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The Might of the Moss

There’s around 22,000 species of mosses in the world. One may often be able to recognize a moss as one of those green mats on the floor of a forest, at the edge of a river, or in the cracks of the sidewalk on moist city streets. But what is a moss?

“Mosses are often described by what they lack in comparison to higher [vascular] plants,” writes Professor Robin Wall Kimmerer in her book Gathering Moss. “They are the most simple of plants, and in their simplicity, elegant.” Despite this elegant simplicity and because they are often described by what they lack, we know so little about what mosses do, argues David Eldridge and colleagues in a recent study published in Nature Geosciences.

To find out what it is mosses do for ecosystems around the world, Eldridge and colleagues curated and an analyzed a global dataset on mosses. This dataset contained information about the environment – information on land area covered by mosses, local biodiversity, carbon and nutrient cycles, temperature, and plant diseases – and the mosses themselves – information on growth rates, life cycles, and growth form (more like mats or more like lawns).

The researchers found that mosses cover a surprisingly large land area, roughly equivalent to the land area of the United States, Canada, or China. The genus most accounted for in the study’s dataset was Byrum. Byrum is notable because, as Kimmerer points out in her book, this is the genus that has found its home in the city. Between cracks in the sidewalk, on windowsills white with bird poop, and down damp, dark alleyways – species of Byrum opportunistically thrive in otherwise unfavorable environmental conditions in the city.

Most mosses are opportunistic. In fact, they’re what’s known as “pioneer species”, occupying bare regions of landscapes sucking up intermittent rainfall running along rocky or sandy surfaces, the researchers note. In time boreal and temperate and tropical rainforests tower over carbon and nitrogen rich soils free from plant pathogens that benefitted from species from the genera Rosulabryum, Leucobryum, Funaria, Campylopus, and Desmatodom among others.

But sometimes mosses stake their own claims to land. “There is no ecosystem on Earth where mosses achieve greater prominence than in a sphagnum bog,” writes Kimmerer. “There is more living carbon in Sphagnum moss than in any other single genus on the planet… in sphagnum bogs [mosses] are supreme.” (In all mosses contribute around 6.4 billion metric tons of carbon to soils around the world.)

Species of the genus sphagnum grow as dense mats over water making one of the world’s most unique wetlands. Sphagnum bogs are rich in biodiversity because they create an oxygen-poor and highly acidic aquatic environment. And it is because this oxygen poor environment that the amount of carbon sphagnum bogs is so high – decomposition, the breakdown of dead organic matter, cannot occur, or occurs very slowly.

As Kimmerer notes, “what amazes me most about sphagnum is that most of the plant is dead. Under the microscope you see that every leaf has narrow bands of living cells which border the patches of dead cells…only one cell in twenty is actually alive.”

Wetlands like bogs, however, are fast on the decline: since 1970 more than a third of all the world’s wetlands have been lost, and with them populations of moss like those belonging to sphagnum. And in systems like bogs – though not only bogs – their contributions cannot be replicated, not even by vascular plants.

Eldridge and colleagues' study identified the importance of protecting these small, yet mighty mosses.

Click here to read the original research.

 One may often be able to recognize a moss as one of those green mats on the floor of a forest or at the edge of a river, but what is moss?



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