices can be used in North Carolina’s diverse wetland types, given the many cost-saving benefits that can be realized from using such indices. Vegetation plot data from 2030 North Carolina wetland plots were analyzed to test how well two floristic quality assessment indices, based on cover-dominant species and based on non-graminoid species, were correlated with full index values based on a comprehensive species list.Dominance based indices (Mean C and FQI) significantly correlated with Mean C and FQI using all species, but Mean C was more strongly correlated than FQI. Mean C of cover-dominant species correlated with the Ohio Rapid Assessment Method, but could only distinguish the lowest and highest North Carolina Wetland Assessment Method ratings. Removal of graminoids as a group, which are difficult to identify, did not appear to affect Mean C, even in herbaceous wetlands, though some wetlands were comprised of only graminoids; a dominance based index would still be useful in graminoid marshes. The availability of this cost-saving assessment tool will benefit researchers and practitioners looking for more expedient ways of assessing wetland quality or validating rapid assessments with direct measurements.

Stoichiometry patterns of plant organ N and P in coastal herbaceous wetlands along the East China Sea: implications for biogeochemical niche

Nitrogen (N) and phosphorus (P) are essential nutrients for plant growth, and their availability and stoichiometry play pivotal roles in trophic dynamics and community composition. The biogeochemical niche (BN) hypothesis claims that each species should have an optimal elemental composition and stoichiometry as a consequence of its optimal function in its specific ecological niche. Little attention, however, has been given to N and P stoichiometric patterns and test the BN hypothesis in coastal wetland communities from the perspective of organ and species-specific comparisons. We investigated factors responsible for changes in N and P stoichiometry patterns in different functional groups in coastal wetlands and tested the BN hypothesis by evaluating N and P composition in whole aboveground plants and organs. Both plant N and P concentrations were high in coastal wetlands, indicating that N and P were not likely limiting, although the N:P ratio was slightly lower than the ratio reported in global and Chinese terrestrial flora. N and P concentrations and N:P ratios varied strongly between C3 and C4 species, among species, and among organs within species. N and P concentrations were not correlated with latitude, mean annual temperature and precipitation, although N:P ratio was weakly correlated with these factors. The differences in N and P concentrations and N:P ratios along the wetland gradients were mainly because of the species-specific community composition of each site. The results are consistent with the BN hypothesis. First, N and P composition is species-specific (homeostatic component of BN), each species tends to maintain its own composition even growing in different sites with different species composition. Second, different species, despite maintaining their own composition, have distinct degree of composition phenotypic flexibility (flexibility component of BN); this different size of “biogeochemical space” was observed when comparing different species living in the same community and the shifts in species BN space and size was observed when comparing populations of the same species living in different sites.

Forested versus herbaceous wetlands: Can management mitigate ecohydrologic regime shifts from invasive emerald ash borer?

Wetlands self-organize through reciprocal controls between vegetation and hydrology, but external disturbance may disrupt these feedbacks with consequent changes to ecosystem state. Imminent and widespread emerald ash borer (EAB) infestation throughout North American forested wetlands has raised concern over possible ecosystem state shifts (i.e., wetter, more herbaceous systems) and loss of forest function, calling for informed landscape-scale management strategies. In response, we employed a large-scale manipulative study to assess the ecohydrologic response of black ash wetlands to three alternative EAB management strategies: 1) a do-nothing approach (i.e., simulated EAB infestation via tree girdling), 2) a preemptive, complete harvesting approach (i.e., clearcut), and 3) an overstory replacement approach via group selection. We analyzed six years of daily water table and evapotranspiration (ET) dynamics in six blocks comprising black ash wetlands (controls) and management strategy treatments to quantify potential for hydrologic change and subsequent recovery. In both the do-nothing approach and complete harvesting approach, we found persistent changes in hydrologic regime defined by shallower water tables and lower ET rates coupled with increased herbaceous vegetation growth, indicating ecosystem state shifts driven by vegetation-water table interactions. The do-nothing approach showed the least hydrologic recovery after five years, which we attribute to reduction in overstory transpiration as well as greater shade (via standing dead trees) that reduces open water evaporation and herbaceous layer transpiration compared to complete harvesting. We found no evidence of ecohydrologic disturbance in the overstory replacement approach, highlighting its potential as a management strategy to preserve forested wetland habitat if periodically executed over time before EAB infestation. Although the scale of potential disturbance is daunting, our findings provide a baseline assessment for forest managers to develop preemptive mitigation strategies to address the threat of EAB to ecological functions in black ash wetlands.

Multi-temporal, multi-frequency, and multi-polarization coherence and SAR backscatter analysis of wetlands

Despite recent research into the Interferometric Synthetic Aperture Radar (InSAR) technique for wetland mapping worldwide, its capability has not yet been thoroughly investigated for Canadian wetland ecosystems. Accordingly, this study statistically analysed interferometric coherence and SAR backscatter variation in a study area located on the Avalon Peninsula, Newfoundland and Labrador, Canada, consisting of various wetland classes, including bog, fen, marsh, swamp, and shallow-water. Specifically, multi-temporal L-band ALOS PALSAR-1, C-band RADARSAT-2, and X-band TerraSAR-X data were used to investigate the effect of SAR frequency and polarization, as well as temporal baselines on the coherence degree in the various wetland classes. SAR backscatter and coherence maps were also used as input features into an object-based Random Forest classification scheme to examine the contribution of these features to the overall classification accuracy. Our findings suggested that the temporal baseline was the most influential factor for coherence maintenance in herbaceous wetlands, especially for shorter wavelengths. In general, coherence was the highest in L-band and intermediate/low for both X- and C-band, depending on the wetland classes and temporal baseline. The Wilcoxon rank sum test at the 5% significance level found significant difference (P-value < 0.05) between the mean values of HH/HV coherence at the peak of growing season. The test also suggested that L-band intensity and X-band coherence observations were advantageous to discriminate complex wetland classes. Notably, an overall classification accuracy of 74.33% was attained for land cover classification by synergistic use of both SAR backscatter and interferometric coherence. Thus, the results of this study confirmed the potential of incorporating SAR and InSAR features for mapping Canadian wetlands and those elsewhere in the world with similar ecological characteristics.

Wetland Mapping Using SAR Data from the Sentinel-1A and TanDEM-X Missions: A Comparative Study in the Biebrza Floodplain (Poland)

This research is related to the eco-hydrological problems of the herbaceous wetland drying and biodiversity loss in the floodplain lakes of the Middle Basin of the Biebrza River (Poland). An experiment was set up, with its main goals as follows: (i) mapping the vegetation types and the temporarily or permanently flooded areas, and (ii) comparing the usefulness of the C-band Sentinel-1A (S1A) and X-band TerraSAR-X/TanDEM-X (TSX/TDX) for mapping purposes. The S1A imagery was acquired on a regular basis using the dual polarization VV/VH and the Interferometric Wide Swath Mode. The TSX/TDX data were acquired in quad-pol, a fully polarimetric mode, during the Science Phase. The paper addresses the following aspects: (i) wetland mapping with the S1A multi-temporal series; (ii) wetland mapping with the fully polarimetric TSX/TDX data; (iii) comparing the wetland mapping using dual polarization TSX/TDX subsets, that is, the HH-HV, HH-VV and VV-VH; (iv) comparing wetland mapping using the S1A and TSX/TDX data based on the same polarization (VV-VH); (v) studying the suitability of the Shannon Entropy for wetland mapping; and (vi) assessing the contribution of interferometric coherence for wetland classification. Though the experimental results show the main limitations of the S1A dataset, they also highlight the good accuracy that can be achieved using the TSX/TDX data, especially those taken in fully polarimetric mode. Some practical outcomes significant for the study area management using SAR were also described.

Habitat Characteristics and Management of Abandoned Rice Paddy Field Wetlands in Mountain - In Case of the Uldae Wetland in Bukhansan National Park -

The purpose of this study is to identify the ecological characteristics and biological interactions between species of the abandoned rice paddy field in mountainous areas and to suggest a management strategy for stable food chain formation and biodiversity enhancement. The study site is located in Uldae wetland of Songchu district Bukhansan National Park, site characteristics and biological habitat characteristics were identified through site survey and literature survey. With regard to physical environment, among geographical features, the Uldae Wetland and the neighborhood inside the basin was a gently sloping area(5∼15°). And 64.0% of basin faced the north. With regard to water environment, the Uldae Wetland was wetland of rainfed paddy field depending on precipitation and the system of stream flowing into the wetland from valley. According to the results of examining flora in plant ecology, in general, they were herbaceous wetland species. 88.6% of existing plants inside the Uldae Wetland basin was a forest in the mountain. And Quercus spp. community and Pinus densiflora community accounted for 64.6% of that, and was dominant. Except for that, Salix koreensis community was distributed. The existing vegetation of Uldae Wetland inhabited wetland species and terrestrialization indicator species, and it was thought that partial terrestrialization inside the Uldae Wetland was in progress after the discontinuation of paddy cultivation, such as the expansion of Salix koreensis distribution area. In the status of appearing faunae in the Uldae Wetland with regard to wildbirds of appearing principal species. The Uldae wetland was based on a abandoned rice paddy field various wildlife, and was a wildlife feeding, spawning, and resting place. The water environment was an important factor in maintaining the wetland living creatures function, habitat of waterbirds and benthic macroinvertebrates, amphibians and odonate are spawning ground and habitat, it was affecting the vegetation ecosystem based on wetlands. In order to maintain the diversity of wildlife, it was important to maintain smooth water supply and water level. A stable food chain will be formed and the Uldae wetland biodiversity will be abundant by establishing the relationship between the species of Uldae wetland, which is abandoned rice paddy field, and the habitat environment favored by species belonging to the ecosystem stepwise linkage. The ecological characteristics of the Uldae wetlands and the relation between the species were analyzed and the environmental conditions were reflected in the planning and management plan of Uldae wetland ecology.

Ecosystem-Based Management strategies to improve aquaculture in developing countries: Case study of Marismas Nacionales

The Ecosystem Based Management approach is an opportunity to maximize ecosystem services while promoting ecological resilience and appropriate productive activities. However, implementing this management strategy relies on acknowledging spatial interactions between economic activities and ecosystem services as well as an effective communication between scientists and decision-makers. The lack in understanding those interactions and management decisions based on limited information has led to an unsuccessful transition between artisanal and intensive aquaculture in a Wetland of International Importance (NW Mexican Pacific). In this study, we evaluated the effect of aquaculture as a driver of wetland degradation and water quality and analysed the perceptions of decision makers and scientists concerning the spatial scale of aquaculture impacts on ecosystem services.From 1997–2013, we found that herbaceous wetland and croplands have been lost while grasslands, urban areas, aquaculture and mangroves have increased. Shrimp ponds were built on natural water bodies, herbaceous wetlands and croplands. However, perturbed mangrove patches are found near aquaculture ponds, mostly downstream. Water samples were analysed and differences were found between upstream and downstream sampling sites in the concentration of DO, COD, TS, salinity, SO42-, Cl-1, CaCO3, Na, Cr, Ni and Al. Sediment analysis showed that the amount of coarse sediment such as sand and gravel diminished significantly upstream and does not reach the river mouth. Finally, perceived spatial relationship analyses showed that most academics surveyed recognized that aquaculture could have a far-reaching impact outside the immediate production area. On the other hand, more than half of the decision makers who responded did not perceive any impact and the majority of the rest considered that the impact occurred close to the ponds. The likelihood of integrated coastal management strategies being implemented depends on the close collaboration of scientists and decision makers, on their understanding of complex spatial interactions, on developing appropriate management alternatives and on incorporating science in spatial planning and decision making.

Random forest wetland classification using ALOS-2 L-band, RADARSAT-2 C-band, and TerraSAR-X imagery

Wetlands are important ecosystems around the world, although they are degraded due both to anthropogenic and natural process. Newfoundland is among the richest Canadian province in terms of different wetland classes. Herbaceous wetlands cover extensive areas of the Avalon Peninsula, which are the habitat of a number of animal and plant species. In this study, a novel hierarchical object-based Random Forest (RF) classification approach is proposed for discriminating between different wetland classes in a sub-region located in the north eastern portion of the Avalon Peninsula. Particularly, multi-polarization and multi-frequency SAR data, including X-band TerraSAR-X single polarized (HH), L-band ALOS-2 dual polarized (HH/HV), and C-band RADARSAT-2 fully polarized images, were applied in different classification levels. First, a SAR backscatter analysis of different land cover types was performed by training data and used in Level-I classification to separate water from non-water classes. This was followed by Level-II classification, wherein the water class was further divided into shallow- and deep-water classes, and the non-water class was partitioned into herbaceous and non-herbaceous classes. In Level-III classification, the herbaceous class was further divided into bog, fen, and marsh classes, while the non-herbaceous class was subsequently partitioned into urban, upland, and swamp classes. In Level-II and -III classifications, different polarimetric decomposition approaches, including Cloude-Pottier, Freeman-Durden, Yamaguchi decompositions, and Kennaugh matrix elements were extracted to aid the RF classifier. The overall accuracy and kappa coefficient were determined in each classification level for evaluating the classification results. The importance of input features was also determined using the variable importance obtained by RF. It was found that the Kennaugh matrix elements, Yamaguchi, and Freeman-Durden decompositions were the most important parameters for wetland classification in this study. Using this new hierarchical RF classification approach, an overall accuracy of up to 94% was obtained for classifying different land cover types in the study area.

Seasonal Change in Wetland Coherence as an Aid to Wetland Monitoring

Water is an essential natural resource, and information about surface water conditions can support a wide variety of applications, including urban planning, agronomy, hydrology, electrical power generation, disaster relief, ecology and preservation of natural areas. Synthetic Aperture Radar (SAR) is recognized as an important source of data for monitoring surface water, especially under inclement weather conditions, and is used operationally for flood mapping applications. The canopy penetration capability of the microwaves also allows for mapping of flooded vegetation as a result of enhanced backscatter from what is generally believed to be a double-bounce scattering mechanism between the water and emergent vegetation. Recent investigations have shown that, under certain conditions, the SAR response signal from flooded vegetation may remain coherent during repeat satellite over-passes, which can be exploited for interferometric SAR (InSAR) measurements to estimate changes in water levels and water topography. InSAR results also suggest that coherence change detection (CCD) might be applied to wetland monitoring applications. This study examines wetland vegetation characteristics that lead to coherence in RADARSAT-2 InSAR data of an area in eastern Canada with many small wetlands, and determines the annual variation in the coherence of these wetlands using multi-temporal radar data. The results for a three-year period demonstrate that most swamps and marshes maintain coherence throughout the ice-/snow-free time period for the 24-day repeat cycle of RADARSAT-2. However, open water areas without emergent aquatic vegetation generally do not have suitable coherence for CCD or InSAR water level estimation. We have found that wetlands with tree cover exhibit the highest coherence and the least variance; wetlands with herbaceous cover exhibit high coherence, but also high variability of coherence; and wetlands with shrub cover exhibit high coherence, but variability intermediate between treed and herbaceous wetlands. From this knowledge, we have developed a novel image product that combines information about the magnitude of coherence and its variability with radar brightness (backscatter intensity). This product clearly displays the multitude of small wetlands over a wide area. With an interpretation key we have also developed, it is possible to distinguish different wetland types and assess year-to-year changes. In the next few years, satellite SAR systems, such as the European Sentinel and the Canadian RADARSAT Constellation Mission (RCM), will provide rapid revisit capabilities and standard data collection modes, enhancing the operational application of SAR data for assessing wetland conditions and monitoring water levels using InSAR techniques.

Influence of Local, Landscape, and Regional Variables on Sedge and Marsh Wren Occurrence in Great Lakes Coastal Wetlands

We determined the influence of habitat, landscape, geographic, and climate variables on Sedge Wren (Cistothorus platensis) and Marsh Wren (C. palustris) occurrence in 840 coastal wetland survey points throughout the Great Lakes. Variables included surrounding land use and configuration out to 2000 m; latitude; longitude; temperature; precipitation; and vegetation characteristics within 100 m. Classification trees predicted Sedge Wren occurrence at points in the western Great Lakes with < 11 km of roads within 1000 m. Emergent herbaceous wetland within 500 m, woody wetland within various distances, and sedge within 100 m were also positively associated with Sedge Wren occurrence. Marsh Wren occurrence was predicted at points in the southern Great Lakes with < 42% developed land within 500 m. Emergent herbaceous wetland within 500 m, cropland within various distances, and cattail within 100 m were also positively associated with Marsh Wren occurrence. Our results suggest limiting development around wetlands is important for conserving these bird species throughout Great Lakes coastal wetlands. Landscape-scale land cover variables are easily obtainable and significantly increase our ability to predict occurrence of these species across a broad geographic scale.

Long-term landscape changes in vegetation structure: fire management in the wetlands of KwaMbonambi, South Africa

In wetlands the effects of fire on vegetation dynamics are somewhat uncertain. A change detection analysis in the herbaceous wetlands of KwaMbonambi, South Africa, which were subject to frequent fires, revealed that in 1937 the study area comprised grassland (69%), herbaceous wetland (25%), indigenous swamp forest (4%) and tree plantations (1%). However, by 1970, tree plantations occupied 78% of the landscape and grasslands and herbaceous wetlands had declined to 9% and 6%, respectively, whereas indigenous swamp forest had increased to 6%. By 2009 tree plantations had been removed from the wetland areas. Despite this opportunity for herbaceous wetlands to recover their historical extent, they decreased to only 2%, mostly changing to indigenous swamp forest or to an herbaceous/fern (Stenochlaena tenuifolia)/woodland mosaic. Fire records showed suppression of fire to be an important contributing factor, particularly in wetlands that had been disturbed by tree plantations, although subsequently removed. A pilot burning experiment revealed that S. tenuifolia did not inhibit fire. It is therefore practicable to increase fire frequency to prevent the mosaic developing into forest. A conceptual model of the influence of fire regime on wetland vegetation type is presented and priorities for further research on wetlands and fire are recommended.

WETLAND MAPPING WITH SAR/QUAD-POL DATA ACQUIRED DURING TANDEM-X SCIENCE PHASE

The aim of this study was to exploit fully polarimetric SAR data acquired during TanDEM-X – Science Phase (2014/2015) over herbaceous wetlands of the Biebrza National Park (BbNP) in North-Eastern Poland for mapping seasonally flooded grasslands and permanent natural vegetation associations. The main goal of this work was to estimate the advantage of fully polarimetric radar images (QuadPol) versus alternative polarization (AltPol) modes. The methodology consisted in processing of several data subsets through polarimetric decompositions of complex quad-pol datasets, classification of multitemporal backscattering images, complementing backscattering images with Shannon Entropy, exploitation of interferometric coherence from tandem operations. In each case the multidimensional stack of images has been classified using ISODATA unsupervised clustering algorithm. With 6 QUAD-POL TSX/TDX acquisitions it was possible to distinguish correctly 5 thematic classes related to their water regime: permanent water bodies, temporarily flooded areas, wet grasslands, dry grasslands and common reed. This last category was possible to distinguish from deciduous forest only with Yamaguchi 4 component decomposition. The interferometric coherence calculated for tandem pairs turned out not so efficient as expected for this wetland mapping.

WETLAND MAPPING WITH SAR/QUAD-POL DATA ACQUIRED DURING TANDEM-X SCIENCE PHASE

Abstract. The aim of this study was to exploit fully polarimetric SAR data acquired during TanDEM-X – Science Phase (2014/2015) over herbaceous wetlands of the Biebrza National Park (BbNP) in North-Eastern Poland for mapping seasonally flooded grasslands and permanent natural vegetation associations. The main goal of this work was to estimate the advantage of fully polarimetric radar images (QuadPol) versus alternative polarization (AltPol) modes. The methodology consisted in processing of several data subsets through polarimetric decompositions of complex quad-pol datasets, classification of multitemporal backscattering images, complementing backscattering images with Shannon Entropy, exploitation of interferometric coherence from tandem operations. In each case the multidimensional stack of images has been classified using ISODATA unsupervised clustering algorithm. With 6 QUAD-POL TSX/TDX acquisitions it was possible to distinguish correctly 5 thematic classes related to their water regime: permanent water bodies, temporarily flooded areas, wet grasslands, dry grasslands and common reed. This last category was possible to distinguish from deciduous forest only with Yamaguchi 4 component decomposition. The interferometric coherence calculated for tandem pairs turned out not so efficient as expected for this wetland mapping.

Response of Plant Height, Species Richness and Aboveground Biomass to Flooding Gradient along Vegetation Zones in Floodplain Wetlands, Northeast China.

Flooding regime changes resulting from natural and human activity have been projected to affect wetland plant community structures and functions. It is therefore important to conduct investigations across a range of flooding gradients to assess the impact of flooding depth on wetland vegetation. We conducted this study to identify the pattern of plant height, species richness and aboveground biomass variation along the flooding gradient in floodplain wetlands located in Northeast China. We found that the response of dominant species height to the flooding gradient depends on specific species, i.e., a quadratic response for Carex lasiocarpa, a negative correlation for Calamagrostis angustifolia, and no response for Carex appendiculata. Species richness showed an intermediate effect along the vegetation zone from marsh to wet meadow while aboveground biomass increased. When the communities were analysed separately, only the water table depth had significant impact on species richness for two Carex communities and no variable for C. angustifolia community, while height of dominant species influenced aboveground biomass. When the three above-mentioned communities were grouped together, variations in species richness were mainly determined by community type, water table depth and community mean height, while variations in aboveground biomass were driven by community type and the height of dominant species. These findings indicate that if habitat drying of these herbaceous wetlands in this region continues, then two Carex marshes would be replaced gradually by C. angustifolia wet meadow in the near future. This will lead to a reduction in biodiversity and an increase in productivity and carbon budget. Meanwhile, functional traits must be considered, and should be a focus of attention in future studies on the species diversity and ecosystem function in this region.