Moss: The Breakfast of Champions

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It’s not just carbon dioxide that feeds a forest. Trees also depend on nitrogen to grow. And the best buffet of nitrogen comes from moss-loving bacteria. But to get a really nutritious growth of bacteria going, the moss needs to age.

Bacteria, called cyanobacteria, that grow in moss on centuries-old trees, are twice as effective at fixing nitrogen as the same type of bacteria living in moss on the ground, according to research by Zoë Lindo of McGill University.

That means old-growth trees may be vitally important to the long-term survival of the coastal temperate rainforests that stretch from Southern Alaska to Northern California.

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“What we’re doing is putting large old trees into a context where they’re an integral part of what a forest is,” said Lindo in a McGill University press release.

“These large old trees are doing something: they’re providing habitat for something that provides habitat for something else that’s fertilizing the forest. It’s like a domino effect; it’s indirect but without the first step, without the trees, none of it could happen,” said Lindo.

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“You need trees that are large enough and old enough to start accumulating mosses before you can have the cyanobacteria that are associated with the mosses,” Lindo said.

“Many trees don’t start to accumulate mosses until they’re more than 100 years old. So it’s really the density of very large old trees that are draped in moss that is important at a forest stand level. We surveyed trees that are estimated as being between 500 and 800 years old.”

Lindo compared the quantities of nitrogen produced by bacteria living in moss on branches about 50 and 100 feet up in the forest canopy to the quantity produced by bacteria living with moss on the ground. In addition, there were more cyanobacteria in the moss high in the tree than on the ground.

So next time you take a walk in the forest you’ll know why rolling stones may gather no moss, but ancient trees do.

 IMAGE 1: Unprotected ancient temperate rainforest in the Upper Walbran Valley on Vancouver Island, BC. (Wikimedia Commons)

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