Answer: The Cornus sericea is a shrub to begin with, with multiple stems and is naturally very densely twiggy. It is renewal pruned by cutting it to the ground to encourage vigorous growth of new stems. (or alternatively it can be thinned selectively each year to remove some of the oldest growth.) This treatment is done to enhance the bark color on that shrub -- many of the shrub dogwoods have colorful bark on their newer growth. These types of pruning also helps to keep the shrubs from becoming overgrown, or prevents them from reaching their maxiumum size and spreading beyond their allowed space, some will try to colonize an area and this helps contain that. This type of pruning would really not be appropriate for a tree such as a Japanese maple.
Japanese maples will tolerate some careful pruning to direct their shape slightly or to control size to some extent, but in my experience trying to maintain a 20 foot tree at a much shorter height is just not realistic. It will ruin the graceful natural shape of the tree and is likely to limit its lifespan significantly. If you are willing to experiment, you could certainly try it and see how it works out but it is not something I personally would suggest.
In my experience, if you only have room for a smaller plant it is better to plant something that matures to an appropriate size rather than set yourself up for a regime of high maintenance by frequent pruning. If you have your heart set on a Japanese maple you might look into some of the smaller maturing cultivars, or if you already have this particular cultivar, consider planting in a different spot.
I'm sorry I can't be more encouraging.
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