The Achilles'-heel of redwoods

Self-destruction of root tissue from extreme weight

by Mario D. Vaden - Copyright 2008. This is an off-shoot of Largest Redwoods

 

After looking at a lot of fallen redwood logs hollow under the base, and estimating the weight of live redwood titans, my hypothesis is that giant redwoods self-destruct their own root system tissue. A type of Achilles'-heel.

Apparently, a coast redwood like Lost Monarch with over 42,000 cubic feet of wood, will weigh in the range of about three million pounds (3,000,000 lbs). Or with the metric system, 1,363,636 kilograms.

One of the largest known coast redwoods, the Lindsey Creek Redwood, would have weighed as much as a Saturn V rocket, in the range of 6,000,000 pounds.

My hypothesis is that weight of old redwoods causes so much pressure beneath the trunk, that the soil beneath is compacted and cambium growth on the underside is halted. This in regards to the oldest, a millenium or more in age. The cambium is the living thin layer under the bark where cell division occurs.

You may have seen how thin cambium can be if you ever scratched the outside of a young plant stem before, revealing some green tissue beneath. The cambium of a giant redwood is not really thicker than the cambium of of a small redwood.

A giant redwood is cloaked around it's exterior beneath the bark with a thin living skin that expands with new cell division, adding girth to it in all directions. The vascular cambium is always moving outward, and it gives in two directions, inward and outward. As the cambium grows away from the center of the redwood, it makes and leaves behind more wood or xylem. Simultaneously, it makes and builds more phloem outside of it, just under the visible bark.

That is, of course, unless something blocks it.

A redwood like Lost Monarch exerts downward roughly 30 to 50 pounds of pressure per square inch - psi - due to its own weight. That's like stacking 600 - 1000 bags of concrete over a 30 inch x 50 inch area the size of a table top. Or like stacking 20 pallets of concrete one on top of another in a tall column of crushing weight. For a redwood like the Lindsey, the pressure would be comparable to 40 pallets of concrete stacked in a column: up to 100 p.s.i.

That kind of pressure on the underside of the root plate is comparable to redwood roots trying to heave a sidewalk 50 to 80 feet thick. And that's not going to be seen in our life time. Redwood roots generally can't even lift a 2 story house, mainly hollow inside, with thin concrete foundation. This great pressure must be a factor limiting the future stability and lifespan of redwoods.

Redwoods can exert quite a bit of pressure at times when the conditions are right, but there are limits. The skinny thin layer of cambium is only so thick and powerful. Much of the inner trunk tissue is not living. Its merely the outer living layer of cambium that exerts pressure outward. So it does not matter how massive a trunk is, the cambium is still sort of a weenie.

Again, the cambium moves outward producing a layer of wood toward the inside where it just left, and at the same time produces some phloem and bark ahead of itself as it pushes outward. That's one reason bark cracks and furrows, from this living layer underneath that advances outward, leaving tissue behind itself and ahead of itself.

It does not take much of an obstacle to constrain or constrict cambium growth. Cambium growth on tree roots for example, may be able to lift a sidewalk a few inches thick weighing several hundred pounds, but it won't be able to lift a sidewalk of concrete several feet thick.

That's why you may find a big tree that cracked the foundation of a single story house floor slab, but not one that lifted the side of a two story house.

At some point, even a redwood can't produce cambium tissue when pressure reaches a certain threshold. And with redwoods, they have enough weight at old age to restrict their own growth. Probably causing their own soil compaction too.

The aggregate photograph to the right shows just a few examples of how cambium and phloem tissue can be constricted and stopped from expansion. Look at the first image. See how a small branch that was not pruned away, was enough to stop the tree from expanding tissue outward? The cambium did not have the energy to force and bend the limb out of the way. Next - the second image. That's where a bigger stem of a flowering plum was removed. See how the two stems expanded and met in the middle, preventing each other from expanding on the inside? It left a flat-sided area where no cambium could grow and expand. In the third image, the root of a white birch encircled it's own trunk on one side, stopping its cambium and tissue from expanding. The fourth image is a bit similar to the second image, where two small stems grew and became big stems that constricted growth in-between.

The fifth image is a metal hook someone hung in a flowering cherry to hang a plant. See how the cambium failed to have energy and power to bend the metal out of it's way?

Same relates to redwoods, their cambium is not much stronger. Underneath the living stumps or root plates, the tremendous weight of hundreds of thousands or millions of pounds should easily produce enough pressure to constrict or kill cambium tissue.

In addition, if the weight of the redwood compacts the soil beneath, that means that exchange of gasses like oxygen and carbon dioxide will be minimal, affecting the redwood tree and microorganisms.

All the evidence provided by living trees connotes that redwoods self-destruct their own tissue beneath during old age. Even though some downward weight will be transferred beyond the trunk a little bit, the energy won't be dispersed to the entire root system.

The effects of the weight may be at least two-fold. One part is the pressure from the weight on the cambium tissue underneath the root plate. The other aspect is potential soil compaction affecting the movement of water and air in the soil.

Reduced air exchange in soil can also negatively affect the health of mycorrhizal fungi and other microorganisms that live with the roots of redwoods.

The weight of a titan redwood over a potentially deteriorated root system may even lead to something similar to liquifaction experienced under buildings during severe earthquakes.

The middle photograph is the bottom end of a fallen redwood at Simpson Reed Discovery Trail. The bottom, as with many fallen redwoods is concave and partially hollow beneath: typical for deterioration prior to falling. This log should be around for centuries. The Simpson Reed trail is a great little redwood stroll through the woods, and might be one of the best trails if someone is in a wheelchair.

The bottom photo is Dyerville Giant, now one of the longest redwoods in the world. It used to be one of the tallest redwoods in the world. Likewise, you can see the concave middle beneath.

This redwood is in the Founders Grove along the Avenue of the Giants close to where Bull Creek meets the Eel River - south of Fortuna, California.