Wood is alive. Even when it's dead. That's why we cut angle joints, so that as dry summer follows wet winter, these redwood 2x6's will ease apart and then ease back together without an ugly gap on top.
The board on the left was added 8 years ago when I extended my deck. The board on the right is part of the original deck built 29 years ago. On the older board, lichen is growing, and a leaf from a rose bush has fallen. The grain is raised - or, more accurately, the soft parts of the grain have weathered away, leaving the hard parts like ribs. I don't know how much longer that board can last, but it's already survived 29 summers, 29 winters, 3 snowfalls, 1 major earthquake and the relentless onslaught of insects, fungus, and children.
It isn't premium lumber. We call it Con Heart, meaning construction-grade heartwood, which usually has knots and flat grain from relatively young second growth redwood trees, which grow like weeds around here. Weeds that we love. Weeds that we feel guilty cutting down, and that provoke major battles whenever somebody submits a logging plan.
When these boards were installed, they were "green" - that is, wet. The trees are milled at the sawmill and sold at the lumberyard and installed before they dry out. When you cut them, your saw blade smokes. When you nail them, water squirts out, sometimes onto your face or into your eyes. To me it always seemed that the boards were bleeding, and that's why the book cover of Clear Heart shows blood oozing from a nail. That's the guilt of a carpenter, for all the world to see.