Question
What can you fill the hole in the tree with? So I can prevent the tree from rotting. Thanks Jeff...

Answer
Filling of hollow trees, a process called "cavity filling," was practiced by arborists for many years. Thanks to modern research, it has been discovered that cavity filling is not needed to support or improve the health of hollow trees.

Tree experts have found that cavity filling with cement can actually damage a hollow tree. According to Bob Rouse, Staff Arborist at the National Arborist Association, "The column of cement created in the tree by a cavity fill doesn抰 move, just like a column on a building, but the tree is always moving. It sways with the wind constantly. The rubbing created by the swaying tree and the solid column of cement further damages the tree."

Decay organisms, such as rot fungi, that created the hollow in the first place are able to take advantage of the new injuries created by the rubbing and invade the healthy tissue of the tree. Rouse adds, "If that wasn抰 bad enough, the cement holds moisture, creating a favorable environment in the filled cavity for the decay organisms!" Tree experts explain that it is much the same as when carpenters place a vapor barrier between a house抯 foundation and the wooden sills. If they put the sills directly on the concrete foundation, the wood will rot rapidly. If you place cement in a tree cavity, it will speed the wood decay! If cavity filling is desired for aesthetic reasons, there are some new synthetic foams that can be sprayed into the cavity by professional arborists. These materials will bend with the swaying tree, but Rouse warns, "There is really no reason to fill a cavity; it doesn抰 improve the tree抯 health and doesn抰 offer any added support. If structural support of a tree is required, a professional arborist will recommend cables, braces, or tree guys, not cavity filling." Source: National Arborist Association