Aspens by nature are suckering trees...they send up sucker shoots from the roots; these become new trees, all interconnected in a common root system.  Aspen trees in mountain groves are all interconnected in a common root system.

In your photo 1, I see aspen suckers.  There is another type of plant between/behind the aspen stems.

Photo 2 is an ash tree seedling

Photo 3 is another aspen sucker.  It's juvenile leaves do not yet look quite like aspen leaves on a mature tree.

Spraying aspen suckers with an herbicide may harm the "mother" tree, as suckers are connected by a common root system to the "mother".

Digging them out is counter-productive, as several new suckers will form at the pint where the old one was severed from roots.  About the only thing you can do is cut suckers down or mow them down.   If you wish, allow a few to grow into trees if they are in an acceptable spot.

Aspens in the landscape = dealing with aspen suckers.