Something that i have considered several times as the seasons swing and the sap rises... when is a tree limb at its strongest?

When the tree freezes (does it freeze or does _meta_bolism in the tree prevent this?) does it's absolute strength increase but become more brittle? Or does the ice interfere with the lignin fibres and weaken the limb?

When the sap rises, what effect does this have. Do limbs become more turgid? Does this mean they become less flexible and hence more prone to breaking?

I've never ventured to load a branch to breaking point under scientific scrutiny over the course of a year. Has anyone done any loading experiments or through out the course of many years experience come by an understanding?

In my experience, the limbs seem to be strongest from late summer through winter. During the growing season they seem a bit more flexible and sometimes brittle.

It would be hard to say with much certainty though. Lots of variables.

A more important thing to consider is the branch attachment. A codominant included bark attachment is the weakest. Stay away from them.

Originally posted by Tom Dunlap
IA codominant included bark attachment is the weakest. Stay away from them.

Tom, you'll have to elaborate for be. What's a codominant?

This winter I was in a beech grove (on the ground) when I heard several deep cracking sounds coming from the beeches. It sounded like either the main trunks or large limbs were splitting along the grain. The air temperature was around 8 degrees farenheit. From this observation I'd say that beech has greater potential to fail when the temperature is very low. I could be totally wrong

Originally posted by bareroots

Tom, you'll have to elaborate for be. What's a codominant?

I was curious about this as well. I did a little searching and found this on a web page explaining tree pruning concepts:
Pruning approaches

Here's a good de_script_ion from the section on crown pruning:

"Included bark forms when two branches grow at sharply acute angles to one another, producing a wedge of inward-rolled bark between them. Included bark prevents strong attachment of branches, often causing a crack at the point below where the branches meet. Codominant stems that are approximately the same size and arise from the same position often form included bark."

There's an illustration (fig. 3a and 3b) on the web page showing a strong "U" shaped codominant branch attachment and the less sound "V" shaped codominant branch attachment with bark inclusion.
-moss

Good reply Moss on the co-dominant issue. It is always refreshing to see folks helping others with their questions.

I look at branch angles when I do tree inspections. When you see a ridge or bulge of wood below a tight V crotch it means it is weak and the tree is responding to the weakness by laying down reinforcing _layer_s of wood.