A tree surgeon.I would photograph the growths and have an arborist or nurseryman positively identify the growth....
He may be concerned as an arborist / tree surgeon with trees which form no part of a forest and do not qualify as growing timber.
Bob Rouse, staff arborist with the National Arborist Association in New Hampshire, suggests that you mount your tire swing with an eyebolt rather than wrap rope around the tree's limb.