I have cut stock blanks directly out of standing trees. I reserve this method for dying trees that may have lost their tops in a storm, or rotten on the inside. There is often a shell of live wood surrounding a rotten heart. I look for the curve where the trunk meets the roots; that's the area where you'll be almost guaranteed to have some wicked curl or flame.
I take a chalkline, lay out the width and length, top and bottom cuts. These will be plunge cuts, and a lot of muscle is required, as well as a really sharp saw. When the plunge cuts are made, you've got to come in from ninety degrees and free the stock from the tree. There's a lot of waste in this method, and there's a pretty rough blank to show for it. Make sure you paint the ends of the wood where the endgrain shows, or you'll have a checked stock!