- Shopping Bag ( 0 items )
The Reedgrass Pool
September 24, first full day of autumn, 4:47 P.M. Reed canary grass rustles momentarily on a slight dance of evening air that quickly dies away. High above, long trails of cloud race eastward on the winds streaming over the near-breathless layer of air close to earth. Not a single blade of the long dry curls of grass stirs now. The steady pulse and drill of insects becomes an evening raga. Light has begun to fade from the alder thickets behind me, though it lingers in the open, grassy, shrub-scattered hollow before me, a topographical depression set among rounded knolls to the west and north and a high, steeply ascending ridge to the east. Slipping through a screen of reed canary grass on the low ridge of the hollow's southern rim, I step down into it.
From time to time, unseen sparrows punctuate the intensifying insect drone with their final furtive soundings of the day. There is something outward-bound about their shadowy movements, their brief, almost whispered calls. Swamp and song sparrows arrive in spring, animated in flight and exuberant in song, and settle in around and above the water that fills this basin in the earth to overflowing at that season, as though they have come to stay forever. But, like the water, they are seasonal. Most years they depart just before the water starts to return to the pool. But the water and birds are perennial as well as seasonal: in the course of the year they always come back. They will continue to do so every year unless the landscape and the cycles of its water are disrupted.
Theopen hollow I have stepped into looks like an unmown pasture. The footing is firm and dry, the earth strewn with the straw of the past years' growth. The matted floor-weavings of stems and blades form artful arrangements: the over the seasons tall grasses die, dry and lie down under their own weight, or are toppled by wind and rain, pressed by snow and ice and the weight of standing water. Scanning the drapings and carpetings of reed canary grass, I see a more deliberately designed structure, a carefully wrought casing nearly an inch and a half long, built from the same grassy materials in which it lies. This is not the work of the elements or a form created by plant growth but the construct of an animal, a small insect larva. This house made of straw, fashioned from cut pieces of reed canary grass and sedge, adhered to an interior tube of spun silk, served as protection for a caddis fly larvae. Until its metamorphosis into mothlike, winged adult, the larva had lived an entirely aquatic life, molting through a series of five encasings like this, making a larger one each time as it grew. In what now seems to be a grassy upland field in which meadow grasshoppers, crickets, and katydids sing and feed, an insect larva that can live only in water completed the subadult phases of its life.
Lifting a decaying sections of alder stem that has become partially embedded in the turf of the basin floor, I find an even more readily recognizable indication of an aquatic environment, the shells of half a dozen tiny fingernail clams, ranging in size from an eighth to three-eighths of an inch. The shells are huddled where the last of the season's water collected as summer came on. Fingernail clams inhabit a wide variety of permanent wetland habitats, but they are also able to live in pools that dry up every year. Adults and young burrow into the substrate during the dry season and emerge when their pools refill.
The casing of the larval caddis fly and the shells of the fingernail clams lie close to the base of a tussock of grasslike growth. A number of symmetrical mounds of inflated sedge have colonized a deeper pocket of the two-acre basin. They look like a village of straw huts settled into a small clearing in a forest of grass four feet tall. The reed canary grass, growing on rises a foot or so above the pits in which the sedge grows, towers all the higher. Slight differences in elevation in a wetland can affect the depth of the water and its duration at any given site; those factors in turn dictate what plants are able to grow there.
Inflated sedge can grow only in wetlands. Like the caddis fly casing and fingernail clamshells, it indicates an environment that is, over the long term, ruled by water. Reed canary grass is also virtually confined to wetlands. Its luxuriant growth dominates this seasonally ponded hollow, which I call the Reedgrass Pool. On the sloping rim of the basin, swordlike leaves of blue flag iris thrust from sedgy tangles. Beyond these grow brushy stands of sweet gale, thickets of taller winterberry holly, and alders. The native iris and sweet gale are obligate wetland plants, and winterberry and speckled alder rarely grow outside of wetlands. Even if I had never been here before, never seen this pool at the height of its flood season in spring, the plants and the signs of aquatic animal life would tell me that this currently waterless, grassy place is in fact a wetland, more specifically a vernal pool, which every year alternates between being flooded and drying up.
Earlier in the year, at spring thaw, this pool is filled to overflowing, and even before its central block of ice and the surrounding snowbanks have completely melted, a tumultuous evocation of the changing season begins. First comes the ructious cacophony of wood frogs, quickly followed and joined by the shrill piping of spring peepers. In a week or two, after breeding in the water, the wood frogs depart to a terrestrial life of silence in surrounding upland woods. The peepers pipe on and are joined in time by the high-pitched, drawn-out, sweetly descending trills of American toads, and then by the echoing trills of gray treefrogs, punctuated at times by the clamorous twangs of green frogs.
I come wading here during the season of water, from thaw in early April until the drying up that occurs sometime between the summer solstice and the end of July, depending on the year's rainfall. This is the time of mosquitoes, mayflies, and caddis fly larvae, early-breeding wood frogs, spring peepers, and spotted salamanders. These are followed by insect-hunting green frogs and bullfrogs, who breed in more permanent waters, and later-breeding gray treefrogs and American toads, who come to trill and mate. It is the time of other annual migrants: spotted turtles, young Blanding's turtles, occasional wood and painted turtles, juvenile snapping turtles, and northern water snakes, all drawn to the rich foraging waters where so many amphibians and insects breed. These reptilian predators are accompanied by wading hunters who wing in and out while the water is here — American bittern, spotted sandpiper, sora, Virginia rail — and the furred hunters of the night, raccoon and mink. Swamp sparrows come early in spring to work the water lines, deftly snaring mosquito larvae and other aquatic insects and at times tadpoles, I think, from the pool. These dark, musically trilling sparrows stay on to nest and, as the pool dries up to become a field again, hunt crickets and grasshoppers where spotted turtles swam in pursuit of tadpoles.
Although vernal pools are not permanent wetlands like swamps, marshes, and peatlands, the only plants that can persist in them are those adapted for life in water or in soils that are periodically flooded or saturated and thus deprived of oxygen into the rooting zone through all or much of the growing season. Such plants are called hydrophytes — literally, water plants. All of the plants around me, the reed canary grass, sedges, blue flag, alder, and winterberry, are hydrophytes.
During cycles of drought, some wetlands may be dry for several seasons, even years. If water does not stand on the surface or if the water table — the upper level of water in the ground — does not rise into the rooting zone during the growing season, seeds of upland plants will germinate. Soil areas formerly deprived of oxygen through flooding or the persistence of water become aerated. Oxygen filters into spaces in the soil, and burrowing animals go to work. Upland annuals move in and may live their full cycle, from germination to seeding. Upland perennials, from grasses to trees, begin to infiltrate and replace entrenched wetland vegetation. But unless a major transformation occurs in the topography, by way of natural causes or human engineering, or a pro found shift in climate takes place, the water will return, saturating the root zone and drowning out upland plants, all of which require well-drained, oxygenated soil. Then wetland plants will return.
Two dead pine trees, standing in reed canary grass behind a hedge of winterberry, are testament to such a cycle in this vernal pool basin. During a succession of drier years, the white pines, upland trees that can tolerate some degree of wet footing, germinated on a shelf of land abutting the trough in which the winterberry grows. Though struggling in the seasonally soggy environment, the pines grew to a height of fifteen feet or so, until years of more abundant rainfall restored the hydrology of the pool. They stand skeletal now, surrounded by northern arrowwood, maleberry, silky willow, and the ubiquitous alders. In death, the pines provide hunting perches for eastern kingbirds, seasonal birds who take insects over the seasonal waters here, as well as nesting and hunting places for year-round chickadees, who seem able to find food in the dead branches and beneath the last shinglings of sloughing bark during every season.
As dusk nears, the cadence of crickets grows louder. Light lingers here, as it does in many wetlands, after the surrounding upland forests have darkened beneath their dense canopies. Wetlands, with the exception of low-light cedar, spruce, and hemlock swamps or shadowy forested wetlands crowned with red maples in leaf, lie open to the sky. Even when this hollow holds no sky-reflecting pool, it remains an arena of light in the twilight landscape. It may be the light, as well as the water, that draws me here.
I thread my way among the tussocks of inflated sedge. Not far from where I found the casing of the caddis fly larva, I come upon rabbit droppings under arching blades of sedge: the husk of a completely aquatic life adjacent to the droppings of an animal as terrestrial as I. I think back three and a half months or so, when I waded here as thousands of wood frog tadpoles swam through the grasses and sedges that snowshoe hares nibble now without so much as getting their namesake feet wet Where hares dine, foxes hunt. From late summer into winter, and at times on winter's frozen water, foxes track hares here; from early spring to early summer, the hunters are bitterns stalking frogs.
Being dry for most of the year, vernal pools are uninhabitable by fish and are critical breeding places for a small group of invertebrates and amphibians: fairy shrimp, wood frogs, and spotted, Jefferson, blue-spotted, and marbled salamanders. While many other animals make significant use of vernal pools, the life cycles of these six species make them dependent upon seasonal wetlands. They are considered indicator species; the presence of any one of them in a seasonal wetland identifies it as a vernal pool habitat.
The specialized wetlands known as vernal pools are extremely variable, ranging from broad, heavily vegetated lowland depressions of over two acres in extent, like the Reedgrass Pool, to unvegetated, water-filled clefts a few feet in diameter in hemlock-shrouded ledges of mountain forests. Although typically associated with wooded areas, vernal pools can be situated in open meadows, sandy washouts, and river floodplains. Some feature rank growth of grass and sedge, some are crowded with emerald-mossed islands of highbush blueberry and swamp azalea, encircled by a high canopy of red maple; many are bowls of dark water with sunken black-leaf floorings in which no plants grow, ringed by a narrow band of wetland trees like swamp white oak and black gum, or surrounded by upland trees like pignut hickory and white oak. They may be set within an extensive wetlands complex or, more typically, entirely isolated from other wetlands in an upland forest setting. Within this bewildering array of physiographic settings and plant associations, vernal pool habitats are defined by a common key set of ecological parameters: they lie within confined depression that lack a permanent outlet stream; have seasonal, impermanent flood periods that generally last from two to five months; dry out completely most years, usually by late summer; are free of fish; and, most significantly, support the life cycles of animals that are utterly dependent upon this habitat for the perpetuation of their species. The pools define these animals, and these animals in turn define the pools.
Although the term vernal pools comes from the Latin vernus, "belonging to spring," most of these pools refill over the course of autumn's transition to winter and could be thought of as autumnal pools. But it is at snowmelt and ice-out, the last sleets, first rains, and earliest warming breaths of spring that they beckon wood frogs, salamanders, and spring peepers from surrounding upland woods, where they have passed the winter in rotted-out tree roots, under layers of bark and litter, in small mammal tunnels and other hibernacula in the earth. The vernal pools summon spotted and Blanding's turtles from wetlands near and far and birds from thousands of miles away.
6:23 P.M. Strange, unsettling cries break the deep silence surrounding the low swishing sound I make as I brush my way through difficult meadowsweet thickets at the north end of the Grass Pool. Two eerie calls, silence, then two more calls. The pattern continues. The repeated drawn-out cries sound like the downscaled bleating of a lamb. I have never heard anything like them, but they seem to express the epitome of distress. I cannot even decide whether the animal who cries out is a bird or a mammal; I can only determine that it is not very big. I begin to track the sounds around a high shrub-and-sweetfern knoll, drawn to them yet at the same time put on edge, touched by a feeling that I would just as soon not see what they are all about. My naturalist's curiosity is compelling, but there are some fates I would as soon not witness. The cycle of two long, drawn-out calls followed by an interval of silence continues. I trace their source to heavy sweetfern cover at the base of the knoll. The cries become even more penetrating. I search the brush hesitantly, knowing that I am virtually on top of whatever utters them. I still cannot guess what kind of animal I am hearing. I sweep aside the low sweet fern with my walking stick, allowing enough twilight to enter and reveal the scene: a wood frog, caught in the teeth of a young garter snake, cries out. Of all the possibilities that went through my mind as I searched for the source of these wails, I never imagined a frog. The snake has one of the frog's hind legs in his mouth, and, winding backward, is dragging him up the slope. This maneuvering takes considerable effort. The snake is not much bigger around than my little finger. I do not see how he could have captured a full-grown frog in the first place, but he has managed to latch onto the frog's foot and steadily work his grip to midthigh, having no more to work with than his jaws and teeth. The frog continues to cry out. The snake coils and uncoils, flexing his belly plates, resolutely seeking traction in soft, plush haircap moss. He has twisted his tail around a sweetfern stem to gain more leverage.
I am not given to interfering with nature, but I find myself unable to walk away from this scene. Snakes have legendary capacity for swallowing prey that seems impossibly large, but the wood frog is in fact well beyond swallowable size for jaws that are already almost completely unhinged in the effort to encompass one hind leg. My human perception that no good can come of this for prey or predator moves me to gently tap the garter snake with my walking stick. The tenacious young hunter lets go of the frog's hind leg at once. He curls back into the sweetfern and is gone. It surprises me to see the snake disengage so quickly. I had expected the release of such an engulfing hold from a mouth full of recurved teeth to be arduous, an additional struggle for both parties, perhaps not even possible. The wood frog pulls his bleeding leg back under himself and settles into a familiar crouching position, completely still. He may well fear that any move he makes will have the teeth of an unseen predator fastened upon him again.
I continue on my way. Snake and frog will soon be entering their separate hibernacula in the uplands around the vernal pool basin to wait out the long winter. The male wood frog, certainly one of last spring's chorusing revelers, is silent now that he has been released from his distress. (I could not tell if the young snake was a male or a female; it is hard for me to refer to any animal as "it," so I report to the convention of using the masculine pronoun except where I know the animal to be a female.) He will not give voice again until he emerges in the spring and migrates back to the Reedgrass Pool, the site of his metamorphosis from a pool-swimming tadpole to a land-dwelling frog. Wood frogs are silent throughout their approximately three-year lifespans, except for the eruptive vocalizations of breeding males. These are confined to their mating season in vernal pools, which generally lasts no more than two weeks. Following this, they return to land and live in the forest in silence.
Some frog species have distress calls, but other than the prolonged, loud, almost childlike wailings of a struggling bullfrog, they are seldom heard. It is thought that such cries may startle a predator and facilitate an escape. I have captured and observed many wood frogs in their upland haunts, and I have never heard one of them make a sound. The terror, or whatever response the frog felt, of being caught in the teeth of a snake brought forth a rare utterance. The wood frog's nerve-jarring expressions of distress fell on literal and figurative deaf ears in the case of the young garter snake. His was truly a voice crying out in the wilderness. The frog's calls, like the rest of his history, go back hundreds of millions of years farther than the history of my own species. How could such a primordial crying-out ever imagine ears and a sensibility that might interpret it as an appeal for intervention? Neither protest nor imploration would seem to have a place in the natural world, yet their embodied evocations can be sensed in such dramatic existential voicings as the wood frog's distress call. It is hard for a human perception, with its own evolution of cries, to ignore such an expression, even from the nonhuman world. One could well wonder about the possibility of plea and protest, and how far back they might go in the history of living forms. I have seen birds wing to a scene of distress in response to piercing alarm calls of their own kind. No band of wood frogs rushed in here. None ever will. And yet, in the face of an unfathomable unhearing, life cries out at times.
Posted January 1, 2011
No text was provided for this review.