It’s Raining – But Only Under This Tree

I had an arresting experience when I went out into the woodland the other day. It has been extremely dry this winter in Oregon, but there is often a lot of fog. As I walked under one of the larger Douglas firs there was a sound of dripping rain on dried oak leaves and yet, it was not raining.

I’m not sure if I have ever experienced fog drip first hand in quite this way. I learned about it many years ago as a very significant (in the statistical meaning) source of ground water and soil moisture in the western Cascades.

Have I ever been in the woods when they are dripping? Yes, but standing under one single tree, that is collecting and dropping water is kind of eerie when everything else is quiet, the ground is dry, and it’s just very foggy. Being present as a tree essentially waters itself and channels the water into ground storage, reveals how trees = water = more trees and life.

So, come along with me and experience it for yourself. You might be able to see the raindrops falling in this cellphone movie:

Here, stand in the open where no rain is falling, and look back toward the mixed oak and the big Doug fir in the ravine. These trees were left behind when the forest was logged the first and/or second time in the last century. We left them too, when we thinned trees to revive the oak woodland. They protect a riparian zone of seasonal streamflow – the source of some of that flow is now apparent! That’s a Steller’s Jay imitating a Redtailed Hawk in the background.

So, why fog drip under conifers and not oaks (I asked myself)? I believe that the answer lies in leaf architecture. Moisture runs off the vast surface area of thousands of needles intercepting fog. Oaks are leafless in winter, but besides that, they support a huge biomass of lichens and mosses, which are designed to soak up nutrients and water from the air, as it’s their life support. Hence, lichens and mosses may tend to increase the humidity around a tree, but they sponge up rather than repel moisture like fir needles. Fir needles don’t need the moisture – they send it to the roots where they can use it.     Wow.

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