OBX of NC. Years later but maybe a little helpful. No soil scientist either. Anyway I have a flourishing Quercus Virginiana and for lack of another spot tried growing Colocasia IN A VERY LARGE POT under it this past summer. The Colocasia thrived! I was really surprised. Guess enough light filtered through/under AND the plant was in a huge pot with the correct soil and water retention properties. So maybe the leaf breakdown under the tree canopy is more impactful to the soil than the light/water. The tree does cap a dome that was a little dune-let and so the canopy doesn't cut off early morning and evening light like a tree on a more level surface might. also for anyone reading along the mid Atlantic or Southeast Coastal areas Juniperus Virginiana, also known as eastern redcedar needles and especially trimmed live needles seem to be a really strong growth inhibitor. Put and trimmings or prunings over something you want to seriously discourage.
