Sure - you can see that in the oak (2nd sketch) I used stippling to add texture to the trunk of the tree and it has strong line weight to emphasise the mass and shadow of the trunk. Trees with lighter barks would certainly benefit from a more delicate treatment (e.g. finer lines) such as Silver Birch.

With the fountain pen I was using, there's a limit to the line-weight range available - it's not a very flexible nib and the drawings were only about 8cm x 8cm.