Sutro Cloud Forest’s Micro-climate

Sutro Cloud Forest is in the fog belt, and all summer long, its gets fog nearly every day. It’s never dry — and here’s why.

The trees grab the moisture from the fog and clouds (1 in the picture); it rains down onto the forest floor (2). There, it soaks into the duff — the  crumbly layer of dead and decaying leaves, twigs and other plant material accumulating on the ground beneath the trees (3). This material holds it like a sponge.

Above the duff, there’s a dense layer of understory plants that stop the water from evaporating – blackberry, ivy, ferns, poison oak, and 90 or so other plant species (4).  And above it all, there’s the tree canopy, which not only captures the moisture in the fog, but by shading  the forest floor, further helps to slow evaporation (5).

The result is that not only is the forest damp all the time, it also would take a long time to dry out – especially since the longest period it goes without rain or fog  is about 7-10 days in a year.


The best fire-protection for a cloud forest is to make sure that it doesn’t actually dry out. Here’s what would help:

1. Disturbing the duff as little as possible, so it retains the ability to hold the water.

2. When building trails,  cut channels  across trails so water crosses and soaks into the duff on the other side to reduce run-off along the trail.

3. Preserving the undergrowth so it insulates the duff from evaporation.

4. Preserving the trees so they both capture moisture and provide the shade of the canopy.

Thinning the trees and the underbrush would break this mechanism. Tree canopies are not where fires start, it is the dry grass and underbrush. Thinning opens up the forest, increasing evaporation, and  making it  drier and more flammable. Especially around areas of trails, it’s important  to preserve the duff at the edges, the undergrowth, and the trees.

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17 Responses to Sutro Cloud Forest’s Micro-climate

  1. Todd says:

    This is so good In its simplicity that I do not want suggest additions that might lengthen or complicate the message. However, you might add-in a couple words or so that the duff provides habitat for many animal, reptile and insect species.

  2. Alicia Snow says:

    We need to emphasize that an uninterrupted canopy provides the necessary shade for the trees to keep the moisture in the forest at all levels. Where the canopy is compromised, the dessication is immediately evident.

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