When to cut down over-mature trees?

[IndyIan]

I've got a few large hardwood trees that are starting to have large dead branches.  Also they are loosing some leaf cover at the top of the crowns.  
I'd like to keep them as long as possible but also be able to get some useful lumber out of them.  
I guess using a tree auger to take a core sample of the bole a good way to tell how the wood is doing without taking down the tree.
The auger will injure the tree, is this significant?  Can I do something to make sure the auger wound doesn't get infected?
Here's couple pics of them

[Mark M]

I used to use an increment bore on trees a long time ago. It never seemed to hurt them much as the hole was pretty small and soon filled in with sap. There are probably ways to plug the hole nowadays but we didn't do anything.

[IndyIan]

Thanks Mark,
I guess its best to do it in spring so the sap will fill the hole quickly?

Ian

[Jeff]

Da foresters must be in da forest. I'll try to round one up.

[Ron Wenrich]

Well, I was kinda waiting to see what the other guys were going to say.

Actually, your increment borer won't give you too much information as to "how the wood is doing".  You'll be able to get a sample at about chest height, unless you get a ladder.  Then you won't want to go all the way to the heart.  You risk snapping it off in that white oak.

An increment borer will have a permanent hole in it until it heals over.  But, the hole remains in the bole.  The sap bleeding out is just the trees response to an open wound.  It also opens the tree to other pathogens.

All the information you need is on the outside of the tree.  Bark will start to look unusual when the tree is really going south (with the exception of diseases like oak wilt or insect infestations).  

Swollen knots are a sign of heart rot.  Patchy bark on white oak is a sign of worm, which kills the veneer value but not the tree.  Frost cracks or seams may or may not be a sign of rot.  Usually when they form, it is time to get rid of the tree, unless it is a yard tree.  If the bark is sluffing off, then you don't have a long time before the tree is dead.

Conks are also a sign that there is rot present.  Conks are fruiting bodies of fungus which are feeding off of the tree.

Limbs die off on a normal basis.  Large ones just hang on longer before they naturally prune.  Top thinning out could be due to dieback or due to weather.  We've been having drought for the past couple of years, so that could have an effect.

White oak normally have a life span of 400-500 years.  Even after they die, the wood would be okay for a couple of years.  However, the sapwood often gets stained and may become punky.

[IndyIan]

Thanks for the information Ron.
I'll watch for the signs of weakness you explained.  
I had forgotten that white oak is so rot resistant so that we could wait until the tree is nearly dead to cut it down.  
We've got some large white ash trees as well, I'll check some of my tree books for its rot resistance and signs of imminent death.  I don't really want to cut them but it would be a shame to waste all that wood by waiting too many years...
We are building a house in next few years and it would be nice to use some of the wood for floors.  

Ian

[Sylvus]

Mature trees often begin to host an increasing amount of wood-eating fungi, which generally get a "foothold" in a tree through a wound in the root system, or from an above-ground injury.  This is basic biology stuff.  "When" this happens is a function of tree species, tree age, site conditions, etc.  An increment borer (auger) can assess wood condition at the point of insertion.  Boring a tree at the the base, rather than chest-high,  is one way to minimize damage to a high quality stem.  Time is always on the side of fungi.  Tree wounds never heal, they only become overgrown.  There comes a point in tree growth where vigor and value decline.  Usually, value declines before any sign of vigor decline.  If you are thinking of using the trees for lumber, then a few years growth aren't likely to make much difference in wood volume, but could potentially make a large difference in wood value.  If your trees are showing decline, the chances are good that fungi have been active for many years already.  A few trees must be pretty darn good quality to attract the interest of a buyer (or forester), or be in close proximity to an existed timber sale.  You will have the weigh the importance of the visual value versus the potential timber value.  

[Ron Scott]

Yes, just got back from the UP last night and the woods this afternoon.

Really no need to "drill" the large trees and interject another defect. There are enough outside indicators as previously stated to determine if the tree has become a risk or liability and should be harvested now.

Position, location in relation to other crop trees, form, etc should also be considered along with your real objectives for the tree whether it be for timber, wildlife, aesthetics, wind or snow protection, noise abatement, etc.

[IndyIan]

Thanks for responses guys.
Sylvus,
The trees aren't veneer quality and probably have some metal in them as they are on the edges of fields.  I'm sure a forester has seen them already as part of my woods has been logged by the previous owner.  There is just a lot wood in the first 10 feet or so that would be a shame to burn or have rot.  

Also Ron's points about other values that the trees provide is quite important.  The tree in the close up is my wife's prime Morel mushroom tree so it's been given 'protected' status and the other trees will be in the back yard of our house when we build it.  They will probably look nice and provide shade, wind break, and seed for new trees long after the main trunk is useless as far as lumber goes.   I guess I can't have it both ways!

Ian