In the Lower Mississippi Alluvial Valley (LMAV), losses of bottomland hardwood forests have been severe, with less than 30% of the original 10 million ha remaining. Reforestation of abandoned farmland is occurring, but there has been little research on natural reestablishment of these forests. We examined understory succession and tree establishment patterns in a 3.2-ha field in northeast Louisiana, USA, abandoned in 1984. Relative elevation, strongly correlated with flooding depth and frequency, varied by approximately 1m. Ground-layer composition was monitored from 1985 to 1999 in twenty 1-m² quadrats stratified along the elevation gradient. In 2000, shrubs and tree saplings were mapped and their relative elevations determined. Ordination of the ground-layer data revealed that the major trends in species composition were related to time-since-abandonment and elevation. Annual species gradually declined, woody perennials became more abundant, and a shrub and young tree layer emerged from beneath the ground layer, but species composition in low and high elevation plots did not converge. Obligate species were more common at lower elevations, while facultative species were more common at upper elevations. By 16 years after abandonment, a total of 16 tree and shrub species had established in the field; eleven of these had potential local seed sources on levees adjacent to the study site. Abundance of dominant species was significantly related to elevation in most cases. In addition, distance to seed source influenced density and spatial distribution of Celtis laevigata and Fraxinus pennsylvanica. Our study suggests that rate and pattern of secondary succession in LMAV bottomlands are strongly influenced by elevation, dispersal mode of species, and the composition and proximity of forest remnants. Successful restoration of bottomland forests will require an improved understanding of these factors

Insufficient sedimentation, coupled with high rates of relative sea-level rise (subsidence plus eustatic sea-level rise), are two important factors contributing to wetland loss in coastal Louisiana, USA. We hypothesized that adding nutrient-rich, secondarily treated wastewater effluent to subsiding wetlands in Louisiana could promote vertical accretion in these systems through increased organic matter production and subsequent deposition and allow accretion to keep pace with estimated rates of relative sea-level rise (RSLR). However, we also hypothesized that nutrient enrichment could stimulate the decomposition of organic matter, thus negating any increase in accretion due to increased organic matter accumulation. To test these hypotheses, we measured leaf-litter decomposition, litter nutrient dynamics, and sediment accretion in a permanently flooded and subsiding forested wetland receiving wastewater effluent and in an adjacent control site, both before and after effluent applications began. We also measured organic and mineral matter accumulation in the treatment site before and after effluent applications began. A Before-After-Control-Impact (BACI) statistical analysis revealed that neither leaf-litter decomposition rates nor initial leaf-litter N and P concentration were affected by wastewater effluent. A similar analysis revealed that final N and P leaf-litter concentrations did significantly increase in the treatment site relative to the control after effluent was applied. Total pre-effluent accretion, measured 34 months after feldspar horizon markers were laid down, averaged (± SE) 22.3 ± 3.2 mm and 14.9 ± 4.6 mm in the treatment and control sites, respectively, and were not significantly different. However, total accretion measured 68 months after the markers were installed and 29 months after effluent additions began in the treatment site averaged 54.6 ± 1.5 mm in the treatment site and 19.0 ± 3.2 mm in the control site and were significantly different. Additionally, after wastewater applications began, the estimated rate of accretion in the treatment site (11.4 mm yr⁻¹) approached the estimated rate of RSLR (12.3 mm yr⁻¹). Most of this increase in accretion was attributed to organic matter inputs, as organic matter accumulation increased significantly in the treatment site after effluent application began, while mineral accumulation rates remained constant. These findings indicate that there is a potential for using wastewater to balance accretion deficits in subsiding wetland systems.

Black poplar (P. nigra ssp. betulifolia) is a tree species that is a subject of concern in the United Kingdom because of its rarity, skewed sex ratio, and apparent inability to regenerate naturally. In its natural habitat, it is an early successional tree that occurs on floodplains. It is dependent on channel movement for the provision of suitable habitats for regeneration. In the United Kingdom, there is considerable interest in using black poplar in river restoration schemes. This study was carried out to determine the importance of choice of black poplar clones in such schemes. Cuttings were collected from 11 female and 8 male black poplars from a wide geographical range in Britain. Of these, cuttings from 7 males and 6 females were rooted and grown successfully for one season in a field experiment designed to determine the difference in growth response of the range of individuals to a variety of soil moisture conditions. The propagated cuttings were described morphometrically, and measurements of growth response were recorded. The source trees were also described genetically, using analysis of AFLPs (Amplified Fragment Length Polymorphisms), in order to determine relatedness. Results showed that genetic diversity of the source trees used in this study was low. However, there were some significant differences in growth response and morphometric characteristics (mean leaf area, mean branch angle) among the plants derived from different source trees. Growth was always best in the wettest sites, and females grew better than males at these sites. The results suggest that, in riparian forest restoration schemes, choice of clone affects the balance of sex ratios, viable genetic diversity and survival of plantings on varied sites.

We evaluated treatments designed to remove saltcedar (Tamarix ramosissima) monocultures from riparian habitats using root plows (mechanical treatment) and aerial applications of the herbicide imazapyr (chemical treatment) within twelve 4-ha impoundments in the Middle Rio Grande Valley in central New Mexico, USA. Following these treatments, impoundments were flooded and water levels were reduced to stimulate native species re-establishment from seed. Water manipulations within saltcedar-removal areas consisted of stage drawdowns of 5 cm/day and 10 cm/day. Mechanically cleared areas had fewer saltcedar resprouts (26 resprouts/ha) than chemically treated areas (2,500 resprouts/ha). Saltcedar and cottonwood (Populus deltoides subsp. wislizinii) seedling density and cottonwood survival were greater in mechanically treated areas than in chemically treated areas. This effect is attributed to soil disturbance resulting from root plowing. Cottonwood seedling density and survival did not differ between 5 cm/day and 10 cm/day stage drawdowns and decreased throughout summer as a result of excessive moisture stress. The absence of a drawdown treatment effect indicates that both drawdowns were too fast for seedling roots to keep up with declining water tables. Seedlings that survived were using moisture from the unsaturated zone.

Paired plots were established across a soil moisture gradient (dry, periodically flooded, flooded) in three forested wetland watersheds in Louisiana and South Carolina, USA in 1986–1987. All trees greater than 10-cm diameter at breast height were tagged and measured annually through 1999 to determine density, basal area changes, ingrowth, and mortality. A greater number of tree species was found in South Carolina dry and periodically flooded sites than in Louisiana. Flooded sites in both states were dominated by water tupelo (Nyssa aquatica) and baldcypress (Taxodium distichum). The overall trend in density in both states was flooded > periodically flooded > dry. From 1987 to 1999, density decreased in all of the Louisiana sites except one, while in South Carolina, density remained the same or increased in four of the sites and decreased in the other four. The greatest changes in density occurred in those sites where water-level changes were occurring and in areas where storm winds struck. Basal area in 1987 was similar in both states, ranging from 20.8 to 55.2 m²/ha in Louisiana and 24.0 to 49.5 m²/ha in South Carolina. Flooded sites had the greatest basal area, and periodically flooded and dry sites had similar basal areas. Mortality rates in Louisiana and South Carolina forested wetlands are typically low (around 2%/year) in areas that have not been altered hydrologically. Annual mortality in Louisiana plots with increased water levels rose from 4% in 1987 to 16% in 1997. Wind storm events significantly increased mortality rates, and mortality rates remained high for years after the event, as damaged trees died. Of special concern are areas like the Verret Basin site where the exotic, invasive species Chinese tallow (Sapium sebiferum) invaded after Hurricane Andrew and has the potential to become a dominant canopy tree in the future.

Field studies and aerial photograph interpretation suggest that large sections of Jamaica Bay salt marshes in New York City near John F. Kennedy International Airport are deteriorating rapidly. The relatively recent salt marsh losses may be caused by a variety of factors, potentially interacting synergistically. Possible factors include reduced sediment input, dredging for navigation channels, boat traffic, and regional sea-level rise. Field work included aboveground biomass measurements of Spartina alterniflora, mapping plant community distribution, and documenting biogeomorphological indicators of marsh loss. Current productivity (standing crop biomass), which ranged from approximately 700 to 1500 g m⁻², was typical of healthy marshes in this region, in spite of other indicators of marsh degradation. Historical aerial photographs of several islands showed that sampled marshes have diminished in size by ∼12% since 1959. Overall island low marsh vegetation losses since 1974 averaged 38%, with smaller islands losing up to 78% of their vegetation cover. Ground observations indicate that major mechanisms of marsh loss include increased ponding within marsh interiors, slumping along marsh edges, and widening of tidal inlets. Projections of future sea-level rise, using outputs from several global climate models and data from local tide gauges, in conjunction with a range of plausible accretion rates, suggest that under current stresses, Jamaica Bay salt marshes are unlikely to keep pace with accelerated rates of sea-level rise in the future.

In 1990, the North American Waterfowl Management Plan (NAWMP) implemented a small-wetland restoration program in Prince Edward Island (PEI), Canada. Wetlands were restored by means of dredging accumulated sediment and organic debris to create open water and emulate pre-disturbance conditions. Three call surveys were conducted in the spring and summer of 1998 and 1999 to estimate abundance and occurrence of spring peepers (Pseudacris crucifer), wood frogs (Rana sylvatica), northern leopard frogs (Rana pipiens), American toads (Bufo americanus), and green frogs (Rana clamitans) on restored and reference wetlands. Numbers of species calling and abundance indices of northern leopard frogs, green frogs, and spring peepers were significantly higher on restored versus reference wetlands. The number of species calling in restored wetlands was positively correlated with proximity to freshwater rivers; in reference wetlands, the number was positively associated with forested perimeters and area of open water. Occurrence of calling green frogs in restored wetlands was positively correlated with percent cattail and, in reference wetlands, with proximity to other wetlands. Our results suggest that small wetland restoration projects may be a good conservation tool for anurans. We recommend further research on reproductive success and on local population trends in restored wetlands to determine if restoration is beneficial for anurans on PEI.

Despite the importance of peatlands in the global carbon cycle, no widely applicable ecosystem model exists for peatlands. Simulations of three montane fens in Colorado, USA were conducted to test the capabilities of the CENTURY ecosystem model to simulate 1) long-term carbon accumulation and 2) short-term changes in carbon accumulation due to hydrologic changes. The CENTURY model was calibrated to simulate long-term carbon accumulation in two fens for up to 10,000 years by adjusting three variables that represent anaerobic soil conditions. CENTURY was unable to simulate long-term carbon accumulation in a third fen using settings for the two calibrated fens. However, CENTURY correctly simulated total carbon storage by adjusting two of the three anaerobic variables. A sensitivity analysis revealed that carbon accumulation in CENTURY is highly sensitive to anaerobic soil conditions. CENTURY predicted that half of the fen peat is composed of structural root material. The majority of the remaining peat was composed of recalcitrant slow and passive soil organic matter. Precipitation levels were altered to determine if CENTURY could predict the change in carbon accumulation rates due to periodic drier conditions. The simulated drying scenario predicted an average carbon loss of 70 g C m⁻² yr⁻¹ during the 100-year simulation. The loss of carbon occurred despite plant production increasing from an average of 249 g C m⁻² yr⁻¹ to 391 g C m⁻² yr⁻¹. Slightly more than 90% of the carbon lost was from the structural root pool and slow organic matter pool, while there was no carbon loss or a slight net carbon gain in the passive organic matter pool and above-ground structural and metabolic pools. Despite several shortcomings, our results indicate that an ecosystem model, such as CENTURY, can be useful for simulating carbon dynamics in peatlands.

Secondary succession in wet grasslands has received surprisingly little attention. We analyzed the vegetation of a eutrophic alluvial wetland of western France and the relationship between its composition and environmental variables. The objectives of our study were twofold: (1) to describe species assemblages of wet grasslands and oldfields and correlate their species composition to hydrologic stress and (2) to study the changes in species composition, species richness, and species diversity when mowed meadows are abandoned. More than 100 species were recorded, and five species assemblages (‘A’ to ‘E’) were identified. Hydrology and land use (mowing versus land abandonment) were the two main ecological factors that affected plant community development. Hydrologic regime contributed to separate ‘A’, ‘B’ (on the wettest end of the gradient) from ‘C’, ‘D’, and ‘E’ (on the driest end of the gradient). Land use helped to discriminate ‘B’, ‘C’ from ‘A’, ‘D’, and ‘E’. Larger-scale disturbances such as mowing maintain meadow species, leading to a high level of species richness, species diversity, and evenness. We compared the species richness, species diversity, and evenness according to the duration of land abandonment since last mowing disturbances (<5 years, 6–10 years, 11–15 years, 16–20 years). No significant differences were observed. Botanical composition of these plots did not differ significantly. In the first five years of land abandonment, there was an increase of litter, which reduces the species richness, diversity, and evenness. Live, above-ground biomass of grasslands was significantly greater than that of oldfields, but total organic matter (biomass litter) was significantly greater for oldfields than for grasslands. Total biomass showed a negative logarithmic relationship with species richness, with species richness being initially high at very low standing crop levels (grasslands) and decreasing at greater levels of standing crop (oldfields).

Floristic quality assessment is potentially an important tool for conservation efforts in the northern Great Plains of North America, but it has received little rigorous evaluation. Floristic quality assessments rely on coefficients assigned to each plant species of a region's flora based on the conservatism of each species relative to others in the region. These “coefficients of conservatism” (C values) are assigned by a panel of experts familiar with a region's flora. The floristic quality assessment method has faced some criticism due to the subjective nature of these assignments. To evaluate the effect of this subjectivity on floristic quality assessments, we performed separate evaluations of the native plant communities in a natural wetland complex and three restored wetland complexes. In our first assessment, we used C values assigned “subjectively” by the Northern Great Plains Floristic Quality Assessment Panel. We then performed an independent assessment using the observed distributions of species among a group of wetlands that ranged from highly disturbed to largely undisturbed (data-generated C values). Using the panel-assigned C values, mean C values (C̄) of the restored wetlands rarely exceeded 3.4 and never exceeded 3.9, with the highest values occurring in the oldest restored complex; all but two wetlands in the natural wetland complex had a C̄ greater than 3.9. Floristic quality indices (FQI) for the restored wetlands rarely exceeded 22 and usually reached maximums closer to 19, with higher values occurring again in the oldest restored complex; only two wetlands in the natural complex had an FQI less than 22. We observed that 95% confidence limits for species richness and percent natives overlapped greatly among wetland complexes, whereas confidence limits for both C̄ and FQI overlapped little. C̄ and FQI values were consistently greater when we used the data-generated C values than when we used the panel-assigned C values; nonetheless, conclusions reached based on these two independent assessment techniques were virtually identical. Our results are consistent with the opinion that coefficients assigned subjectively by expert botanists familiar with a region's flora provide adequate information to perform accurate floristic quality assessments.

Simulated grazing techniques were used to investigate livestock impacts on structural and vegetation characteristics of streambanks in central Idaho, USA. The treatments, continued over two years, consisted of no grazing, simulated moderate early summer grazing, simulated moderate mid-summer grazing, and simulated heavy season-long grazing. The moderate treatments depressed the streambank surface about 3 cm, while the heavy season-long treatment resulted in an 11.5-cm depression. There were no differences between the no-grazing and moderate-grazing treatments for change in stream width, bank angle, bank retreat, or root biomass. The heavy season-long treatment, however, produced significant changes in these variables. The amount of foliage biomass (i.e., kg ha⁻¹) removed by treatment was similar between the two years of study for the moderate treatments. The foliage removed from the heavy season-long treatment plots greatly decreased in the second year as plant growth decreased. Ten months after the last treatment application, the average spring foliage growth was 20–43% lower on the moderate treatment plots and 51–87% lower on the heavy season-long treatment plots than on the untreated control plots.

Knowledge of wetland hydrology, soil redox potential, pH, and temperature dynamics are key components required to understand the capacity of tidal wetlands to function, in particular to attenuate agrichemicals. In a freshwater tidal wetland along the James River in Virginia, USA, redox potential, pH, water-table level, and soil temperature were monitored continuously at two depths (20 and 50 cm) at three sites during a 12-month period from September 1, 1997 to August 31, 1998. Redox potentials were at or below −150 mV (methanogenic or sulfate reducing conditions) at the 50-cm depth during the entire monitoring period. At the 20-cm depth, redox potentials remained highly reducing 95% of the time. The soil is continuously wet throughout the year, with the water-table level above the 20-cm soil depth for 95% of the time. Water-table level or hydrology was the primary factor controlling fluctuations in the redox state. Soil pH values were generally between 6 and 8, and they dropped 1 pH unit upon an oxidation event, which was reversible. Soil temperature at the 50-cm depth never dropped below 5° C, indicating a year-round biological activity season. This wetland supports a large diversity of plant species. Permanently reduced sub-surfaces, year-round biological activity, and large organic matter accumulations are characteristic features of this freshwater tidal wetland.

Purple loosestrife (Lythrum salicaria) is considered one of the worst invasive non-native species of North American wetlands, but its reputation rests on few published, quantitative field studies. This study described the vegetation of two sites (one flooded, one drier) within a heavily invaded wetland in southeastern New York, in order to investigate the common claim that purple loosestrife produces monospecific stands. Native species richness per square meter was 6.8, on average, with mean percent cover ranging from 0.03 to 6.7%, compared to 49% for purple loosestrife. One grass, Phalaris arundinacea, covered on average 31.1% of the area in drier site plots. Twenty-six native taxa were found in a total of 18 1-m² plots. I also conducted an experimental manipulation of the plant community in both sites to demonstrate the role of purple loosestrife in gap colonization. Three 1-m² experimental gaps in each site were recolonized by purple loosestrife at very low density after three years (mean percent cover 1.7), even though recruitment in the drier site was heavy in the first summer. I compared vegetation in the three recolonized gaps, three additional gaps in which purple loosestrife recolonization was prevented, and three unmanipulated control plots. Community structure was not statistically different among these treatments after three years (measured as species richness, Shannon diversity index, or percent cover) because removal plots became dominated by one or two grass or sedge species that replaced purple loosestrife in the community. Recolonized plots contained an average of 6.3 native taxa. Six of the colonizing taxa at each site were not present prior to manipulation. The results show that purple loosestrife stands were not monospecific in this wetland, that other non-native species may dominate if purple loosestrife is removed, and that small gaps may provide regeneration niches for other species.

A controlled feeding study and field collections of duck feces were used to examine the potential of ducks for dispersing wetland plant species in the prairie pothole region of North America. To determine how long seeds of wetland species remain in their digestive system, captive mallards were fed known quantities of seed of either Atriplex patula, Chenopodium album, Chenopodium rubrum, Echinochloa crusgalli, Polygonum spp., Scirpus acutus, Scirpus validus, or Sparganium eurycarpum. Fecal samples were collected hourly from ducks for 24 to 30 hours after seeds were ingested. On average, 23% of the seeds ingested were recovered intact, and 36% of these were still viable. In other words, only 7% of the seeds ingested were still viable when they were evacuated, with a range from 1% for Echinochloa crusgalli to 16% for Scirpus validus. The mean passage time of seeds was 7.6 h, with a range of 5.1 h for Echinochloa crusgalli to 11.1 h for Chenopodium rubrum. Nearly all seeds were evacuated after 24 to 30 h. Seed size and seed coat strength (lignin content) were negatively correlated with the probability of a viable passage but not correlated with passage rates. After ingestion, mallards are estimated to be able to transport internally viable seeds up to 1,400 km but more typically 20 to 30 km. Field collections of duck feces at five locations in the prairie pothole region confirmed that ducks are dispersing intact seeds of common wetland species (Carex sp., Echinochloa sp., Panicum sp., Polygonum spp., Potamogeton spp., Salix sp., and Scirpus spp.). There were between 0.3 to 5.2 intact seeds per duck. Only 1.6% of this intact seed of four taxa (Carex sp., Potamogeton spp., Salix sp., and Scirpus spp.) germinated under greenhouse conditions. Although any given duck is carrying only a few viable seeds, the millions of ducks moving among wetlands, especially during spring and fall migrations, collectively are effective dispersal agents for many wetland plant species.

We investigated population size, nest success, and nest-site characteristics of Saltmarsh Sharp-tailed Sparrows (Ammodramus caudacutus) from 1993 to 1998 in a salt marsh near Galilee, Rhode Island. From 1956 to 1997, tidal flow was restricted in the marsh by construction of a road with small culverts, which resulted in conversion of the marsh from short- and tall-form cordgrass (Spartina alterniflora) and marsh hay (S. patens) to one dominated by >5 m tall common reed (Phragmites australis). In fall 1997, self-regulating tide gates were installed to restore the historic tidal regime and vegetation. We documented declines in adult sparrow population sizes (17–25% annual decline) and productivity (48% annual decline) while the tidal regime was restricted. Nest success was variable (10–83%) before 1998, with predators accounting for most nest losses. Saltmarsh Sharp-tailed Sparrows usually nested in marsh hay, short-form cordgrass, and short common reed. After restoration, sparrows nested where vegetation was taller, which permitted greater nest elevation. However, 91% of nests failed due to flooding following installation of new tide gates. We hypothesize that restoration efforts will have short-term negative impacts on Saltmarsh Sharp-tailed Sparrow populations until salt marsh habitats are restored in higher sections of the marsh.

Because the North American Breeding Bird Survey provides inadequate coverage of wetland habitat, the Wetland Breeding Bird Survey was recently established in Ohio, USA. This program relies on volunteers to conduct 3 counts at each monitored wetland. Currently, all counts are conducted during the morning. Under the premise that volunteer participation could be increased by allowing evening counts, we evaluated the potential for modifying the methodology. We evaluated the sampling efficiency of all 3-count combinations of morning and evening counts using data collected at 14 wetlands. Estimates of overall species richness decreased with increasing numbers of evening counts. However, this pattern did not hold when analyses were restricted to wetland-dependent species or those of conservation concern. Our findings suggest that it would be reasonable to permit evening counts, particularly if the data are to be used to monitor wetland-dependent species and those of concern.

Effects of dry cold storage and sterilization of Juncus effusus seeds were assayed, with seeds stored dry in the dark at 4°C for 2 and 52 weeks compared with freshly collected seeds. At 28–29°C, with a 14-hour photoperiod, germination of non-sterilized, 2-week-stored seeds lagged considerably behind similarly treated seeds stored for 0 or 52 weeks (52%, 75%, and 81% final germination, respectively). Additional germination trials at 4, 6, 8, 10, 12, 16, and 24 weeks indicated that reduced germination in non-sterilized, cold-stored seeds persisted through 24 weeks of cold storage. Sterilization with sodium hypochlorite stimulated germination to almost 100%, irrespective of the length of dry cold storage in seeds stored for 0, 2, or 52 weeks. Results of these studies support the general stimulation of seed germination by sodium hypochlorite treatment and indicate that while short periods of dry cold storage may depress germination percentages somewhat, long periods of storage impose no significant germination deterrence in J. effusus.