The answer to 'mulch dead trees' is that mulching dead trees is generally not recommended. Dead trees should be removed entirely, as leaving them can pose safety hazards and attract pests. Mulching a dead tree will not revive it or prevent further decay. Instead, it's best to have the dead tree professionally removed and properly disposed of.
If the tree is not completely dead but appears to be declining, mulching around the base may help retain moisture and nutrients. However, this is only a temporary solution, and the underlying issues causing the tree's decline should be addressed. Consulting a certified arborist is the best way to determine the appropriate course of action for a struggling or dead tree.