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10.1.13

Moss and Lichen

These tiny, ancient organisms are vital cogs in the Island’s ecosystem.

moss tree

They’re everywhere. Plastered to stone walls, dangling from branches, hugging salt-sprayed sand, growing among grasses and wildflowers in lawns, fields, and bogs. Without them, a Vineyard landscape would look oddly barren and unfamiliar. But whether it’s because of their size or their ubiquity, mosses and lichens don’t always get the attention they deserve.

These so-called “lower plants,” basic in structure and low in physical stature, also sit low on the totem pole of evolution. In a moss or a lichen, you find a design that hasn’t changed much for hundreds of millions of years. But their simple, ancient technology, paradoxically, helps keep these organisms relevant in today’s ecosystem.

Mosses echo the distant evolutionary past of plants. They exhibit the relatively recent (in evolutionary terms) innovation of sexual reproduction, and unlike even simpler plants like algae, mosses show a measure of specialization in their cells – for example, their outer layer of cells are toughened into a water-retaining cuticle. But they lack the specialized structures of higher plants, such as flowers, to enhance the effectiveness of sexual reproduction or the system of tiny vessels by which higher plants transport water and food. (Mosses, limiting their height to an inch or two, rely on simple diffusion to circulate what water they need.)

Lichens, meanwhile, reflect an even more remarkable approach to survival. Though they occur in stable, recognizable forms, and we think of them as single species, each type of lichen in fact represents an intimate partnership between a fungus and an alga (or, sometimes, multiple algae). This basic model is subject to astonishing variation: Scores of algal and fungal species can form lichens, and the physical forms these take – crusts, pads, cups, even tiny branching, tree-like structures – vary as widely as do the specifics of how the partners live and reproduce. But in essence, the fungus retains water and creates a place for the alga to live, while the alga, with its photosynthetic ability, produces food to support both members of this odd marriage.

Largely thanks to our marine climate, which sooner or later produces the dampness that mosses and lichens adore, the Vineyard is extraordinarily well-endowed with these interesting organisms. The volume Island Life: A Catalog of the Biodiversity On and Around Martha’s Vineyard (Allan R. Keith/The Marine Biological Laboratories, 2008), compiled by birder Allan Keith and botanist Stephen Spongberg, both of Chilmark, reports that at least 124 moss species are known on the Island, along with 156 lichen varieties.

Some of these are common and widespread, though it’s fairly typical for mosses and lichens to require very specific substrates or conditions, according to Fred Rhoades, a noted lichenologist and retired professor at Western Washington University in Washington state. Such fussiness complicates the use of mosses and lichens as ornamentals, a practice that appears to be mildly trendy among Island gardeners. However, relocating mosses or lichens often doesn’t work, says Dr. Rhoades, because it moves the plant outside its required climate regime.

rock moss
Carpets of moss and lichen-encrusted bark are part of the low-lying scenery at the Sheriff’s Meadow Sanctuary in Edgartown.

Still, it can be fun to experiment with primitive plant gardening. One method for propagating mosses and lichens takes advantage of their biological simplicity: Entire plants can regrow from just a few cells. So a slurry made in a blender from a desirable moss or lichen and water can be painted onto a promising substrate. Some sources suggest including beer or buttermilk in the mix, which may provide carbohydrates to boost the initial growth of the plant, or to thicken the mixture to keep it where you spread it. If you’ve picked a suitable location for your chosen species, your “moss smoothie” may give rise to a new population.

Meanwhile, some Island landscapers reportedly charge a premium for “aged” rocks that come already covered in lichens. While I worry that old stone walls may be furnishing the stock for this practice, the surcharge itself seems reasonable. Lichens generally grow very slowly, with a millimeter’s expansion per year being a reasonable average, according to Dr. Rhoades. So if you’re employing local rock with well-developed lichen on it, you’re acquiring not just added beauty but a snippet of Vineyard history in the form of decades or even centuries of slow but steady growth.

Think small

The next time you’re in a natural Island setting, look closely at what’s around you. Ignore the scenery and study instead the tree trunks, rocks, and spaces on the ground between the stems of plants. Note how much of the space is occupied by lichens and mosses, and contemplate how different things would look if these organisms didn’t exist. Often, mosses and lichens occupy space that would otherwise support nothing living. Removing these organisms from the ecosystem would leave gaps on boulders, soil, bark, and other surfaces that don’t afford any purchase for the roots of more advanced plants.

It’s a point so obvious that naturalists like me have to keep learning it over and over: The vast majority of animals in the world are much smaller than we are. For most living things, objects on the scale that matter to humans are largely irrelevant. A tiny beetle may range, during its entire life, only inches or feet from where it hatched. With limited vision, it’s unaware of grand vistas, and it spends its life – guided mostly by tactile cues and chemical traces – seeking edible substances, a beetle of the same species to mate with, and, if it’s a female, a suitable place to park some eggs.

For tiny invertebrates, the important objects are ones that offer shapes on a beetle-like scale: places where a tiny mote of an insect can hide or search for food. Mosses and lichens, with their intricate branching or flaky structure, are perfect. What fields and woodland are to a deer, for example, a patch of moss or a scab of lichen is to a beetle. For an obscure multitude of Vineyard invertebrates, mosses and lichens are home.

Prominent roles

While they may be a secondary element in most habitats, hugging their substrate and occupying space between more impressive plants, there are a few situations in which mosses or lichens play a critical role. You might even say that, in the Island’s distant past, these organisms started making our modern landscapes possible. Optimized for cool, wet climates and able to colonize sterile surfaces, mosses and lichens were surely among the first growths to occupy the heap of post-glacial rubble that would one day be called Martha’s Vineyard. Their knack for colonizing infertile sites and beginning the critical process of soil formation set in motion the processes that sustain the woods and grasslands of today.

Wherever they occur, mosses and lichens contribute to fertility. The algae in many lichens, reports Dr. Rhoades, are capable of “fixing” the vital nutrient nitrogen – that is, taking nitrogen molecules from the air, which most plants can’t make use of, and combining them into other chemical forms that are biologically active. (Beans and other legumes perform the same function through a pairing with special microbes in nodules on their roots.) As mosses and lichens break down, they contribute organic matter to the soil, and while one moss or lichen doesn’t amount to much, the vast volume of these plants across the landscape adds up to a significant contribution to productivity of the Island’s soils.

More remarkably, these ancient plants occasionally play locally dominant roles. Consider, for example, the shaggy, hanging lichens of the genus Usnea, or “beard lichen.” Preferring the bark on tree limbs for their attachment point, Usnea lichens can virtually cover a full-grown oak in some of the Island’s more humid nooks. Since the lichen is self-contained, attached to the tree but not extracting water or nutrients from it, such festoons have no detrimental effect on the tree. But countless insects hide in the grayish “beard” – many birds hunt them there, or incorporate lichen fibers into their nest. In fact, one uncommon species, the northern parula warbler, constructs its nest entirely within large clumps of Usnea.

leave moss
Mosses house small invertebrates, improve soil quality, and contribute to Island verdure, as seen at West Tisbury’s Cedar Tree Neck Wildlife Sanctuary.

A still more dramatic example of dominance by lower plants involves the various mosses known collectively as Sphagnum (Island Life lists nine Vineyard members of this genus). Sphagnum is associated most closely with bogs, and indeed it is the moss itself that makes a bog: Accumulated generations of Sphagnum form mats extending across a glacial kettle-hole pond, floating on a layer of groundwater and serving as the substrate that supports the bog’s ecosystem. (The Vineyard Open Land Foundation’s Cranberry Acres bog in Vineyard Haven, visible from Lambert’s Cove Road, is a great example.) Sphagnum can be found in other wet settings, too: around seeps at the heads of our Great Pond coves, for example, or even in low-lying areas in fields where the level of the groundwater, on average, flirts with the surface of the soil.

Wherever they occur, Sphagnum communities can persist for millennia if conditions remain constant. Defunct generations compress into peat, the substance used as a soil amendment or, in some cultures, mined for use as fuel. Sphagnum bogs, highly acidic and generally lacking in nutrients, support a host of equally specialized plants, like cranberry and sundews (which capture and digest insects to obtain nitrogen), as well as associated insect specialists. The caterpillars of the bog copper butterfly, for example, subsist exclusively on wild cranberry, and this insect rarely strays beyond the margins of a bog.

Hugging the ground or plastered to a rock, a moss or a lichen may not look like much. But these organisms, perfectly suited to their simple lifestyles, are ancient, diverse, and indispensable – vital cogs in the enormously complicated machine that is the Island’s ecology. It’s worth bending down to take a closer look at them.

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