I made leaves of various sizes, both for the undergrowth and for the
trees. For undergrowth leaves, I took large pieces of crepe paper and
folded them each like a concertina, with each fold directly on top of
the previous fold.
I then cut a leaf shape through all of the folded layers, so that one cut-out made several leaves simultaneously. I cut as many as each length of paper allowed. After this, I cut slits around the tops of one of the leaf sets. I then varied the cut details on other leaf sets; some had longer slits, some had curved slits, some had
larger bits cut-out between each slit, etc etc. I also used different colours.
Some of these I glued to the base MDF board, either randomly placed or grouped with other bits of growth, and some I simply scattered across the board unglued, so that I could rearrange them as I needed when photographing the story.