Nyssa Aquatica Research Articles

Macroinvertebrate and diatom metrics as indicators of water-quality conditions in connected depression wetlands in the Mississippi Alluvial Plain

AbstractMethods for assessing wetland conditions must be established so wetlands can be monitored and ecological services can be protected. We evaluated biological indices compiled from macroinvertebrate and diatom metrics developed primarily for streams to assess their ability to indicate water quality in connected depression wetlands. We collected water-quality and biological samples at 24 connected depressions dominated by water tupelo (Nyssa aquatica) or bald cypress (Taxodium distichum) (water depths = 0.5–1.0 m). Water quality of the least-disturbed connected depressions was characteristic of swamps in the southeastern USA, which tend to have low specific conductance, nutrient concentrations, and pH. We compared 162 macroinvertebrate metrics and 123 diatom metrics with a water-quality disturbance gradient. For most metrics, we evaluated richness, % richness, abundance, and % relative abundance values. Three of the 4 macroinvertebrate metrics that were most beneficial for identifying disturbance in c...

Sediment accretion rates and radial growth in natural levee and backswamp riparian forests in southwestern Alabama, USA

Riparian forested wetlands improve downstream water quality by trapping suspended sediment from adjacent waterways. Waters that transport sediment and nutrients into adjacent wetlands also create wet and dry hydrologic periods and thus, have the potential to impact site productivity. In this study, we used a dendrogeomorphic technique with green ash (Fraxinus pennsylvanica Marsh.) to estimate sediment accretion for two time periods (1881–2012 and 1987–2012) along a natural levee (35m from river) and backswamp (75m from river) and identified the influence of hydrology and climate on radial growth in green ash and water tupelo (Nyssa aquatica L.) along the Tensaw River in southwestern Alabama. We detected significantly higher sediment accretion rates for the 1987–2012 time period along the natural levee (p=0.00; 1.6cmyr−1) and backswamp (p=0.03; 1.2cmyr−1) than for the 1881 to 2012 period (0.4 and 0.5cmyr−1). Using previously measured (2010) soil bulk density for the site, estimated mass of sediment trapped per unit area ranged from 55–135Mgha−1yr−1 for the 1987–2012 period and 17–61Mgha−1yr−1 for the 1881–2012 period. We identified positive, significant correlations between green ash radial growth and the number of days the backswamp was flooded (1.4m stage), days the Tensaw River was at bankfull (2.1m), and average daily river stage during the overall growing season (April to August) and for the month of April. Green ash radial growth also illustrated a positive, significant response to April precipitation totals demonstrating the overall role of moisture availability just prior to the onset of xylem formation. Green ash trees along the natural levee and backswamp were more responsive to hydrology and climate than water tupelo trees located further in the backswamp, illustrating the potential resistance of water tupelo to perturbations. This study illustrates the important role forested wetlands play in improving water quality through quantification of sediment accretion rates and the potential impact that introduced disturbances (i.e., forest harvest-related disturbances) can have on ecosystem services.

Roost Selection by Rafinesque's Big-Eared Bats (Corynorhinus rafinesquii) in a Pristine Habitat at Three Spatial Scales

Although several studies have described roost use by Rafinesque's big-eared bats (Corynorhinus rafinesquii), few studies have examined roost selection. We examined roost use and selection by Rafinesque's big-eared bat at the tree, stand, and landscape scales during the maternity season in pristine old-growth habitat in the Coastal Plain of South Carolina. We located 43 roosts (14 maternity, 29 solitary) through cavity searches and radio-telemetry. Maternity colonies and solitary individuals selected roosts based on similar characteristics. The best model explaining roost selection by all bats included tree and stand characteristics; landscape factors had little influence on roost use. Bats selected large diameter trees in areas with a high density of trees with cavities in the surrounding area. Most roosts (67.4%) were in water tupelo (Nyssa aquatica) in semi-permanently flooded and saturated areas. Half of maternity roost cavities had upper bole openings whereas only 25.8% of solitary roosts had upper bo...

Impacts of Changing Hydrology and Hurricanes on Forest Structure and Growth Along a Flooding/Elevation Gradient in a South Louisiana Forested Wetland from 1986 to 2009

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.

Electrical energy production from forest detritus in a forested wetland using microbial fuel cells

AbstractMicrobial 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.

Roosts of Rafinesque's Big-Eared Bats and Southeastern Myotis in East Texas

Abstract Because diurnal roosts can be important in determining bat occupancy and abundance in forested habitats, we identified characteristics of cavity trees that influence roost selection by Corynorhinus rafinesquii (Rafinesque's Big-eared Bats) and Myotis austroriparius (Southeastern Myotis) in east Texas. We identified used and non-used cavity trees with a combination of transect searches, radiotelemetry, and historical records at 7 study areas. Both bat species selected similar cavity trees for summer diurnal roosts, showing an affinity for tupelo trees (Nyssa spp.), with 55% of diurnal roosts in Nyssa aquatica (Water Tupelo) and 33% in N. sylvatica (Blackgum). Of 17 tree and habitat variables we measured at used and unused cavity trees, those related to cavity size and availability (cavity height and diameter, tree diameter, density of large trees in the area) were the most important predictors of use. Characteristics of the surrounding stand at both local and landscape scales were less important. ...

Woody vegetation communities of tidal freshwater swamps in South Carolina, Georgia and Florida (US) with comparisons to similar systems in the US and South America

AbstractQuestionsWhat 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?LocationsTidal floodplains of major rivers along the Atlantic and Gulf coasts of the southeastern US: Savannah, Altamaha, Suwannee and Apalachicola Rivers.MethodsAn 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.ResultsFour 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.ConclusionsDescriptions 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 várzea), as are basal area values.

Divergent Roosting Habits of Rafinesque's Big-eared Bat and Southeastern Myotis During Winter Floods

Despite the importance of winter roosts to bat ecology, much less is known about tree roosts used by bats in winter than in summer. Rafinesque's big-eared bat (Corynorhinus rafinesquii) and southeastern myotis (Myotis austroriparius) are species of concern whose winter tree roost selection may be constrained by seasonal flooding in cypress-gum swamps. To evaluate winter roost selection by these species, we compared characteristics of winter roosts to trees not occupied in winter and to summer roost trees in the Oconee River floodplain, Laurens County, Georgia. We located 23 Rafinesque's big-eared bat winter roosts and 5 southeastern myotis winter roosts by climbing and visually inspecting hollow trees and by radio telemetry. We analyzed differences between used and unused trees in winter and between winter and summer roosts. Despite extensive flooding in winter, Rafinesque's big-eared bats roosted in cypress-gum swamps in summer and winter. Accordingly, they used similar large hollow water tupelo (Nyssa aquatica) in both seasons, although roost entrances were higher in winter. In contrast, southeastern myotis roosted in cypress-gum swamps in summer and switched to a diverse hardwood floodplain forest with shallower flood waters in winter. As a result they used smaller roosts in different tree species in winter than in summer. The divergent roosting habits in winter are likely due to the height of roost entrances in relation to flood waters. In summer Southeastern myotis use basal openings that are submerged during winter flooding, whereas Rafinesque's big-eared bats use openings located higher on the tree bole that are not submerged. Therefore, management for southeastern myotis may require provision of separate summer and winter roosting habitats.

Carbon pools and fluxes in a tupelo (Nyssa aquatica)-baldcypress (Taxodium distichum) swamp 24-years after harvest disturbances

Bottomland forests are often productive ecosystems with large quantities of above- and belowground carbon, yet few long-term research projects relating to harvest effects in bottomland hardwood forests exist. This project evaluated the long-term (24-years after harvest) effects of three disturbance treatments on the carbon budget of a tupelo-baldcypress swamp in southwestern Alabama. The site was clearcut in 1986 and timber removed by helicopter. Disturbance treatments were: 1. helicopter (HELI), 2. skidder transportation simulation (SKID), and 3. glyphosate herbicide removal of vegetation following harvesting during years one and two (GLYPH). An adjacent portion of the original stand provides a non-harvested reference (REF) condition. Measurements included aboveground biomass, belowground biomass, soil carbon, soil CO2 efflux and estimates of buried coarse woody debris on the site. SKID treatments had the highest aboveground biomass (73.9 Mg ha−1) and total carbon storage (206.1 Mg ha−1) of the three treatments. GLYPH treatments had the lowest carbon storage (144.2 Mg ha−1) and lower aboveground woody biomass (26.4 Mg ha−1). HELI and SKID treatments were similar, but have slightly less in total forest carbon (168.7 Mg ha−1) than the REF condition. Belowground coarse woody debris storage increased carbon storage on these sites with an additional 8–13 Mg ha−1 being stored. GLYPH treatments had the highest total soil CO2 efflux followed by HELI and SKID treatments, respectively. Higher biomass and carbon storage of SKID treatments is explained by the flood tolerance of tupelo, diverse microtopography created by skidder traffic, and decreased soil aeration of skidder-rutted areas immediately after harvest which favored tupelo coppice.

Use of sediment amendments to rehabilitate sinking coastal swamp forests in Louisiana

Coastal wetlands are losing elevation worldwide, so that techniques to increase elevation such as sediment amendment might benefit these wetlands. This study examined the potential of sediment amendment to raise elevation and support the production and regeneration of vegetation in coastal forests in Louisiana. Before sediment amendment, the vegetation did not differ in these Taxodium distichum–Nyssa aquatica forests with respect to herbaceous and tree seedling composition, and sapling and tree characteristics. After the application of sediment in January 2007, sediment-amended swamps had higher elevations and salinity levels than natural swamps. The layer of sediment applied to Treasure Island in Jean Lafitte National Historic Park and Preserve was relatively deep (sediment depth at Site One and Site Two: 0.89 and 0.69m, respectively, six months after application), and may have exceeded an optimal threshold. Sediment-amended swamp with the highest elevation had some tree mortality and little tree growth of T. distichum. Also, sediment-amended swamp had higher root biomasses of ruderal species, and lower species richness and cover of herbaceous species. Nevertheless, during controlled water releases during an oil spill emergency in 2010, both sediment-amended and reference forest had higher production levels than in other years. While sediment amendment is a compelling management alternative for sinking coastal wetlands, optimal thresholds were not determined for these T. distichum–N. aquatica swamps.

Resilience of Bottomland Hardwood Stands Following Agricultural Use on the Santee Experimental Forest

Resilience is a key function that affects an ecosystem’s ability to recover from disturbance. Understanding the extent to which forest communities recover after a long period of disturbance without direct intervention is important to provide context for considering ecosystem response to disturbance regimes. Species composition and structure were recorded on bottomland hardwood stands that were once inland and freshwater tidal rice fields. We sampled 17 old-field sites and 7 reference sites across three geomorphic settings. The old-field sites ranged from 30 to 120 years since agricultural abandonment. A total of 89 species were found across the old field sites and reference sample areas. Of that total, trees comprised 33 species, shrubs—5 species, and vine/herbs/forbs—51 species. Using field data, combined with stand inventory records, aerial photography (1936-2010), and high-resolution LiDAR imagery, we chronicled the evolution of the forest since the cessation of agriculture. Our findings demonstrate how Pinus taeda seeded directly after the rice fields went to fallow; and this conversion of bottomland swamp to rice to pine was a direct result of water management embankments constructed across the landscape to aid in crop irrigation. The remnant water management features may still alter flooding patterns thereby affecting development of Taxodium distichum and Nyssa aquatica in the old-fields. These results suggest, that over the 100+ years forest stands on the Santee Experimental Forest have developed to represent bottomland hardwoods characteristic of the southeastern United States coastal plain.

Summer heterothermy in Rafinesque’s big-eared bats (Corynorhinus rafinesquii) roosting in tree cavities in bottomland hardwood forests

Many small mammals are heterothermic endotherms capable of maintaining an elevated core body temperature or reducing their thermoregulatory set point to enter a state of torpor. Torpor can confer substantial energy savings, but also incurs ecological costs, such as hindering allocation of energy towards reproduction. We placed temperature-sensitive radio transmitters on 44 adult Rafinesque's big-eared bats (Corynorhinus rafinesquii) and deployed microclimate dataloggers inside 34day roosts to compare the use of torpor by different sex and reproductive classes of bats during the summer. We collected 324 bat-days of skin-temperature data from 36 females and 4 males. Reproductive females employed fewer torpor bouts per day than non-reproductive females and males (P<0.0001), and pregnant and lactating females had higher average (P<0.0001) and minimum (P<0.0001) skin temperatures than non-reproductive females. Pregnant females spent less time torpid (P<0.0001) than non-reproductive females, but lactating females used relatively deep, long torpor bouts. Microclimates varied inside tree species with different configurations of entrances to the roost cavity (P<0.0001). Bats spent more time torpid when roosting in water tupelo (Nyssa aquatica) trees possessing only a basal entrance to the cavity (P=0.001). Of the tree species used as roosts, water tupelo cavities exhibited the least variable daytime and nighttime temperatures. These data demonstrate that use of summer torpor is not uniform among sex and reproductive classes in Rafinesque's big-eared bat, and variation in microclimate among tree roosts due to species and structural characteristics facilitates the use of different thermoregulatory strategies in these bats.

Long-Term Sediment Accretion in Bottomland Hardwoods Following Timber Harvest Disturbances in the Mobile-Tensaw River Delta, Alabama, USA

Sediment accretion from overbank floodwaters is an important function in bottomland forests, yet few long-term data exist. A long-term research project (1986–2010) investigated effects of disturbances on sediment accretion in a water tupelo (Nyssa aquatica L.)-baldcypress (Taxodium distichum L. Rich.) bottomland in the Mobile-Tensaw River Delta, southern Alabama. Disturbance treatments subsequent to clearcutting were helicopter extraction (HELI), skidder simulation of ground based extraction (SKID), and removal of regeneration with glyphosate herbicide (GLYPH). An adjacent portion of the original stand provided a reference (REF). Periodic measurements of sediment pins (324 pins declined to 252 through attrition) indicate that REF trapped 19.2 cm of sediment between 1986 and 2010. During the same 24 years, HELI, SKID, and GLYPH trapped 31.2, 28.9, and 40.8 cm of sediment, respectively. Annual sediment accretion within the treatments was positively correlated to herbaceous biomass (r = 0.6624) while cumulative sediment accretion was positively correlated with days of overbank flooding (r = 0.8673). Site elevation surveys conducted in 1986 and 2010 matched closely with overall sediment accretion and 137Cs evaluations of the pre-disturbance period between 1964 and 1986. All methods indicated a long-term sediment accretion rate of 0.7–1.25 cm/yr, which is similar to accretion rates found in other bottomland hardwood systems. This study indicates that riparian forest management practices that increase herbaceous vegetation are of critical importance to sediment accretion rates.

Dissolved organic matter and nutrient dynamics of a coastal freshwater forested wetland in Winyah Bay, South Carolina

Seasonally flooded, freshwater cypress-tupelo wetlands, dominated by baldcypress (Taxodium distictum), water tupelo (Nyssaaquatica), 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.

Long-term site productivity of a tupelo-cypress swamp 24 years after harvesting disturbances

Long-term (24-year) research regarding harvesting in bottomland hardwoods was conducted to determine the effects of different timber harvests on a water tupelo ( Nyssa aquatica L.)-baldcypress ( Taxodiumdistichum L. Rich.) swamp. The study is located in the Mobile-Tensaw River Delta in southern Alabama. Disturbance treatments were clearcut followed by: (1) helicopter extraction (HELI), (2) skidder simulation of ground-based extraction (SKID), and (3) complete removal of coppice and seedbank regeneration with glyphosate herbicide (GLYPH). An adjacent portion of the original forest stand provided a reference condition (REF). The overall project goal was to determine long-term treatment effects on aboveground and belowground biomass accumulation patterns in the regenerating stands. Previous studies on this site at stand ages 7 and 16 years indicated that SKID treatment areas had the largest aboveground biomass accumulations while HELI treatments had greater species diversity. Twenty-four years after disturbance, results followed the same pattern with SKID treatments having more above- and belowground biomass accumulation (242.6 Mg ha −1) while HELI treatments had less biomass (173.6 Mg ha −1). GLYPH treatments are recovering (86.8 Mg ha −1) and are progressing through an herbaceous–shrub–scrub–pioneer tree succession pattern. SKID and HELI treatments appear to be progressing towards original stand species and biomass accumulation. The resiliency of the site following disturbance appears to be due to soil physical properties, sediment accumulations, and vegetation adaptations to flooded conditions.

Daily MODIS Data Trends of Hurricane-induced Forest Impact and Early Recovery

We studied the use of daily satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors to assess wetland forest damage and recovery from Hurricane Katrina (29 August 2005 landfall). Processed MODIS daily vegetation index (VI) trends were consistent with previously determined impact and recovery patterns provided by the snapshot 25 m Landsat Thematic Mapper optical and RADARSAT-1 synthetic aperture radar satellite data. Phenological trends showed high 2004 and 2005 pre-hurricane temporal correspondence within bottomland hardwood forest communities, except during spring green-up, and temporal dissimilarity between these hardwoods and nearby cypress-tupelo swamp forests (Taxodium distichum [baldcypress] and Nyssa aquatica [water tupelo]). MODIS VI trend analyses established that one year after impact, cypress-tupelo and lightly impacted hardwood forests had recovered to near prehurricane conditions. In contrast, canopy recovery lagged in the moderately and severely damaged hardwood forests, possibly reflecting regeneration of pre-hurricane species and stand-level replacement by invasive trees.

Individual-based modeling of flooding and salinity effects on a coastal swamp forest

Coastal swamps are among the rapidly vanishing wetland habitats in Louisiana. Increased flooding, nutrient and sediment deprivation, and salt-water intrusion have been implicated as probable causes of the decline of coastal swamps. We developed a two-species individual-based forest succession model to compare the growth and composition of a cypress-tupelo swamp under various combinations of flooding intensity and salinity levels, using historical time-series of stage and salinity data as inputs. Our model simulates forest succession over 500 years by representing the growth, mortality, and reproduction of individual Taxodium distichum (baldcypress) and Nyssa aquatica (water tupelo) trees in a 1-km 2 spatial grid of 10 m × 10 m cells that vary in water levels and salinity through differences in elevation. We independently adjusted the elevations of each cell to obtain different grid-wide mean elevations and standard deviations of elevation; this affected the temporal and spatial pattern of flooding. We calibrated the model by adjusting selected parameters until averaged basal area, stem density and wood production rates under two different mean elevations (partially versus highly flooded) were qualitatively similar to comparable values reported for swamps in the literature. Corroboration involved comparing model predictions to four well-monitored contrasting habitat sites within the Maurepas Basin, Louisiana, USA. Model predictions of both species combined showed the same patterns among sites as the data, but the model overestimated wood production and the dominance of T. distichum. Exploratory simulations predicted that increased flooding leads to swamps with reduced basal areas and stem densities, while increased salinity resulted in lower basal areas at low salinity concentration (∼1–3 psu) and complete tree mortality at higher salinity concentrations (∼2–6 psu). Our model can provide insight into the succession dynamics of coastal swamps and information for the effective design of restoration actions.

Filling the gaps in the Neogene plant fossil record of eastern North America: New data from the Pliocene of Alabama

Nine angiosperm taxa are described, based on megafossils from the Citronelle Formation of Alabama, that are significant in either clarifying previous identifications, or in providing the first records of their kind in the North American Pliocene. Liquidambar styraciflua is identified from leaves. Stones are attributed to Cornus sp. and Nyssa aquatica. Although Nyssa stones from the Citronelle Formation were originally described as N. aquaticaformis and later attributed to N. ogeche, the new fossil specimens and a leaf indicate affinity with extant N. aquatica. Fruits of Cyrilla racemiflora are the first North American fossil record of the Cyrillaceae. An endocarp and leaf are attributed to Cocculus. Populus deltoides is represented by two leaves, and a partial leaf is attributed to Gordonia. Planera aquatica was previously identified from the Citronelle Formation from leaves, and a new fossil fruit supports this record. Leaves and a seed provide the first Neogene record of Vitus rotundifolia. The presence of numerous extant taxa suggests climatic conditions similar to those of the region today. However, other recent finds from the Citronelle Formation and fossil localities in Florida and Tennessee indicate that a considerable number of “exotic” taxa persisted into the Pliocene of southeastern North America.

Ingestion by a Freshwater Turtle Alters Germination of Bottomland Hardwood Seeds

Seed dispersal by animals is well documented in many habitats; however, this knowledge is depauperate in bottomland hardwood forests. The alligator snapping turtle (Macrochelys temminckii) is a large freshwater turtle of the southeastern United States that consumes primarily fish but also eats vegetation, including seeds of trees. To evaluate the role this species may play as a seed disperser in bottomland hardwood systems, we investigated the effect of ingestion by M. temminckii on germination of seeds of the following trees: common persimmon (Diospyros virginiana), water tupelo (Nyssa aquatica), and willow oak (Quercus phellos). Captive turtles were presented seeds of these three species in a series of feeding trials. Ingestion reduced the proportion of seeds that germinated compared to uneaten controls for D. virginiana and N. aquatica but had the opposite effect on Q. phellos. Ingested D. virginiana and N. aquatica seeds also germinated more slowly than uneaten controls; however, ingested Q. phellos seeds germinated faster than uneaten controls. This study suggests M. temminckii may have a role as a disperser of Q. phellos, N. aquatica, and D. virginiana; however, information on post-dispersal seed fate is needed to completely assess this species and other freshwater turtles as dispersers of wetland vegetation.

Growth rates of baldcypress ( Taxodium distichum) seedlings in a treated effluent assimilation marsh

Wetlands have proven effective at improving water quality of treated wastewater effluent, which in turn promotes increased primary productivity and vertical accretion. Baldcypress ( Taxodium distichum) seedlings grown under different conditions (bare root and potted) were planted in four subunits of an effluent assimilation marsh and a control marsh in southeast Louisiana, USA, and basal diameter growth was monitored over one growing season. Mean basal diameter growth for seedlings in the assimilation subunits ranged from 16.1 (±1.4) mm to 9.5 (±0.9) mm, whereas growth for seedlings planted in the control marsh was 6.4 (±0.9) mm. Seedlings planted nearest the outfall experienced greater basal diameter growth (18.1 ± 2.6) compared to those planted 700 m away (8.0 ± 0.9), with growth generally decreasing with distance. Potted seedlings experienced greater growth (19.1 ± 1.0 and 20.6 ± 1.0 for five-month-olds and ten-month olds, respectively) than bare root seedlings (4.6 ± 0.6 and 4.0 ± 0.4 for one-year-olds and two-year olds, respectively). Planting assimilation marshes with baldcypress seedlings can be an effective restoration tool for coastal Louisiana, which will provide hurricane protection and improved surface water quality. Wastewater treatment wetlands may offer an effective tool for restoring coastal baldcypress ( T. distichum)–water tupelo ( Nyssa aquatic) swamps in Louisiana.