Burls and Trees on Stilts

The reasons burls grow on trees are still not fully understood, but infection by viruses, fungus and bacteria are likely causes.

December 5, 2019 | | Notes from the Wild

The spring and summer woods has abundant stories to tell – of birds, wildflowers, insects and much more. The winter woods is quieter, but it too has stories. Stories that emerge after the wonderful biotic clamour of the warm months has been muted. Not surprisingly, trees are the source of many of these winter tales.

Before reading on, look at the first two photos below and think about the “why” behind the unusual structure of the trees. They are supported by a network of stilt-like aerial roots. How did these forms arise?

Hemlock growing on an old stump. Photo by Don Scallen.

Hemlock growing on an old stump. Photo by Don Scallen.

Yellow birch. Photo by Don Scallen.

Yellow birch. Photo by Don Scallen.

These trees, hemlock and yellow birch, sprouted years ago atop the trunks of other trees. In their early years the little trees sank roots deep into the decaying trunks, eventually reaching the earth below. When the trunks decayed entirely, the roots of the birch and hemlock were left exposed above ground.

Birch seedlings often grow best on logs or stumps where they aren’t smothered by the leaf litter of the forest floor. The deaths of older trees gives them life.

Another tree story is told by the growths pictured below. These are “burls”. The massive burl is growing on sugar maple, the smaller on red oak. The reasons burls grow on trees are still not fully understood, but infection by viruses, fungus and bacteria are likely causes.

Trees can host multiple burls and still lead long, robust lives. Photo by Don Scallen.

Trees can host multiple burls and still lead long, robust lives. Photo by Don Scallen.

Burls are much sought after by woodworkers. Photo by Don Scallen.

Burls are much sought after by woodworkers. Photo by Don Scallen.

Burl on a red oak. Photo by Don Scallen.

Burl on a red oak. Photo by Don Scallen.

Regardless, these woody tumours are benign. Trees can host multiple burls and still lead long, robust lives. In fact, big old trees gnarled with burls evoke an Ent-like charisma.

Burls are much sought after by woodworkers. Their growth rings swirl and contort in fanciful patterns, and when enhanced by polishing and lacquer, become exquisite works of art. This makes burls valuable, tempting the unscrupulous to harvest them illegally – a serious problem in Californian redwood groves.

Quiet isn’t boring. The winter woods have fascinating stories to share.

About the Author More by Don Scallen

Don Scallen enjoys sharing his love of nature through his writing and presentations. Check out his blog "Notes from the Wild".

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