There is this one tree (I believe an oak tree) near my road that is very large in size. Practically at the base of its trunk, it diverges into four other large trunks:
What causes this phenomenon in trees? Is it possible that this was actually a few trees that have grow into one another? To me, this looks like one tree that early on in it's life, somehow split off into four trunks like so.
In the US this is sometimes called a schoolmarm (alt school-marm) there are a number of ways they can form. OSHA Logging terms
As mentioned in the existing answer some trees like willow grow very aggressively and a low cut stump can have several shoots that grow in to trees.
Two or more seeds growing in the same location can grow multiple trees. If there is sufficient sunlight neither new sapling will have a significant advantage and both will prosper. This can occur naturally or from manual over planting.
Sometimes two forks of a tree will grow about the same. This can be an internal event for the tree, or due to an external trauma like the top of the main trunk of the sapling being browsed by wild life, leaving lower branches to compete to become one or more primary trunk.
Schoolmarm's pose risks on two fronts.
If in the past a fairly large tree had been cut there, the stump, if left high enough to sprout could feasibly have a group that could grow to that size Because it doesn't appear to be from lightning or some other natural damage.
