Yes, no thinning needed. What can and ususally does happen is that "nature" sorts things out over time. Thus, you may have planted species A at a rate twice as heavy as species B, but over time, B could become more numerous than A, just for an example. But in any such case, this is something that you do not need to do. The plants fight things out on their own.

Over time, you may wish to augment one species, or bring the occurrence of another down a bit. Then you would need to manipulate, via fire, herbicides, hand pulling, etc. But that's a special case, not the norm.

+oM