Tree pruning is both an art and a science. Too much art—treating your tree like it is clay to be shaped—can seriously reduce the leaf mass, stressing the tree and forcing it to grow a proliferation of shoots to compensate.
Too much science ignores the aesthetic and leaves eyesore branches that even the least artistic arborist would usually remove.
I believe the aesthetic eye can be learned, but you are ahead of the game if you are born with it. It also helps to look a lot, walk around, check out different angles, watch what you are doing.
Like any talent, tree pruning ability greatly increases with practice, lots of practice.
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