This is probably a staghorn sumac which is actually a native plant and is considered beneficial for birds and insects.  Unfortunately, it can be an aggressive grower with tough roots. 

Here is some information on types of sumac plants. 

Sumac Trees: Types, Leaves, Berries (Pictures) - Identification Guide (leafyplace.com)

If possible, it would be best to manually remove the smaller plants. But an alternative is to cut the stem down close to the ground and then within 5 minutes, brush on a triclopyr herbicide.
Triclopyr (such as Garlon) is a stump and brush
killer. When using herbicides, read the entire label and observe all precautions listed, including proper disposal.

I hope this helps. Robin

Hi Robin,