Wood as a material

According to the relative size and distribution of pores, woods of broad-leaved species are further classified into ring-porous and diffuse-porous types. In ring-porous woods, such as oak and chestnut, the pores of earlywood are large compared with those of latewood. In diffuse-porous woods, such as basswood and poplar, all pores are about the same size and evenly distributed.

In many tree species the central part of the transverse section of trunk is darker in colour than the peripheral wood. This inner part is called heartwood, and the surrounding zone sapwood. Sapwood comprises the newer growth rings and participates in the life processes of a tree. As the diameter of the tree increases with growth, the older, inner layers no longer take part in the transport and storage of water and nutrients and become heartwood. After a certain age, heartwood exists in all species, even though there may be no colour change.