Question
I cut down this tree about 2 years ago, but left about 3 feet of the trunk and roots. It was totally hollowed out and it is about 5 feet across. Just today I noticed that there are 3 tan colored large(3-4") discs formed on the outside of the tree.
Can you identify what they are and if this a sign of something that we should be aware of?
Thank you,

Answer
These are the fruiting bodies of the decay fungi in the hollow. They will not kill the tree -they infect the woody cells only. The fungi itself is growing in the wood cells and over time will cause the tree to become hollow. This will not really effect the health of the tree except may over time weaken the trunk and if the decay fungi grows into the limbs may cause the limb to break off in a wind storm.   There is no chemical that can be applied to treat the fungi but fertilizing the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter in the spring and again in the Fall will help the overall health of the tree and strengthen the tree against the fungi.