Trees are pillars of their communities, a role they can maintain even in death. An upright dead tree offers vital habitat to certain birds and bats, for example, while a fallen tree is a bonanza for life on the forest floor, including future trees.
Yet rotting in place is not the only natural afterlife for a tree. Sometimes, instead of giving back to its birth forest, a tree will embark on an odyssey to pay it forward, carrying its ecological wealth away from the only home it has ever known.
These traveling trees don't mean to betray their roots; they're just going with the flow. They've become driftwood, a term for any woody remnants of trees that wind up moving through rivers, lakes or oceans. This journey is often brief, merely leading to a different part of the same ecosystem, but it can also send a tree far out to sea — and maybe even across it.
Driftwood is a common sight at beaches around the world, although many people dismiss it as unremarkable scenery or useless debris. And while some driftwood is a little short on mystique — like twigs from a nearby tree, or boards that fell off a fishing pier — it can also be a ghost from a distant forest or shipwreck, transformed by its adventures into something beautiful. Along the way, driftwood tends to return the favor by reshaping and enriching the environments it visits.
In an age when oceans are plagued by plastic trash, driftwood is a reminder that natural marine debris can be benign, even beneficial. It embodies the fragile ecological links between land and water, as well as the subtle beauty commonly hiding in plain sight. In hopes of shedding more light on these qualities, here's a deeper look at why driftwood deserves more attention:
Windows of opportunity
Long before humans built boats from dead trees, the raw materials were out there exploring uncharted waters on their own. Driftwood may have even inspired our first wooden rafts and boats, as ancient people noticed its strength and buoyancy.
Dead trees have always served as boats, though, just usually for smaller passengers. Driftwood not only feeds and shelters lots of tiny wildlife, but can also help them colonize otherwise unreachable habitats. And its arrival can benefit local residents, too, introducing new resources to sustain coastal wildlife and help buffer their exposed home from wind and sun.
Depending on the driftwood and where it washes up, seafaring trees can be valuable additions to waterfront habitats that lack the canopy and roots of live trees, such as rocky beaches or coastal sand-dune ecosystems. Even in places with plenty of trees, like the banks of a forested river, driftwood often plays an integral role in building up and shaping the habitat's infrastructure.
The adventures of driftwood often begin in rivers, and many of them stay there. Driftwood is an important part of virtually all natural waterscapes around the world, including freshwater streams, rivers and lakes as well as oceans.
Rivers that flow through or near forests tend to collect pieces of dead trees, sometimes resulting in accumulations of driftwood known as logjams. Over time, these clusters can help build up the banks of rivers and even shape their channels, influencing not only the way water moves through the ecosystem, but also what kind of solutes, sediments and organic matter it contains.
Driftwood also slows down the flow of a river, helping it retain more nutrients to nourish its native wildlife. And by forming lots of different microhabitats within a river channel, driftwood has a tendency to boost local biodiversity, too.
Similar to long-lived beaver dams, driftwood logjams have been known to persist for centuries if left alone, eventually becoming huge, landscape-altering rafts. One such logjam, known as the Great Raft, may have been growing for 1,000 years before the Lewis and Clark expedition encountered it in 1806. The raft, reportedly sacred to the native Caddo people, held tens of millions of cubic feet of cedar, cypress and petrified wood, covering nearly 160 miles of the Red and Atchafalaya rivers in Louisiana.
The Great Raft may have been a natural wonder, but because it blocked navigation of the Red River, the U.S. Army Corps of Engineers launched an effort to dismantle it. Initially led by steamboat captain Henry Shreve, the project kicked off in the 1830s and took decades to complete, inadvertently transforming the geology of the Lower Mississippi River watershed in the process.
"[T]he many lakes and bayous that the Red River had created in Louisiana and East Texas drained away," according to the Red River Historian. "The river shortened its path to the Mississippi. To stop the destabilization of the land surrounding the river, the Corps of Engineers had to implement billions of dollars in lock and dam improvements to keep the river navigable."
Even under natural conditions, however, rivers rarely hold onto all of their driftwood. Depending on the size of a waterway, it may let trees and woody debris keep flowing downstream, eventually reaching a new environment like a lakeshore, estuary or beach.
Although driftwood often decays within two years, some pieces last much longer under certain conditions. The Old Man of the Lake, for one, is a 30-foot-tall (9-meter) tree stump that's been bobbing vertically in Oregon's Crater Lake since at least 1896.
As streams and rivers carry driftwood seaward, large "driftwood depositories" sometimes collect at a waterway's mouth. These buildups have existed for roughly 120 million years, dating back almost as far as flowering plants themselves. Some of their driftwood may eventually continue out to sea, while other pieces stick around in a river delta, estuary or a nearby shoreline.
As with driftwood upstream, old trees are a boon for the environments where they end up. In many estuaries and beaches, they provide structure and stability where not enough live plants grow to anchor the sandy, salty soil with their roots.
These persistent crowds of driftwood — or "driftcretions," as researchers dubbed them in a 2015 study — interact with plants and sedimentation to influence the evolution of shorelines, encouraging "the formation of complex, diverse morphologies that increase biological productivity and organic carbon capture and buffer against erosion," the study's authors write.
Whether it's a persistent pile of woody debris or just one big tree, large pieces of driftwood can add a skeleton to sunbaked, erosion-prone ecosystems like open beaches, potentially boosting their ability to support live vegetation.
In coastal dune habitats, driftwood "provides partial stabilization of sand dunes, reducing wind erosion and allowing plants to gain purchase," according to Beachcare magazine, produced by the Waikato Regional Council in Waikato, New Zealand. "The driftwood may also create a small wind barrier (or microclimate), which can allow seeds and seedlings to stay damp and protected from wind erosion. Driftwood may even carry seeds from the forest to the coast, which may germinate if it is hardy enough."
Driftwood can offer shelter for beach-dwelling animals, too, as can the vegetation it enables. Some shorebirds, for example, nest beside driftwood as a way of hiding their eggs from predators and protecting them from being buried in sand.
And even for coastal wildlife that doesn't really need driftwood, it's hard to deny the convenience of a dead tree on the beach:
For driftwood that leaves terra firma to begin a new life at sea, the odds of ever returning to land are pretty slim. But being lost at sea doesn't necessarily mean their travels are a lost cause. As writer Brian Payton noted recently in Hakai Magazine, driftwood can stay afloat in the open ocean for about 17 months, where it offers rare amenities like food, shade, protection from waves and a place to lay eggs. As such, pelagic driftwood becomes a "floating reef" that can host a variety of marine wildlife.
That includes wingless water striders (aka sea skaters), which lay their eggs on floating driftwood and are the only insects known to inhabit the open ocean. It also includes more than 100 other species of invertebrates, Payton adds, and some 130 species of fish.
As marine driftwood decays near the surface, it hosts a specific succession of tenants. It's typically first colonized by salt-tolerant, wood-degrading bacteria and fungi, along with a few other invertebrates that make wood-degrading enzymes. (These include gribbles, tiny crustaceans that bore into driftwood and digest it from within, creating burrows that other animals later exploit.) These initial settlers are followed by secondary colonizers like talitrids, aka driftwood hoppers, that can't digest wood on their own.
Gribbles are key colonizers of dead trees in shallow waters, but they aren't the only animals that bore holes into driftwood. There are also bivalve mollusks like wood piddocks and shipworms, for example, which make their homes by boring into waterlogged wood. Although wood piddocks and shipworms are known for causing damage to ships, piers and other wooden structures, they also serve valuable roles in marine ecosystems, helping open up driftwood to a broader assortment of marine life.
After a year or more of floating near the surface, any driftwood that doesn't wash back onto land somewhere eventually sinks toward the seabed. At a certain depth and pressure, "the ocean squeezes the last bit of terrestrial air out of the wood, replacing it with brine," writes evolutionary marine ecologist Craig McClain. "So begins the story with a tree sinking into the deep."
This descent, called a "wood fall," claims driftwood ranging from small fragments to 2,000-pound giants, McClain adds. It draws trees into yet another new ecosystem, where different communities of creatures are waiting to finish it off. This includes deep-sea bivalves of the genus Xylophaga, which convert the wood into droppings that in turn support dozens of other invertebrates.
Sometimes, though, even large driftwood finds its way back ashore before disappearing into the abyss. And aside from the ecological benefits mentioned earlier, this can let people on land see the abundance of driftwood dwellers that are typically out of sight and out of mind. In December 2016, for example, the tree pictured above received international news coverage when it washed ashore in New Zealand, thanks to its thick coating of gooseneck barnacles.
A brave new whorl
Even without the oddity of a barnacle blanket, driftwood that washes ashore often wows humans who bother to look closely. Its travels tend to embellish the wood in aesthetically interesting ways, resulting in a wide range of intricate shapes and patterns.
These driftwood designs range from mesmerizing swirls and whorls to smooth ripples and gnarled protrusions, all abstract effects of the environmental forces a particular piece of wood has experienced during its mysterious journey.
The gift of driftwood
On top of its aesthetic charms, driftwood also has a long history of practical uses by people. It has been key to indigenous people in the Arctic, for instance, whose mostly treeless environments offer few sources of wood other than logs washing in from faraway forests. Traditional boats like the kayak and umiak were built from driftwood frames wrapped in animal skins.
Beyond boats, driftwood has found myriad other uses as a coastal construction material throughout human history, from dog sleds and snow shoes to fishing spears and children's toys. The washed-up remains of trees also provide useful timber for beachfront shelters, as driftwood is still sometimes used by modern beach-goers.
From the Arctic Circle to tropical islands, driftwood can be especially useful as firewood. Even in places with a lot of living trees, driftwood can help discourage deforestation by offering a source of timber that doesn't add pressure to local forest resources. That's a potentially big deal in places where deforestation has increased the risk of erosion, flooding and landslides.
In many settings, however, the best way to use driftwood may be to just leave it alone, letting it drift wherever fate takes it. It might sprout a new tree that will become driftwood itself one day, or wash back out to sea and nourish a cascade of marine creatures.
Or it might just sit there in the surf for a while, quietly waiting to fascinate anyone who happens to drift by.