Finding environmental constraints on the establishment in salt marshes of Phragmites australis may help elucidate human activities that facilitated its invasion. We tested the effects of rhizome burial, salinity, anoxia, and sulfides on emergence, survival, growth, biomass production, and spread. In greenhouse and field experiments, rhizome burial facilitated initial emergence in well-drained soils. Rhizome emergence was prohibited in poorly drained treatments, regardless of salinity or sulfide concentrations. Emergence in well-drained treatments was not affected by salinity or sulfides, but survival, growth, and biomass storage of the culms and rhizomes were diminished in salt treatments. Combined with other studies, these results indicate that Phragmites invasion is a multi-stage process, with emergence constrained by poor drainage and survival constrained by lack of burial opportunities and salinity. These conditions constrain early stages of the invasion only, as later stages of the invasion can spread into anoxic and high salinity areas. These results also suggest that the process of invasion is facilitated by different human activities at different stages. Emergence is facilitated by soil disturbance, rhizome burial, and altered drainage. Survival through the first season can be facilitated through activities that lower porewater salinity.

Denitrification is a major process for reducing the nitrogen load in floodplains. Soil samples from depth profiles of a hardwood forest of the floodplain of the Upper Rhine were analyzed for their potential to denitrify under permanent nitrate supply. The soils were silty to silty-clayey in the surface layer and had increasing sand content with depth. The rate of denitrification was greatest in top soil and decreased with depth. Organic matter content along profiles decreased exponentially with depth. The denitrification rate showed a very close correlation with the organic matter content of the hardwood forest soil. A denitrification rate of 0.57 mg N day⁻¹ g⁻¹ organic matter present in the soil was calculated for all depths and sites and was constant for up to 23 days. This rather straightforward relationship may support predictions of the (maximum) potential denitrification rates in situ. Furthermore, this relationship may support modeling of the nitrogen balance and contribute to an efficient flood management strategy for the restored floodplains of the Upper Rhine in order to support nitrate removal by denitrification.

Low water tables typically found in peatlands during dry summer periods or in the vicinity of drainage ditches may lead to moisture deficiency in porous surface peats. Episodes of drought stress might compromise the growth benefits brought about by lower ground-water levels. We examined the water relations of black spruce (Picea mariana) trees on a natural peatland during relatively wet (1990) and relatively dry (1991) summers. Seasonal patterns of pre-dawn and mid-day shoot water potentials and stomatal conductance were not related to peat water content or to water-table depth. There was no evidence of water stress or osmotic adjustment in sampled trees during wet and dry growing seasons. Our soil moisture data showed that although water-table levels were as low as −66 cm in 1991, water availability in the root zone remained high. Even with the absence of mid-day water stress during the summer of 1991, a 50% reduction in stomatal conductance as compared with the previous year was found. We suggest that signals from the bulk of the roots located in dry peat top layer contributed to the regulation of stomatal conductance.

In aquatic habitats, both vegetative and sexual reproduction are involved in vegetation maintenance. Restoration projects carried out in such habitats rarely consider the role of both sexual reproduction (seeds) and vegetative (vegetative propagules or clonal fragments) components of propagule banks in vegetation regeneration. Moreover, changes in the seed bank due to the restoration itself have rarely been studied. The aim of this paper is to answer the following questions. Does restoration consisting of sediment removal in a cut-off meander lead to a change in the propagule bank (both sexual and vegetative propagules), and does the vegetation regeneration involve vegetative propagules created by plant breakage during the disturbance? Vegetation was visually surveyed three times during a 15-year period before the restoration and two years afterwards in both the restored zone and an upstream undisturbed zone. The propagule bank was characterized just before and one year after the restoration in the restored zone by sampling of sediment cores and propagule germination in a greenhouse. The impact of restoration on the propagule bank was very pronounced. Sprouting propagules were three times more abundant in post-restoration samples than in pre-restoration samples. The ratio of seeds / vegetative propagules in the bank was lower in the year following restoration. Links between propagule bank and established vegetation were assessed through calculation of correlation and similarity indices. We observed a large difference between established vegetation and the propagule bank before restoration, suggesting that recruitment from the propagule bank was low before restoration. Restoration enhanced the recruitment from rhizomes and vegetative fragments, which were highly correlated with the established vegetation. The pre-eminent role of some vegetative propagules in the recolonization and the increasing abundance of an invasive species are related to the season (June) in which restoration was carried out. Impact of restoration on both the propagule bank composition and environmental conditions (especially those promoting or inhibiting germination or sprouting) thus has to be considered in further vegetation management work.

Ephemeral or “vernal” pools occur commonly throughout the forests of the northeastern United States and adjacent eastern Canada. These pools are critical breeding habitat for a number of amphibian species and support a diverse invertebrate community. The hydroperiod or duration of surface water of vernal pools affects faunal composition and reproduction. We conducted bathymetric surveys of 34 vernal pools located in central Massachusetts in early spring when the pools were at maximum extent after receiving snowmelt runoff. With these data, we estimated maximum pool depths, surface areas, perimeters, volumes, and basin profile coefficients. We calculated relative hydroperiod indices for the pools based on the presence or absence of surface water during periodic pool visits over the three-year study. The ranges of estimated pool morphological parameters were 0.11–0.94 m for maximum depth, 68–2941 m² for maximum surface area, 6–506 m³ for maximum volume, and 30–388 m for maximum perimeter. Basin profile coefficients ranged between 0.60 (convex) and 2.24 (concave), with a median value of 1.02 (straight slope). Maximum pool depth was positively correlated with area and perimeter, but the correlations were only moderately strong, and there were many shallow pools with large surface areas. Correlations between basin profile coefficients and other morphological parameters were weak or non-significant. Maximum pool volume was proportional to the product of area and depth, but the proportionality constant was dependent on the basin profile coefficient. Relative hydroperiod was weakly correlated with pool morphometry; the strongest relationship was found between hydroperiod and maximum pool volume. In general terms, pools with a maximum depth greater than 0.5 m, a maximum surface area larger than 1000 m², or a maximum volume greater than 100 m³ had surface water more than 80% of the times they were visited. In contrast, shallower pools, smaller pools, or pools with lesser volumes had varying hydroperiods. The weak relationships between pool morphometry and hydroperiod indicate that other factors, including temporal patterns of precipitation and evapotranspiration and ground-water exchange may have significant influence on vernal pool hydrology and hydroperiod.

Tillage can destroy or greatly disturb indicators of hydric soils and hydrophytic vegetation, making delineation of tilled wetlands difficult. The remains of aquatic invertebrates (e.g., shells, drought-resistant eggs, and trichopteran cases) are easily identifiable and persist in wetland substrates even when wetlands are dry. Additionally, these remains are not easily destroyed by mechanical tillage. To test the feasibility of using invertebrate remains to delineate wetlands, we used two methods to identify the wetland edge of ten seasonal and ten temporary wetlands, evenly divided between grassland and cropland landscapes. First, we identified the wetland edge using hydric soil and vegetation indicators along six evenly spaced transects in each wetland (our “standard” delineation). We then identified the wetland edge along the same transects using aquatic invertebrate remains as our indicator. In grassland landscapes, delineations of the wetland edge made using invertebrate remains were consistently at the same location or closer to the wetland center as the standard delineations for both seasonal and temporary wetlands. In cropland landscapes, however, many of our invertebrate delineations of seasonal and temporary wetlands were on the upland side of our standard delineations. We attribute the differences to movement of remains during tillage, increased maximum pool levels in cropland wetlands, and disturbance of hydric soils and plants. We found that the elevations of the wetland edge indicated by invertebrate remains were more consistent within a wetland than elevations determined by standard delineations. Aquatic invertebrate remains can be useful in delineating wetlands when other indicators have been destroyed or severely disturbed by tillage.

Nutrient loading is a subtle, yet serious threat to the preservation of high diversity wetlands such as peatlands. Pathways of nutrient loading and impacts on plant diversity in a small peatland in New York State, USA were determined by collecting and analyzing a suite of hydrogeological, hydro-chemical, soil, and vegetation data. Piezometer clusters within an intensive network constituted hydro-chemical sampling points and focal points for randomly selected vegetation quadrats and soil-coring locations. Hydrogeological data and nutrient analyses showed that P and K loading occurred chiefly by means of overland flow from an adjacent farm field, whereas N loading occurred predominantly through ground-water flow from the farm field. Redundancy analysis and polynomial regression showed that nutrients, particularly total P in peat, total K in peat, extractable NH₄-N, and NO₃-N flux in ground water, were strongly negatively correlated with plant diversity measures at the site. No other environmental variables except vegetation measures associated with eutrophication demonstrated such a strong relationship with plant diversity. Nitrate loading over 4 mg m⁻² day⁻¹ was associated with low plant diversity, and Ca fluxes between 80 and 130 mg m⁻² day⁻¹ were associated with high plant diversity. Areas in the site with particularly low vascular plant and bryophyte species richness and Shannon-Wiener diversity (H′) occurred adjacent to the farm field and near a hillside spring. High H′ and species richness of vascular plants and bryophytes occurred in areas that were further removed from agriculture, contained no highly dominant vegetation, and were situated directly along the ground-water flow paths of springs. These areas were characterized by relatively constant water levels and consistent, yet moderate fluxes of base cations and nutrients. Overall, this study demonstrates that knowledge of site hydrogeology is crucial for determining potential pathways of nutrient loading and for developing relationships between nutrient inflows and wetland plant diversity.

The Peace-Athabasca Delta, Canada, a RAMSAR Wetland of International Significance, has since the 1970s been viewed as an ecosystem in decline. The putative reason for its decline has been the regulation of the Peace River by the W.A.C. Bennett Dam in British Columbia. The dying delta paradigm has its origin in a short-term study that coincided with a transient drawdown of the open drainage lakes in the delta. The paradigm has circumscribed all subsequent studies of the delta in its a priori assumption that all detected changes are due to the dam and are negative. As a result, the growth of scientific understanding has been stifled. Factors that contribute to the lack of ecological understanding include problems of data quality, quantity, and scale, ecological complexity, media marketing, failure to consult or analyze older/historical datasets, over-reliance on gray literature, too few wetland ecologists, and too little interdisciplinary thinking. Factors that may be involved in the recent changes, or lack of changes, include climatic variation and change, normal wetland dynamism, stochasticity, flow regulation, weirs, dredging, avulsions and their prevention, influxes of weeds and contaminants, delta evolution, and cultural change. The assessment of health in a delta is problematic since deltas are naturally stressed, dynamic ecosystems. Indicators of anthropogenic stress, such as declines in diversity and abundance, changes in biomass and primary production, or retrogressive succession may be difficult to apply in deltas. Long-term datasets are required that allow differentiation of normal from anthropogenic changes. Critique of the ‘dying delta’ view reveals little scientific support. The often-stated decline in flood frequency seems to have no statistical basis. The ecological health of the Peace-Athabasca Delta was assessed based on 26 attributes; 18 attributes indicated health, 3 indicated stress/disease, and 5 attributes were either neutral or required study. When compared to other major deltas in North America, the Peace-Athabasca Delta stands out as a paragon of ecosystem health. This study presents a cautionary lesson in the power of unchallenged paradigms in shaping scientific and popular opinion. A new paradigm views the delta as predominantly healthy, driven by large-scale natural processes, complex, and dynamically varying.

A study of more than 70 fens in the Midwestern United States and a review of the literature indicates that these temperate zone wetlands may differ from fens of the boreal zone and are not adequately differentiated from them by present classification systems. Fens of the Midwestern temperate zone 1) are wetlands with high botanical diversity, 2) are supported in part by ground water with conductivity > 100mS/cm and circumneutral pH, 3) contain water in the root zone during most of the growing season yet are not usually inundated, and 4) accumulate organic and/or carbonate substrates. Individually, none of these descriptors is adequate to distinguish fens from other wetland communities of the Midwest such as marshes, sedge meadows, and wet prairies; yet, when they are taken together, such discrimination is possible. While fens of this zone share many species, our study does not support using indicator species because too few are both faithfully represented and geographically widespread. Midwestern temperate fens are sustained by forces of climate, landscape, and geology, which permit ground water to seep continuously into the root zone in a focused location. Since water availability in the temperate Midwest is less than in the boreal zone, continuous discharge is needed to maintain the saturation conducive to peat formation.

In this study, we explored the habitat associations of the five most abundant passerine species nesting in the Ebro Delta reedbeds (NE Spain). Habitat characteristics (water depth, vegetation height and density, and plant-species composition) and abundance of all passerine species were measured at each of the 68 sampling points. The sampled area included most of the reedbeds in the Ebro Delta. Sampling points were classified according to the habitat parameters measured using cluster analysis. The resulting four habitat types differed in the composition and attributes of their passerine communities. The abundance of the great reed warbler (Acrocephalus arundinaceus) and reed warbler (Acrocephalus scirpaceus) was greatest in tall, permanently inundated and almost monospecific Phragmites reedbeds. In contrast, the numbers of the reed bunting (Emberiza schoeniclus) and Savi's warbler (Locustella luscinioides) were greatest in areas of drier soils and a denser basal stratum. Finally, the fan-tailed warbler (Cisticola juncidis) showed no clear habitat association. In the Ebro Delta, reedbed management includes freshwater inputs and burning of standing reeds. These practices promote tall, permanently inundated reedbeds with minimal detrital accumulation. Bird species richness and diversity were greater in less intensely-managed habitats, but only diversity was significant (p < 0.001). We conclude that, since reedbeds are important habitats for several scarce bird species, and the abundance of these species seem to be influenced by vegetation structure, bird conservation considerations should be incorporated into future reedbed management practices.

Recently, Phragmites australis (common reed) in North American wetlands has changed from a species with limited distribution to an invasive species producing dense monospecific stands. This expansion has forced out other wetland vegetation, potentially changing the functions of these ecosystems. Little research has focused on whether P. australis stands serve as valuable wetland habitat and foraging areas for terrestrial animals and resident marsh nekton. This study addressed the effect of different hydrologic and geomorphic conditions among P. australis stands on abundance of resident nekton in Piermont Marsh, located on the lower Hudson River Estuary. Three P. australis-dominated sites (erosional creekbank, depositional creekbank, interior) were sampled for nekton using bottomless lift nets during day and night spring high tides during the months of July, August, and September, 1998. Hydrology data were collected for ten continuous days during each sampling period and included mean flooding depth, duration, and frequency for the three sites. Species captured on the marsh surface included Fundulus heteroclitus (common mummichog), Palaemonetes pugio (dagger-blade grass shrimp), Callinectes sapidus (blue crab), and Uca minax (brackish water fiddler crab). Results indicate that nekton and macrobenthos are using all areas sampled, and measured densities are comparable to those measured in some non-P. australis dominant wetlands elsewhere on the Hudson River. Although no strong correlation was made between nekton densities and hydrology, definite patterns were observed in the data. The results indicated that additional variables, such as geomorphology, might interact with hydrology to influence nekton use of the marsh surface. Although exact mechanisms controlling spatial variation of nekton use within P. australis stands still need to be elucidated, P. australis does seem to serve as nekton habitat.

Cottonwoods (Populus sp.) and willows (Salix sp.) generally dominate riparian landscapes across western North America. To investigate their relative tolerances to water-table decline, rooted shoot cuttings (saplings) of two willows, Salix exigua and S. drummondiana, and two cottonwoods, Populus angustifolia, and P. balsamifera, were grown in rhizopods, controlled growth devices that allow water-table manipulation. Water-table-decline rates of 0 to 12 cm/d were applied and plant growth and survival were monitored. In a second study, seedlings of S. exigua, S. lutea, P. balsamifera, and P. deltoides were grown in rhizopods and exposed to water-table-decline rates of 0 to 8 cm/d. For saplings and seedlings of both genera, gradual declines of 1 or 2 cm/d promoted root elongation and often promoted shoot growth relative to the constant water-table treatment (0 cm/d). More abrupt declines (> 2 cm/d) reduced growth and survival, and there were some differences in sensitivity within as well as across the two genera. Thus, the willow and cottonwood saplings were similarly affected by abrupt water-table decline, but willow seedlings were slightly more vulnerable than cottonwood seedlings. It is recommended that gradual stream stage recession along regulated rivers of about 2.5 cm/d in the late spring would encourage the recruitment of cottonwood seedlings, but subsequently, more gradual recession of about 1 cm/d through the lower elevational streamside zones would enable recruitment of S. exigua and other willows.

Tiller dynamics and net aerial primary productivity (NAPP) were studied in permanent sample plots of Spartina densiflora at Otamendi Natural Reserve (Buenos Aires Province, Argentina) from June 1996 to December 1997. Emergence, growth, senescence, survival, biomass dynamics, and tiller productivity were analyzed. These population attributes varied seasonally during the first study year, whereas variations were not detected in the subsequent year. Tiller density increased slightly during the first twelve months, attaining 2445 ± 869 tillers·m⁻², then remaining constant until the end of the study period. Senescence rate was lower than emergence rate on most sampling occasions. Cohorts originated in different seasons showed distinct survival curves. The life span of tillers was at least 18 months. Green biomass reached maximum values (771 ± 410 g·m⁻²) during the first year but decreased during the last six months of observations. Annual NAPP was 1450 ± 566 g·m⁻²·y⁻¹. Average productivity rate was higher in the first year than in the second year. The decrease in the population density of tillers of S. densiflora and the increase in its senescence rate were more likely related to grazing and flooding than to population dynamics.

Four small mires, located at an altitude of 1520 m in the forest complex of Elatia, western Rhodope Massif, northern Greece, were examined in terms of shape, physical and chemical features, plant communities, hydrologic regime, geotectonic setting, and developmental history. The data suggest that the terms bog or fen cannot strictly describe the mires. The mixed vegetation cover of both bog and fen species, the water supply regime (meteoric and surface), the low electrical conductivity, the slightly acidic to sub-neutral pH values, and the high ash contents support the notion that the mires at Elatia forest can be initially classified as transitional mires. This term is for the first time attributed to mires in Greece. Peat deposition at one of the sites was initiated c. 2,380 years ago but was intermittent to the present day.

Hydrology frequently has been reported as the environmental variable having the greatest influence on Florida snail kite (Rostrhamus sociabilis) populations. Although drought has received the most attention, high-water conditions also have been reported to affect kites. Years of high water generally have been reported to be favorable for nesting, although prolonged high water may be detrimental to sustaining suitable habitat. During 1994 and 1995, southern Florida experienced an extreme high water event. This event enabled us to compare survival, nesting success, number of young per successful nest, and spatial distribution of nesting before, during, and after the event. We found no evidence of an effect (either negative or positive) on survival of adult kites. In contrast, juvenile kites experienced the highest survival during the event, although our data suggest greater annual variability than can be explained by the event alone. We found no evidence of an effect of the high water event on nest success or number of young per successful nest. Nest success was highest during the event in the southern portion of the range but was quite similar to other years, both before and after the event. Our data do indicate a substantial shift in the spatial distribution of nesting birds. During the event, nesting activity shifted to higher elevations (i.e., shallower water) in the major nesting areas of the Everglades region. Nesting also occurred in Big Cypress National Preserve during the event, which is typically too dry to support nesting kites. Thus, our data indicate a potential short-term benefit of increased juvenile survival and an expansion of nesting habitat. However, the deterioration of habitat quality from prolonged high water precludes any recommendation for such conditions to be maintained for extended periods.

Evapotranspiration and other surface-energy balance components of a wet prairie community dominated by Panicum hemitomon (maiden cane), Ptilimnium capillaceum (mock bishop's weed), and Eupatorium capillifolium (dog fennel) in Central Florida, USA were investigated. Drought conditions resulted in water-table levels from 0.58 to 1.20 m below ground level and variable soil wetness conditions during the observation period. Energy-balance measurements were made using the eddy correlation approach. The overall evapotranspiration rate was 4.16 mm d⁻¹, and the average Bowen ratio was 0.42. Energy partitioning had an enhanced sensible heat-flux component and a dampened latent heat-flux component when the volumetric soil water content was less than or equal to 0.09 for the sandy soil. Evapotranspiration was classified into a two stages, first stage (wet) and second stage (dry) based on the soil water availability. The Penman-Monteith model gave good results for the first stage evapotranspiration. The Priestley-Taylor and the Penman models overestimated first stage evapotranspiration. A simple second stage evapotranspiration model, developed by applying a reduction factor based on soil moisture to the Penman-Monteith model, provided improved estimates of evapotranspiration for second stage observations.

The Wisconsin Wetlands Inventory (WWI) was conducted by the State of Wisconsin, USA using a classification system and methods that are similar but not identical to those of the National Wetlands Inventory (NWI). Dissimilarities between the two inventories present problems for applications that cross state boundaries, such as inter-state comparisons or compilation of regional wetland statistics. The methods and classification systems of the two wetland inventories were compared, and GIS coverages were analyzed where the two inventories overlap near the cities of Superior and Baraboo. The NWI mapped both wetland and deepwater habitats and included Lacustrine and Riverine deepwater habitats that were intentionally not mapped by the WWI. Of the 178 km² Superior study area, 52% was mapped as upland by both, 22% was mapped as wetland by both, 10% was mapped as Palustrine wetland by NWI but not WWI, and 6% was mapped as wetland by WWI but not NWI. Of the 281 km² Baraboo study area, 91% was mapped as upland by both, 2% was mapped as wetland by both, 1% was mapped as Palustrine wetland by NWI but not WWI, and 1% was mapped as wetland by WWI but not NWI. Errors of omission were found for both inventories, but errors of commission (i.e., areas incorrectly mapped as wetland) were found only for the NWI maps in the Superior study area, which were prepared using 1:80,000 black and white panchromatic aerial photos. In theory and in practice, the two inventories were nearly equivalent with regard to Palustrine wetland class and subclass. The WWI “hydrologic modifier” has fewer categories than the NWI “water regime,” but a preliminary conversion table was developed to recode the WWI digital maps to their equivalent NWI categories based on the modal NWI water regime associated with each NWI class. Methods were developed for converting the WWI digital databases to make the two inventories more compatible; recommendations for future updates of the WWI include use of leaf-off color infrared aerial photography and merging of the digital WWI with a digital database of deepwater habitats.

We examined the utility of five measures of salt marsh function, focusing on angiosperms and microbes, as potential indicators of salt marsh health. We studied twelve salt marsh creeks around Charleston Harbor, South Carolina, USA, six of which were polluted with metals and/or organic compounds and six of which were relatively pristine. Physical variables (sediment clay-silt content, creek water salinity) did not differ between impacted and reference sites. Microtox toxicity measures (expressed as wet or dry units) did not differ between impacted and reference sites. Photosynthesis and transpiration rates of creekbank Spartina alterniflora did not differ between impacted and reference sites, nor did measures of peroxidase activity in S. alterniflora. The glutathione concentration of S. alterniflora was lower at impacted sites than at reference sites; however, glutathione concentration did not respond to pollution in an earlier study in Georgia, likely because glutathione responds differently to particular chemicals rather than being a generic indicator of plant stress. Overall, these measures showed little promise as rapid indicators of salt marsh health. Other methods, such as quantifying benthic invertebrate taxa, may be more reliable for assessing ecosystem health in salt marsh systems.

The introduction of invasive species such as Phragmites australis in the Chesapeake Bay has been viewed to be deleterious to habitat quality. Little is known, however, on the extent to which the replacement of Spartina alterniflora by Phragmites affects hydrodynamics and sediment trapping on the surface of impacted marshes. This study examined sediment deposition, sediment mobility, and flow conditions in adjacent Phragmites australis and Spartina alternifora marshes in Prospect Bay, Maryland, USA in order to determine if differences in plant morphology affect surficial flow properties and particle dispersion patterns. Measures of fine-scale flow dynamics, total suspended sediment (TSS) concentration, and particulate deposition were obtained at various distances from open water across the marsh surface over four sequential tidal cycles in Fall 1999. The hydrodynamic data indicate that both the gross and fine-scale properties of tidal flows were similar in both types of vegetation and that flow conditions were conducive to particle deposition. TSS concentrations did not differ between canopy types and decreased over time in both systems. There was no difference in TSS reduction over distance between Spartina and Phragmites. The sediment trap data indicate that maximum deposition occurs closer to open water in both Spartina and Phragmites and that the organic content of deposited matter increased with distance into the marsh interior. This study provides the first in situ, high resolution, over-marsh flow data for marshes dominated by Phragmites. The data provided herein suggest that differences in vegetative cover do not significantly affect flow regime, sediment transport, and sediment deposition patterns in the marsh systems examined.

Nutrient availability strongly affects the species composition and productivity of most upland ecosystems, but the importance of nutrient availability is largely undefined for riparian ecosystems in semi-arid regions of the western United States. The establishment and persistence of riparian cottonwood (Populus spp.) seedlings depends largely on water availability, but this does not preclude an important role for nutrient availability. To investigate how nitrogen availability may influence the composition and productivity of riparian communities, we tested the hypothesis that the growth and survival of first-year Fremont cottonwood seedlings is limited by the availability of both water and nitrogen. Plots of naturally germinated cottonwood seedlings along the Yampa River in Northwest Colorado were randomly assigned one of four treatments: control, water, nitrogen, or water plus nitrogen. Additions of nitrogen or water doubled total (root plus shoot) seedling and shoot length. Water additions did not increase root growth, while N addition doubled the root extension of first-year cottonwood seedlings. The water-plus-nitrogen treatment doubled total seedling and root length, and tripled shoot length. Additions of water or nitrogen also more than doubled cottonwood seedling survival through the first growing season. This co-limitation of cottonwood germinants by both water and nitrogen suggests that the productivity and species composition of riparian vegetation may need to be examined in relation to supplies of resources other than water.

We measured the effects of prescribed fire during January (dormant season) and May (growing season) on flowering of three perennial grasses, muhly (Muhlenbergia capillaris), gulfdune paspalum (Paspalum monostachyum), and south Florida bluestem (Schizachyrium rhizomatum), which are dominant grasses in wet prairies of south Florida, USA. Flowering was promoted by growing season fire but not by dormant season fire. Flowering was significantly greater for all species following prescribed fire conducted during May compared with areas burned during January of the same calendar year. The strong positive effect of growing season fire on flowering of all three species decreased after the first growing season. We rejected the hypothesis that season of fire did not influence flowering. Our results indicated that flowering by these dominant, wet prairie grasses is promoted by early growing season fire, which corresponds to historical patterns of lightning-ignited fire in south Florida.

Compensatory mitigation has been a keystone of state and federal programs for regulating wetland loss. This study reviewed mitigation performance in Indiana, USA to propose mitigation ratios (area to be mitigated/area permitted for fill) based on the rate of wetland establishment by type. Between 1986 and 1996, the Indiana Department of Environmental Management (IDEM) required 345 mitigation sites. Of these, applicants constructed 214 of the sites; another 70 were not completed. No attempt was made to construct the required mitigation on 49 of the sites. Measurements of both the total wetland area and the area of each vegetation community in the mitigation site were taken at 31 of the sites identified as “constructed.” IDEM required 34.33 ha to compensate for the 13.73 ha of state waters lost through the permit actions associated with these sites. The mapping effort found that a total of 15.21 ha of wetland and other waters had established, a net gain of 1.48 ha. Vegetation community mapping revealed that palustrine forested areas, which had a failure rate of 71%, and wet meadow areas (87% failure) were harder to establish than shallow marsh areas (17% failure) and open water areas (4% failure). These results suggest that federal and state regulatory agencies would have to require minimum mitigation ratios of 3.5:1 for palustrine forested, 7.6:1 for wet meadow, 1.2:1 for shallow marsh, and 1:1 for open water to compensate for the risk of failure. Additional mitigation may be needed to offset the effects of temporal loss of wetland function.