In Andrew Hiron's Applied Tree Biology, the author points out an interesting tidbit about trees. There is no one formal definition of what constitutes a tree. In fact, a court ruling determined this. The court concluded that as long as something looks like a tree, then it can be defined a tree. Similar to the saying, 'if it walks like a duck and quacks like a duck, then it is a duck.' Now this 'law' about trees if truly amazing. Trees are an abstract notion, yet so grounded in reality. They can take up so many unique forms, even between similar species! Who knows all the different kinds of trees that are out there? The trees wait - ready to be discovered, measured, and classified by a curious arborist.
Our curious arborists have brought us very far with their immaculate observation and classification of all the different kinds of trees, but what if we stepped the arbor game up a notch? After all, who says a tree has to grow in the ground? Let's see just how far we can stretch the definition of a tree, and if we make any curious arborists angry along the way ; )
Is this a tree?
Yes, a shrub is a tree.
Why is a shrub considered a tree?
Overall, shrubs have very little specific characteristics to them. A shrub has a woody structure, very similar to our notion of a classical tree - and it has leaves and flowers that multiply in quantity as the shrub grows bigger. It has a root system, something to hold it firm to the ground and immutable to the environment. Some shrubs even have gorgeous fall colors. Shrubs can come in all kinds of sizes, some as big as 5 meters. You might say that a shrub has multiple stems, and that is something that makes them different from trees. But this doesn't really hold up because there are many classical trees such as the Japanese Maple (below) with multiple, beautiful stems coming from the ground to create the tree. Considering all these caveats, it's probably best for the curious arborist to address a shrub as a tree.
A Tree (Data Structure)
A Data Structure is a specific way of ordering information. A Tree Data Structure orders data in a format like below. There are roots, branches and leaves all defined in a tree data structure, albeit very abstractly.
Is this a tree?
Yes! This is a tree.
Why is a data structure considered a tree?
In a sense, a tree data structure is the simplest possible tree; all the elements of classical trees exist. The woody skeleton so important to trees is described here by the circles and lines that connect together in specific ways. Branches spread out, taking up more spacial volume just like an ordinary tree. The canopy of leaves important to photosynthesis of classical trees are metaphorically represented in a tree data structure by the leaf nodes, the widest area of the bottom of the model that keeps growing proportionally to other dimensions of the tree. It is abstract, but a tree data structure is as much a tree as anything else.
Am I a tree?
I think I am.
Why am I a tree?
Trees are living beings, and we as humans tend to forget that too often. We centralize ourselves in the grand story of the universe and fail to fully realize the scale of time that we are just a part in. We forget about trees, our cosmic brothers and sisters that have withstood the test of time. Trees exist not only in a current moment in time, but also hold a deep understanding of their environment. Trees are a type of life on earth that can take the resources it is given and make something beautiful out of it - whether it be a high standing Giant Sequoia or a battle hardened Desert Willow. Just like trees, we humans also learn, adapt, and grow!
Thank you for spending the time with me to explore all the different trees in our world. Now go out there and find more trees, you curious arborist!! : )