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In the 1850s, German scientists were trying to figure out how to weigh a forest, but they weren't particularly interested in the trees, and that's because, as it turns out, forests are much more than trees, and trees aren't even the heaviest or even the second heaviest part of a forest. Hi, I'm Cameron, and this is Minute Earth. Of course, the trees are the most visible part of a forest, and foresters have cut down, measured, and weighed enough whole trees that we can get a pretty good idea of how much a tree weighs just by measuring the diameter of its trunk at a standardized height. And if we did that for all of the trees in, say, a 100 by 100 m section of a typical temperate forest, we'd find that they
weigh about 400 tons in total. Then there's the animals, all the squirrels, birds, bugs, and bunnies that live on or even munch on our forest trees. If we collected and weighed them, they would weigh on average only about half a ton. But both trees and animals shed detritus, like leaves and poop that accumulates on the forest floor, and in that temperate forest, this layer is hugely important because of its role in cycling nutrients, but it's only a few centimeters deep on average, and so the litter layer ends up weighing only about 20 tons. So, that's less than the trees, but it's a lot heavier than the animals, which by comparison seem light as air. Wait a minute, air has mass, and it is the source of all of the
carbon that ultimately becomes trees, animals, and detritus, so let's weigh it too while we're here. If we count just the air up to the tops of the trees, it weighs 350 tons, almost as much as the trees themselves. So, never mind nothing about being light as air. If we are counting the air that the trees and the animals breathe, we should also count the water they drink, because you can't have a forest without water. Surface water and water being held in the soil is a critical part of a forest ecosystem, cuz without it, they die. Because trees are really good at catching water and directing it down their stems and trunks into the soil below them, as well as how tree roots create cavities in soil, forest soil is so much better at absorbing water than
non-forest soil is. To the point where most of a forest's water is not even in the streams or ponds, but it's in the soil. The water soaked into the topsoil can weigh as much as 3,500 tons after a rainstorm. But even then, water isn't the heaviest part of a forest either. In a temperate forest, the top 1 m of soil is where the most active tree roots are anchored. And it's where the bulk of a forest's decaying material and nutrients are. And it's where all of the fungi hang out that break down those nutrients and also help plants access those nutrients. A cubic meter of this soil weighs around 1.1 tons. So, the 10,000 cubic meters in our 100 by 100 m patch weigh right around 11,000 tons, making the soil the heaviest thing
in our forest. It's almost 30 times heavier than the trees. And this brings us back to those German scientists who wanted to weigh the forest. They were meteorologists who were interested in how trees affect flooding. So, they were most interested in the far more fascinating and important, well, to a meteorologist anyway, water absorbing soil right beneath their feet. This video is made in collaboration with the National Science Foundation and friend of the channel Dr. John Van Stan, a luxuriously bearded professor in the Department of Biological, Geological, and Environmental Sciences at Cleveland State University. Remember how I said that trees help funnel water into the soil? Well, it also turns out that the
trees are covered in dirt and all sorts of other stuff. And as water flows downward, it carries lots of vital nutrients from the tree canopy into the soil. Professor Van Stan is currently running an NSF-funded Macrosystems project to measure and map all of the specific ways rainwater washes nutrients through trees and into soils in order to better understand all of the ecological roles that this tree tea fills. It's a big job, so he's working in collaboration with INCAR, the University of Utah, and Utah State with field support from Battelle and the National Ecological Observatory Network. Thanks, John, and thanks, NSF.
