Minimizing damage - attaching a zip line and platform to a tree

[Beth33]

I'm looking to install a backyard zip line starting at a large pine tree in my backyard and ending at a deciduous tree (sorry, not sure what type) that's about 90' away. I want it to be safe and I want to minimize damage to the trees. I've seen conflicting advice on minimizing tree damage in two areas.

1. Attaching the zip line cable to the trees. I was planning on using a cable sling with a Tree Saver Block Kit (like this, or maybe just making my own out of wood pieces), but I've recently come across people saying that a through bolt is actually better for the tree long term.

2. Anchoring the platform to the tree. I was thinking of using posts (almost like a freestanding deck) and just strapping the platform to the tree somehow, but given the above I'm wondering if it'd be better to bolt it to the tree in some way, maybe with a tree house bolt.

I'd appreciate any advice you could offer.

 

[ATH]

Speaking for the tree (not Zipline safety...I'll bow out of that one):
Bolts are better IF you aren't going to loosen whatever is around the tree. The tree needs to grow in diameter.

 

[Reach]

The tree block kit is better than just wrapping a strap around a tree, but it’s still harder on the tree than a bolt would be.

My go-to, take it for what it’s worth to you, is to through bolt the tree with a forged eyebolt, and then install a cable around the trunk and through the eye of the zipline cable. The cable is left VERY loose, to allow plenty of room for the tree to grow, it’s just there in case of bolt failure. If installed properly, your 90’ cable will have 2-3,000 pounds of tension on it, so your anchors need to be VERY solid.

Your best bet for the platform is to build it freestanding, but it will take a lot of bracing to keep it solid. Alternatively, you can use treehouse bolts; that would be my preference for any platform more than about 5-6’ above the ground.

 

[Beth33]

Well, this is totally different from the approach I had been thinking about just yesterday. And here I was thinking I was being kinder to the tree by avoiding penetrations. The platform would be 7.5' off the ground (as the land goes uphill a bit before going back down, the line will have to be a bit higher) so it sounds like a bolt might be the way to go. Poor tree!

 

[ATH]

Think of the bolt hole kinda like a pruning wound. Would you hesitate to prune off a 3/4" diameter branch off of the trunk? A through bolt isn't much more impact to the tree. Yes...it goes through the heart wood, but that is dead anyhow and CODIT wall 2 is not terribly effective (compared to wall 4).