Given the choice of doing the shading digitally, where things can be undone at the click of a button, IMHO I'd leave the shading until you can do it electronically on the digital map
Voolf's maps are indeed very beautiful, and to be quite honest I hadn't actually noticed that he didn't draw the whole tree at the edge of the forest.
Which way you go with this must definitely be your choice, not mine, but here are a few pros and cons to the alternatives:
Drawing the whole tree at the edge of the forest makes it more obvious that what you are drawing is actually a forest, but it does have the tendency to clutter the edge of the forest area with a great deal of detail that just isn't there in the interior of the forest. Shading on top of that can make it look a bit strange if its not very subtle.
Drawing the edge of the forest the way you have done, and the way that Voolf has done, removes the complicated edge detail straight away, but makes it a bit awkward when trying to express the shading that you will probably need to 'lift' the forest off the ground. It works well in Voolf's map, but he is drawing forests at a much smaller scale - as relatively small areas on a totally massive continent. It's easier for him in that situation to get away without any edge shading.
Its up to you, but whichever way you go with the style of the linework, bear those things in mind and the consequences (either way) for your map.