Wood burning squares?

Question

Why when burning wood dose it burn and fall off in square chunks? I know wood aka trees grow in rings but I dont understand why it ends up in square chunks when burning

Answer 1

This is a little hard to explain without pictures, but I'll give it a try. The two main vessels that transport water and food are the xylem and phloem cells. The xylem cells transport water and minerals from the roots to the top of the tree. These form the rings you were referring to. They die each year and grow new ones for the next year (thus the rings). The phloem tissue transport the products of photosynthesis (by the way or sap) from the leaves downward to all parts of the tree. They are arranged very much like the xylem tissue except that is living tissue and does not die off each year during the winter. The phloem forms phloem rays, growing from the center of the tree outward as the tree grows. This would look very much the way you would slice a pie if you looked at a cross section (only is much smaller pieces). These rays form a weakness in the wood. This is why a piece of wood will split straight when splitting wood for the fire place. It also is the way the wood separates into little squares  when you burn it. As the wood burns it separates along the rays and also along the xylem rings to form what looks like the squares you are seeing.

Answer 2

my theory all trees grow in annular rings therefor the growth rates of each annul would depend on the variables of that year taking this into account the burn rate of each ring would be different, some quicker wide cells more oxygen burns to a powder ash quickly, some slow narrow cells tends to carbonate "turn to charcoal "still burning but at lower temp.

now when the fast burning rings have traveled far enough along the wood a cooling action on the slower burning wood would contract fracturing its radius the timber would also contract along its length losing its strength when sufficient weight of timber is reached it would fracture under its own weight forming a square like shape.

i'll probably get hung for this theory but what the heck.

I was right John h above who beet me by 27 sec.s has definitely a better way with words more accurate do I care.

..........................YES.     no only jesting.  



All this said its just nice to kick back staring at a log fire pondering the marvels of the world like why does beer taste better cold .!!!!! & does it really matter if wood burns in squares or not  as long as it stop our bums freezing.  :-)