Of Driftwood and Journeys
by Anna McNairy
Broadcast 2.2002, 5.2014, 4.26 & 4.29.2023

Photo by John Fowler, CC by 2.0.




You can find piles of it around any lake in Western Montana. Sturdy, dry, bleached white by the sun and plentiful, these bits of driftwood have undergone a miraculous transformation since they were once parts of trees. Upon inspection the “tree time” of these bone-like objects seems very distant—almost inconceivable. Looking at driftwood at the edge of a lake, it is easy to see that “tree time” was only a fragment of this object’s existence, and that much has happened for this piece of driftwood to arrive at its current location, in its current state.

Driftwood leads quite a turbulent life before arriving peacefully on lakeshores. A tree, such as a ponderosa pine or western larch, will live long but eventually will fall to enter into the journey of driftwood. Creating habitat for numerous species and altering the flow of a stream, driftwood is a key player in many aquatic ecosystems.

When flooding occurs, limbs, branches, and twigs of a tree are carried away by the stream’s current. The tree pieces are then scoured by the banks of the stream and lose their bark. Often, the woody debris accumulates on a stream’s obstacles, such as a bridge or a large rock. This frequently affects stream flow, generally by deflecting the current and widening stream beds. Sediment deposits can grow, and the complex workings of current and flow are increased. These accumulations also give the pieces of wood significant time in the water, often until the next flood. It is during this time that driftwood plays its largest part in the ecosystem.

This time in the stream waterlogs the driftwood. It decomposes in thin layers, beginning on the outside with the help of fungi and organisms attracted to the wood. Accumulations of driftwood make deep pools in streams where fish like coho salmon lay their eggs. Cool, dark and serene, these areas are full of food and flow slower than the passing current. Because of this, they quickly become preferred habitat for young fish.

These driftwood pools, which can account for up to 80 percent of all pools in a stream, provide an area of rich diversity. Good to escape predators and conserve energy, these pools allow for the coexistence of various types of fish, as well as fish of various ages. Juvenile coho salmon will overtake the area of the pool near the water’s surface, while cutthroat trout idle near the bottom and steelhead trout over a year old inhabit the upstream head of the pool.

Insects also use the decomposing driftwood. When partially submerged, it is used as a land bridge upon which many insects will emerge as adults. If the driftwood has landed near a stream bank, insects—especially stoneflies—will often choose it over rocks to make their transformation from water nymphs to land and air adults. Equipped with long legs and sturdy tarsal claws, climbing nymphs like dragonflies and stoneflies have no problem walking on driftwood. Mayfly nymphs use gill plates along their lower abdomens as suction cups to allow them to move along driftwood with ease.

After creating this rich habitat for stream species, the driftwood generally gets pushed along by flooding or further decomposition that enables it to move past a stream obstacle. It may lodge again, creating new habitat in a new location, or perhaps it will make it to an alpine lake. If the piece of driftwood makes it to the lake, currents and wind will push it to one side. Once on the lake’s edge, the driftwood washes onto the shore where the process of bleaching by the sun takes place. This process dries the wood and brings it to the familiar shade of light grey that is indicative of driftwood. It now becomes habitat to many small mammals and nesting sites for birds. Already decomposed and scoured a great deal from its journey downstream, the final bleaching process is what brings this piece of a tree—once alive and full of sap—to a fascinating artifact of nature.


Every week since 1991, Field Notes has inquired about Montana’s natural history. Field Notes are written by naturalists, students, and listeners about the puzzle-tree bark, eagle talons, woolly aphids, and giant puffballs of Western, Central and Southwestern Montana and aired weekly on Montana Public Radio.

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