Answer: If you have completely removed the tops of the trees and shoots are coming from the stumps and buried roots, you may have to use an herbicide such as Round-Up to kill the roots. Do this only if you do not want any of the original trees - if the roots have grafted themselves together underground, and you apply an herbicide, it can travel to other trees sharing the same root system.
There are other products on the market, as well, that will kill the roots. You must apply theses chemicals very carefully to only the stumps. If you spill some on the ground, your new shrubs can be at risk.
Check your favorite garden center for stump removal products or read the Round-Up label for the right timing and the right amounts to apply to the stumps to kill the roots. Once the roots are dead, they won't send up any more shoots.
Best wishes with your landscape!
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