For the sake of simplicity, we can break urban trees into three categories; large, ornamental, and fruit bearing.
Large trees: This is going to be your big stately elms, maples, ashes, birch, linden, poplar, and willows. Though these trees should be monitored for signs of instability; they’re generally going to do fine with a pruning every 4-5 years to remove dead wood, thin the canopy, and remove excess horizontal weight.
Ornamental: This is going to be any tree that maxes out around 20′. Primarily; mountain ash, Amur maple, mayday, and lilac. These trees generally pose less of a safety risk due to their size, and so pruning is primarily focused on tree health and aesthetics. They do however tend to over take the area, since once they reach their maximum height, they continue to grow horizontally for the duration of their life. Every 4-5 years is typically adequate to keep them happy and under control.
Fruit Trees: Fruit trees tend to have much more specific needs, especially if you cultivating with the intent to harvest the fruit. If left to their own devices for too long, they will begin to over crowd, resulting in too much vegetation, very poor fruit quality, and an ideal environment for fungi and pests to colonize. Its generally advisable to prune your fruit tree every second fall, or every 3 years at most.