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As rising sea levels alter coastal ecosystems, there is a pressing need to examine the effects of saltwater intrusion on coastal communities. Using 16S Illumina profiling, we characterized the communities of baldcypress tree (Taxodium distichum) root endosphere and rhizosphere soil bacteria. Our study utilized established sites along salinity and flooding gradients in the United States of Georgia, Louisiana, and South Carolina. We hypothesized that environmental variables, namely salinity and water level, as well as distance between sites would be correlated with baldcypress-associated rhizosphere and root endosphere bacterial communities. We found that geographic distance correlated with rhizosphere but not root endosphere bacterial communities, suggesting that the trees may have stabilized their endosphere communities via recruitment of a more specific suite of taxa from the surrounding soil. Mean water level, mean salinity, and the volume of woody debris were associated with both endosphere and rhizosphere bacterial communities in baldcypress trees. The density of host trees was also associated with endosphere community composition. Our study is the first to use 16S Illumina sequencing to characterize bacterial communities in baldcypress trees— a key restoration species in coastal swamp ecosystems under threat from rising sea levels.

Plant roots assemble in two distinct microbial compartments: the rhizosphere (microbes in soil surrounding roots) and the endosphere (microbes within roots). Our knowledge of fungal community assembly in these compartments is limited, especially in wetlands. We tested the hypothesis that biotic factors would have direct effects on rhizosphere and endosphere assembly, while abiotic factors would have direct and indirect effects. Using a field study, we examined the influences of salinity, water level and biotic factors on baldcypress (Taxodium distichum) fungal communities. We found that endosphere fungi, unlike rhizosphere fungi, were correlated with host density and canopy cover, suggesting that hosts can impose selective filters on fungi colonizing their roots. Meanwhile, local abiotic conditions strongly influenced both rhizosphere and endosphere diversity in opposite patterns, e.g. highest endosphere diversity (hump-shaped) and lowest rhizosphere diversity (U-shaped) at intermediate salinity levels. These results indicate that the assembly and structure of the root endosphere and rhizosphere within a host can be shaped by different processes. Our results also highlight the importance of assessing how environmental changes affect plant and plant-associated fungal communities in wetland ecosystems where saltwater intrusion and sea level rise are major threats to both plant and fungal communities.

With rising sea levels, mortality of glycophytes can be caused by water and nutrient stress under increasing salinity. However, the relative effects of these two stressors may vary by species-specific functional traits. For example, deciduous species, with leaves typically emerging during low salinity periods of the year, may suffer less from water stress than evergreen species. We sampled two woody species with contrasting functional traits: the evergreen and N2-fixing waxmyrtle (Morella cerifera), and the deciduous and non-N2 fixing baldcypress (Taxodium distichum) along a coastal river (South Carolina, USA) showing an increasing pattern of plant mortality along a salinity gradient. We first analyzed oxygen and hydrogen isotope ratios of plant stem water and river water to determine changes in plant source water at different sites. Then we analyzed foliar carbon and nitrogen isotope ratios (δ13C and δ15N) along with nitrogen and phosphorus content (%N and %P) as proxies for the water and nutrient stress. Results showed that: (1) the two species had different water sources at the higher salinity sites; (2) foliar δ15N values of baldcypress decreased with higher salinity while retaining a constant δ13C value, and both of these isotope values were positively related with foliar %P, suggesting greater nutrient stress but minor water stress under high salinity; and (3) foliar δ13C values of waxmyrtle increased with higher salinity while retaining a constant foliar δ15N value, and neither of the values was significantly related to foliar nutrients, suggesting greater water stress but minor nutrient stress under high salinity. The different responses of the two species to high salinity may be related to their differences in leaf phenology and N2-fixation. Our results suggest that nutrient stress, particularly of P, can contribute to stress and eventual high mortality of baldcypress exposed to salt water intrusion.

Forested wetlands dominated by baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) are commonly found in coastal regions of the southeastern United States. Global climate change and in particular sea level rise will alter the frequency and magnitude of wet/dry periods and salinity levels in these ecosystems. Soil microcosm experiments were set up to identify the effects of water level variations (0.4–3.0 g-water g-soil−1) and salinity changes (0, 1 and 5 ppt of NaCl) on greenhouse gas emissions (CH4, CO2, and N2O) and dissolved organic carbon (DOC) characteristics from forested wetland soils. Our results indicate that, the effect of water level was much greater than salt intrusion on C and N cycling. Wet–dry treatments significantly decreased DOC production and total CH4-C loss, aromatic and humic-like substance compounds in DOC were increased in both flooding and wet–dry treatments after 60-d incubation. The molecular weight (MW) of DOC, as indicated by E2/E3 ratio and spectral slope, after flooding treatments was higher than that in wet–dry treatments. A first order kinetic model showed there was a positive linear correlation (r2 = 0.73) between CO2 emission rate and DOC concentration which indicated that CO2 was mainly generated from DOC. An exponential kinetic model was applied to describe the correlation between CH4 emission rate and DOC concentration (r2 = 0.41). This study demonstrates that an increase in salinity, and in particular variations in wet–dry cycles, will lead to changes in the formation of climate-relevant greenhouse gases, such as CH4, CO2, and N2O.

Tidal freshwater forested wetlands (TFFW) of the southeastern United States are experiencing increased saltwater intrusion mainly due to sea-level rise. Inter-annual and intra-annual variability in forest productivity along a salinity gradient was studied on established sites. Aboveground net primary productivity (ANPP) of trees was monitored from 2013 to 2015 on three sites within a baldcypress ( Taxodium distichum ) swamp forest ecosystem in Strawberry Swamp on Hobcaw Barony, Georgetown County, South Carolina. Paired plots (20 × 25-m) were established along a water salinity gradient (0.8, 2.6, 4.6 PSU). Salinity was continuously monitored, litterfall was measured monthly, and growth of overstory trees ⩾10 cm diameter at breast height (DBH) was monitored on an annual basis. Annual litterfall and stem wood growth were summed to estimate ANPP. The DBH of live and dead individuals of understory shrubs were measured to calculate density, basal area (BA), and important values (IV). Freshwater forest communities clearly differed in composition, structure, tree size, BA, and productivity across the salinity gradient. The higher salinity plots had decreased numbers of tree species, density, and BA. Higher salinity reduced average ANPP. The dominant tree species and their relative densities did not change along the salinity gradient, but the dominance of the primary tree species differed with increasing salinity. Baldcypress was the predominant tree species with highest density, DBH, BA, IV, and contribution to total ANPP on all sites. Mean growth rate of baldcypress trees decreased with increasing salinity, but exhibited the greatest growth among all tree species. While the overall number of shrub species decreased with increasing salinity, wax myrtle ( Morella cerifera ) density, DBH, BA, and IV increased with salinity. With rising sea level and increasing salinity levels, low regeneration of baldcypress, and the invasion of wax myrtle, typical successional patterns in TFFW and forest health are likely to change in the future.

Deepwater swamps, primarily baldcypress-water tupelo, pondcypress-swamp tupelo, or Atlantic white-cedar, are freshwater systems with standing water for most or all of the year. Probably the first classification of deepwater swamp forests was Shaler, who used both physical and vegetational characteristics to identify two types of forested wetlands: freshwater swamps and estuarine swamps. Other classification systems developed in the 1950s were based on vegetation, habitat, and the quantity, depth, and duration of water as diagnostic criteria. Deepwater swamps occur in a wide variety of geomorphic situations ranging from broad, flat floodplains to isolated basins. Soils of deepwater swamps generally have ample nutrients. Major flows of nutrients most frequently measured in these swamps include decomposition, wood accumulation, sedimentation, and return of nutrients from the forest canopy as litterfall. Fire is generally infrequent in natural deepwater forests of the southern United States because of the continuously moist conditions.

Downed woody debris is an important component of the forest floor, responsible for long-term storage of nutrients in many ecosystems. In large floodplain forests of the southeastern United States, wood loads are relatively low, suggesting these landscapes may promote rapid decomposition and nutrient turnover rates. The goals of this study were to identify the major factors responsible for wood decomposition and associated nutrient dynamics in an old-growth floodplain forest at Congaree National Park, South Carolina (USA). In situ decomposition and nutrient dynamics were quantified for 700 days (April 2011–March 2013) using wood from a common overstory species, red maple (Acer rubrum L.). During the study period, regional drought conditions allowed red imported fire ant (RIFA, Solenopsis invicta Buren) colonization and infestation of the study wood after 183 days in the field. Carbon (C) content decreased throughout the study, indicating net mineralization was occurring year-round. Invertebrate activity contributed to extremely fast decomposition rates (mean k 0.650 ± 0.02 year−1) and wood turnover times (mean 4.79 ± 0.15 years). In contrast to C, wood nitrogen (N) and phosphorus (P) content increased following RIFA infestation, displaying net nutrient immobilization. The rapid turnover rates measured at CONG indicate that the C storage function of woody debris may be diminished, but availability of mineralized N and P may also have increased the importance of wood stocks to support forest net primary productivity.

Salinity intrusion is responsible for changes to freshwater wetland watersheds globally, but little is known about how wetland water budgets might be influenced by small increments in salinity. We studied a forested wetland in South Carolina, USA, and installed sap flow probes on 72 trees/shrubs along a salinity gradient. Species investigated included the trees baldcypress (Taxodium distichum [L.] Rich.), water tupelo (Nyssa aquatica L.), swamp tupelo (Nyssa biflora Walt.), and the shrub waxmyrtle (Morella cerifera (L.) Small). This study improves upon past reliance on greenhouse seedling studies by adding measurements of trees/shrubs along a salinity gradient, and better describes the role of low salinity on water use in freshwater wetland forests. We measured patterns of water use related to salinity, atmospheric conditions and season, and hypothesized that salinity would influence wetland forest water use through two mechanisms: salinity disturbances would yield stands with species and size classes that transpire less and individual trees with less conductive xylem tissue (i.e., sapwood). Both hypotheses held. At salinity concentrations ranging from fresh to 3 psu, forest structural changes alone resulted in stand water use reductions from 494 mm year-1 in freshwater stands to 316 mm year-1 in stands of slightly higher salinity. Tree sapwood function (inferred from radial sap flux profiles) also changed along this gradient and reduced sap flow rates by an additional 13.3% per unit increase in salinity (psu). Thus, stand water use was further reduced to 190 mm year-1 on saline sites. We found that forest structure is not the only change that affects water use in salinized watersheds; individual tree eco-physiological responses to salinity, manifesting in different radial sap flow profiles, are important as well.

An assimilation wetland is a natural (non-constructed) wetland into which secondarily-treated, disinfected, non-toxic municipal effluent is discharged. In the Mississippi River Delta, the wetland is typically either a freshwater forested wetland (e.g., baldcypress-water tupelo) or a freshwater emergent wetland. These wetlands have been hydrology altered, some extensively, with freshwater input reduced from historical norms. Discharge of freshwater effluent with nutrients and suspended sediments into an assimilation wetland increases vegetation productivity and accretion and combats subsidence. Effluent discharge rate into an assimilation wetland depends on wetland size and effluent nutrient concentrations. Design and construction of an assimilation wetland requires a Louisiana Department of Natural Resources (LDNR) Coastal Use Permit (CUP), a Louisiana Department of Environmental Quality (LDEQ) Louisiana Pollutant Discharge Elimination System (LPDES) permit, a US Army Corps of Engineers (USACE) 404 permit, and an LDEQ Water Quality Certification, along with potential levee board permit applications. Both a feasibility study and an ecological baseline study are conducted before discharge of treated effluent begins. Assimilation wetlands are designed with a minimum of four monitoring sites; three located along a transect from the discharge to the area where surface water leaves the wetland, and the fourth, a reference area, located in an ecologically similar wetland nearby. As part of the LDEQ LPDES permit, study sites within an assimilation wetland are monitored continually for the life of the project, including vegetation productivity and species composition, sediment accretion, hydrology, and surface water nutrient and metals concentrations. There are ten active assimilation wetlands in coastal Louisiana and another four with permit applications pending. Results of annual monitoring show nutrient concentrations of surface waters decrease with distance, reaching background levels before water leaves the wetland. While nutrient concentrations decrease, vegetative productivity is enhanced. In degraded forested wetlands being used as assimilation wetlands, baldcypress and water tupelo seedlings are often planted, which thrive in the nutrient rich environment. However, nutria are attracted to vegetation with increased nutrient concentrations, and herbivory severely damaged one emergent wetland receiving municipal effluent, killing both herbaceous vegetation and unprotected tree seedlings. After culling of nutria, the wetland recovered. This introduced species must be monitored and controlled in any assimilation wetland. Here we review the history of assimilation wetlands in the Mississippi River Delta to show how advances in scientific understanding, growing regulatory sophistication, and controversy have shaped this program.

Alterations to Louisiana’s coastal landscape during the last 200 years have resulted in major changes to the natural hydrologic regime. Hurricane and tornado winds further impact coastal forests by exacerbating conditions that affect community structure, growth, and regeneration. Twenty-three years of study of forested wetlands in the Lake Verret watershed provide an opportunity to relate changes in forest communities to precipitation, drought, storms, and rising water levels. The area had two communities in 1986, but four communities were present by 2009. A major change in community composition occurred in drier sites after Hurricane Andrew (1992), when Chinese tallow (Triadica sebifera) became established. Swamp plots were generally not affected by hurricanes, but composition continued to change as a result of flooding. After Hurricane Andrew, net primary productivity (NPP) declined dramatically until 2001. Subsequent hurricanes in 2004 and 2005 also caused reductions in NPP, but recovery was rapid. Low-lying and transition areas are trending from bottomland communities toward more of a deepwater swamp as baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) increase their stature, likely due to the system-wide flooding. Natural ridges are flooded less often and have remained primarily bottomland, though Chinese tallow (Triadica sebiferum) numbers increased following Hurricane Andrew.

Microbial fuel cell (MFC) technology has shown great potential for harvesting energy from waste organic materials. Here, we explored the potential of MFC-based electricity generation from forest detritus, a large untapped biomass pool. Electricity generation from in situ MFCs and relevant environmental parameters (i.e., carbon sources and concentrations, temperature, water depth) in a seasonally flooded freshwater cypress-tupelo wetland were monitored intensively for two flooding periods. Current outputs ranged from 0 to 1.27 mA (mean of 0.40 mA for flooding period) and were highly sensitive to environmental changes, showing seasonal and diel dependences. Excluding the influence of heavy storms, drought, or wetland icing, current output was highly temperature-dependent dielly. Seasonally, current output gradually increased in the first 3–4 months (limited by temperature) and decreased slightly during the last 1–2 months (probably limited by carbon and nutrients) of both flooding periods. Litter extract of baldcypress (Taxodium distictum) with lower C/N ratio and aromatic content showed greater stable current outputs (0.57 mA) based on 50 mg l � 1 biological oxygen demand compared to extracts of water tupelo (Nyssa aquatica) and longleaf pine (Pinus palustris), suggesting that the current output of in situ MFCs could depend on the vegetation within a wetland. Our study highlights the potential application of MFC in generating green and sustainable electricity from forest biomass for powering remote sensors in wetland ecosystems.

Little is known of the ability of baldcypress (Taxodium distichum (L.) L.C. Rich.) in a suppressed sub-canopy position to respond to increases in light. We measured 3 years of diameter growth response of long-suppressed baldcypress saplings to canopy gap creation in a hydrologically altered, water tupelo-dominated backswamp of the lower Roanoke River floodplain in eastern North Carolina. Baldcypress saplings responded strongly to gap creation. Saplings showed a significant positive growth trend, with mean basal area growth in gaps expanding from 2.5 cm2 in year one, 4 times that of control saplings, to 8.5 cm2 in year three, 20 times that of control saplings. Within canopy gaps, a positive trend between growth and initial sapling diameter was evident, while such a trend among controls was non-existent. Mortality was similar between gap and control saplings after 1 year, but by year three gap sapling mortality had declined to 2 %, while control mortality increased to 16 %. It is clear that long-suppressed baldcypress, sometimes at the brink of death, are able to respond vigorously to an increase in light from canopy gaps with decreased mortality and increased growth. This has important implications for wetlands requiring restoration or baldcypress management within the framework of two-age or uneven-aged silvicultural systems.

Questions What are the general tree communities found in tidal freshwater swamps along four large coastal rivers in the southeastern United States (US)? How do these communities compare to other tidal freshwater swamps in the US and South America? Locations Tidal floodplains of major rivers along the Atlantic and Gulf coasts of the southeastern US: Savannah, Altamaha, Suwannee and Apalachicola Rivers. Methods An extensive survey of trees and shrubs was conducted to describe the communities from a range of tidal freshwater swamps. River basins studied include micro-tidal (Gulf coast) and meso-tidal (Atlantic coast) regimes, and study areas were located both near and distant to primary channels. A total of 128 plots (100 m2 each) were inventoried, distributed evenly over the Savannah and Altamaha Rivers along the Atlantic coast, and the Suwannee and Apalachicola Rivers along the Gulf coast. Multivariate statistics helped discern communities and the significant indicator species in each. Results Four general communities were characterized and named according to the strongest individual indicator species in each: Water Tupelo (Nyssa aquatica) Community, Swamp Tupelo (Nyssa biflora) Community, Dwarf Palmetto (Sabal minor) Community and Cabbage Palm (Sabal palmetto) Community. Conclusions Descriptions of most tidal freshwater swamps in the southeastern US fit within the communities described in this study. Because studies that make inferences between environmental drivers (e.g. salinity, hydroperiod, hurricanes) and specific community types are best applied to the same communities (but perhaps different river systems), this work provides a framework by which tidal freshwater forested wetlands can be accurately compared based on their tree communities. We suggest that, within the broad range of our inventories, the four communities described identify the primary associations that should be tracked within most tidal freshwater swamps of the US. However, we identify some river basins in the US that do not fit this construct. Diversity of major tree communities in tidal freshwater swamps outside the US is generally much lower (with the notable exception of Amazonian hardwood tidal varzea), as are basal area values.

Hummock and hollow microtopography is pervasive in tidal freshwater swamps. Many tree species grow atop hummocks significantly more than in hollows, leading to the hypothesis that hummocks provide preferred locations for maximizing physiological proficiency of inhabiting trees that experience repeated flooding. We used thermal dissipation probes to measure the ecophysiological proficiency of a very flood-tolerant tree, Taxodium distichum, as manifested through in-situ changes in sapflow (a proxy for transpiration) in 11 trees on hummocks and 11 trees in hollows. Overall, sapflow increased significantly by 3.3 g H2O m−2 s−1 (11 %) in trees on both hummocks and hollows during flooding, contrary to our expectations. We found no significant differences in sapflow rates between T. distichum trees positioned on hummocks versus hollows in relation to discrete flood events. Coincidentally, hummock elevations were equivalent to the flood depths that promoted greatest physiological proficiency in T. distichum, suggesting a physiological role for the maintenance of hummock height in tidal swamps. While we reject our original hypotheses that flooding and positioning in hollows will reduce sapflow in T. distichum, this research reveals a potentially important feedback between hummock height, flood depth, and maximum tree physiological response.

Seasonally flooded, freshwater cypress-tupelo wetlands, dominated by baldcypress (Taxodium distictum), water tupelo (Nyssa aquatica), and swamp tupelo (Nyssa sylvatica var. biflora) are commonly found in coastal regions of the southeastern United States. These wetlands are threatened due to climate change, sea level rise, and coastal urban development. Understanding the natural biogeochemical cycles of nutrients in these forested wetlands as ecosystems services such as carbon sequestration and nitrogen processing can provide important benchmarks to guide conservation plans and restoration goals. In this study, surface water and soil pore water samples were collected weekly from a cypress-tupelo wetland near Winyah Bay, South Carolina and analyzed for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), inorganic nitrogen, and phosphate during its flooding period between October 2010 and May 2011. DOC was further characterized by specific ultra-violet absorbance at 254 nm, spectral slope ratio (SR) (ratio of two spectral slopes between 275–295 nm and 350–400 nm), E2/E3 ratio (ratio between A254 and A365), and fluorescence excitation-emission matrix. In addition, litterfall was collected on a monthly basis for a year while the biomass of the detritus layer (i.e., decomposed duff lying on the wetland floor) was determined before and after the flooding period. Results of the field study showed that concentrations of DOC, DON, NH4 +–N, and (NO2 − + NO3 −)–N in the surface water were generally higher during the fall, or peak litterfall season (October to December), than in the spring season (March to May). Highest concentrations of 54.8, 1.48, 0.270, and 0.0205 mg L−1, for DOC, DON, NH4 +–N, and (NO2 − + NO3 −)–N respectively, in surface waters were recorded during October. Lower SUVA, but higher SR and E2/E3 ratios of DOC, were observed at the end of the flooding season comparing to the initial flooding, suggesting the wetland system converts high aromatic and large DOC molecules into smaller and hydrophilic fractions possibly through photochemical oxidation. A similar trend was observed in soil pore water, but the pore water generally had greater and relatively stable concentrations of dissolved nutrients than surface water. No obvious temporal trend in phosphate concentration and total nitrogen to total phosphorus ratio (N:P) were found. Results of the laboratory extraction and mass balance calculation suggested fresh litter was a major source of DOC whereas decomposed duff was the source of dissolved nitrogen in surface water. In summary, the biogeochemistry of this isolated cypress-tupelo wetland is not only driven by the vegetation within the wetland system but also by hydrology and weather conditions such as groundwater table position, precipitation, and temperature.

Tidal freshwater forested wetlands occupy a relatively narrow range, occurring where wind and lunar tides interact with coastal river systems, causing freshwater flooding onto the floodplain. A prominent component of this wetland type is hummock and hollow microtopography. Tidal freshwater forested wetlands along the Savannah River were differentiated into backswamp and streamside areas, and the degree to which trees occupied hummocks and hollows were compared at three scales: landscape (backswamp vs. streamside), tree community, and species (within community). The community- and species-level analyses were extended to determine whether trees were using either hummocks or hollows in a nonrandom manner. Trees in the backswamp setting were found to use hummocks more than trees in the streamside setting. At the community scale, three of the five treatment groups investigated differed based on the degree to which trees on hummocks outnumber trees in hollows. Further examination of microtopography usage confirmed that hummocks are used significantly more than hollows in two communities, both of which are located in the backswamp setting. Though no tree community used hollows significantly more than hummocks, species-level analyses confirmed that, within a specific tree community in the streamside setting, alder (Alnus serrulata [Ait.] Willd.) is found more in hollows than on hummocks. Fourteen different species between the two communities in the backswamp setting are found on hummocks more than in hollows, and only one species, sweetgum (Liquidambar styraciflua L.), is found more on hummocks than in hollows in the tree community in the streamside setting.

This report documents changes in forest structure and growth potential of dominant trees in salt-impacted tidal and non-tidal baldcypress wetlands of the southeastern United States. We inventoried basal area and tree height, and monitored incremental growth (in basal area) of codominant baldcypress (Taxodium distichum) trees monthly, for over four years, to examine the inter-relationships among growth, site fertility, and soil physico-chemical characteristics. We found that salinity, soil total nitrogen (TN), flood duration, and flood frequency affected forest structure and growth the greatest. While mean annual site salinity ranged from 0.1 to 3.4 ppt, sites with salinity concentrations of 1.3 ppt or greater supported a basal area of less than 40 m2/ha. Where salinity was < 0.7 ppt, basal area was as high as 87 m2/ha. Stand height was also negatively affected by higher salinity. However, salinity related only to soil TN concentrations or to the relative balance between soil TN and total phosphorus (TP), which reached a maximum concentration between 1.2 and 2.0 ppt salinity. As estuarine influence shifts inland with sea-level rise, forest growth may become more strongly linked to salinity, not only due to salt effects but also as a consequence of site nitrogen imbalance.

Above-ground net primary productivity (NPP), decomposition of water tupelo leaves, and nutrient dynamics were investigated from 2000 to 2002 within a coastal, tidally influenced forested wetland on Bull Island, SC. Flooding of the island is influenced by flooding events of the Pee Dee River (PD) on the western side of the island, Big and Little Bull Creeks (BC) on the eastern side, and daily tidal fluctuations. Above-ground NPP ranged between 477 g/m2 and 1117 g/m2 while mean above-ground NPP was 743 g/m2 when all data were combined regardless of growing seasons or sites. Mean annual litterfall and stemwood production were 463 g/(m2 year) and 279 g/(m2 year), respectively, for all three growing seasons. Analyses also showed that the 3-year average above-ground NPP was significantly higher (p

Regeneration of baldcypress (Taxodium distichum (L.) Rich.) and water tupelo (Nyssa aquatica L.) in swamps of the deltaic plain of the Mississippi River are of major importance for ecosystem sustainability and forest management in the context of regional hydrological changes. Water tupelo often forms prolific sprouts from cut stumps, and baldcypress is one of few conifers to produce stump sprouts capable of becoming full-grown trees. Previous studies have addressed early survival of baldcypress stump sprouts, but have not addressed the likelihood of sprouts becoming an important component of mature stands. We surveyed stands in southeastern Louisiana that were partially logged 10–41 years ago to determine if stump sprouts are an important mechanism of regeneration. At each site we inventoried stumps and measured stump height and diameter, presence and number of sprouts, sprout height, and water depth. We determined age and diameter growth rate for the largest sprout from each stump from increment cores. The majority of stumps did not have surviving sprouts. Baldcypress sprout survival was about the same (median 10%) as previously found for stumps up to 7 years old, so it appears that, although mortality is high soon after sprouting, it is low after age 10. Water tupelo sprouting was rare at our sites but it was not clear whether this may have been because trees were not cut at our sample locations. Baldcypress stump sprouts were more likely to survive on shorter, smaller-diameter stumps, and baldcypress sprout growth was greatest on drier sites with less competition from overstory trees. Surviving baldcypress stump sprouts had high growth rates, but were not regularly spatially distributed within stands and many had advancing decay from stumps into sprouts. # 2006 Elsevier B.V. All rights reserved.

Coastal baldcypress (Taxodium distichum) forests are being killed in the southern United States as a result of saltwater intrusion. Tank studies have indicated substantial intraspecific variation in salt tolerance within baldcypress populations, but only one field study has been conducted and it used a limited seed source. The major objective of this project was to expand the collection range of baldcypress across the southeastern United States and determine if there are baldcypress populations that can survive and grow in saltwater damaged areas. Seeds were collected in 1996 from eight estuarine areas (James River = VA; Cape Fear River = NC; Winyah Bay = SC; Ogeechee River = GA; Ochlockonee River = FL; Mobile Bay = AL; Biloxi River=MS; Chalmette = LA). Seeds were stratified and planted, and seedlings were grown for 2 years before planting in two abandoned ricefields on Hobcaw Barony near Georgetown, South Carolina in 1999. Salinity levels reached 18.5ppt during 2001 at the peak of the worst drought on record. By 2002, the only seedlings surviving were those from LA, AL, and FL. After 5 years in the field, LA seedlings were the best performers with a mortality rate of only 27%. More detailed analyses of the biologic and genetic characteristics of trees growing in the LA site need to be completed to determine if they represent a source of baldcypress seed possessing greater tolerance to saline conditions. If so, seeds need to be collected and nurseries established to grow seedlings to help restore degraded wetland swamp areas along the Gulf and Atlantic coasts.

While coastal forested wetlands of the southern United States have developed with hurricanes as normal aperiodic events and suffer little damage or mortality due to wind, they can be heavily impacted by saltwater storm surges. Three wetland stands (Boardwalk, Crabhaul, and Marsh Road) were studied on Hobcaw Barony, SC, USA, from 1991 to 2001 to determine the recovery of trees following Hurricane Hugo. Five 0.05 ha plots were established during the spring and summer of 1990 in each stand, and diameter measurements were made annually. In terms of the number of trees, basal area, and importance value, baldcypress (Taxodium distichum) and swamp blackgum (Nyssa sylvatica var. biflora) were the most important tree species in the Boardwalk and Marsh Road sites, while baldcypress, water tupelo (Nyssa aquatica), and swamp blackgum were most important in the Crabhaul site. The influx of saltwater from the storm surge killed all individuals of five species (sweetgum (Liquidambar styraciflua), red maple (Acer rubrum), sugarberry (Celtis laevigata), redbay (Persea borbonia), and waxmyrtle (Myrica cerifera)) in the Boardwalk site, as well as three species (sweetgum, red maple, and laurel oak (Quercus lauriflolia)) in the Marsh Road site. Of the remaining trees in both of these sites, baldcypress was the most impacted by saltwater, and mortality continued for several years after the hurricane. No saltwater damage occurred in the Crabhaul site. Mean annual growth rate of baldcypress was greater than other species in all three sites. Diameter change of baldcypress in the Boardwalk site averaged 1.80±0.77 mm per year (±1S.D.), followed by swamp blackgum at 0.85±0.39 mm per year and water tupelo at 0.46±0.84 mm per year. In the Crabhaul site, average growth of baldcypress was 2.00±0.52 mm per year, followed by water tupelo at 1.35±0.62 mm per year and swamp blackgum at 0.51±0.59 mm per year. Baldcypress growth was 2.12±1.2 mm per year in the Marsh Road site, while only 0.60±0.84 mm per year and 0.55±0.45 mm per year growth occurred for water tupelo and swamp blackgum, respectively. The loss of a majority of the mature trees in the Boardwalk and Marsh Road sites, combined with the lack of a viable seed bank and the loss of most of the shrub layer, means that it will take years before these stands fully recover. The Crabhaul site, on the other hand, had less than 3% mortality from the hurricane, and canopy recovery was complete after only one growing season.

Depressional wetlands provide habitat for birds, mammals, reptiles, amphibians, invertebrates, and rare plant species. In order to protect, restore, and manage depressional wetlands, it is important to know more about the vegetative composition and productivity of these systems. The species composition and aboveground productivity of three seasonally flooded depressional forested wetlands were studied on the coastal plain of South Carolina from January 2000 to January 2001. The dominant tree species in the depressions were Taxodium distichum [L.] Rich., Nyssa aquatica L., and Nyssa sylvatica var. biflora [Walt.] Sarg. Annual diameter at breast height (dbh) growth was measured for all trees >10 cm dbh in five 20 × 25 m plots within each depression, and changes in dbh were used to estimate annual biomass and stem production. Aboveground net primary productivity (ANPP) was calculated for each wetland by summing stem and leaf litter production. There were no significant differences in ANPP among site...

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.

Decomposition of site-specific litter mixtures was monitored for 100 wk in four Roodplaht communities: (i) a mixed oak community along the Cache River in central Arkansas, (ii) s sweetgum (Liquidambar styracijlua L.)-cherrybark oak (Quercwfalcata vwpagodaefolia ELI.) community along Iatt Creek in central Louisiana, (iii) a sweetgum-swamp tupelo [Nyssu sylvaticu var. bifroru (Walt.) Sarg.] community, and (iv) a laurel oak (Quercus luurifolia Michx.) commnnity along the Coosawhatchie River in southeastern South Carolina. Soil temperature, hydroperiod, and litter quality (C:N, C:P, N:P, fignin:N) were used to interpret differences in the rates of mass loss and nutrient dynamics. After 100 wk, litter mixtures retained 33, 18, 8, and 5% of original mass on the Cache, Coosawhatchie (laurel oak community), Coosawhatchie (sweetgum-swamp tupelo community), and Iatt floodplains, respectively, and these differences appeared related to hydroperiod. Decay rates were comparable to rates reported in similar floodplain environments. Net mineralization of both N and P was observed after 100 wk, but both elements accumulated in litter mixtures periodically. Differences in hydroperiod were observed among the four floodplain communities and decomposition of and nutrient mineralization from litter among them appeared to be inversely related to the number and duration of flood events. Litterbags containing leaf litter of a single-species (i.e., cherrybark oak) were also monitored on three of the four sites to compare decay rates and nutrient dynamics with the litter mixtures. On the Cache River floodplain, slower decay of poorer quality cherrybark oak litter suggested that titter quality drove decomposition under similar edaphic conditions.

The use of tree shelters to enhance survival and growth of bald cypress, water tupelo, green ash, and black tupelo were evaluated in the riparian and swamp forest of the Pen Branch delta. Survival at the end of the five years ranged from 67% to 100% for seedlings in shelters and 2% to 90% for those in the open. Mortality resulted primarily from beavers. Height growth was only improved for seedlings in shelters for the first few years.

Morphology, physiology, and growth of 16 poplar clones (Populus deltoides Marsh.) were investigated during a 42-day flooding experiment. Three treatments were applied: watered, flooded to 3 cm above the soil surface, and completely submerged. Although all plants survived the entire 42-day period, leaf initiation was inhibited by flooding and chlorosis and abscission occurred. Leaf size, leaf area, and number of leaves were reduced for all flooded plants relative to watered plants. Flooding inhibited root growth and caused some deterioration of the original root system. Other responses to flooding included formation of hypertrophied lenticels and adventitious roots on submerged portions of stems, decreased chlorophyll a fluorescence, decreased transpiration rate, and increased leaf diffusion rate. There was no significant difference in leaf water potential between flooded and watered plants. Based on data of all measured values and by means of cluster analysis, the clones can be divided into three types. Type 1 clones (ST197, ST91, ST163, ST75, ST165, ST260, ST259, LU) were resistant to flooding. Type 2 clones (ST264, 800, CL723, CL552) were moderately tolerant to flooding, and Type 3 clones (ST261, ST238, ST202, ST229) were flood intolerant.

Buttonbush (Cephalanthus occidentalis) and swamp tupelo (Nyssa sylvatica var.biflora) seedlings were exposed to flooding and salinity conditions simulating the chronic exposure of sea-level rise and the acute exposure of hurricane storm surge. Chronically exposed seedlings were either watered or flooded with 0, 2, or 10 ppt salinity. Those in the acute experiment were watered or flooded with freshwater until exposed to a 21-ppt salinity surge for 48 hours. Freshwater flooding reduced photosynthesis (A), water pressure potential (Ψ), height, and stem and root biomass for swamp tupelo while biomass of buttonbush roots decreased and stem increased. Chronic watering with 2 ppt salinity reduced height, basal diameter, and stem and root biomass for swamp tupelo but did not significantly affect buttonbush. Both species were negatively affected by watering with 10 ppt salinity, with total mortality of swamp tupelo. Flooding with 2 ppt salinity also caused a 100% mortality for swamp tupelo. All buttonbush seedlings survived with reducedA, Ψ, and stem and root biomass. Plants chronically flooded with 10 ppt salinity were more affected, with drastically decreasedA, stomatal conductance (g s ), and Ψ within the first day of treatment and all dying within three weeks. Watering with 21 ppt salinity reducedA andg, of both species during the second day of the surge, but buttonbush recovered within the next 20 days. Flooding with 21-ppt saline water also greatly impacted buttonbush, which did not recover as when watered with 21 ppt salinity. Swamp tupelo was already stressed due to flooding and showed no further reduction in A org s due to the 21-ppt salinity flood surge. Buttonbush seedlings were more tolerant of salinity and flooding conditions than swamp tupelo seedlings, although it is unlikely that either species could survive long-term exposure to 10-ppt salinity flooding.

Numerous investigations have examined the growth of wetland tree species under a variety of hydrologic conditions. Most studies have compared flooded versus non-flooded conditions in greenhouses or in one to a few field sites near each other or within the same region. Comparisons of wetland tree growth among widely separated areas of the country are rare. This study compared the diameter growth of Nyssa sylvatica var. biflora, Nyssa aquatica, and Taxodium distichum trees from Louisiana (Gulf Coastal Plain) and South Carolina (Atlantic Coastal Plain). In both regions, individual trees were distributed along a gradient of hydrologic regimes from infrequent to permanent flooding. Nyssa sylvatica var. biflora was restricted to periodically flooded sites in both regions. Within these sites, this species showed little response to differences in mean water depth. In contrast, significant differences among hydrologic regimes were detected for N. aquatica in both regions. In Louisiana, patterns of growth response did not correlate with the gradient of hydrologic regimes, but in South Carolina maximum growth was inversely related to mean water levels during the growing season. Maximum growth of T. distichum trees was observed at sites with shallow, permanent flooding in both regions.

The survival, growth, and biomass of baldcypress (Taxodium distichum (L.) Rich.), water tupelo (Nyssa aquatica L.), Chinese tallow (Sapium sebiferum (L.) Roxb.), and green ash (Fraxinus pennsylvanica Marsh.) seedlings were examined in an experiment varying water levels (watered, flooded) and salinity levels (0, 2, and 10 ppt, plus a simulated storm surge with 32 ppt saltwater). All seedlings, except for those flooded with 10 ppt saltwater, survived to the end of the experiment. In 10 ppt saltwater, flooded baldcypress, water tupelo, and green ash survived two weeks whereas Chinese tallow survived for 6 weeks. However, a second set of slightly older baldcypress, water tupelo, and Chinese tallow seedlings survived eight weeks of flooding with 10 ppt saltwater. When carried through the winter to the beginning of the second growing season, flooded baldcypress and Chinese tallow seedlings from the 0 and 2 ppt treatments leafed out, but only Chinese tallow recovered from the saltwater surge treatment. The diameter and growth (height) of each species was not affected when watered with 2 ppt saltwater, except for the effects of the height growth of baldcypress. Growth was reduced for all species when watered with 10 ppt saltwater. The diameter growth of green ash was reduced by freshwater flooding. The diameter growth of baldcypress and water tupelo was greater when flooded with fresh water. Flooding with 2 ppt saltwater caused a significant reduction in diameter growth in water tupelo, green ash, and Chinese tallow, but not in baldcypress. Root and stem biomass values were not significantly different for any species between the 0 and 2 ppt salinity watering treatments. However, seedlings watered with 10 ppt saltwater had significantly lower root and stem biomass values, except for baldcypress roots and green ash stems. Baldcypress was least affected by flooding with 0 and 2 ppt saltwater, although there were slight reductions in root biomass with increasing salinity. Because of the susceptibility of the seedlings of these four species to increases in flooding and salinity, their regeneration may be limited in the future, thereby causing shifts in species composition.

The influence of flooding and salinity on photosynthesis and water relations was examined for four common coastal tree species [green ash (Fraxinus pennsylvanica Marshall), water tupelo (Nyssa aquatica L.). Chinese tallow (Sapium sebiferum (L.) Roxb.), and baldcypress (Taxodium distichum (L.) Richard)]. Both chronic (as might be associated with sea level rise) and acute (similar to hurricane storm surges) exposures to these stresses were examined. Chronic freshwater flooding of green ash, water tupelo, and Chinese tallow seedlings reduced photosynthesis (A) relative to that of watered seedlings, while baldcypress was unaffected. Chinese tallow A declined with increasing length of flooding. A salinity increase of the floodwater to 2 ppt decreased A of baldcypress and water tupelo, but not A of green ash and Chinese tallow, which was already severely reduced by freshwater flooding. All seedlings of the four species died within 2 to 6 weeks when flooded with 10 ppt saltwater. Photosynthesis of all four species did not differ between 0 and 2 ppt watering. Watering with 10 ppt salinity initially reduced A of all four species, but the seedlings recovered over time. Photosynthesis was severely decreased for all species when flooded with 21 ppt salinity for 48 hours. Reduced A continued following the treatment. Photosynthesis of only green ash and water tupelo was reduced by watering with 21 ppt salinity for 48 hours. Flooding of low-lying areas with increased salinity would lead to shifts in species composition of coastal forests due to these differential tolerances.

Spatial and temporal variations in net above-ground primary production (NPP) and litter turnover rate were studied, from 1987 to 1993, in a mangrove forest bordering Laguna de Terminos, Mexico. NPP, the sum of total litter fall and wood production, was measured over the entire study period in three zones in a basin forest: zone I, where Rhizophora mangle (red mangrove) occurs but Avicennia germinans (black mangrove) is the dominant species; zone II, a scrub forest of A. germinans; zone III, where larger A. germinans trees occur. In 1991, a fringe zone dominated by A. germinans and R. mangle was added to the study. Three distinctive climatic seasons occur in the region: rainy, dry, and cold front (locally named ‘nortes’). Average total litter fall in the fringe zone (793 g m−2 year−1) was significantly higher than in the basin forest (496, 307, and 410 g m−2 year−1 for basin zones I, II, and III, respectively). All zones showed significant differences among seasons with the norte season having significantly lower litter fall. Litter turnover rates were about 7 months in zones I and II and 10 months in zone III, reflecting the low tidal range that occurs in the basin forest. Low litter turnover rates in the basin forest were reflected in a high organic matter standing crop. Annual average stem growth was significantly higher in zones I and III (1.27 and 1.36 kg per tree year−1, respectively) than in zone II (0.62 kg per tree year−1). Above-ground NPP rates in the basin forest (399–695 g m−2 year−1) were lower than in fringe and riverine forests, reflecting patterns of litter fall and wood production. There was no seasonal variation in soil salinity but the basin forest had significantly higher soil salinity than the fringe forest. Spatially, mean soil salinity was inversely related to litter fall. Long-term patterns in soil salinity, precipitation and air temperature explained 74% of the inter-annual litter fall variability. Over the 7 year study, productivity in zone II was more variable than in zones I and III, and productivity (litter fall and wood growth) were less variable than litter standing crop and turnover.

Long-term monitoring began in 1990 to follow community changes resulting from hurricane disturbance. In addition, one-year-old Taxodium distichum seedlings were planted to determine if planting was feasible in saltwater-flooded areas. The canopy of the least impacted swamp recovered rapidly, but there were few seedlings growing in the understory. Planted seedlings survived well, but they grew very little. Both lack of seedlings and poor growth of planted seedlings were probably due to intense shading and flooding. Two impacted areas contained a greater number of seedlings, most of which were found growing on raised microsites like Taxodium knees. The majority of the seedlings in all areas were shrub species. Planted seedlings grew cell (30 cm/yr) where open canopy conditions allowed sunlight to reach the forest floor and no new saltwater has been introduced since the hurricane.

Freshwater forested wetlands commonly occur in the lower Coastal Plain of the southeastern US with baldcypress (Taxodium distichum [L.] L.C. Rich.) and water tupelo (Nyssa aquatica L.) often being the dominant trees. Extensive anthropogenic activities combined with eustatic sea-level rise and land subsidence have caused widespread hydrological changes in many of these forests. In addition, hurricanes (a common, although aperiodic occurrence) cause wide-spread damage from wind and storm surge events, with impacts exacerbated by human-mediated coastal modifications (e.g., dredging, navigation channels, etc.). Restoration of forested wetlands in coastal areas is important because emergent canopies can greatly diminish wind penetration, thereby reducing the wind stress available to generate surface waves and storm surge that are the major cause of damage to coastal ecosystems and their surrounding communities. While there is an overall paucity of large-scale restoration efforts within coastal forested wetlands of the southeastern US, we have determined important characteristics that should drive future efforts. Restoration efforts may be enhanced considerably if coupled with hydrological enhancement, such as freshwater, sediment, or sewage wastewater diversions. Large-scale restoration of coastal forests should be attempted to create a landscape capable of minimizing storm impacts and maximizing wetland sustainability in the face of climate change. Planting is the preferred regeneration method in many forested wetland sites because hydrological alterations have increased flooding, and planted seedlings must be protected from herbivory to enhance establishment. Programs identifying salt tolerance in coastal forest tree species need to be continued to help increase resilience to repetitive storm surge events.

In the interest of increasing productivity of forested wetlands for timber production and/or wildlife value, management schemes that deal mainly with water-level control have been developed. The three forest types in the southeastern U.S. most commonly affected are cypress/tupelo forests, bottomland hardwood forests, and wet pine sites (including pocosins). In forested wetlands, hydrology is the most important factor influencing productivity. In bottomland and cypress/tupelo forests, water-level control can have mixed results. Alterations in natural hydrologic patterns leading to increased flooding or drainage can cause decreased growth rates or even death of the forest. Bottomland hardwoods respond favorably in the short term to water-level management, but the long-term response is currently under study. In wet pine sites, timber volume can be increased significantly by water-level management, but the impact upon other ecological functions is less understood. It is difficult to adequately describe productivity relations in wetland forests because of the great diversity in habitat types and the lack of data on how structure and function might be affected by forestry operations. There is a definite need for more long-term, regional studies involving multidisciplinary efforts.

The Verret basin was formerly an overflow area between the Mississippi and Atchafalaya rivers and contains about 41,000ha of forested wetlands. Water levels are rising at the rate of over 1 cm/year in this area, and the forests are subjected to longer and deeper flooding. Tree growth, litterfall, and species composition were monitored across a flooding gradient during January 1985–December 1986. The driest area was only 20 cm higher in elevation than the wettest area, but the structure of the forest changes greatly over this range. The drier area was dominated by sweetgum (Liquidambar styraciflua L.), oaks (Quercus spp.), and sugarberry (Celtis laevigata Willd.), while green ash (Fraxinus pennsylvanica Marsh.), red maple (Acer rubrum L.), and baldcypress (Taxodium distichum (L.) Rich.) were dominant in the wetter area. Green ash and bitter pecan (Carya aquatica (Michaux. f.) Nutt.) were found in all plots, but these two species are under severe stress in the more flooded area as evidenced by dead and dying trees. Stem wood production increased from 1985 to 1986 in the driest (392 to 473 g/m2/yr) and wettest (199 to 399 g/m2/yr) plots, but remained relatively unchanged in the transitional area (386 to 380g/m2/yr). Leaf litter production decreased across the gradient from dry to flooded plots during both years. Over 40% of the litterfall in the drier plot was from flood-tolerant shrub species. In the flooded plots, red maple and baldcypress were major contributors to total litterfall. Increased flooding of dry bottomland forests in the future could lead to decreased litterfall and increased tree death over the entire watershed.

Bald cypress has long been a dominant timber species in Louisiana's wetland forests. Early settlers recognized the value of this species, and because of its durability and workability bald cypress remained a stable commodity of the lumber industry from the 18th through the early 20th Centuries. Early estimates of the area of bald-cypress forests range from 0.67 to 3.64 million ha. Bald-cypress timber was cut extensively from 1890 to 1925 when the last virgin stands of timber in the state were depleted. In 1934 there were 0.66 million ha of cutover bald-cypress forests in Louisiana. Recent estimates indicate that there are 0.14 million ha of bald-cypress swamp forest left in the state. Regeneration problems have increased in recent years due to human changes in hydrology and natural subsidence (> 1 m per century) and the introduction of the rodent, nutria, (Myocastor coypus) from South America. Even though the volume of bald-cypress growing-stock in the state continues to increase, the total acreage of bald-cypress swamp is declining. More work needs to be done in these wetland forests to ensure their survival for the future.

Common woody species growing on tree islands in the Water Conservation Areas of South Florida include redbay, sweetbay, coastal-plain willow, wax myrtle, dahoon holly, cocoplum, pond-apple, red maple, cypress, gumbo-limbo, strangler fig and buttonbush. Very little is known about the flooding tolerance of most of these species. In this paper, we review flooding impact studies, describe the most common species and discuss two methods that might be used to examine woody plant growth response to water level fluctuations. Although tree coring has been used effectively in many areas, the general lack of discernible rings and poor quality rings observed in these species makes this method of questionable use. Dendrometer bands, however, work well in any environment with any species and are recommended for further studies on tree islands.

As global climate changes, sea level rise and increased frequency of hurricanes will expose coastal forests to increased flooding and salinity. Quercus species are frequently dominant in these forest, yet little is known about their salinity tolerance, especially in combination with flooding. In this study, 1-year-old seedlings of Quercus lyrata Walt. (overcup oak), Q. michauxii Nutt. (swamp chestnut oak), Q. nigra L. (water oak), and Q. nuttallii Palmer (Nuttall oak) were chronically (simulating sea level rise) and acutely (simulating hurricane storm surge) exposed to increased flooding and salinity, individually and in combination. The four species demonstrated two response patterns of photosynthesis (A), conductance, and leaf water potential, apparently related to their relative flood tolerance. In Q. lyrata, Q. nuttallii, and Q. nigra (moderately flood-tolerant), A was not immediately reduced after the initiation of the freshwater flooding, but was reduced as the duration of flooding increased. In the second pattern, demonstrated by the weakly flood-tolerant Q. michauxii, A was immediately reduced by freshwater flooding with an increasing impact over time. Watering with 2 parts per thousand (ppt) saline water did not consistently reduce A, but flooding with 2 ppt reduced A of all species, similar to the response with freshwater flooding. Photosynthesis of all species was reduced by 6 ppt watering or flooding, with the latter treatment killing all species within 8 weeks. When acutely exposed to 30 ppt salinity, A was quickly and severely reduced regardless of whether the seedlings were watered or flooded. Acutely flooded seedlings exposed to high salinity died within 2 weeks, but seedlings watered with 30 ppt saline water recovered and A was not reduced the following spring. As saline flooding of coastal areas increases due to sea level rise, photosynthesis of these species will be differentially affected based primarily on their flood tolerance. This suggests that increased flooding associated with sea level rise will impact these tree species to a greater extent than small increases in soil salinity. High salinity accompanying storm surges will be very harmful to all of these species.

hardwood site (BLH) and 500 g dry wt/m2 for a baldcypress-water tupelo site (CT). Litter-fall was 574 g dry wt/m2/yr for BLH and 620 g dry wt/m2/yr for CT. Harvest samples within the two plots yielded 200 g dry wt/m2 and 20 g dry wt/m2 for BLH and CT, respectively. Minimum net primary production was calculated as the sum of the three: 1574 g dry wt/m2/ yr for BLH and 1140 g dry wt/m2/yr for CT. Maximum estimates of herbaceous production and insect consumption were made by using values from the literature. Estimated total net primary productivity was 1733 g dry wt/m2/yr for BLH and 1516 g dry wt/m2/yr for CT. Tree composition was determined by the point-centered quarter method. Relative frequency, relative density, absolute density, relative dominance, and importance value (IV) were calculated for the tree species along each transect. In the bottomland hardwood area many woody species exist with Acer rubrum var. drummondii (IV = 23.9) and Nyssa aquatica (IV = 18.4) the most dominant. In the baldcypress-water tupelo area, fewer woody species exist and Taxodium distichum (IV - 39.2) and N. aquatica (IV = 37.6) dominated. Comparison of productivity data from several southeastern swamps indicate that flowing water regimes tend to result in the highest swamp forest productivity.

Net primary productivity and community structure were studied at three adjacent swamp sites that were all once subject to seasonal flooding. Because of man-related activities one is now permanently flooded, and a second is managed on a summer-fall dry period and a winterspring flooded period. In the permanently flooded area such flood-intolerant trees as green ash are dying while shrubs and aquatic plants are increasing. Competition among overstory trees is reduced, enhancing growth of existing baldcypress and water tupelo trees. Total areal production, however, is low (887 gIm2/yr) because of fewer trees. Productivity in the managed area is high (1,780 gIm2/yr). The baldcypress-water tupelo community is being replaced by a swamp maple-ash community typical of bottomlands. In the natural swamp forest, baldcypress and water tupelo have remained dominant. Canopy closure has limited understory and aquatic growth but has also increased competition among overstory trees, resulting in a slow increase in basal area. Productivity is about 1,166 gIm2/yr. It is suggested that the flooding regime is an important controlling factor in each of the areas. SWAMP FORESTS are recognized as integral parts of wetland ecosystems, serving as habitats, spawning and nursery grounds, and sources of food for many organisms (Brown, Brinson and Lugo, 1979; Wharton and Brinson, 1979). Seasonal flooding and draining of swamps are vital to the maintenance of these functions. Recent studies have illustrated the high productivity of seasonally flooded swamp forests (Conner and Day, 1976; Mitsch and Ewel, 1979; Carter et al., 1973) and the export of large amounts of organic and inorganic nutrients from the swamp to downstream lake and marsh environments (Day, Butler and Conner, 1977; Kemp, 1978; Wharton and Brinson, 1979). In many wetlands the construction of canals, spoil deposits, embankments and impoundments associated with mining, timber, highway activities, and, in Louisiana, crawfish culture, has altered the flow of water. The purpose of this study was to compare plant community structure and productivity of three swamp areas with different flooding re1 Received for publication 20 February 1980; revision accepted 11 September 1980. Contribution No. LSU-CEL-79-17 of the Coastal Ecology Laboratory, LSU Center for Wetland Resources, Baton Rouge, La. This research was supported by the LSU Sea Grant College Program, a part of the National Sea Grant College Program maintained by the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. We would like to thank Ron Paille, Lynne Bowers, Paul Kemp, Steve Whipple, and John Day whose assistance and comments helped make this paper possible. gimes. Three major tree species, baldcypress (Taxodium distichum), water tupelo (Nyssa aquatica), and ash (Fraxinus sp.) are emphasized. MATERIALS AND METHODS-Study sitesThe Lac des Allemands swamp is located at the upper end of the Barataria Bay estuary, between the Mississippi River and Bayou Lafourche, La. (Fig. 1). During a routine examination of 1972 infrared false color imagery of this swamp, we noticed a 970-ha area that appeared white in comparison to the red and bluegreen of the other forested areas. Earlier imagery (December 1940 and March 1952) showed that extensive logging operations had occurred throughout the swamp, but the distinctive pattern of the 1972 imagery was not evident. Natural water flows through this swamp forest are northeast to southeast. However, the 970-ha site was found to be impounded and permanently flooded by water up to 1 m deep. Impoundment began when Louisiana Highway 20 was completed in 1930 along the western boundary, blocking overland flows from upstream. A natural ridge runs along the southeastern side of the area. The Vacherie Canal was dredged in 1955 along the northern boundary, and Bayou Chevreuil along the southern boundary in 1959, impounding the area with spoil deposits so that natural water flow has been altered for at least 20 yr. North of the permanently flooded area is a dense, healthy forest (320 ha). This area was isolated by construction of a board road in the

Due to large reserves of second-growth cypress ( Taxodium distichum and T. distichum var. nutans ) in the southeastern United States, logging of cypress is once again becoming attractive. This increased activity has led to the question of whether adequate natural regeneration will be established after logging. Four logged cypress stands in the Barataria Basin region of Louisiana were sampled to determine vegetation characteristics and survival and growth of baldcypress seedlings and stump sprouts. Coppice regeneration was prolific during the first year after cutting, however, most of the sprouts died in the following years. In addition, even though observations were made during a particularly dry year, no seedling establishment occurred.

One-year-old baldcypress (Taxodium distichum [L.] Rich.) seedlings were planted across a flooding gradient in a Louisiana bottomland forest in March and September 1985. One half of the seedlings were protected with a chickenwire fence. Survival and height growth were monitored from 1985 through 1987. First year survival was high in all areas for both plantings, except for the unprotected March-planted seedlings, which were destroyed by animals. After three growing seasons, survival of March-planted seedlings in the flooded and intermittently flooded plots was still over 70%. Natural mortality of March-planted seedlings in the unflooded plot was high, with only 40% of the seedlings surviving to the end of the study. Survival of the September-planted seedlings was also best in the flooded and intermittently flooded plots and least in the unflooded plot. Height growth, like survival, was best for seedlings in the flooded and intermittently flooded plots. It seems that baldcypress seedlings can be planted in a swamp and grow well if animal damage is controlled.

The composition and productivity of two mangrove sites surrounding the Laguna de Terminos, Mexico, were studied from March 1979 to January 1984. Measurements were made of the tree composition, above-ground woody biomass changes, and litterfall production at a high-salinity fringing site and a low-salinity riverine site. Rhizophora mangle L. was the dominant tree at the fringing site, but occurred only at the water's edge at the riverine site. Avicennia germinans L. dominated the inland area of the riverine site. Laguncularia racemosa Gaertn. f. had a more even distribution from shore to inland and from site to site. Average diameter at breast height (DBH) was greater at the riverine site for each of the three species; however, tree density (trees > 2.5 cm DBH) was more than twice as high at the fringing site (7510 ha −1 ) than at the riverine site (3360 ha −1 ). Wood production (1206 g m −2 year −1 vs. 772 g m −2 year −1 ) and litterfall (1252 g m −2 year −1 vs. 835 g m −2 ) were higher at the riverine site than at the fringing site. Total estimated above-ground net production was 2458 g m −2 year −1 at the riverine site and 1607 g m −2 year −1 at the fringing site.

Net primary production and nutrient levels were measured from February 1978 through March 1979 at four Spartina patens marsh sites with varying environmental conditions surrounding Lake Pontchartrain, Louisiana. Live and dead aboveground vegetation was harvested at 3-6 week intervals over an annual cycle. Litter bags were used to determine loss rates of dead vegetation from the marsh surface. Net aboveground production estimates ranged from 2541-4411 g dry wt ? m"2 ? year"1 by the Smalley method, and 3053-5509 g dry wt ? m"2 ? year"1 by the Weigert and Evans method. Decomposition rates ranged from 34-40% loss of original weight after 6 months. Higher productivity values and decomposition rates occurred at sites with elevated nutrient levels and free tidal flushing.