The Vital and Surprising Role of Driftwood

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You may see a piece of driftwood at the beach or on the shore and wonder about its journey from land to water, and back to land again. As Brian Payton reports at Hakai Magazine, Driftwood is not only beautiful. It’s a critical piece of the marine ecosystem that offers vital sanctuary to breeding insects and invertebrates on shore and in the sea, who in turn feed species all the way up the marine food chain.

Dead trees were sailing the seas long before our ancestors conceived of the ax or skiff, long before the continents split and went their separate ways. And yet, when a tree falls in a river or stream today, it can set out on a journey that remains little studied and poorly understood.

A tree undergoes reincarnation when it lands in flowing water. Branches, bark, and heartwood—what appears to be nothing more than floating debris—become either home to or sustenance for a range of plants and animals. In old-growth forests, up to 70 percent of the organic matter from fallen trees remains in streams long enough to nurture the organisms living there, passing through the digestive tracts of bacteria, fungi, and insects. Caddis flies and mayflies undergo their metamorphosis into adults while anchored to floating wood. When they emerge, they in turn become food for salmon fry, salamanders, bats, and birds. Larger logs control the very shape and flow of streams, creating pools and back eddies where returning salmon rest and spawn. These pools provide critical shelter for young salmon as they hatch, feed, and hide from predators before they make a break for the open sea.

As wood passes through the floodplain, it collides with and remakes the shore. Some becomes anchored there, trapping silt and seeds. As new vegetation takes root, deer mice, voles, shrews, and chipmunks move in for the harvest. Weasels, minks, and hawks make meals of them and fertilize the soil. Wood that drifts into estuaries becomes perches for hungry bald eagles and herons; rafts for weary cormorants, pelicans, and seals; and nurseries for herring eggs.

It is estimated that, in the habitat associated with a single large piece of oceangoing driftwood, the combined weight of the associated tuna alone can add up to as much as 100 tonnes—or the equivalent of well over half a million cans of tuna.

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