I have both paper birch and river birch. The river birch are from a native nursery and appear to be doing OK. The paper birch is just leafing out and the bottom 2/3 of the tree is noticeably bare, with leaves only in the upper canopy. All these trees are sited in a soggy field with a year-round creek and farm pond close by. We struggle with beavers, and we have an active family again. They have dammed up the creek two properties downstream from us which has risen the level of our pond and really saturated the already soggy surrounding grassy field. I note in our database that paper birch perhaps does not tolerate wet soil as well as river birch. I assume now that the lower branches have died back, they likely won't rejuvenate themselves, and I am looking at a slow tree death. Sadly. The paper birch is older than the river birch, and was really starting to form a presence.
No camera at the moment, so no photos available.