The trees in your yard are an important investment, but they could be dying because of a mistake that a lot of homeowners make.

Neighborhoods take a great deal of pride in their leafy sentinels, but there's a silent epidemic in our urban forests.

"The epidemic will kill more trees over the next 10-15 years than gypsy moths and all the natural pests we have," said Alan Siewert, an urban forester.

The pest is homeowners who over mulch trees, contributing to a slow death. We pile mounds of mulch, killing them with kindness.

The problem, however, is twofold. Anything more than 2 to 3 inches actually prevents water from getting to the roots, but the bigger danger occurs when people pile mulch directly against the trunk like a volcano. That fools the roots into thinking there is soil close to the tree and the roots begin circling around the trunk like a python, strangling the tree.

The tree then dies from top to bottom because the culprit is hiding under all the mulch. The owner probably will not know anything is wrong until it's too late.

Siewert said you should create a 2- to 3-inch thick doughnut, keeping the mulch away from the trunk. If possible, extend the donut out as far as the longest branch so that the turf grass isn't competing for food and water. Mulch is good for your tree, but less will do more good in the long run.

For more information about the benefits of proper mulching and types of mulch, visit the International Society of Arboriculture's Web site.