Naked Science Forum

Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: petelamana on 13/02/2018 21:48:25

Title: Why do trees sometimes grow loop-shaped branches?
Post by: petelamana on 13/02/2018 21:48:25

Recently, while hiking in the forest behind my house I noticed a large Elm tree.  Curiously this tree had a loop growing to one side of the trunk, about 9-feet above the ground.  Immediately I thought it was formed by a mis-grown branch, but the bark, both above and below...and to the sides, of the loop shows no indication of any branch grown.  I'm not an arborist, environmentalist, forest ranger, or even a botanist of any kind.  I am a "forest appreciator."  Can someone tell me what is going on with this tree?  I am at a loss.


tree 1.jpg (125.07 kB . 216x288 - viewed 7443 times)


tree 2.jpg (114.49 kB . 216x288 - viewed 7431 times)

Title: Re: Why do trees sometimes grow loop-shaped branches?
Post by: Colin2B on 13/02/2018 23:11:43

These are quite common in the beech woods near us, but I’ve not seen it with elm. Usually happens when the end of a branch rubs against another part of the tree or an adjacent tree, it rubs the bark off both parts and then the 2 grow together. It’s the same process as grafting, called inosculation.

Title: Re: Why do trees sometimes grow loop-shaped branches?
Post by: petelamana on 13/02/2018 23:18:12

Very interesting.   Thank you.

I wonder what could've done it in this case?  The only tree within 10 feet of this particular tree is a sapling, hardly of a size, or age to affect this tree.  Additionally, there is no evidence of a past tree near it. 

Could a tree spontaneously loop like this?

It is a curiosity.

Title: Re: Why do trees sometimes grow loop-shaped branches?
Post by: chiralSPO on 14/02/2018 01:42:25

I'm pretty sure the tree pictured is a beech, not elm  :)

Title: Re: Why do trees sometimes grow loop-shaped branches?
Post by: Colin2B on 14/02/2018 09:18:12

Quote from: petelamana on 13/02/2018 23:18:12

I wonder what could've done it in this case?  The only tree within 10 feet of this particular tree is a sapling, hardly of a size, or age to affect this tree. 

Could a tree spontaneously loop like this?

You don’t need a nearby tree. If a branch of same tree hangs down and touches trunk wind will cause abrasion and eventually self grafting.

Quote from: chiralSPO on 14/02/2018 01:42:25

I'm pretty sure the tree pictured is a beech, not elm  :)

I missed that. Leaves are similar bark is not.

Title: Re: Why do trees sometimes grow loop-shaped branches?
Post by: evan_au on 14/02/2018 10:07:13

In the pictures, the two ends of the looped branch appear quite different where they touch the trunk:
- One end grows out radially from the center of the tree, like a normal branch. I think this is the origin of the branch.
- The other end grows out tangentially from the perimeter of the trunk, and shows a shadow where it merges around the outside of the tree. This looks like the place where the growing branch rubbed against the trunk.

There appears to be two sharp bends in the looped branch:
- Could the original branch growing out radially have been snapped off, leaving a branchlet (at right-angles to the original direction) as the main point of growth?
- Repeat once more, and the branch does a U-Turn, to strike the surface of the trunk.
- Apply a little friction from wind, and you have a self-grafted looped branch!

I've heard of landscape gardeners planting trees down both sides of an avenue.
- When the trees get tall enough, they graft the branches of the trees together over the road, forming an interconnected network of branches overhead.

Title: Re: Why do trees sometimes grow loop-shaped branches?
Post by: chiralSPO on 14/02/2018 15:07:21

Quote from: Colin2B on 14/02/2018 09:18:12

Quote

I'm pretty sure the tree pictured is a beech, not elm 

I missed that. Leaves are similar bark is not.

Correct.