If all the bark is gone then so is the orange. Sooooo sorry. 😔

I don't know where you live, Wayne, but it's been really hot and dry here in CA. Animals are thirsty and will eat the bark to get to the layers that have sap/water. This might have been a squirrel or rabbit.

How old is the tree?

The tree was only planted about a month ago in Queensland, Australia. Not too many squirrels or rabbits around here, but I imagine the young bark would be appealing for a small rodent or large insect.

Maybe Poncirusguy will chime in since he seems to know about grafting. I'm wondering, since it's so young, if you could graft the top to the bottom.

You can take a twig and graft the lower bark with the upper bark and if both grafts take the tree will survive.

Repairing girdled trees

Repairing girdle tree

Thanks Poncirusguy. I think that is beyond my grafting ability, especially given how small the stem is (about 1cm diameter). The video makes a good point though, since the xylem is probably still intact and the phloem is disrupted, the top of the plant may survive for a while, but the root stock will eventually die due to lack of nutrition from the leaves. Do you think air layering would be an option to propagate the top section? It's like the pest has very expertly completed the first step in the process. Also, I guess I could graft a bud from the top of the plant under the cambium below the damage.

That is a great idea.

 I can't say because I've never done any citrus grafting

You pretty much have the makings of an air layer, and that would be the route that most favors survival.

Hackberry being layered this spring

Same tree separated in mid-July

This is a trident maple seedling (below) had a root system too ugly to become a bonsai, and it wasn't worth trying to fix. So I layered it off of it's roots using the tourniquet method. You can still see the heavy wire tourniquet right above the saw cut used to separate the plant.

You could very likely salvage the plant by A) removing any existing vascular cambium down to sapwood, B) cleaning up the top of the wound with a sharp tool to remove any small tags of bark and cambium which is where rot would likely begin, C) applying rooting gel (not soluble in water) to the top ring of the wound, then D) Piling soil up high enough on the trunk to cover the wound by at least an inch and making sure the soil remains wet for at least 6 weeks. To help hold moisture in you could make an aluminum foil cover that fits the trunk snugly and covers the soil. Make sure there are no large chunks of mulch in the soil you use to cover the wound as that will reduce the soil's ability to resist drying out. You could also pack sphagnum moss around the wound after treating with rooting gel and before covering everything with soil. Sphagnum moss (not peat moss) is a natural antifungal and helps stimulate root growth.

Sphagnum moss ^^^

Al

  It could have been the deer    so check the ground for hoof prints

  It could have been the deer    so check the ground for hoof prints

All species of deer have 8 front teeth on the bottom jaw, 6 incisors and 2 premolars. No deer species are capable of clean cuts because they have no upper front teeth; instead, they have a hard fleshy surface (dental pad). When browsing, leaves are pulled off, twigs are broken off, and herbaceous growth pulled off by pinching vegetative matter between teeth and the dental pad, then using neck muscles to tear the browse from the tree, or from roots in the case of grasses and forbs. It was likely a rabbit or small rodent, perhaps the equivalent of our vole, chipmunk, ground squirrel, ..... .

Al

 I thought that was  a possibility of that too  for all I know it could have been a muskrat

..... not sure they're on the list of fauna that make Australia their home. I'd stick with rabbit as they're a serious problem in parts of Australia.

Rabbit damage:

Stupid critters left too much evidence behind to think it might be anything else.

Al

 To be honest I didn't think it was Australia   and no deer there  so forgive me  for my ignorance  of reply  earlier

I have worked out what it was. It was small roaches in the mulch around the tree. I had originally left a gap between the mulch and the trunk, however with the activity of the roaches and other critters it brought the mulch into contact with the trunk where the roaches could hide and munch away at the bark. They are small, only about 1 cm (half inch) long, but I caught them in the act. I've started air layering above the damage, but I have left the plant unattended while travelling for a week, so hope it doesn't dry out too much.

It's possible or even probable the bugs are simply taking advantage of the damage created by another creature by feeding on sugar-rich phloem sap and water/nutrient-rich xylem sap.

If you used the method of wadding moist sphagnum moss around the wound and covering it tightly with plastic, and applying something opaque to keep the sun from over-heating the layer, you'll likely be ok. But, if you used a technique that doesn't provided long term moisture retention, you're likely in trouble.

Fockea edulis being layered:

This ball gets covered with aluminum foil now to prevent passive solar (heat) gain. Using black opaque plastic will also help keep the layer cooler.

Al