Caring for a Temperate Cloud Forest

clouds blowing in
Managing a temperate cloud forest is quite different from managing a regular dry forest.

The most important thing is: Don’t open it up to dry out.

When the forest is opened up, the area immediately becomes dryer. Today, on a foggy day in June, we hiked up the Southern side of the forest to the Native Plant Garden on top. The trail on the South side was dry – but only a foot to the side, the soil was damp.

This is even more obvious when you compare the forest with the open Native Garden on the summit, which is bare of trees. NPG Grass
sprinkler system NPG It has been planted with native plants theoretically drought-tolerant. And yet, the garden is very dry -even on a foggy day. It survives only because it has a sprinkler system. (This is referred to as the “intact Rotary meadow” on the Nature in the City website. Rotary it most certainly is, since they paid $100K for it; meadow it may be; intact, not so much.) [Edited to add: In Oct 09 we learned that the garden isn’t actually being watered; so presumably the plants are managing. Perhaps that’s why they look rather dry. The green bushes at the back, “black acacia” (we think) are part of the forest.]

Only steps away, the trails under the trees are wet. Without sprinklers.
sutro forest june 25 09 012


Here’s how it works:
1. The tall trees catch precipitate moisture from the fog.
2. The moisture is absorbed by the duff, and protected from evaporation by the undergrowth.
3. The canopy of trees over all shades the undergrowth and further restricts evaporation.

Sutro Forest gets 8-12 inches annually of fog-precipitation moisture every year – nearly 50% of the regular winter rainfall. This fog-moisture is spread out through the year, particularly in the summer months. According to the 2001 report, there are around ten dry days each years. Ten.

[ETA: We kept a Fog Log for 2009. We found only seven dry days.]

What’s more, the duff, covered in rampant undergrowth, acts as a sponge and retains this moisture, releasing it gradually. That’s why the forest is green year round and never dries out. The moisture is trapped by the tall eucalyptus, and precipitates into the forest like rain. This water goes into the duff where it’s used and protected from drying by the undergrowth. And then the forest canopy keeps it shaded and prevents it from drying out.

As the volunteers opening trails on Mt Sutro have found, it’s the duff that holds in the water. The ground below it is dry. When all that duff and undergrowth is removed, the water will run straight off.

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5 Responses to Caring for a Temperate Cloud Forest

  1. NatureLover says:

    YES! I just walked the forest on Tuesday and observed the same…the understory of the tree canopy is green while the attempt to create a native grassland at the summit is dry AND THEREFORE MORE FLAMMABLE THAN THE GREEN UNDERSTORY. The native plant garden on the summit was installed 5 years ago and still being irrigated. So much for claims that native plants are more drought tolerant than non-natives. Yet another bogus claim by native plant advocates who struggle for justification to support their preferred plants. Is UCSF planning to irrigate all 14 acres of the forest after they destroy all the trees and attempt to replace them with native plants? Wow, that’s going to be quite a water bill. Your tax dollars at work. Meanwhile the students of the UC system are being asked to pay tuition increases of 9.3% to compensate for the loss of State funding during this economic crisis. Does this make sense? Not to me!

  2. savesutro says:

    If they are going to irrigate it, they might as well do it without chopping down anything. They could just have arrangements to water it for ten days in the year when it’s hot and dry. They’re already watering the Native Garden. It would be as easy to water these other two areas.

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