Answer: The ants are finding a source of food on your tree - some sugary sap of some kind. Check to make sure there are no aphids; ants 'herd' aphid colonies and milk them of honeydew, a sugary residue. Spray your tree with a strong stream of water to dislodge any aphids you find. To keep ants from climbing up your tree, place 'Tanglefoot' at the base of the trunk. Tanglefoot is an extremely sticky substance that traps insects if they fly or walk onto it. To protect the trunk of your tree, first wrap it with paper and apply the Tanglefoot to the paper. You may have to remove the paper coated Tanglefoot trap and replace it as it becomes filled with ants - if there are enough dead ants trapped, live ants will use them as a bridge and cross the Tanglefoot barrier!
Ants don't bring termites to a tree; if termites are present, they are finding dead wood within your tree. I'd prune out the dead wood and that should take care of any termites.
Best wishes with your garden!
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