Off the Press

January 25, 2011

By Laura Geggel

My weather knowledge was a little foggy

Every morning, when I get off Interstate 90 to drive into Issaquah, I look up at Tiger, Squak and Cougar mountains to get a glimpse of their surreal greenery. Mostly, I just see a bunch of fog.

Laura Geggel Press reporter

That dense, whitish-gray stuff isn’t on my A list. It reminds me of Harry Potter’s dementors. It’s gloomy and makes me feel claustrophobic. Fog hides the sun — which, I guess means I don’t have to wear sunscreen, but it shields all of the vitamin D I could potentially be making from those ultraviolet rays.

And don’t even get me started on literary metaphors. Charles Dickens used it to set a dismal scene in “Bleak House.” In Mark Twain’s “The Adventures of Huckleberry Finn,” fog causes Huck and Jim to miss a turn, making them head south into slave country, away from the freedom of the North.

Still, it turns out my understanding of fog was, well, foggy.

Recently, I read that California’s redwood trees depend on fog for moisture during the dry summer months. A study in the “Proceedings of the National Academy of Sciences” found that fog in Northern California had decreased 33 percent in the past 100 years, endangering the giant trees that are not known to reproduce naturally anywhere else in the world.

“Really?” I thought. “These trees are doomed because it’s not foggy enough?”

I called three arborists about town. Chris Welch, with Pacific Plants, said fog acts as a source of water for many trees.

It works like a dribble down effect, literally.

Clouds and fog hang around the tops of trees. The moisture condenses on tree foliage, where it is either absorbed by the tree, or falls from the tree, watering the undergrowth.

“If you actually put a bucket in a parking lot near the redwood trees, the bucket wouldn’t have any water in it,” Tom Hinckley, interim director and professor at the University of Washington School of Forest Resources, said. “The bucket you put in the forest would have water in it,” about 15 inches annually, actually.

Issaquah hikers might notice this phenomenon, too. Hiking through a cloud of fog in the woods might cause precipitation or make moisture cling to your clothes. If you walk across a foggy, open field, it might be cold, but not wet.

“The trees can intercept very fine droplets of water that would otherwise not fall to the ground,” Hinckley said.

Old-growth forests can ensnare fog. When trees are larger and of varying heights, there is more surface area that interacts with the fog. These forests cause the fog to dive down into their canopy, like a sheet of water on a broken surface.

Trees of a uniform height, usually second- or third-growth forests, buoy the fog above them, preventing the fog from its downward swooping. Those poor trees are missing out of a slurpfest of moisture — compliments of the fog.

Fog’s benefits don’t stop there. It can carry nutrients that flora can absorb, just like children who pop Flintstones Vitamins.

Fog from the ocean can carry important sulfates, magnesium and sodium — yum. Further inland, fog carries less attractive items — air pollution, for one.

“It’s sort of a good news, bad news,” Hinckley said.

Fog means plants and trees don’t have to transpire as much, letting them retain more water. It also means they don’t get as much sunlight so they can’t photosynthesize like plants in Hawaii, so it’s a mixed blessing, City Arborist Alan Haywood said.

But, our native plants thrive in low sunlight and high moisture: Western red cedar, sword ferns, salal, Sitka spruce and vine maples. On the downside, ornamental, non-native plants can’t deal with our Pacific Northwest weather.

“I would say don’t grow roses,” Haywood said.

Laura Geggel: 392-6434, ext. 241, or

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One Response to “Off the Press”

  1. Janet Wall on January 31st, 2011 4:21 pm

    I wanted to thank you so muchfor the article, which was I found very interesting. I knew about the general importance of fog, especially to the cloud forests in Costa Rica, but I didn’t know that it was that critical to the California redwood forests or that old-growth forests are more effective than second-growth in snaggng the fog. Thanks for an informative, well researched article!

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