CAPE LOOKOUT Vegetation and Ecological Processes on Shackleford Bank, North Carolina NPS Scientific Monograph No. 6

Geological and Historical Factors

Geological history indicates that Shackleford Bank is of recent origin and is probably less than 2000 years old. Through years of colonization and succession by plants, the once barren island became covered with a diversified maritime vegetation. If the U.S. Coast and Geodetic Survey map of 1853 is dependable, the island was almost completely covered with maritime forest prior to human occupation. However, the force of wave erosion, the deposition of sand by longshore current, the opening and closing of inlets (Dunbar 1956), and occasional hurricanes all contribute to the physical and biological oscillations of the island. Consequently, a high degree of instability is an inherent characteristic of Shackleford Bank.

The western end of the island provides a vivid example of such instability. According to Engels study (1952), the configuration of that part of the island in 1851 was similar to the present one except that it was covered with maritime forest. In contrast, the 1949 map shows that a large area at the western end of the island has been eroded away. Now, in a 10-year period, approximately 1956-66, about 150 acres (60 ha) of land have been deposited back on more or less the same locality. Radical changes seem possible in less than 100 years. Oosting (1954) stressed the point that "such a bank, once formed, is still constantly subject to the same forces which created it and, as a consequence, it is essentially a transient physiographic feature, or at least an unstable one." Therefore, it is impossible to acquire a full understanding of the ecological processes on the island without paying due consideration to geological factors.

The intervention of European man on Shackleford Bank about 200 years ago initiated a gradual attrition and degradation of the primeval vegetation. Such disturbance of vegetation by man and domestic animals is also reported by De Bolos and Molinier (1958) on the Spanish island of Majorca, by Whitehead (1964) on sand dunes of New Zealand, and by Esler (1967) on Kapiti Island of New Zealand. The modification on vegetation by human activities such as tree cutting, forest burning, and livestock grazing accelerated wind erosion and sand movement of the area. Finally, the catastrophic hurricane of 1899 almost denuded the whole island. The present geomorphological status of the island is thus the end product of a combination of both natural and man-caused havoc. Ominously, human activities on Shackleford Bank are more likely to increase than subside in the future.

Climate

Under the amelioration of the ocean and the nearby Gulf Stream, the general climate of Shackleford Bank is warmer than inland areas. Snow is a rare event on the island, occurring on an average only once in 2-3 years; a monthly mean minimum temperature never drops below 4°C. Only in 5 months, from November to March, does the lowest temperature occasionally drop below the freezing point. Engels (1952) found that the frost-free season is more than 8 weeks longer at Beaufort than at Rockingham, which is located about 120 miles inland at about the same latitude and has an elevation of only 210 ft. There is no lack of water supply as indicated by the annual precipitation of 129 cm and no prolonged drought period as shown by the even distribution of 103 rainy days per year. Therefore, the general climate of the island is quite favorable for plant growth. Consequently, such a mild oceanic climate ought to be considered as a factor in determining the species composition on the island.

In regard to the microclimate of the dune environment, the temperature and humidity conditions are quite extreme for plant growth. In summer, the temperature on the surface of bare sand usually reaches 51-52°C. Even inside a white shelter, the temperature still reaches 35°C for 8 weeks and 30°C for 13 more weeks during the summer period. In addition, the plants growing in such an environment must be prepared to endure a temperature fluctuation with an amplitude of 20°C in a week or even in a day. At the same time, the vapor pressure deficit can be as high as 15 mm Hg in the atmosphere. Under high air temperature, constant air turbulance due to sea breezes. and a high vapor pressure deficit in the air, dune plants growing on the island are subject to high evaporative stress on a summer day.

Wind and Salt Spray

The wind regime of Shackleford Bank is characterized by a predominant southwest wind in summer. Such oceanic wind is heavily loaded with salt spray (Pl. I-3), and after blowing over beach and fore dunes is loaded with fine sand particles. The salt- and sand-laden wind thus becomes a particularly important environmental factor for maritime vegetation. As early as the turn of the century, Shreve (1910) suggested that salt wind rather than salt soil is the factor most detrimental to the maritime vegetation. Wells and Shunk (1937, 1938) emphasized the toxic effect of salt spray on the buds and young leaves of the woody species. Oosting and Billings (1942), Oosting (1945), Boyce (1954), and Numata et al. (1948) demonstrated, with both field measurements and control experiments the harmful effects of salt spray on plant growth. Since a salt-laden southwest wind prevails on the island at the time of fast plant growth, salt spray rather than desiccation probably is the chief fatal factor in the death of young tissues (Pl. III-19) of susceptible species. However, Davis (1942) suggested that the dehydration effect of wind due to excessive transpiration may be more important in the south (Florida) to the formation of flag-form trees.

Oosting and Billings (1942) observed a correlation between intensity of salt spray and zonation of dune grasses. Martin (1959) suspected that it is difficult to distinguish between the effects on plants of flying sand particles and salt spray because both are carried by the wind and the zonation pattern of dune grasses may also be due to the amount of sand deposition. The evidence of dune bluestem at the mid-section of Bogue Banks, immediately on the back of the high fore dunes facing the open ocean, may clarify such doubt. Since the deposition of sand is largely at the back of the fore dunes while the intensity of salt spray is drastically reduced on the leeward side of the fore dunes (Oosting and Billings 1942), sand deposition should be disregarded as the chief limiting factor. The zonation of dune grasses is thus determined mainly by the intensity of salt spray. However, the extent of salt spray affecting the characteristics of maritime forest is still open to discussion.

Strong wind may cause mechanical injury such as the frequently observed broken branches and defoliation of woody species. Sand blasting also injures plant leaves (Cowles 1899; Purer 1936), which in turn become vulnerable to salt spray (Boyce 1954). The silvery colored "ghost trees" on the island often reach a height of 15 ft (5 m). This distinctive color is the polishing work of sand blasting, intensive sunlight, heat, and possibly salt spray. The height of "ghost trees" thus may serve as an indication of the height that sand blasting can reach. Doutt (1.941.) stated that salt, ice, and sand carried by wind, together with the drying effect of wind, produce the sheared effect on trees.

The maximum wind velocity afar least 40mph has been recorded in every month, and the monthly average is also rather high during a whole year. Violent wind is able to produce "blow-outs" or at least cause sand movement on the dunes. Salisbury (1952) stated that a wind velocity of only about 1 mile an hour is necessary to make grains of 0.25-mm diameter begin to move along the surface. As the present measurements along the dune transect demonstrated, a detectable amount of change in the dune profile has taken place in a year in the form of sand deflation on the windward slope and deposition on the leeward slope of the dunes. Also, the amount of change is very much a function of the vegetational cover. Nevertheless, the change is relatively small, no more than an average of 20 cm/yr. Ranwell (1958) reported sand accretion up to 2-3 ft/year on lee slopes and sand erosion up to 3-4 ft/year on windward slopes in the most mobile dune regions of Newborough Warren, England. However, extensive sand movement may be caused by erratic hurricanes or wind storms and it is therefore possible that the original vegetation will be buried or destroyed by encroaching sand, as evidenced by the present "ghost trees" standing on the island (Pl. I-6). Moreover, wind causes an unstable substratum which is unsuitable for the growth of some species. Hence, Willis et al. (1959a, b) regarded wind and sand movement as the most important factors of the dune environment in England.

In contrast to Lewis' (1917) estimation of 4-12 ft/year sand movement on the island, the present study at the back of the sand wall shows no measurable sand encroachment upon the forest in a normal year. Cowles' (1899) similar measurements on Lake Michigan dunes showed that a rapidly advancing tee slope of the rear dune covered up a 1-m stake in a year; Ranwell (1958) detected the sand encroachment at a rate of 5-22 ft/year in England. Apparently, in the absence of a catastrophic hurricane, the overall sand encroachment upon the forest on the island has largely subsided and dunes are not an imminent threat to the remnant forest.

The wind velocity on the island by no means subsides in winter, though its duration and frequency are reduced. Consequently, winter gales may cause sea-water erosion on the beach, flooding to the strand, and acceleration of sand movement which in time will cause weakening of the vegetational cover on the dunes. Northerly winds have been undercutting maritime forest on the sound side of the island in winter (Pl. III-22). Nobuhara et al. (1962) stated that wind-borne salt spray, mechanical action of the wind, the invasion of sea water, and sand movement caused by winds inflict damage to coastal vegetation in Japan. They (Nobuhara and Toyohara 1964) considered sand movement and wave erosion to be the most important factors of the strand vegetation. As shown in the present study, their statements also hold true for Shackleford Bank.

It seems that apart from the manifold effects of wind on the coastal vegetation, wind-borne salt spray is the most important factor in summer, while sand movement replaces salt spray as the most active factor in winter. During the winter, herbaceous plants are either dormant or dead and thus nothing can prevent the movement of sand.

Of all physical environmental factors influencing coastal vegetation, wind seems to be the most important. Its profound impact on vegetation can be summarized as follows: (1) wind-borne salt spray kills susceptible species growing close to the ocean; (2) abrasive sand blast created by strong winds causes tissue wounds which enhance the toxic effect of salt spray on plants; (3) constant and excessive wind may induce desiccation of leaves; (4) strong wind inflicts mechanical injury on plants such as breaking branches or defoliation; (5) winter storms cause salt-water erosion and flood the strand vegetation; and (6) wind causes shifting sands which in turn bury and destroy all vegetation in their path.

Edaphic Factors

The soils of Shackleford Bank have been developed from medium to coarse siliceous sands containing various amounts of shell fragments. The size of sand particles and the quantity of shell fragments depend on the closeness to the Atlantic Ocean, as a result of the sorting effect of the onshore wind (Pl. I-5). Hence, the soil on the fore dunes has the highest proportion of coarse sand and highest percentage of shell fragments. Due to their sandy nature water contents of all soils at 1/3 and 15 atm are generally tow, averaging 1-6% of oven-dry weight at 1/3 atm and 0.2-2.2% of oven-dry weight at 15 atm. Although measurements of available water in soils are low in percentage (0.8-4.2%) of oven-dry weight due to high permeability and low water-holding capacity of sandy soil, there is no real lack of moisture in the subsurface layers of the dunes. In places, the water table approaches the ground surface at a depth of only 60 cm. This phenomenon was first recognized by Cowles (1899) and Kearney (1900) and later by Olsson-Seffer (1909b) and Conard (1935). Also, the available water in sandy soil is higher than shown by the data because of the higher bulk density of sand. The percentage of water content will be higher if it is expressed on a volumetric basis. Moreover, sand particles do not hold soil water as firmly as fine clay particles, i.e., the matrix potential of sand is higher than that of clay.

Measurements of water content in soil profiles show a rapid downward movement of rainwater in such well-drained sandy soils over a period of time. Only 3 days after rain, the distribution of soil moisture in the soil profile becomes almost the same as the soil profile after a long period (2 weeks) of drought. The surface layer of dune soil drys quickly after rain and is unsuitable for plant growth. However, the dry surface layer acts as a mulch and substantially reduces evaporation of soil water of subsurface layers.

There is a general increase in soil moisture as the soil progresses to maturity, probably due to the accumulation of humus. Kearney (1904) recognized that the strand plants are not true halophytes on the low salinity beach soil. The same conclusion can be drawn from the present study which shows the salinity of soil solution in a range of merely 10^-4N. Similar results have been obtained by Olsson-Seffer (1909a), Kelly (1925), Davis (1942), and Oosting and Billings (1942) in the United States; Robertson and Gimingham (1951) and Gorham (1958) in England; and Tsuda (1961) in Japan. The salt in soil apparently comes from the wind-borne salt spray which is carried downward through the soil by rainwater. The continuous leaching by rainwater results in little salt accumulation in soil. Though tidal fluctuation of the water table occurs in foreshore regions, Ranwell (1958) found no penetration of sea water beneath the coastal dunes in England.

Soil chemical analysis shows that soil reaction changes from alkaline to acid and the organic matter increases in relation to distance from the ocean shore. Salisbury (1922, 1925) explained the cause of this trend as progressive leaching of the carbonates and progressive increase in the organic matter with increasing age of the vegetation. Much the same pattern is shown in data obtained by Kelly (1925) and Davis (1942) in the United States; Gooding (1947) in British West Indies; and Wilson (1960), Ranwell (1959), and Etherington (1967) in England. Olson (1958) and Scott (1965) concluded that plant succession is dependent basically on the accumulation of humus in the soil from dead plant remains. Webley et al. (1952) found a close association between the development of the soil microflora and the progress of vegetational succession. However, the development of the sandy soil progresses very slowly. Even under mature live oak forest, the distinction of horizons is vague in a poorly differentiated soil profile (Bourdeau and Oosting 1959). Wright (1955, 1956) also observed, in England, no measurable effect of trees on the mechanical composition of the sand, apart from the deposition of litter and humus.

The organic materials in soils range from an extreme low of 0.01% at fore dunes to as high as 5% in the top soil under mature live oak forest. The same trend occurs as regard to nitrogen and phosphorus. Apparently, soil fertility may be an important factor in determining the species composition on the dunes. On the other hand, soil fertility will not be a limiting factor in maritime forest. A comparison of maritime dune soil and Carolinian Sandhills soil reveals that they are similar in many aspects except for a higher calcium and magnesium constituent in the maritime dune soil. Maritime dune soil has a little higher sodium content than inland soil due to the continuous supply from wind-borne salt spray. However, the amount of potassium in maritime dune soil is not much different from inland soil. Some Sandhills soil could have been of submarine origin, but after thousands of years of leaching, both calcium and magnesium have been reduced to the point of nearly complete depletion.

Two pieces of evidence may help to explain the importance of such a difference between maritime sandy soil and inland Sandhills soil. A small area behind Front Street in Beaufort not far from the ocean is possibly a relict of Sandhills soil on which turkey oak (Quercus laevis), black jack oak (Q. marilandica), and wire grass (Aristida stricta) grow. The surrounding areas are occupied by maritime forest. Such an island of Sandhills vegetation can only be explained on the basis of edaphic conditions. Another example is red cedar which grows in the mountains and piedmont areas, but not in the Sandhills and coastal plain (except a few planted for decoration). It reappears along the coast as a major component of maritime forest. Sometimes it even grows on a little brackish substratum or at the fringe of beach with sea water only a meter away at high tide. From leaf analyses, red cedar shows a higher calcium content (0.35% by oven-dry weight) than either live oak (0.05%) or sea oats (0.01%). Coile (1937) found a higher calcium content (2.2% by oven-dry weight) in undecomposed litter of red cedar than those of pines and oaks in Piedmont, N.C. Under the influence of calcium, the litter of red cedar has reaction of about pH 6.0, whereas the litter of pines and oaks has a very acid reaction (pH 4.1). It is possible that a certain amount of calcium is essential for the growth of red cedar; if less than the required minimum quantity is available, the growth of the species may be retarded. Edaphic factors, possibly the richness in calcium and magnesium, may act as compensatory factors to red cedar on the coast, which would explain the disjunct distribution of the species.

Topography

The importance of topography lies in its indirect effects on the gradient of other environmental factors: mainly, soil water content; distance to the water table; exposure to wind; intensity of salt spray; and amount of sand movement. On grassy dunes the water table usually approaches the ground surface at dune trough, where consequently many mesophytic to hydrophytic species grow. In maritime forest, a depressed area frequently becomes an intraforest fresh-water marsh, or at least a wet thicket. In contrast, dry thicket develops from places higher than surrounding areas. The effects of topography on the intensity of salt spray and sand movement have previously been discussed in detail. Temperature and light may also be modified directly or indirectly to some extent. In short, the topography modifies the microenvironments of the organisms. A moist, well-protected area is always a better place for plant succession. Willis et al. (1959a) suggested that the zonation of coastal vegetation in England closely reflects differences in shelter and accessibility of available water.

Plant Adaptation

Most of the anatomical work on strand plants was done early in the century by Kearney (1900), Chrysler (1904), Harshberger (1908, 1909), Starr (1912), and later by Purer (1936). Their general findings can be summarized as follows. Morphological adaptations of dune plants include reduction in plant size; dwarf, prostrate, or creeping growth form; massive root system or rhizome; and smaller leaves. Xerophytic adaptations in leaf structure include dense hair, heavy wax, or cutinization on the epidermal surface; thick and multiple epidermal layers; stomata in depressions; the presence of palisade tissue both under upper and lower epidermis; increasing number of palisade layers; and succulent or latex-bearing structure. They regarded such xeromorphic structure as a means of adaptation to reduce transpiration. The same idea was expressed by Bowman (1918), Martin and Clements (1939), and Davis (1942).

Maximov (1931) defined xerophytes as dry-habitat plants, with transpiration reduced to a minimum in time of drought and an ability to endure desiccation. From the foregoing soil analyses, soil salinity and soil water content should be discounted as causes of a xerophytic environment on Shackleford Bank. Since there is always a supra-optimal water supply in the subsurface layers of the soil, the structural adaptations appear to be mainly connected with atmospheric stress upon the leaves. The high vapor pressure deficit in the atmosphere coupled with constant wind in summer provides an extremely arid condition in the air for plants. The author is inclined to agree with Kearney (1900) and Olsson-Seffer (1908) that strong wind, intensive light, and great heat are the three physical environmental factors which tend to accelerate transpiration and thus cause xeromorphic characteristics in strand plants. Water deficiency occurs in plants when the rate of transpiration (loss through leaves) far exceeds the rate of absorption (uptake through roots). Consequently, the plant develops xeromorphic characteristics on its above-ground portion not because of soil-dryness, but rather, air dryness.

Root systems of strand plants do not have to extend as deep as those of desert plants because there is always adequate water in the soil not far below the surface. Though dune species showed a mild drought resistance in the control experiment, the measurements of water potential indicate that herbaceous dune species do not develop as high water stress in leaves as those of xerophytes in deserts (down to -80 atm, Scholander et al, 1965) or halophytes (-25 to -75 atm, Yabe et al, 1965; -35 to -60 atm, Scholander et al, 1965). On the contrary, the lowest water potential accounted in the afternoon falls in a range from -5 to -15 bars in dune species studied.

The value of leaf water potential measured in the afternoon within a species varies from 3 to 6 bars. Such variation is relatively small as compared with Klepper's (1968) findings that a 7- to 8-bar difference was detected on the same pear trees at one time. Daily measurements of water potential of selected species indicate that the replenishment of water is generally completed overnight. The lower water potential detected among the woody species may be explained in terms of the lag in transporting water from the root through a longer distance to the leaf. Matubara (1965) found that the higher the tree, the lower the water content of the leaf.

Coupin (1900) stated that 1.5% of common salt in soil will kill the nonhalophytic dune plants in France. Kearney (1904) also recognized that dune plants are not true halophytes. Under my treatments of full strength sea water as well as 1:3 diluted sea water, the dune species under study died quickly. Similar results were obtained by Oosting (1945). It seems that species usually found on dunes are not edaphic halophytes after all.

Although dune plants are not true halophytes, their above-ground portion must structurally adapt to wind-borne salt spray and sand blasting due to their proximity to the ocean. Investigations of Oosting and Billings (1942), Oosting (1945), Boyce (1954), Martin (1959), and the present study show that dune species are generally tolerant to salt spray. Sauer (1965) suggested that seashore plants are adapted to tolerate salt spray, sand blast, and other special habitat conditions. In the case of prostrate species such as seaside spurge and seaside pennywort, the plants also are possibly adapted to tolerate high temperature (frequently recorded at 51-52°C on the ground surface in the afternoon), and great fluctuation of diurnal temperatures. The slightly succulent stem with milky latex of spurge and the more or less vertically orientated leaves of water pennywort may serve as a structural and morphological adaptation to such extremes.

Organic matter content of forest soil is rich, whereas that of dune soil is extremely low, especially the nitrogen and phosphorus components. The treatment of complete nutrient solution increases plant growth drastically. However, adding potassium alone does not improve the growth of dune plants. It is clear that low fertility of dune soil may reduce or even limit the growth of dune plants. Boyce (1954) and Willis (1965) both found vigorous growth of dune plants after adding complete nutrients to the sand, though at the expense of becoming more susceptible to salt spray (Boyce 1954). Willis and Yemm (1961) noticed that the deficiency of nitrates and phosphates in dune soil limits the growth of tomato plants. Therefore competition for meager nutrition in the soil may explain to some degree the open vegetation in the dune environments.

Dune plants must have the ability to survive under sand (the result of sand deposition) or partial root exposure (the result of sand erosion) because of the inevitable sand movement in a dune environment. Wagner (1964) demonstrated that moderate sand deposition stimulates the growth of sea oats and that its massive branching roots (Pl. I-4) firmly hold considerable amounts of sand. It is no wonder that sea oats make up 90% of the vegetational cover on the unstable dunes on Shackleford Bank. The stimulative effect of sand deposition on dune grasses also is reported by Farrow (1919), Greig-Smith et al. (1947), and Gemmell et al. (1953) in England, and by Laing (1958) on inland dunes in the United States. Finally, seeds of dune plants also have to germinate and send down a root quickly and deep enough to reach the moist subsurface soil. Under the condition of deep burying, young seedlings must also be able to grow out into the light.

Wells and Shunk (1938) explained the almost complete absence from the spray zone of inland species such as turkey oak, wire grass, longleaf pine (Pinus palustris), and persimmon (Diospyros virginiana) by their susceptibility to salt spray. Wells (1939) named the live oak-dominated forest as the "salt spray climax" and attributed this to the greater salt tolerance of the species. In my opinion, salt spray may kill intolerant trees which openly face the ocean. However, it is difficult to conceive that salt spray can penetrate very deeply into the maritime forest. Persimmon and another inland species—flowering dogwood—are quite common and thoroughly mixed with live oak inside the maritime forest on Shackleford Bank.

As mentioned earlier, an island of Sandhills vegetation surrounded by maritime forest makes it impossible to explain the absence of these Sandhills species on the Banks solely on the basis of salt spray, without a consideration of edaphic factors. Furthermore, turkey oak and longleaf pine can be found within 0.25-0.50 mile (400-800 m) of the ocean at Southport, N.C. At that location, no Outer Banks exist and the strand vegetation develops directly on the fringe of the mainland. A comparison among the maps of live oak distribution, late Pleistocene deposition, and 20°F isothermal line of average annual minimum temperature (Fig. 13) shows remarkable resemblance. In addition to the possible geologic or edaphic effects on the distribution of the species, the lower limit of temperature may possibly be another effective factor. The extension of live oak up to the southern Virginia coast may be attributed to the amelioration of the Gulf Stream on the coastal climate. Therefore, salt spray, edaphic conditions, and temperature may be important in determining the distribution of live oak.

Fig. 13. (A) Distribution of live oak (adapted from USDA Agriculture Handbook No, 271, 1965); (B) Pamlico shore line (adapted from Richards, 1950); (C) Average annual minimum temperature (°F) (adapted from USDA Yearbook, 1941).

Conclusions

Cain (1944) stated that it is erroneous to single out one factor as limiting and forget the others. The present study shows that no single factor can explain satisfactorily the occurrence of the coastal vegetation. Actually, it is difficult to evaluate accurately the relative importance of different factors to the vegetation or to give preference to one factor. Numerous distinctive factors are operating on the Outer Banks. For example, a milder climate prevailing on the Banks may affect the species composition of the maritime forest, especially when closely allied with edaphic factors. On the other hand, the extreme dune environments require specially adapted species.

Although a great deal of similarity exists between coastal dunes and inland dunes, such as high light intensity, high evaporative stress in the air, excellent drainage, and shifting sand, the prevailing southeastern sea breeze loaded with salt spray becomes an extremely important factor for the sand strand plants. Moreover, coastal dune soils contain a higher amount of calcium and magnesium than do the inland sands. The instability of coastal habitats is augmented by the occasional, unpredictable, and catastrophic hurricane. Sea water erosion and invasion created by winter storms are also special factors pertaining to the strand vegetation. Consequently, the species composition of the coastal dunes is almost completely different from that of inland dunes.

A diversified maritime vegetation with a rich flora on Shackleford Bank is due to the existence of diversified habitats. Each vegetation type is determined by a combination of a few critical environmental factors which produce a specific habitat. A single factor may be predominant at a certain time and space. For examples, salt spray exerts a limiting effect on the strand plants within a short distance from the ocean; and the leaching of calcium and magnesium through time also modifies the chemical properties of coastal soils, which in turn affects the vegetation. Time and space are considered by Billings (1952) as four dimensions of the holocoenotic environment.

As a result of this study, I consider wind, soil, and topography to be the most important factors in the maritime environment. Wind influences the vegetation, salt spray, sand blast, sand movement, and wave erosion directly; but it also indirectly affects temperature and humidity in the atmosphere. The effects of topography on other environmental factors are always indirect (Billings 1952). Edaphic factors, mainly the chemical properties of the soil, are emphasized here for determining the characteristics of maritime forest.

As a whole, maritime vegetation on the island is determined by the interactions of edaphic, biotic, topographic, and environmental factors, as well as the interactions among the organisms themselves, There are interrelated, simultaneous, and compensative effects which cannot be dealt with separately. The maritime vegetation, without exception, is also a biotic expression of the holocoenotic environment.

Conservation

Due to its relative isolation and lack of permanent residents, though after intensive devastation caused by both men and hurricanes, Shackleford Bank still possesses a relatively rich flora and sufficient diversified habitats to make the island scientifically most interesting. It is an irreplaceable remnant of the maritime vegetation of the Atlantic Outer Banks. The isolation which has spared the island for the past 6 decades now is challenged again by man.

The National Park Service is planning to acquire the island as a part of the Cape Lookout National Seashore. Fortunately, an earlier proposal to build a causeway connecting the island to the mainland at Beaufort has been dropped. Nonetheless, such a threat may be revived in the future. Iltis (1967) warns us that we "need to keep watch of a major trend in national and state parks in this country which can have disastrous consequences; namely, the efforts, under tremendous pressure from the public and from vested interests, to turn these into giant amusement parks and picnic grounds."

For years, concerned ecologists have attempted to preserve representative ecosystems for experimental research at a time when human population and activity expands in an unrestrained way. Oosting (1954), in his gloomy prediction of such expansion, said. "Dunes have been leveled, vegetation has been destroyed, and roads have been built, and this goes on at an accelerated rate from year to year. Each time a new causeway makes accessible another island, it dooms another segment of the natural vegetation." The active dunes, the rich maritime forest, and the productive salt marsh on Shackleford Bank are extremely valuable for ecological and physiographic studies. Adding to its isolation and small size, the island is a unique ecosystem for scientific investigations and should be set aside as an example of the natural ecosystem of the Outer Banks for the benefit of generations to come—generations who have no voice in present decisions. Shackleford Bank unquestionably is one of those precious natural features. One thing is certain: a few days of bulldozing is enough to destroy the vegetation produced in centuries, and we may lose such prime vegetation forever.