Q: I have a large tree in my front yard that is very sick. A big part of the trunk at bottom seems infested with some sort of insect. There are lots of little holes & sawdust…plus a good bit of rot. The odd thing is that the rest of tree has lots of leaves.
A: Woooo….this isn’t a happy tree!
My bet is that the damage was done several years ago, maybe when the house was built. The bark may have been damaged by heavy machinery or a big root might have been removed by a trencher.
In any case, the damage never reversed. The tree tried to heal over the rot but was never able. Now naturally-occurring ambrosia beetles have made a home in the open trunk.
You need a consulting arborist to take a look. Don’t be surprised if they recommend removal.