William A. Niering

Vegetation change on a northeast tidal marsh: interaction of sea-level rise and marsh accretion

Increasing rates of relative sea—level rise (RSL) have been linked to coastal wetland losses along the Gulf of Mexico and elsewhere. While such losses have yet to be reported for New England tidal marshes, rapidly rising RSL may still be affecting these systems. Studies of the Wequetequock—Pawcatuck tidal marshes over four decades have documented dramatic changes in vegetation that appear to be related primarily to differential rates of marsh accretion and sea—level rise. Other environmental factors such as sediment supply and anthropogenic modifications of the system may be involved as well. When initially studied in 1947—1948 the high marsh supported a Juncus gerardi—Spartina patens belting pattern typical of many New England salt marshes. On the most of the marsh complex the former Juncus belt has been replaced by forbs, primarily Triglochin maritima, while the former S. patens high marsh is now a complex of vegetation types–stunted Spartina alterniflora, Distichlis Spicata, forbs, and relic stands of S. patens. These changes are documented by vegetation sampling that closely followed the 1947—1948 methods and by peat core analysis. Marsh elevations were determined by leveling, and the mean surface elevation of areas where the vegetation has changed is significantly lower than that of areas still supporting the earlier pattern (4.6 vs. 13.9 cm above mean tide level). The differences in surface elevation reflect differences in accretion of marsh peat. Calculations based on sandy overwash layers deposited during historically recorded storms as well as on experimentally placed marker horizons of known age indicate that stable areas have been accreting at the rate of local sea—level rise, 2.0—2.5 mm/yr at least since 1938; changed areas have accreted at about one half that rate. Lower surface elevations result in greater frequency and duration of tidal flooding, and thus in increased peat saturation, salinity, and sulfide concentrations, and in decreased redox potential, as directly measured over the growing season at both changed and stable sites. It is proposed that these edaphic changes have combined to favor establishment of a wetter, more open vegetation type dominated by to distinctive communities–Stunted S. alterniflora and forbs. Changes documented on the Wequetequock—Pawcatuck system have been observed on the other Long Island Sound marshes and may serve as a model for the potential effects of seal—level rise on New England tidal salt marshes.

Salt marsh vegetation change in response to tidal restriction

Vegetation change in response to restriction of the normal tidal prism of six Connecticut salt marshes is documented. Tidal flow at the study sites was restricted with tide gates and associated causeways and dikes for purposes of flood protection, mosquito control, and/or salt hay farming. One study site has been under a regime of reduced tidal flow since colonial times, while the duration of restriction at the other sites ranges from less than ten years to several decades. The data indicate that with tidal restriction there is a substantial reduction in soil water salinity, lowering of the water table level, as well as a relative drop in the marsh surface elevation. These factors are considered to favor the establishment and spread ofPhragmites australis (common reed grass) and other less salt-tolerant species, with an attendant loss ofSpartina-dominated marsh. Based on detailed vegetation mapping of the study sites, a generalized scheme is presented to describe the sequence of vegetation change from typicalSpartina- toPhragmites-dominated marshes. The restoration of thesePhragmites systems is feasible following the reintroduction of tidal flow. At several sites dominated byPhragmites, tidal flow was reintroduced after two decades of continuous restriction, resulting in a marked reduction inPhragmites height and the reestablishment of typical salt marsh vegetation along creekbanks. It is suggested that large-scale restoration efforts be initiated in order that these degraded systems once again assume their roles within the salt marsh-estuarine ecosystem.

Vegetation Patterns and Processes in New England Salt Marshes

Salt marshes are grass-dominated tidal wetlands fringing the land-water interface of many temperate regions. They are an integral part of the larger tidal marsh-estuarine ecosystems, which are among the most biologically productive in the world. There is considerable evidence that fin and shell fisheries depend on the biological activities occurring on these tidal wetlands (Cruz 1973, Odum and Skjei 1974, Teal 1962). Tidal marshes play an important role in nutrient cycling within estuaries (Welsh 1980, Woodwell and Whitney 1977). They can also serve in pollution filtration, sediment accretion, and erosion control (Grant and Patrick 1970, Sanders and Ellis 1961, Windon 1977). Their distinctive flora, as well as their rich spectrum of waterfowl and other wildlife, make them attractive to sportsmen and naturalists. Their economic value has been estimated at more than

Development of a tidal marsh in a New England river valley

197,600 per hectare (

Structure, pattern, and diversity of a mallee community in New South Wales

80,000 per acre, Gosselink et al. 1974). Chapman (1960) has described nine different geographical coastal marsh regions throughout the world. The New England type marshes, extending from Maine to New Jersey, have developed a distinctive layer of fibrous peat along resistant rocky shores, where silt has been somewhat limited compared to other marsh areas. In New England, they tend to occur as relatively small individual systems in drowned valleys or behind barrier beaches. This paper deals primarily with the origin, vegetation patterns, and productivity of southern New England marshes and the role of mans impact on them,

Restoration of an impounded salt marsh in New England

A model for the geomorphic and vegetation development of a river valley tidal marsh in southern New England (Connecticut) is based on both the species composition of roots and rhizomes and on the mineralogic sediments preserved in peat. The maximum depth of salt marsh peat is 3.8 m and in the deepest areas this can overlie up to 1.9 m of fresh to brackish water peat. Based on a radiocarbon date of 3670±140 yr before the present (B.P.) for basal peat at a depth of 4.0 m, vertical accretion rates have averaged ca. 1.1 mm yr−1. Salt marsh formation began in response to rising sea level 3800–4000 yr B.P., as brackish marshes, dominated by bulrush (Scirpus sp.), replaced freshwater wetlands along stream and river channels. Gradually salt marsh vegetation developed over submerging brackish marshes, adjacent uplands, and accreting tidal flats. By 3000 yr B.P. the lower estuary was tidal, with sufficient salinity for salt marsh to dominate most wetlands. Spikegrass (Distichlis spicata) was an important early colonizer in salt marsh formation and its role in marsh development has not been documented previously. Blackgrass (Juncus gerardi), currently a typical upper border species, appears in the peat record relatively recently, perhaps within the last few centuries. In contrast, reed (Phragmites australis) has been present for at least 3500 yr. The dominance of reed along the upper border today, however, appears to be a relatively recent phenomenon.

Comparison of created and natural freshwater emergent wetlands in Connecticut (USA)

An intensive sample of Australian mallee included a strip of 100 1 sq. m plots and counts of species numbers in expanding areas (1, 10, 100, and 1000 sq. m) to a full hectare. Reciprocal averaging (RA) produced an effective arrangement of the sq. m plots and their species along an axis of internal pattern from mallee patches to the openings between them. RA scores permitted definition of the patches and transitions and comparisons of relative difference between successive sq. m plots (mean RA score differences of 6.9 in the openings, 11.9 in mallee patches, and 14.7 in transitions). Pattern diversity, measured as degree of species turnover along the first RA axis, was 2.3 half-changes. Groups of species most characteristic of openings, transitions, and mallee patches could be recognized; but many species are of wide amplitude along the pattern axis, and neither RA nor association measurements showed distinct species groups separate from one another. The mallee sample is rich in species (mean of 53/0.1 ha, total of 101/ha) compared with North American samples; it is roughly similar to North American woodlands and shrublands in life-form spectrum but different in growth-form representation. Mean heights of species formed an apparent lognormal distribution with the concentration of species in the 0.2–0.4 m oetave. Species numbers in relation to areas (A, in sq. m), traced from 1 sq. mm to 105 sq. m, were reasonably fitted by either S=5.33 + 15.28 log A or S=8.22A 0.29 at intermediate quadrat sizes (1–1000 sq. m) but not at smaller sizes. The ten replicate 0.1 ha samples gave coefficients of variation of 7% for species numbers and 9–10% for the regression coefficients (except b=5.33 with a CV of 43%).

Tidal energy subsidy and standing crop production of Spartina alterniflora

The restoration of a 20 ha tidal marsh, impounded for 32, yr, in Stonington, Connecticut was studied to document vegetation change 10 yr after the reintroduction of tidal flushing. These data were then compared to a 1976 survey of the same marsh when it was in its freshest state and dominanted byTypha angustifolia. Currently,T. angustifolia remains vigorous only along the upland borders and in the upper reaches of the valley marsh. Live coverage ofT. angustifolia has declined from 74% to 16% and surviving stands are mostly stunted and depauperate. Other brackish species have also been adversely effected, except forPhragmites australis which has increased. In contrast, the salt marsh speciesSpartina alterniflora has dramatically expanded, from <1% to 45% cover over the last decade. Locally, high marsh species have also become established, covering another 20% of the marsh.

Four decades of old field vegetation development and the role of Celastrus orbiculatus in the northeastern United States

Five three- to four-year old created palustrine/emergent wetland sites were compared with five nearby natural wetlands of comparable size and type. Hydrologic, soil and vegetation data were compiled over a nearly two-year period (1988-90). Created sites, which were located along major highways, exhibited more open water, greater water depth, and greater fluctuation in water depth than natural wetlands. Typical wetland soils exhibiting mottling and organic accumulation were wanting in created sites as compared with natural sites. Typha latifolia (common cattail) was the characteristic emergent vegetation at created sites, whereas a more diverse mosaic of emergent wetland species was often associated with Typha at the natural sites. Species richness was slightly higher in created (22–45) vs. natural (20–39) wetlands, but the mean difference (33 vs. 30) was not significant. Nearly half (44%) of the 54 wetland taxa found at the various study sites were more frequently recorded at created than natural wetlands. The presence of mycorrhizae in roots of Typha angustifolia (narrow-leaved cattail) and Phragmites australis (common reed) was greater at created than natural wetlands, which may be related to differential nutrient availability. Wildlife use at all sites ranged from occasional to rare, with more sightings of different species in the natural (39) than created (29) wetlands. The presence of P. australis and introduced Lythrum salicaria (purple loosestrife) may pose a threat to future species richness at the created sites. One created site has permanent flow-through hydrology, and its vegetation and wildlife somewhat mimic a natural wetland; however, the presence of P. australis and its potential spread pose an uncertain future for this site. This study suggests the possibility of creating small palustrine/emergent wetlands having certain functions associated with natural wetlands, such as flood water storage, sediment accretion and wildlife habitat. It is premature to evaluate fully the outcome of these wetland creation efforts. A decade or more is needed, emphasizing the importance of long term monitoring and the need to establish demonstration areas.

Vegetation of the Santa Catalina Mountains: community types and dynamics

Abstract Standing crop biomass of the intertidal graminoid Spartina alterniflora, as determined by clip harvest, has a strong positive linear correlation with tidal range along the Connecticut coastline of Long Island Sound. These findings support the hypothesis that tides provide an ‘energy subsidy’ which accounts for much of the observed variation in the productivity of the salt marsh ecosystem. Although the physiological basis for this phenomenon will demand further research, it is suggested that increased nitrogen availability may be important.