I am (today) in Williamsburg, VA, hauling the family behind for an
"educational experience". It's our fifth or sixth trip in the last 15
years (yeah... I know).

The historic district is an intensely-protected area in terms of both
structural and horticultural preservation. They cry crocodile tears over
a lost tree, and they've got some really well-qualified arborists working
the district. You see hundreds of trees with little colored tags
indicating the type and date of various treatments or inspections.

Here, they lag-bolt equipment right into the trunks. I cannot say what
the material of the bolts is, but suspect it's not a bronze (copper,
toxic) or galvanized (zinc chloride, also toxic). So that leaves
elemental iron, steel, or a corrosion-resistant steel. Iron and
unprotected steel don't last long in a continously wet, unprotected
condition.

I saw this thread before we went hiking down Duke of Glouster Street
today, and took care to note how many fixtures are mounted on living
trees. There are a lot - hundreds of electrical cables, lightning rod
cables, and speaker cables and boxes.

I don't think they'd do this if there were significant chances of harming
them.

LLoyd