I had to cut down a tree in my backyard. It was cut low, quite close to the ground. The stump has since sent out 100 new branches, and the former tree now resembles a shrub and continues to grow.
Which got me thinking: when forests are clear cut, why don’t the stumps send out new growth? Why do they need to be replanted?
In: Planetary Science
Different trees propagate via different means. Most forest clear cutting is pine and spruce. Those propagate from seed. Trees like Aspen and Gambrel Oak propagate from the root. For trees like that, when you cut the top off, it doesn’t kill the tree, so new shoots and branches can continue to grow.
Mostly because the forests being cut down are conifers and hardwoods that aren’t able to do that. It’s primarily broadleafs like willow, poplar, and maple that can regrow from a cut stump like that.
Several reasons.
Trees aren’t tall for no reason. Sunlight is limited. More accurately, area to collect sunlight is limited, and plants are competing for that space. By growing so tall, trees get above the competition so they can get to the sunlight. Once a tree has been cut down, anything growing from the stump has to compete with all the other growth around. That’s also true of saplings, but often trees have additional strategies to help saplings against competition. Some trees drop toxic chemicals in their leaves to kill other plants around them. Others drop their seeds after wildfires so everything else has burned away. A stump may not be able to do anything to beat the competition.
Trees also have to fight off predators and diseases. Since they can’t exactly get up and get out of the way, they grow thick bark which keeps things out. Anything trying to get to the juicy living tissue inside has to go through the extremely tough bark. A stump has a big opening with no protection so predators and diseases can get in. And, water can get out, dehydrating the tree.
Some species of tree store a lot of nutrients in the roots, but not all of them. Growing requires energy and trees get their energy from their leaves collecting sunlight. If you chop down the tree, there are no leaves and there may not be enough energy left in the roots to build a new sapling.
It’s largely because of the lumber industry. Trees that want to sprout branches all over make for very knotty and thinner lumber, so they plant firs and pines which do not regenerate as easily/often. And if they *do* regenerate, they are doing so in a wide open field which causes the new growth to twist as it chases the moving sun daily. By planting very dense seedlings, they all grow straight up to escape each other’s shadow. Seedlings will often be planted with 6-12″ spacing, but mature trees are 6+ feet apart minimum.
However this is not a trait of conifers in general. The common lumber species are chosen for these properties. Californian redwoods are capable of regenerating from the roots, and much of the old growth that was harvested in the early 1900’s did just so and are now rather enormous having benefitted from centuries old root structures.
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