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Tree worship can fall prey to political exploitation, especially when a national or ethnic group claims an immemorial attachment to a patch of land. Jared Farmer, in his 2013 book, “Trees in Paradise: A California History,” notes that California’s sequoias and redwoods were long lauded as emblems of American greatness. Madison Grant, one of the founders of the Save the Redwoods League, was a racist and a eugenicist, notorious for the best-selling 1916 tract “The Passing of the Great Race.” Grant extolled the giant trees in much the same terms that he applied to sturdy specimens of Nordic supremacy. The age of the trees allowed for a kind of backdating of Manifest Destiny, into the mists of prehistory.

In his seminal work, On the Origin of Species, Darwin wrote that bumblebees are the only pollinators of red clover. In 1862 he discovered that this is wrong. Honeybees also pollinate red clover well.

I wanted to ask about death as well. Most people would look at a tree and, if they see that it’s no longer growing any new leaves, they say that the tree is dead. How long does the tree go on communicating even when it’s “dead”?

“As it’s dying and decaying, there’s all kinds of things going on. There’s a dying process, and I don’t think we totally understand it, but from a mycorrhizal point of view—and keeping in mind that there’s also this huge communication going on above-ground with these volatile organic compounds moving across the forest through the air—below ground, as the tree is dying, as long as there’s a carbon source from photosynthesis, it will support the mycorrhizal fungi.

“As the tree is dying, it actually transmits or communicates its carbon to other trees. And the fungus probably has a lot to do with how that’s done, because it’s going to invest in where it’s going to get its energy from multiple sources. Once the tree is dead, it only takes about a year for the fungus to completely disappear. It doesn’t take long—but that process of dying, it can go on for years. And the fungi are around. They’re associated with that tree through the whole process.

“They’ll eventually abandon the dead tree. But even then other plants will start to grow on that dead tree. In our coastal forest, Western hemlock seedlings establish on old logs or old trees. And we know that those living trees around them are linked to those seedlings through the log. The mycorrhizal network just goes right through it. And so the life of that log goes on in those new seedlings establishing on the dead log. They’re linked to the old trees and transmitting carbon into them.

Science Fact Friday: Homology

I’ve also found this a helpful art tool. Whenever you forget which way a particular joint bends you can just reference your own!

Many children have done the simple experiment of placing a cut flower in dyed water and watching as it changed color. The latest video from Beauty of Science relies on some related physics. Since the color of flowers typically depends on acidity, immersing a flower in dilute acid will change its color from pinks and purples to yellows and greens. Watching this transformation, we can learn about how fluids get transported through flowers.

Like the leaves on a tree, flowers are covered in tiny cells called stomata that can open and close. In the daytime, stomata are typically open to allow carbon dioxide to diffuse into the plant. (At the same time, water pulled up from the roots is evaporating out the stomata, as seen previously.) Once immersed in acid, the open stomata are no longer bringing in carbon dioxide; instead, the acid is diffusing in and slowly spreading through the petals. In the timelapse video, some areas of the petal change faster than others. This could indicate more open stomata in the regions that change first or even that some areas inside the petal transport water (and acid) better than others. (Video and image credit: Beauty of Science; see also Making Of)

Trees are incredible organisms, and the physics behind them baffled scientists until relatively recently. Inside trees, there is a constant flow of water up from the roots, through the xylem and out the leaves. We often think of atmospheric pressure and capillary action as the mechanisms for pushing water up against the force of gravity, but this is not how trees work. Instead, the evaporation of water from the tree’s leaves actually pulls the entire water column up the tree. Water molecules really like sticking to one another, which actually allows them to hold together under this tension. 

The result of all this pulling is a negative pressure inside the tree, and, with some clever manipulation, it’s possible to measure just how negative the pressure inside a tree is using a device called a pressure bomb. You can see the whole process in action in the Science IRL video below. The magnitude of a tree’s negative pressure fluctuates over a day, depending on how quickly it’s losing water, but typical values can range from 2-3 atmospheres of negative pressure to 17 or more! To get the equivalent (positive) pressure, you’d have to be nearly 2.7 kilometers under water. (Image and video credit: Science IRL)