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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.

Pyrolysis gas chromatography/mass spectrometry is a potent tool for studying the molecular fingerprints of natural organic matter (NOM). With advances in analytical techniques, a pyrogram generally consists over a hundred pyrolysates, which increases the difficulty of interpreting the associated data. Here, we propose a systematic approach that includes an automatic peak identification and quantification pipeline and statistical techniques for the analysis of NOM. White oak (Quercus alba) and forest floor litter samples from a 48-week field decomposition study including sites along a soil moisture gradient were used to evaluate the applicability. An analysis of variance of the chemical classes indicated that the composition differed among sites, although a trend following the moisture gradient was not observed. Factor analysis of the pyrolysates clearly identified two decomposition stages in both types of decomposition. For the oak litter, 2,6-dimethoxy-phenol originating from syringyl lignin was dominant in the early stage, whereas for the forest floor litter, 2-methoxy-4-vinylphenol was enriched in the early stage, while 4-ethyl-2-methoxyphenol and 3-allyl-6-methoxyphenol were dominant in the later stage. These compounds originated from guaiacyl lignin, which suggested that guaiacyl lignin was relatively constant. The proposed approach provides a convenient and effective way to study the chemical composition of NOM.

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.

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.

Foliar litter is an important terrestrial source of dissolved organic matter (DOM) and disinfection byproducts (DBPs) in the source water supply. Climate changes could alter precipitation patterns and hydroperiods in woody wetlands, resulting in a hydrologic shift along the low elevation gradient and change the productions of DOC and DBP precursors and their exports to source water. Here, we conducted an 80-week field decomposition study using fresh-fallen leaves along an elevation gradient, representing well-drained, relatively moist, and inundated environments, in Congaree National Park, South Carolina. The dissolved organic carbon (DOC) yield and formation potential (FP) of trihalomethanes (THMs; a dominant category of studied DBPs) were 48.9–79.7 mg-DOC/g-litter and 2.23–6.57 mg/g-litter in the freshly fallen leaf litter, respectively. The level of leachable DOM and its DBP FP decreased with time, and during the first 16 weeks of decomposition, the decomposing litter served as an important source of leachable DOM and DBP precursors. Week 28 was a turning point for DOM optical properties, with fewer tyrosine/tryptophan/soluble microbial byproduct-like compounds and more aromatic, humified, and fulvic/humic acid-like compounds. Litterfall primarily occurred from September to January, while less precipitation occurred from October to January, indicating that large amounts of DOC and DBP precursors could be leached from litterfall in February. In the first 16 weeks of field exposure study, we observed higher residual mass and lower water-extractable DOC and DTN in more inundated environments, demonstrating that the shifts of DOM composition and DBP precursors if climate reduces rainfall in the southeastern US.

Considered separately, notifiable disease registries and medical claims data have certain advantages (e.g., consistent case definitions and electronic records, respectively) and limitations (e.g., incomplete reporting and coding errors, respectively) within disease outbreak research. Combined however, these data could provide a more complete source of information. Using a retrospective space-time permutation scan statistic, zoonotic case information from a state registry system (TDH) was compared with administrative medical claims information from a managed care organization (MCO) to examine how data sources differ. Study observations included case information for four tick-borne (Lyme disease, ehrlichiosis, Rocky Mountain spotted fever, tularemia) and two mosquito-borne diseases (West Nile virus, La Crosse viral encephalitis) occurring in Tennessee. One hundred and three clusters were detected, of which nine were significant (P

Tidal freshwater forests in coastal regions of the southeastern United States are undergoing dieback and retreat from increasing tidal inundation and saltwater intrusion attributed to climate variability and sea-level rise. In many areas, tidal saltwater forests (mangroves) contrastingly are expanding landward in subtropical coastal reaches succeeding freshwater marsh and forest zones. Hydrological characteristics of these low-relief coastal forests in intertidal settings are dictated by the influence of tidal and freshwater forcing. In this paper, we describe the application of the Sea Level Over Proportional Elevation (SLOPE) model to predict coastal forest retreat and migration from projected sea-level rise based on a proxy relationship of saltmarsh/mangrove area and tidal range. The SLOPE model assumes that the sum area of saltmarsh/mangrove habitat along any given coastal reach is determined by the slope of the landform and vertical tide forcing. Model results indicated that saltmarsh and mangrove migration from sea-level rise will vary by county and watershed but greater in western Gulf States than in the eastern Gulf States where millions of hectares of coastal forest will be displaced over the next century with a near meter rise in relative sea level alone. Substantial losses of coastal forests will also occur in the eastern Gulf but mangrove forests in subtropical zones of Florida are expected to replace retreating freshwater forest and affect regional biodiversity. Accelerated global eustacy from climate change will compound the degree of predicted retreat and migration of coastal forests with expected implications for ecosystem management of State and Federal lands in the absence of adaptive coastal management.

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.

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.

The use of wetlands for treatment of wastewaters has a number of important ecological and economic benefits. Adding nutrient rich treated wastewater effluent to selected coastal wetlands results in the following benefits: (1) improved effluent water quality; (2) increased accretion rates to help offset subsidence; (3) increased productivity of vegetation; and (4) financial and energy savings of capital not invested in conventional tertiary treatment systems. We present as case studies results from several wetlands that are receiving secondarily treated wastewater in coastal Louisiana. At one site where sedimentation accumulation was measured, rates of accretion increased significantly after wastewater application began in the treatment site (from 7.8 to 11.4 mm yr−1) and approached the estimated rate of regional relative sea level rise (RSLR) (12.0 mm yr−1). No corresponding increase was observed in an adjacent control site. This suggests that the application of nutrient-rich wastewater can help coastal wetlands survive sea level rise. In the same site, surface water nutrient reduction, from the effluent inflow to outflow (1600 m), ranged from 100% for nitrate-nitrogen (NO3-N) to 66% for total phosphorus (P). At a second site, a forested wetland that has been receiving wastewater effluent for 50 years, N and P were both reduced by more than 90%. Nutrient reduction is due to three main pathways: burial, denitrification and plant uptake. Dendrochronological analysis at the second site revealed that stem growth increased significantly in the treatment site after wastewater applications began, and was significantly greater than an adjacent control site. Similar increases in productivity have been measured in a number of wetland treatment sites. Economic analyses comparing conventional and wetland systems indicate savings range from $500,000 to $2.6 million. In addition there are substantial energy savings.

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.

The Pen Banch riparian wetland system was impacted by hot water releases from the reactor operations at the SRS. Several hundred acres of swamp and bottomland forest were destroyed and degraded as a result of thermal effects and sedimentation. The SRS developed a plan to restore the system based upon planting both early and last successional tree species. The goal was to develop a

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.

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.

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.

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.

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.

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.