Kingley Vale has one of Europe's most impressive forests. The forest contains yews as much as 2,000 years old, which are some of the oldest living organisms in Great Britain . Their survival is remarkable because most ancient yew trees across Europe were felled after the 14th century, being the preferred material for the staves of English longbows. In 1472, with the increasing popularity of the longbow, the English government enacted a "yew tax" of four "bowestaffs" for every cask of wine unloaded at an English harbour. This sparked a rush for ancient yew trees across Europe, decimating the forests. Kingley Vale is one of the few major stands remaining; most yews elsewhere are solitary trees or small stands.

Other tree species in Kingley Vale include oak, ash, holly and hawthorn. The chalk grassland is home to many flowers and herbs that form a diverse mosaic of species. Over 50 species of birds are found, although only six species breed in the yew woodland. Mammals include deer, yellow-necked mouse, water shrew and dormouse. The 39 species of butterfly at Kingley Vale are mainly found in the grassland.