Anja Murray: Moss is the unsung hero of the biosphere

Mosses rarely die when they dry out, they simply stop growing. As soon as they get access to a good drink of water, they can revive themselves and begin growing again — even after decades

Instead of producing flowers with pollen for reproduction, mosses have simpler structures called sporophytes which produce its reproductive spores. These are the shoots that you can often see if you look closely at moss: capsules held high on a stalk coming up from the clump of green moss

It's easy to admire flowering plants when out and about. Whitethorn grabs our attention right now, in the midst of a profusion of musky sweet-smelling blossom. Hedge banks are brimming with eye-catching wild violets, pretty primroses, and even the tall heads of richly pigmented pink orchids (early purple orchids are also at their peak flowering right now).

But we rarely tune our attention to the tiny forms of mosses. A comprehensive global study published this month has found that mosses contribute far more than previously understood to ecosystems across the world and in particular to soil health and carbon storage.

Mosses have simpler structures than flowering plants and lack many of the features that are apparent in ‘higher plants’. What we call higher plants have vessels through which to transport water from roots to growing stems, leaves, and flowers, and nutrients from photosynthesising leaves to where they are needed too. Mosses don’t have this network of vessels. Their tiny, geometric, perfectly proportioned leaves are often only one cell thick and can only absorb water directly from the air around them. Though mosses rarely die when they dry out. Instead, they simply stop growing. They can exist in this suspended state of being for decades, dry and shrivelled. But as soon as they get access to a good drink of water, they can revive themselves and begin growing again.

Moss-covered trees at Glenbower Woods in Killeagh, County Cork. Picture: Clare Keogh

This is why mosses thrive in moist environments. Irish woodlands, consistently enveloped in humid oceanic air, are characterised by luscious coverings of moss. Mosses are a defining feature of temperate Irish rainforests, where they cover the trunks and branches of oak trees, form enormous cushions on boulders too, and manage to thrive on almost every surface. Different species are adapted to every conceivable niche in these dazzlingly rich ecosystems, mingling with epiphytic lichens and ferns who also love the humid air. Narrow rods of hazel trees growing in western woodlands are often clad in mosses at the base, in what one ecologist expertly described to me as being like ‘woolly legwarmers from the 80s’.

Semi-natural species-rich grasslands too are rich in a variety of mosses, where an array of specially adapted species inhabit the moist microclimate down among the grasses and flowering plants.

Tuning your vision to the scale of mossy realms, a moss-covered boulder for example, you will begin to see fractal geometry of their tiny leaves arranged around a central stem. It will soon become apparent that rather than just a ubiquitous clump of moss, there are often several species growing together, alternating space between them.

Looking closely requires little more than patience of perception to reveal the mesmerising detail. However, examining moss through a hand lens or a magnifying glass will allow you to see their otherwise invisible features more clearly. Repeating patterns and perfect forms expand what we normally see of the world around us, a scale of existence in which mosses and other small creatures dwell.

Moss-covered tree-trunks: mosses, like all photosynthesising plants, make their own food by absorbing carbon dioxide from the atmosphere, so it’s not surprising that habitats with plenty of moss are associated with greater carbon sequestration

The advantages of being so small are many. Mosses can grow in tiny cracks and crevices, on impermeable surfaces such as bare rock and tree trunks. They can live contentedly with limited access to sunlight and nutrients.

Instead of producing flowers with pollen for reproduction, mosses have simpler structures called sporophytes which produce its reproductive spores. These are the shoots that you can often see if you look closely at moss: capsules held high on a stalk coming up from the clump of green moss.

The findings of a recent scientific study in the academic journal ‘Nature Geoscience’ reveal how vital mosses are to ecosystems around the world. The team of researchers found that moss-covered soils are better able to retain moisture and cycle nutrients, such as nitrogen, phosphorus, and organic matter. While mosses are a distinctive feature of moist environments, they are also successful in dry places too, such as tundra and desert ecosystems. There, the study found, mosses are especially important in binding soils, retaining moisture, and cycling nutrients.

Mosses are so small that they tend to be overlooked, in our everyday lives as well as for their role in ecosystems everywhere. But this new research shows that we should start paying more attention to moss. The coverage that mosses provide on soils, like living, insulating blankets, helps bind soil and provide a stable substrate for other plants to grow too. In this way, mosses provide stability in many ecosystems and can facilitate favourable conditions for other plants and animals too. Soils underneath mosses also have a higher concentration of soil enzymes, key regulators of pathogens, and overall soil health.

Mosses, like all photosynthesising plants, make their own food by absorbing carbon dioxide from the atmosphere, so it’s not surprising that habitats with plenty of moss are associated with greater carbon sequestration. The researchers in this study estimate that mosses currently store about 6.43 billion metric tons of carbon, keeping it out of our oversaturated atmosphere.

In Ireland, this relationship between moss and carbon sequestration and storage is recognised. Peat bogs are made up largely of mosses. Sphagnum mosses, a group consisting of dozens of different species, are the organisms that actively build peat bogs and make up the primary component of peat and turf. By absorbing up to 20 times their weight in water, sphagnum mosses are what keep peat bogs wet and in turn prevent the decomposition of dead plant matter there. This is the process that makes peat bogs such successful stores of carbon. Conversely, when we cut drains in peat bogs to drain them for forestry, turf, or conversion to farmland, much of this stored carbon is released into the atmosphere, surging greenhouse gas emissions. Currently, peatlands in Ireland are releasing 11 million tonnes of carbon dioxide into the atmosphere each year — a similar quantity emitted by the energy sector each year.

We tend to celebrate the larger things in life and undervalue all the little things. We may now begin to appreciate and value the vital role of mosses. Mosses, it turns out, are among the unsung heroes of the biosphere.