I've never been a huge fan of fallen trees. Chop and drop. Sure, it may create some temporary habitat. But for me standing, large, mature trees seem to be the key, especially for brook trout. I cringe when a large tree is dropped in the floodplain. It may be beneficial short term by creating some debris, but you just lost a beneficial structure maker that you can't get back for 100 years.
Aside from shade, a large mature tree is like pounding a stake in the ground. The stream has to build it's channel around them and their very large root systems, which are as extensive as the trees canopy. Those roots penetrate the ground all over, and water seeps along them, and adds groundwater interaction as well. The ground itself is like a dam, filled with reinforcing roots, and the stream has to make it's way through that.
IMO, rock structure, wetlands and all are great. But in my experience, TREES are important for habitat. Standing ones. I can't tell you how many times I've fished brookie streams that are pretty poor in large stretches. Straight chutes, through open land, meadows, or even less mature hardwood forests. And then you come on, say, a mature hemlock stretch. And the entire stream just changes it's character completely. The moment you enter it's like the twilight zone, even the sound changes. Its overall slower, meanders more into S bends trying to find it's way through the wall of roots. There's more pronounced pools and riffles. There's ledges and deep pockets next to riffles. The ground is soft and spongy and holds water, even in drought periods the little spring seeps stay wet. There's no muddy areas, just sponge. Undercut banks and rootwads, but the banks aren't falling in because they are held in place by those roots. The water even seems clearer, I assume more groundwater filtering, and more stable banks, and the slow spots allow sediment to fall out. Everything feels cooler, and if you carry a thermometer, the water is truly a degree or three cooler than it was just upstream.
And the fish are there in numbers.