Short answers, pulled from the story.
Wood is a natural composite of cellulosic fibers strong in tension, embedded in a matrix of lignin that resists compression along with hemicellulose. Cellulose makes up 40 to 50 percent of the cell wall, and by dry weight wood is roughly 50 percent carbon, 42 percent oxygen, 6 percent hydrogen, 1 percent nitrogen, and 1 percent other elements.
A 2011 discovery in the Canadian province of New Brunswick yielded the earliest known plants to grow wood, approximately 395 to 400 million years ago. Wood can be dated by carbon dating and in some species by dendrochronology to determine when a wooden object was created.
Heartwood, also called duramen, is wood that has undergone a chemical change making it more resistant to decay, and its name comes only from its position rather than any vital importance to the tree. Sapwood, or alburnum, is the younger outer wood that conducts water from the roots to the leaves and stores reserves, and all wood begins as sapwood.
Hardwoods are not necessarily hard and softwoods are not necessarily soft. Balsa, a hardwood, is softer than any commercial softwood, while yew, a softwood, is harder than many hardwoods. The wood from conifers is called softwood and the wood from dicotyledons is called hardwood.
Drying produces a decided increase in the strength of wood, especially in small specimens. A completely dry spruce block 5 centimeters in section will sustain a permanent load four times as great as a green, undried block of the same size. Thoroughly air-dried wood retains 8 to 16 percent of its water in the cell walls.
As of 2020 the growing stock of forests worldwide was about 557 billion cubic meters, and in 2023 almost 4 billion cubic meters of wood were harvested, with dominant uses being furniture and building construction. Global roundwood production rose from 3.5 billion cubic meters in 2000 to 4 billion cubic meters in 2021.
Knots usually reduce tension strength and weaken timber most when forces run perpendicular to the grain or under tension, but far less under compression parallel to the grain. Their effect depends on position, size, number, and condition, and knots near the ends of a beam do not weaken it.