Arkberry:

I have a Page Mandarin hybrid on Citrange rootstock. It was damaged like that in the winter of 09/10, except the split was a lot longer. I thought it would have died by now but it has not. Maybe because it has not been wet enough to cause the crown to rot out.

This wound looks old enough to have bare wood already turning grey at ground level. The edges of the split appear calloused and healed. Am I interpreting the photo correctly?

When did it happen? What is the variety and rootstock?

That damage is much deeper than just split bark. As was already noted, the damage is also in the wood.

Arguments go both ways about using a sealer (like Morrison's Tree Seal) or letting the tree "heal" itself.

Trees don't really "heal" a wound; they just produce new growth separating the "infection-cut" from the rest of the tree, essentially "sealing out" the bad stuff. Your problem now is that it is cold and the trees are dormant so there is not much tree growth.

Some say that using a sealant just traps moisture next to the would which encourages fungus and bacteria etc.

So... after all that.... the way I see it is : Trees evolved over a long period when we were not around to fret over them. Maybe they figured out, without us, how to deal with these situations.

I would clear some of the mulch away from the bottom to let it air out and otherwise I would leave it alone and hope.

Mike

Sealants don't help.

If it were my tree, I'd go ahead and seal with a mixture of .5tsp Kocide in 6oz latex paint... I'd remove all that stuff from around the crown down to the dirt and apply over the entire area of the wound, overlapping the undamaged bark.