Read Ebook: Life in the Shifting Dunes A popular field guide to the natural history of Castle Neck Ipswich Massachusetts by White Laurence B

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Preface v 1. The Shifting Dunes 1 2. An Introduction to Dune Ecology 5 3. Plants on the Dunes 10 4. Life at the Edge of the Sea 19 5. Insects and Their Kin 33 6. Meeting the Mammals 50 7. Wings over the Sand 58 8. Now It's Up to You--Check List for Your Discoveries and Field Notes 69

Surprising as it may seem, there was a time when many of our most beautiful beaches, the Castle Neck area included, were far inland from the edge of the sea. This was about a million and a half years ago, when the sea was at a lower level than it is today. In fact, a great many changes have helped to form the beaches we see and enjoy now. Of them all, the one brought about by the Ice Age was probably the most influential. It was some 30,000 or 40,000 years ago that New England was overwhelmed by the final advance of a great continental ice sheet. It came from the northwest, and as it inched its way toward the ocean it pushed chunks of rock and great quantities of soil along with it. The rock was continually breaking up as it was shoved forward under the ice.

This last glacier covered New England for thousands of years. When it melted, all the debris it had been moving along like a giant bulldozer was left deposited irregularly over the land, some debris perhaps a hundred miles from original location. In addition, the water from the melting ice swept finer sands and gravels along, depositing them over land areas and in lakes and bays.

In some places, streamlined hills of debris had been built up under the ice. Later, as the ice melted, they became exposed. They were shaped like the bowl of an inverted spoon, and we call them "drumlins." Hog Island, to the south of Castle Neck, is a perfectly preserved example. From its shape it is easy to tell which way the ice was moving. The steeply sloping end of its long axis is toward the northwest, the direction from which the last ice sheet came. All drumlins are not so easily spotted. About a mile southeast of Castle Hill you will see a hill that looks like an enormous sand dune. It is the highest point on the Neck, about eighty feet, and it, too, is a drumlin. Once it protruded out of a shallow bay that had formed as the ice melted. Modified by the erosion of the waves and veneered with windblown sand, this drumlin by now has quite lost its characteristic shape.

In the general Boston area many drumlins were uncovered as the ice melted; some of them are such well-known landmarks as Beacon Hill, Bunker Hill, or Breed's Hill. Along the coast, as the sea level rose, the drumlins there were surrounded by water and became islands. On the sides exposed to the sea they were eroded by the waves, and the eroded materials collected to form spits. Other sands and gravels carried by longshore currents were added, and, by-and-by, in some cases these sand spits connected one drumlin to another. It was just such a modification of three separate drumlins that formed Castle Neck.

While the Neck was thus taking shape, the glacial debris and outwash sands that had been deposited in New Hampshire and at the mouth of the Merrimack River were being picked up and carried southward by the prevailing currents. Finally this material was wave-tossed onto the newly created beach at Castle Neck, some of it being lifted and carried farther inland. In this way, except for a few protected spots behind the drumlins, the entire area became blanketed with sand. The shape of the Beach as we see it is the result of this ever-continuing modification, the work of wind and waves.

It was on the protected back side of the drumlins that plants first took hold. Since the drumlins were formed from fertile soil scraped from rich inland areas and carried here by the ice, the same kinds of plants sprang up on them--Aspens, Pines, Gray Birches, shrubs, and grasses--as we often see today taking over some abandoned farmland. As these early plants died, the soil was further enriched to stimulate even more and different plant life. In fact, at one time much of the dune area was a fertile spot, abounding with all sorts of plants and animals. In certain places on the Neck today, very fertile soil can be found just a few feet under the sand, evidence that here was once a rich farmland.

The broad flat areas of sand on the Beach were very susceptible to the whims of the wind. Now and then, as the wind eroded the sand particles from one place, and blew them to another, it piled them up against the base of some beach plant. Collecting here, the sand began to form a gentle slope with a sharp drop-off downwind. Continuation of this action sometimes built up a huge mound, which we call a dune.

This process of erosion and deposition still goes on. Usually you can tell the general direction of the prevailing wind by observing which way it builds the gentle slope as it piles the sand into ripples or mounds.

If you should mark a dune's position today and return in several years, you might find that the dune had moved several yards from its original position. Dunes move slowly downwind, such movement being termed "migration." With a normal dune, during windy periods the sand is blown up its gentle slope and dropped over its crest, whence it slides down the lee side. In this way the dune migrates with the wind.

THE FUTURE OF CASTLE NECK

Eventually, of course, the dunes might migrate the entire length of the Neck and again be blown into the sea, which would carry the sands farther south, mayhap to become part of Coffin and Wingaersheek Beaches. In fact, we might expect the eventual removal of the entire Neck if sand wasn't constantly being added from similar erosion going on farther north. Obviously there is a very delicate balance here, adding and subtracting sand. The future of Castle Neck is entirely dependent upon the sand supply from the north. Too little may eventually diminish Crane's Beach; while an increase could create an even larger and more beautiful Neck. Actually, it is impossible to predict the future of a beach, at the mercy, as it is, of changes in any of the several factors controlling its form--sand supply, waves, currents, and position of sea level. Anyway, what has been so long taking shape will not be altered drastically overnight. As a matter of fact, if you really wish to know the future of Crane's Beach, you will have to be patient. Another million and a half years will probably tell the story!

GEOLOGICAL DISCOVERIES YOU CAN MAKE

These small, faceted pebbles found in the dunes have been blasted by the windblown sand. They show the powerful abrasive action of the wind. Most of those you will find here were faceted just after they had been deposited by retreating glacial ice. A migrating dune or a blowout in the sand has left them uncovered.

Large rocks occasionally found in the dunes are called "erratics." In this world of tiny particles they appear very much out of place, but they were carried here by the glacier a million years ago. They have been uncovered by the migration of some dune.

Occasionally lightning strikes the sand, fusing it into a little tube or ball of glass. These fulgurites have been found here but are very rare and a real "discovery."

The original soil deposited by the glacier may be seen by digging into the sand at the drumlin. Such rocky soil is quite surprising to people who think the beach is nothing but a big "sand pile."

Examine a handful of sand. You will find that it consists of light-colored particles and of black particles. Under a microscope many of these dark particles look like little gems. They are actually a deep red and are true Garnets. Large Garnets are used as gem stones, small ones for sandpaper--further proof of the abrasive ability of windblown sand.

In your handful of sand you may find particles that are neither Quartz nor Garnet. Minerals such as Feldspar, Biotite, Mica, Magnetite, Hornblende, and others can be identified by the geologist and are a clue to the original type of rock over which the glacier moved.

These are hard-packed balls of twigs and grasses. Loose vegetable matter is very light and may be blown along by the wind for many miles. As it goes it adds other vegetation to itself, until packed into a very tight, hard ball. It may also get its start in the water by being whirled into a tiny ball; and later it is thrown onto the beach, to begin rolling along. A most curious souvenir!

MORE ABOUT THE DUNES

The face of the land is a storybook waiting to be read. The following books will help you piece together some of the story:

Living things cover the face of the earth from the torrid sands of the desert to the cold wastes of the Arctic, and every variation in environment develops a closely knit community of plants and animals. They are the ones best adapted to living where they do, or they may have been the first to arrive there, filling all available homesites and monopolizing the food and water supply to create a "closed" community. In each environment, a delicate balance is established between its various residents and between them and their surroundings. The study of all these interrelationships is called "ecology."

Beginning with the environment, we have seen in our brief look at the origins of Castle Neck how drastically an area can be altered as conditions change on the earth's surface. Environment is affected in other ways, too. Man's activity can change it almost overnight as a bulldozer clears land for a housing development, a dam alters the flow or course of a river, or careless disposal of a cigarette or campfire lays waste to acres of woodland. Or, as in the slow development of a forest, the growth of the trees themselves can change the environment, the maturity of one species whose seedlings require sunlight contributing to the growth of those better adapted to shade. If you should watch an old abandoned pasture over a period of many years, you could see environment gradually altered. First there are the mosses and grasses that create a fertile soil. Then come the Poplars and shrubs. As these grow they offer shade where Pines and, finally, the broad-leaved trees can flourish. This change in vegetation will also bring about a change in the resident animal communities.

When parts of Castle Neck were rich farmland, specialized forms of life which thrive in that type of environment were abundant there. We have only to look at Castle Hill, just a few hundred yards from the dunes, or at some of the swamps that dot the Neck to see how different are the inhabitants from those of the dunes. On the Hill live the Oaks, Maples, Jumping Mice, Raccoons, and Toads, plants and animals that would be misfits indeed--if they could live at all--in the world of moving sand. Maples and Oaks, relics of the time when the dune area was fertile, may still be found dying and being buried over by drifting sand. Now it is a different community of plants and animals living here. The continually shifting sand and the scarcity of water limit the variety of life found, but each dune dweller is specially adapted to this homesite, and no matter how lush, green, and more attractive a neighboring meadow may look to us, many of these specialized organisms could not survive there at all.

It has taken millions of years for the long, slow process of evolution to develop specific adaptations that suit dune dwellers to their environment. There are variations between individuals in every form of life. Mostly these are normal inherited variations, such as height or color. But sometimes sudden variations, called "mutations," occur through accidental changes in the genes controlling inheritance. These are new characteristics not found in other members of the same species. If the mutation is advantageous it may be passed on, and it is in this way that new life forms slowly develop. If the mutation allows a species to live more easily in its environment, it may displace some older form, which may then be unable to compete successfully for food, water, or shelter.

Indeed, all life is engaged in a constant struggle for survival; it is those individuals and species best able to adapt to the changing conditions of their environment that endure. Think of the whole series of crises faced by any living thing in its lifetime, then of these crises being met and overcome in the seemingly inhospitable environment of the dunes. In the beginning, our dune dweller must be born, a difficult enough task without interference from unkind surroundings; it must feed itself, here in an area where meals would certainly seem at a premium; it must grow, oftentimes shedding its skin in the process; it must live not only in the summer's heat but, if its life span is that long, in the winter's cold; it must endure long periods of drought, flood, wind, and storm; and most important of all, it must survive long enough to reproduce its kind, or else it has missed its goal. But such is the wonder of nature's specializations that our dune dwellers can usually meet these normal crises. Their adaptability and rate of reproduction safely insure the future of their kind, and their overpopulation, if left to nature, is delicately controlled by available food and shelter and their predators.

Exploring the dunes and making the acquaintance of the inhabitants, you can see this environmental community meshing its lives together, and you can observe the fine degree of adaptation developed by each life form. You may find an occasional Apple tree growing out of the sand, rooted in a more fertile soil below, a reminder of the time when that bit of the Neck was a rich farmland. The roots of the Beach Plum also reach down to the water table, and it is thus able to grow out of the sand, although its seedlings cannot take root in the sand. Most of all, you will have an opportunity to note many special animal and plant peculiarities the dune dwellers have developed to suit their particular environment.

SOME ANIMAL ADAPTATIONS

Walking through the dunes, you will frequently notice a small hole in the sand. Poke a blade of grass into it and you will find the hole quite deep. As a matter of fact, it may extend down two feet. This hole is made by the Sand Dune Wolf Spider to provide a home where the female may raise her young. Wolf Spiders are a species that elsewhere carry their young on the back and hunt down their food wolf fashion, not even taking time to construct a web. On the exposed dunes, the Sand Dune Wolf Spider protects its young in this hole far beneath the ground.

Dozens of Common Terns are to be found nesting at the southern tip of the Neck. Long ago, the Common Tern began laying its eggs on the bare sand, and made no nest at all. Each egg is sand-colored, with speckles resembling pebbles. Only a patient search will locate a Tern nest on the Beach, and then, unless you are cautious, the discovery may come after you have accidentally stepped on the eggs.

Bayberries have a hard wax covering that makes them seem quite unpalatable to us, compared to the more succulent berries found away from the dunes. Yet here the Crows, Tree Swallows, and Myrtle Warblers are Bayberry-eaters. The Myrtle Warbler in particular derives most of its winter diet from Bayberries. In fact, its name comes from the scientific classification of the Bayberry, which is in the Wax Myrtle Family.

The sand offers few places of retreat and few for hiding. It is not surprising, then, that many of the living things here have a sand-colored protective coloration. There is a large Grasshopper, or Locust, commonly found on the Beach. Its dull, gray, speckled wing-covers make it practically invisible when at rest. But the underwings, used for flight, are a striking orange with black bands. When discovered, the Locust flies up, confusing its attacker with this bright flash of color and a loud whirring noise. Unlike most insects, this Locust eats the thick-skinned, dry Beach Grass.

PLANT ADAPTATIONS

Any plant that is adjusted to living in a region where there is a decided lack of water is called a "xerophyte." There are many different ways in which plants have adapted their structure and way of life to the dune environment. For instance, to reduce water evaporation they may have a very small leaf, to offer less surface area to the sun; or smaller and more numerous stomata than other plants ; or a very thick cuticle ; or their sap may be changed chemically. Xerophytes may also be very fleshy, like the cactus, to give more storage space for water. Their roots may drive very deep into the ground to reach the water table, or they may be shallow and spread out over a wide area to cover more surface. Their leaves may grow in closely packed bundles to reduce further the surface area, or they may be very thorny and prickly as a protection in exposed surroundings.

Here are just a few common examples of xerophytes and other plant adaptations to be found at Crane's Beach.

Beach Grass is a true xerophyte and has many sand-dwelling characteristics. Its grasslike blade is rolled in at the sides, oftentimes becoming a tube, in order to reduce the surface area. As you will probably discover, it has a pointed tip that can prick a finger and, as you may well imagine, acts as a deterrent to those who would eat or walk through it. Its underground stems, in true xerophyte fashion, extend over a large area in an attempt to gather all possible water, and these dense root-mats serve to anchor the dunes and prevent their migration.

The Woolly Hudsonia carpets the dunes, preferring its place in full sun to more shaded spots. The tiny leaves are awl-shaped and press very tightly against the stem, as though trying to hold in as much water as possible. Hudsonia is covered with a velvet-like down, which is less susceptible to evaporation than a smooth, large surface would be.

Since mushrooms generally require plenty of water, you would not expect to find them at the beach. Several species, however, may be discovered here. The most readily identifiable is the Earth Star , which resembles a Puff Ball but differs in having the outer layer of the skin divided into tough, star-shaped segments. During the dry seasons, this star is drawn up around the ball by its contraction, thus protecting it against further desiccation. In wet weather, the ball swells and holds the star against the ground to allow for water absorption. The "roots" of the Earth Star are shallow, so the plant may readily be dislodged. The wind easily blows it across the dunes, spreading the spores over a wide area.

NOW IT'S UP TO YOU

There is something new to be known about every animal and plant. Now it's up to you! Careful observation will allow you to discover many other examples of special adaptation to life in the shifting dunes, and the next chapters will introduce you to some of the more common of the living things inhabiting this strange sand-world. And if you wish to read more about ecology, try these books:

Plants add embellishment to the earth. For thousands of years people have valued them for their elegance and their usefulness. They may rate no more than a passing glance in fields and woods, but at the beach they stand out boldly, for here they seem almost out of place.

We have already become acquainted with some strange beach-dwelling plants; now let us examine more closely a few of the most common species.

MUSHROOMS ON THE DUNES

Earth Star

Star-shaped fleshy skin at base Main, central body is round

GRASS ON THE DUNES

Beach Grass

Typical grass shape Sharp, stiff tip to blade

Beach Grass is the most common xerophyte here. It forms dense mats everywhere, and once it gains footing, spreads at a remarkable rate. When windy weather bends the blade it sometimes scribes circles in the sand. If these are deeper on one side or incomplete, they help determine the direction of the prevailing wind. Beach Grass can be extremely uncomfortable to bare legs--so beware!

FLOWERS OF THE SEASHORE

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