Answer: I can't tell whether the mulch is causing problems or not. It's natural for organic mulch to decompose and the white mycellium you see is a normal part of the decomposition process. The fungus is feeding on the decomposing mulch material but won't harm the rest of your garden, your plants, or your soil. You can simply rake the mulch around every month or so to incorporate oxygen and stop the white mycellium from growing. I wish I had suggestions for your cherry tree. If it is not behaving well it may never recover. Perhaps the easiest approach will be to replace your sickly tree with a healthy new specimen.
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