Ralph E. Good

The Ecology of Freshwater Tidal Wetlands

ties of less than one percent, but insufficient flow to dampen upstream tidal movement. Odum et al. (1979) conservatively estimate that there are 500,0001,000,000 ha of freshwater tidal wetlands along the Atlantic and Gulf Coasts, of which 100,000-140,000 ha are in New Jersey. Almost all of the major East Coast cities from Trenton, NJ, to Richmond, VA, are near freshwater tidal wetlands. Consequently, these wetlands are greatly affected by human activities. Our discussion of the structure, function, and value of freshwater tidal wetlands is based on studies of three Delaware River wetlands: the Hamilton Marsh near Trenton, NJ, Woodbury Creek Marsh south of Camden, NJ, and Tinicum Marsh near Philadelphia, PA. In freshwater tidal wetlands the major system components-producers, consumers, detritus, sediment, and nutrients-are coupled by biological and physical processes that transfer materials and energy (Figure 1). Materials, such as organic matter, nutrients, heavy metals, and sediment, enter freshwater tidal wetlands from sources including the atmosphere, tides, point-source effluents, non-point-source runoff, groundwater, and consumer immigration. Outputs are via the atmosphere, tides, and consumer emigration. Along the urbanized upper Delaware River estuary, tidal waters provide the most important inputs, although point-source effluent and non-point-source runoff may locally contribute significant quantities of nutrients and heavy metals (Walton and Patrick 1973). Wetland function is ultimately controlled by climate, but hydrologic parameters such as duration and frequency of inundation, and the velocity and source of the water determine the physical and chemical properties of wetland substrates (Gosselink and Turner 1978). In turn, substrate characteristics dictate specific ecosystem responses, including primary production, species diversity, decomposition, and uptake and release of nutrients.

A REVIEW OF PRIMARY PRODUCTION AND DECOMPOSITION DYNAMICS OF THE BELOWGROUND MARSH COMPONENT

Studies of belowground production and decomposition in marsh systems have lagged behind aboveground studies for technical reasons. Sampling is difficult, especially in species where much of the belowground material consists of large irregularly spaced components such as tubers and rhizomes. Despite these and other problems a growing body of literature on belowground production is emerging. Belowground standing crop and productivity are large, typically exceeding aboveground measurements for the same species. Root/shoot ratios are variable, showing the influence of the species, life history, hydrology/habitat, and climate. The most active portion of the belowground zone appears to be the upper 10 cm (approx.). The pathways and contribution of belowground material to food chains and nutrient cycling are poorly known at present. Opportunities for transport of materials are variable; creekside habitats may contribute relatively larger amounts of nutrients to the estuarine system than those only occasionally flooded. In many marshes a considerable amount of belowground material eventually becomes incorporated into the marsh substrate, thereby maintaining the structure of the marsh and even determining future existence in areas of rising water level or land subsidence.

The seedling regeneration niche: habitat structure of tree seedlings in an oak-pine forest

The physical environment to which a seedling is subjected affects its probability of survival and recruitment into a population. Aspects of the physical and biotic environment form components of the plant habitat and regeneration niches defined by Grubb. The importance of different variables may change during the life cycle of a long-lived plant. We measured nine variables that characterize the habitat of six species of one year old tree seedlings in an oak-pine forest in the New Jersey Pine Barrens. Variables were measured for 25 randomly located individuals of each species as well as at 25 random points in the same stand as the seedlings and in two other stands. Principal components analysis (PCA) of seedling plus random point data produced two habitat gradients: Axis I was a gradient from canopy cover to moss and lichen cover and higher light intensity. Axis II was a gradient from high total cover and shallow litter to habitats with less cover and deeper litter layers. Random points were concentrated in areas with deep litter and low light whereas most seedlings grew in areas with more light and less litter. Discriminant functions analysis indicated that seedling habitat breadth was large but that the habitat of Pinus echinata could be distinguished from that of Quercus coccinea and Sassafras albidum. Seedling density differed among the three stands. Analysis by PCA of the random points from the three stands produced similar habitat gradients as in the PCA derived from tree seedling habitats. In the stand where seedling density was lowest, litter layers were significantly deeper, shrub density was greater and light was lower than in the other stands. These trends were confirmed by discriminant functions analysis. The multivariate analysis of seedling habitat and regeneration niches can be used to explain, in part, seedling density in the ground layer of different forest stands.

Spatial heterogeneity in the soil seed bank of a mature coastal plain forest.

(...) Historical records indicate that stands had not been tilled or clear-cut for at least 100 years prior to the study. The seed flora was dominated by herbaceous species typical of early successional and disturbed habitats, but generally absent from the mature forest community. Seed distributions ranged from mildly to strongly clustered at the scale of 100 cm 2 samples, but local abundance of seed was independent of litter composition or density of vegetative stems in adjacent 4 m 2 quadrats. (...)

A mechanism for the accumulation and retention of heavy metals in tidal freshwater marshes of the upper Delaware River estuary

A mechanism for the accumulation and retention of heavy metals in tidal freshwater marshes is proposed. Although metals are incorporated into tidal freshwater marsh substrates through the year by accumulations into live stem and leaf material, absorption by root systems, and transportation on suspended sediments, the bulk of metal accumulations occurs through the incorporation and burial of plant litter. Plant litter acts as a sponge, absorbing metals and holding them as a temporary sink. Due to high sediment accumulation rates and high rates of decomposition, the litter and its associated metals are rapidly buried and incorporated into the marsh substrate. Since litter is most abundant late in the growing season, metal accumulations are greatest during the fall and subsequently dominates the long-term accumulation of metals preserved in the substrate. To utilize preserved metal concentrations in quantitatively assessing historic regional metal budgets, research would be required to determine the relationship between fall metal accumulations and the annual exposure of metals these marshes are subjected to. Differences between salt and freshwater tidal marshes in their ability to assimilate metals from amended soils are due to differences in the accumulation of organic material into the substrates. In tidal salt marshes there is a well developed belowground mat of roots and rhizomes that absorbs metals directly into the substrate while in tidal freshwater marshes metals accumulate primarily in plant litter lying on top of the marsh surface and rely on its burial for incorporation into the substrate. The sequence presented here demonstrates a mechanism for the building of long-term metal sinks in marshes of the upper Delaware River estuary.

Rates of sediment accumulation in a tidal freshwater marsh

ABSTRACT Rates of sediment accumulation were determined for a Delaware River tidal freshwater marsh utilizing radiometric, palynological and sediment flux estimating techniques plus historical reviews. All techniques showed good agreement, indicating that tidal freshwater marshes are capable of preserving evidence of processes and events that have shaped the estuary through time. Prior to 1940, the marsh was a slowly accreting swamp accumulating material at the rate of 0.04 cm yr-1 prior to colonization of the region in the late 1600s and a somewhat more accelerated rate of 0.12 cm yr-1 prior to the introduction of regular tides in 1940. Between 1940 and 1988 average rates of accumulation ranged between 1.04 and 1.38 cm yr-1, being highest near the tidal channe . During the period 1954-65, rates averaged 1.67 cm yr-1 due to increased storm activity. Since 1966, storm activity has decreased and sediment accumulation rates have averaged 0.97 cm yr-1, reflecting these changes. The current average rate of accumulation is four times the rate of sea-level rise for this region of the estuary. It is hypothesized that sediment accumulation will continue to exceed sea level rise until the marsh surface approximates mean high water.

Seasonal Changes in the Productivity, Caloric Content, and Chemical Composition of a Population of Salt-marsh Cord-grass (Spartina alterniflora)

During the 1972 growing season, the productivity of a short form and a tall form ofSpartina alterniflora was studied by the harvest method in the vicinity of the Rutgers Marine Sciences Center on Great Bay near Tuckerton, New Jersey. The aboveground biomass of living and dead grass was determined and subsamples were analyzed for caloric equivalents, ash, nitrogen, crude protein, crude fiber, ether extract, and nitrogen free extract. S. alterniflora had peak standing crops of 1,592 g/m2 for tall form and 592 g/m2 for short form. Standing crops of crude fiber, ether extract, nitrogen free extract, and caloric values are a function of dry matter production while nitrogen components seem to be influenced by some other factor. Seventy percent of the crude protein was present in early summer at a time when dry weight was less than 50% of its maximum value. The data indicate that the amount of nitrogen that the plant accumulates in its aboveground parts early in the growing season is directly related to the peak of dry matter standing crop. The early spring accumulation of nitrogen may act to offset shortages at the peak of the growing season. The chemical composition of litter and soil samples suggests that biological breakdown of plant material occurs at the soil surface.

Production dynamics for above and belowground components of a New Jersey Spartina alterniflora tidal marsh

Above- and belowground portions of Spartina alterniflora, short form, from a New Jersey salt marsh, were analysed for changes in biomass, caloric content and chemical composition over an approximately 14-month period. The belowground portions of this marsh were characterized by a large biomass, averaging 11·4 kg m−2 in the top 30 cm. Annual changes occurring in this layer, defined as net ecosystem production, gave a value of 2·2 kg m−2. The root to shoot ratio was 4·7 and the turnover time, 5·5 years. The distribution of photosynthetically fixed carbon in the plant tissues was determined to a depth of 50 cm by separating plant material into ash, crude protein, crude fiber, crude fat and nitrogen-free extract. Most of the tissue, on an ash-free basis, was carbohydrate; 50% nitrogen-free extract and 43% crude fiber. Seven percent entered the crude protein pathway and 1% the crude fat. Percentage of crude protein increased with depth while percent crude fiber and nitrogen-free extract decreased with depth. Aboveground portions yielded slightly lower caloric values, 4·4 kcal/g ash-free, than those for belowground portions. Caloric content belowground increased with depth; from 4·5 kcal g−1 in the top layer to 5·0 kcal g−1 in the lower portions. High primary production, dense growth habit and root longevity, which characterize the Spartina alterniflora short form community, combine to form a highly stable system. Annual energy and carbon fixation by this primary producer provide a large flow of organic compounds within the stuarine ecosystem with the belowground component and its decomposition products acting as a sink.

Clonal propagation, local disturbance, and the structure of vegetation : ericaceous shrubs in the pine barrens of New Jersey

Abstract Ericaceous shrubs dominate the upland plant communities of the New Jersey coastal plain, both in terms of species diversity and abundance of individuals. Niches of these species are most clearly separated in the character and vigor of their responses to disturbance, particularly to fire and tree canopy gaps. Gaylussacia baccata resprouts quickly from buried rhizomes after mild ground fires, and is most flexible in taking advantage of canopy gaps. Its co-dominant, Vaccinium vacillans, shows superior survival after severe fires by virtue of a deeper rhizome system, and resprouts with greater vigor than Gaylussacia at very high fire frequencies. In the sympatric sub-shrub Gaultheria procumbens long, infrequently branching rhizomes distribute ramets over large areas, possibly colonizing small gaps in the shrub and herb canopies. Thus, shrub community structure in this high-disturbance ecosystem is maintained by subtle evolutionary variations on a common theme of clonal propagation.

Treefall in a Mixed Oak‐Pine Coastal Plain Forest: Immediate and Historical Causation

In a local convective storm, 85 trees were damaged in an 18.3 ha stand in the Pine Barrens region of southern New Jersey, USA. To determine what factors place individual trees at risk, damaged trees were measured and graded for degree of fire scarring and fungal rotting. Similar measurements were made on 280 undamaged individuals. Ages were determined in a subsample by coring. Only two of the seven species present suffered wind damage (Quercus prinus and Q. velutina). Damaged trees were more severely rotted than undamaged individuals both within and among species. Presence of fungal rot was strongly linked to scarring of the trunk by fire, which in turn was determined by date of recruitment relative to historical episodes of fire. Risk was not influenced by either tree size, proximity to existing gaps, taper of the stem, or interspecific differences in wood strength. Vulnerability to wind damage in this stand was determined by a summation of disturbance effects influencing tree recruitment and health over the previous 90 yr.