FIRE ISLAND Ecological Studies of the Sunken Forest, Fire Island National Seashore, New York NPS Scientific Monograph No. 7

The vegetation, biomass, primary production, and nutrient relationships of the Sunken Forest at the Fire Island National Seashore, New York, U.S.A., were analyzed to determine the influence of meteorologic nutrient inputs on the structure and function of an ecosystem with minimal geologic and biologic inputs and weathering.

The Sunken Forest is a 200- to 300-year-old Ilex opaca (American holly)-Sassafras albidum (white sassafras) Amelanchier canadensis (shadbush) forest, with a total basal area of 22.59 m²/ha. The biomass of 17,000 g/m², the net primary production of 1100/g/m²/year, and the leaf area index of 5.9 fall within the range for other temperate forest ecosystems, even though vertical growth of the Sunken Forest is severely restricted by the shearing effects of the salt-laden winds.

Although weathering of soil minerals was found to be a minimal nutrient source, the meteorologic input of 0.73 g potassium/m²/year; 14.15 g sodium/m²/year; 0.98 g calcium/m²/year; and 1.91 g magnesium/m²/year to the Sunken Forest are within the range of weathering plus meteorologic inputs for other forested ecosystems. The majority of the meteorologic nutrient input is dependent upon the impaction of salt spray aerosols on the profusely divided vegetative surfaces. The circulation of potassium, sodium, calcium, and magnesium within the ecosystem is related to hydrologic and organic matter cycles. The retention of cations within the ecosystem is largely a function of the living biomass and the soil organic matter.

The interface between the land and the sea provides unique environments which allow the development of specialized ecosystems. Some of the most productive ecosystems known are found near this interface and are dependent upon the continual exchange of materials across this boundary (Odum 1971). Terrestrial ecosystems, by regulating the composition of ground waters flowing out of them, directly influence the transfer of elements from land to the oceans. The solution and particulate transport of terrestrially derived elements in river water is believed to be the major source of oceanic salts (Clarke 1924; Conway 1942, 1943). Likewise, gases and aerosols of marine origin are important geochemical factors in terrestrial ecosystems (Eriksson 1952a, b, 1955, 1959, 1960, 1961; Gorham 1958, 1961; Blanchard and Syzdek 1972).

With increasing proximity to sea coasts there is generally an increase in the quantity of chemicals contained in the precipitation, not only chloride, sodium, and sulfate but also nitrogen, magnesium, and in some locations calcium and potassium (Leeflang 1938; Wilson 1959; Junge and Werby 1958; Hutton and Leslie 1958; Emmanuelsson, et al. 1954; Nihlgard 1970). Although much ocean-derived material is deposited locally in coastal areas, some is carried great distances inland (Eriksson 1955; Woodcock 1957). In coastal areas the atmospheric load of oceanic salts is so great as to cause the restrictions and zonation of ecosystems (Oosting and Billings 1942; Boyce 1954; Martin 1959). Although the literature on both atmospheric chemistry and the toxic effects of salt spray on vegetation is extensive, it is only recently that investigations of salt spray as a meteorologic nutrient input for terrestrial ecosystems have been undertaken (Etherington 1967; White and Turner 1970; Art 1971; Clayton 1972).

The interactions between marine and terrestrial ecosystems can perhaps be most acutely perceived on barrier islands. Along the Atlantic Coast of the United States a chain of barrier islands extends from Plum Island, Massachusetts, to the Florida keys. These barrier islands, characterized by coarse sediments lying offshore on a gently sloping shallow bottom, are separated from the shore by a coastal lagoon (Price 1951). The sediments of the Atlantic barrier islands represent a gradient from highly siliceous sands in the northern portion to calcareous sands in the southern sections of the system (Oosting 1954). Individual barrier islands may also show mineralogical gradients from headlands and sediment sources to distal sections (Taney 1961a).

This monograph presents the results of a study analyzing the role of the meteorologic input of nutrients in influencing the structure and function of a barrier-island maritime forest on Fire Island, New York (Art 1971; Art et al. 1974). The Sunken Forest on Fire Island was selected for study as an ecosystem in which meteorologic input was hypothesized to be nearly the sole source of nutrients. This situation arises from the minimal release of nutrients from the highly weathered, siliceous sands, coupled with the proximity of the ecosystem to the Atlantic Ocean. In ecosystems with minimal geologic and biologic inputs and weathering releases of nutrients, the structure and function are undoubtedly strongly influenced by the patterns of meteorologic nutrient inputs.

Fire Island is located in the North Atlantic (40° 41' N, 73%deg; 00' W) off the south shore of Long Island, New York (Fig. 1). It extends 51 km from Fire Island Inlet at the west to Moriches Inlet at the east, and is separated from Long Island by the Great South Bay and Moriches Bay. The Sunken Forest (40° 39' 22" N, 73° 07' 03" W), located between the towns of Cherry Grove and Point O' Woods, is a 16-hectare maritime forest in the Fire Island National Seashore.