When spreading mulch around a tree, be careful not to mound it up against the tree trunk. That creates a mulch volcano, which can kill the tree because it allows the bark to be invaded by insects, fungi, and small rodents who burrow into the mulch pile. Moreover, the bark, the necessary protection for the inner wood, is likely to rot, as excess moisture accumulates in the mulch. Instead, apply mulch 3 inches deep and avoid putting mulch directly on the trunk.
For more information about mulching, see Cornell University’s Dept. of Horticulture: http://www.gardening.cornell.edu/factsheets/mulch/toomuch.html
See West Lafayette’s Tree Manual and Guide to the West Lafayette Landscape Ordinance