Taper in trees outside
People just starting off with bonsai often overlook a few simple things when thinking about bonsai. One of them is the taper in the trunks. If you look at trees in a park or in the landscape the trunks are very homogenous only slowly tapering away into a densely branched canopy. However, if you look at bonsai, and the recommendations for trunk thickness and rations, one often hear rations of 12:1 to 3:1 trunk diameter:tree height. How does that relate to reality one may ask !?
Taper in bonsai
Why do bonsai have extreme trunk taper? In a way it is very simple. You have different ways of looking at a tree. If you look at a tree from relatively far away, you see the trunk as a tall, slender trunk in comparison to the canopy. However, as you get closer, the trunk gets bigger in relation to the rest of what you see. If you are standing almost against the trunk, your whole field of view is filled by the trunk. If you then look up you see a very big trunk that tapers very strongly. Just a matter of perspective!
Bonsai: Image is everything
In bonsai one tries to portray an image of a large, old tree. And for most bonsai, the image is of one towering over you. This is also clear from the ideal situation where the tree leans over towards the viewer a little, giving the impression that you are looking up to a large tree. In this perspective, a trunk line with exaggerated taper fits.