I assume Object_Control.Vegetationarray is a collection such as an ArrayList?
Essentially what the for loop is attempting to do is modify the collection at the same time
you are iterating over it, hence the exception.
Two ways round this:
1. Get an iterator from the collection and use Iterator.remove() (not supported by all collections mind and probably not the best approach for this case anyway).
2. Create a new list of objects to be removed and then remove them in a second step.
List<Vegetation> removed = new ArrayList<>();
if( ... ) removed.add( c );
Object_Control.Vegetationarray.removeAll( removed );