Two oak species are native to Britain, the English oak and durmast oak. Their range extends from Scandinavia in the north to Iberia and northern Greece in the south, and eastward to the region of the Black Sea. The English oak extends further into drier regions owing to its preference for moisture-retentive soils. The heartwood of both oaks is very durable, while the sapwood is liable to attack by borers. The timber is excellent for many purposes, the bark was once used for tanning, the acorns were valuable for pannage and small-diameter wood can be used to make cleft fencing.