This last week I went out most days to make small sketches of the trees for the book. I find that just a short time sketching is a million times better than working from photos.
Making a sketch, especially on a very cold day, requires you look hard and make fast, hopefully intuitive, decisions. So you tend to record just the essence of tree, very useful for the woodcuts which will have to be bold and simplified.
Also I have to say that once I have sketched something I understand much more about the thing, how it is put together, what interests me about it and I remember all those things more easily, especially if I make notes.
I am in a hurry too because I need to draw the trees before they all lose their leaves. I need to make sure I draw the right tree. My bark ID skills are not brilliant
I have a tight deadline so I also took the woodblock out to draw directly from the elder tree. This old, much pruned, tree has snaky spotted branches which twist back on themselves. Wonderful and slightly sinister as befits the magical elder!
The tree prints will be based on trees I know well, what I like about them and what I know about them. A personal view rather than an archetype. I have discovered that one elm can look very different from another :).