Splitting wood goes with the grain. Frozen wood does split easier but frozen firewood and a tillered bow aren't even apples and oranges.
I have heard tat yew is susceptible to breaking at very cold temps but have no personal experience.
The only sensible way to split cottonwood for firewood is to cut it late in fall and wait for a hard freeze. But then, you are counting on the moisture in the wood to affect the grain of the wood and encourage the split instead of just absorbing the blow into the mushy soft wood.
I remember an early and extended thaw came to my little hometown in North Dakota back in 1972. Leaves were just beginning to bud on the trees in late February. The old timers were dour, this was a bad bad sign. Sure enough, a frozen hell came roaring down out of Canada and dropped the mercury to 30 degrees below zero. Everyone in town woke to the sounds of artillery exploding up and down the streets. Tree trunks with fresh spring sap had frozen, the moisture swelling until the trunks burst and split.
But who the heck carries a sopping wet, fresh cut greenwood bow in the dead of winter? If properly seasoned, the cold really has no great effect on the bow except to maybe add a little snap.
