Well the fungi is actually a good fungi which trees and other plants use with their root system. There are several specials on YoutTube and Amazon about trees, but here is a video time stamp to the point I'm trying to make.
https://youtu.be/Un2yBgIAxYs?t=578
It is possible that your trees are feeling sad or alone. They aren't communicating with other trees so they become less healthy. It is amazing to see how the trees communicate and how different species help each other out.
