Keep cutting that mature tag alder back, I've cut 90% of mine( leaving some mature stuff to break up the landscape. Make the cut about 2-3' up. Just be careful, there is usually a desired species growing inside the clump. You will have an explosion of growth, leave the cut down stuff where it falls. It holds the grass up, creating prime bedding. It also gives stuff like your elderberry room to expand. You should have a few basswood growing in the area. Add some hinge cuts of them, and you will have some of the best habitat in your area. I'm making mine even better by adding some pine and spruce.
Found a dead 10 pointer in this area two days ago, while planting spruce.