The Elan Estate and the surrounding area was covered in oak, birch and hazel woods until man's clearances for agriculture started about 4,000 years ago. On the Elan Estate there are now 350 hectares of coniferous woodland and 100 Hectares of broadleaved woods. Most of the woods are owned and managed by Dwr Cymru Welsh Water, first and foremost for their wildlife. The remaining broadleaved woods are all in Sites of Special Scientific Interest and known as "semi-natural ancient woodlands". The dominant species is sessile oak. It differs from pedunculate oak in having short stems on the acorns and long stems on the leaves; in pedunculate oak this is reversed.

Conifers have been planted over the last 200 years. The species are larch, norway and sitka spruce, douglas fir and scots pine.

Native broadleaved trees include sessile oak, downy birch, hazel, ash, goat willow, rowan, hawthorn, blackthorn and alder, whilst some beech, sycamore and chestnut have been introduced.

The most important wildlife of the ancient woodlands are the mosses, lichens, ferns and fungi. They often grow all over the trees because of the damp climate and the comparative lack of air pollution.