Occasionally the trunks and roots of trees such as Scots pine, oak, birch and yew are also present in the peat. The similarities and differences between these two types are summarised in the five points below. Fens are alkaline with a pH of 7 to 8. Bogs are acid with a pH of 3.2 to 4.2. Fens and bogs are waterlogged habitats.
Fens are minerotrophic which means that their water supply is from the mineral-rich ground water.
Bogs are ombrotrophic which means that their water supply is from the mineral-poor rainwater. The average peat depth in a fen is up to 2m. Peat depth in a bog varies from 2 to 12m. Raised bogs occur in the midlands of Ireland and in the Bann River Valley where rainfall is between 800 and 900mm per year. Blanket bogs are found along the west coast of Ireland and in mountainous areas around the country where rainfall is 1,200mm per year or more.