Plants don’t lie, and any gardener will tell you that you don’t know a place until you know its plants. If you live on the Vineyard, or visit here, you may think you have a Ph.D. in beach. But unless you pay adequate attention to the plant life of the Vineyard’s margin of sand, you’re missing most of the subtlety of this peculiar habitat.
How could the plant life of beaches not be fascinating? It flourishes amid a gardener’s nightmare. Start with the soil, or what passes for it: finely crushed rock, unyielding of nutrients. Water runs through it unresisted, unretained – how can you ask a plant to put a root down into that? Add the desiccating effects of salt spray, kiln-like summer temperatures, hurricane winds, and periodic pickling in saltwater, and one’s jaw drops with admiration at the thought that a plant, any plant, can survive there.
They survive because of a paradox: A beach is at once the most enduring and most mutable of things. Sand is always moving on a beach. Contours change at the hands of wind and water; a strong storm can strip away or deposit unbelievable quantities of sand. So a beach makes only a tenuous boundary between land and sea; indeed, when a hard gale is blowing onshore, salt spray and lofted sand intermingle so thoroughly that it’s hard to say a boundary exists at all. And over time, the movement of countless grains of sand adds up to movement of the beach itself. The recession or accretion of beaches may seem slow to our video-blurred minds. But on the scale of a plant that can’t move to keep up or get out of the way, these processes matter: A beach plant is always just one storm away from being buried or washed into oblivion.
And yet, migrate how it may, a beach remains a beach. And from a plant’s perspective, this is a valuable fact. No matter how harsh an environment is, given enough time, some intrepid plants are going to adapt to it. Eventually, some are even going to specialize in living there. Plants find wonderful assurance in a place that stays the same; it may be harsh, but at least it’s predictable. Moreover, if you can crack the quandary of how to survive in a place as horticulturally uninviting as a beach, you’ve found a way to circumvent most competitors.
So it is not surprising to find that the vegetation of beaches and dunes tends to be sparse and unvaried. But the plants that do manage to flourish here are all, necessarily, marvels of evolutionary engineering. Indeed, some of them are engineers in their own right, exerting a profound effect on the structure of the shoreline.
For example, an unprepossessing grass Ammophila breviligulata (American beach grass) ranks as one of the most potent ecological forces of a Vineyard shoreline. On the face of it, there isn’t much to like about this plant, known colloquially as dune grass for the setting it prefers; it is rarely found away from the sandy deposits of the immediate shore. Its pallid, gray-green leaves are rough to the touch, the edges stiff and sharp enough to cut. Its inflorescence (flower head) inspires a bit more admiration – a fibrous column that ages to yellow and finally old-shingle gray. But basically, dune grass is ugly: meager rosettes spotting a dune like clumps of bristles on a chin.
The roots aren’t any prettier – quite the contrary, in fact, as one might expect of roots. You can sometimes see them exposed where waves have cut into a dune, a network of unappealing rhizomes and feeder roots. But once you’ve seen them, you’ll have a better understanding of why this perennial grass is so important to a Vineyard beach/dune system. The mat of roots from a healthy patch of dune grass reinforces the dune itself, lending cohesiveness to sand that would otherwise be wholly unanchored. If a dune rolls back to bury dune grass, the plant is unconcerned; it simply sends up new shoots from those ropey rhizomes, reestablishing a new root system closer to the new dune surface. Dune grass, you might say, modifies sand dunes to create its own environment. And in doing so, it turns dunes into a resilient barrier against waves and storms.
Storm-resistant dunes matter because beaches function mainly as dividing lines, an ecological no man’s land wedged between our world and the empire of water. However, it’s a narrow divider; in many places, you can toss a rock underhand from non-beach to the water. Another perspective matters much more to most sorts of wildlife. Stand on a beach. Face the ocean. Look left. Look right. They may be narrow, but beaches, by their very nature, are also long.
And because they are long, beaches function as connectors as well as dividers, facilitating the movement of wildlife. Consider the monarch butterfly, faced with the problem of how to navigate from New England to Florida or Mexico with hardly any brain. To evolve a migratory life history such as the monarch’s, an insect species needs a simple, infallible method for finding the way. For New England monarchs, the instinctive programming amounts to “fly south in September, and if you hit water that you can’t see the other side of, turn right.” One result is that, following a summer during which the species has bred successfully, tens of thousands of monarchs transit the Vineyard. Spectacular roosts of many thousand have been observed around Gay Head in Aquinnah and elsewhere on the Island. But if you pay attention to beaches in late summer, you may also see migrant monarchs following a shoreline south and west in a slow but steady stream.
Navigation is only part of the problem for a monarch. Fuel is another, since flying takes energy – and this is where the beach plants come in. Adult monarchs, everyone knows, can unfurl a deft proboscis, as long as the insect’s entire body, to sip sugar-rich nectar from flowers – a botanical energy drink. But beaches, the butterfly’s most ready source of navigational assistance, rank among the least ready sources of flowering plants.
Therefore, seaside goldenrod is the monarch’s best friend, and if you wanted to name an official Vineyard flower, this one might get my vote too. Visually, it is the most striking of our dozen or more species of goldenrod, a stately plant that may stand five feet tall. In September and October, as monarchs are migrating, it bursts into blooms of startling yellow. It has the showiest flowers among our goldenrods, a magnet not just for refueling monarchs but for numerous species of flies, wasps, and beetles that eat nectar or pollen. Providing a rich, well-advertised food source at a critical point in the life cycle of these insects, seaside goldenrod plays a major role in sustaining the diversity of beach life.
Long-lived and incredibly hardy (seaside goldenrod’s official species name means “living forever”), Solidago sempervirens shrugs off the rigors of life at the beach. The impressive top-hamper is balanced by a fibrous mass of roots, anchoring the plant firmly in the shifty sand and storing water to last through a blazing summer drought. The leaves, leathery and vaguely tongue-like, are fleshy and covered in a thick cuticle; they hold water in and keep salt out. (Waxy leaves are a common adaptation among beach plants, or indeed among plants adapted to any place where water management poses a problem.) Seaside goldenrod grows readily in other settings, if it doesn’t need to compete directly against less-specialized plants (it makes a great ornamental in a Vineyard garden). But seaside goldenrod is at its best at the beach, where its adaptations allow it to look positively lush and comfortable despite the fact that its roots reside in salty, mineral sand.
Surviving in a harsh environment is only one challenge a beach plant faces. Another is successfully launching the next generation. The sterile and unstable sand of beaches and dunes does little to encourage germination of seeds. And the narrow, linear nature of beaches means that populations can disperse only in one dimension without ending up either in competition with a multitude of non-beach plants, or in the drink. Fortunately, the nature of beaches makes dispersal along the beach relatively easy: Inundation from storms and high tides readily transports seeds or roots to new locations, allowing populations to sustain themselves or move.
Wave-borne transport is probably one key to the success of one of best-known seaside plants, the wild rose Rosa rugosa. Believed to have been introduced here from its native Asia around the middle of the nineteenth century, Rosa rugosa has naturalized throughout the Northeast, and on portions of the West Coast too. Tolerant of salt, it’s a mainstay of the seaside cottage garden. Growing as a naturalized wild shrub, this rose is especially prevalent just back from the beach, where it forms impenetrable thickets of spiny stems. The sweet-scented pink or white flowers, though, make up for the plant’s hostile exterior, perfuming the shoreline during this rose’s extended spring/summer bloom period.
The flowers give way to bulbous fruits, called “hips,” that eventually ripen to a bold red and to a size that can approach that of a golf ball (looking at a ripe rose hip, one isn’t surprised to hear that the rose and the apple are cousins). The fleshy exterior of rose hips can be made into a serviceable jam, and it’s also a welcome food source for birds and mammals. The hips also float, making it easy for a patch of roses to launch progeny miles down-drift. Resilience and a talent for dispersal have made this Asian species an integral part of our shoreline community.
Rosa rugosa is not the only non- native that has achieved prominence on our beaches. A native of the western Pacific Rim, beach sage, or dusty miller, has achieved iconic status on the New England coast as a distinctive, common, sometimes dominant plant of back-dune habitats. Here it often mixes with, or even displaces, a native back-dune specialist, a hardy legume known as beach pea. Better known for its gray, flannel-like foliage than for its inconspicuous, yellowish flowers, dusty miller probably arrived here as an ornamental well-suited to seaside gardens. The fuzzy leaves largely account for this plant’s success at the coast: The nap insulates the plant from intense sun and high temperatures of a summertime shore and intercepts salt spray before it comes in contact with the leaf surface proper.
Moving inland from a shoreline, conditions moderate: Salt spray is less intense; soils are more fertile, stable, and water-retentive; sheltered sites are more plentiful. The beach community merges into the adjacent upland ecosystem. On much of the Vineyard’s south shore, this means that dune grass gives way to little bluestem (Schizachyrium scoparium) and huckleberry (Gaylussacia baccala); where clay hills run down to the sea, wetland shrubs like winterberry and viburnum often dominate just back from the shore, and beach specialists, deprived of the competitive advantage they have at the immediate shoreline, drop out of the mix.
The trip home from the beach serves as a reminder that specialization comes with a price: In evolving the equipment necessary to survive on a beach, a plant surrenders its ability to compete successfully in richer, moister, more temperate habitats. But this knowledge simply reinforces the main lesson beach plants teach us: Though we take them for granted, beaches are in fact dynamic, complex, and intricately varied places. They’re pleasant enough to visit. But growing there year-round is not a task for amateurs.
