Bog from the Irish ‘bogach’, or ‘soft ground, wetland’ comes in two forms: raised bog and blanket bog (of which there are two further types--Atlantic blanket bog and mountain blanket bog), all of which are found in Mayo.
There are two main types of bogs: raised bogs and blanket bogs. The former, typically found in the midlands are also found in East Mayo and can be 4-8 metres deep and sometimes deeper, having formed in lake basins as the ice retreated in the last Ice Age of 10,000 years ago.
Blanket bog is well named as it forms a blanket, spreading itself across the landscape and is shallower than raised bog, running 2-5 metres deep. This bog is found only in the west of Ireland and in the mountains of the east, places with annual rainfall of more than 1200mm.
Blanket bogs are ‘younger’ than raised bogs, originating around the same time as Neolithic farming in Ireland, around 6000 years ago. Around 4000 BC, a combination of increased rainfall and tree-felling (for farming) caused them to greatly expand. This effect can be clearly seen at Céide Fields in north Mayo, where Neolithic field boundaries, dwellings and a megalithic tomb were all completely covered by encroaching blanket bog.
All bogs are mainly made up of sphagnum moss (living and partially decomposed) and water. This moss can be considered an ‘engineer species’, in that it actively creates its own preferred environment. Sphagnum acts as an incredible ‘sponge’, capable of holding 20-30 times its dry weight in water, thus raising the water table and keeping the bog water-logged. It also releases negative ions, thereby acidifying the bog. The wet, acidic environment created is ideal for sphagnum moss.
Interestingly, sphagnum was once used as a (quite effective) wound dressing, as, in addition to being highly absorbent, it also contains a natural antiseptic.
Ballycroy National Park, in northwest Mayo is where you can see up close a large swathe of Atlantic blanket bog and mountainous habitat. The Owenduff bog (one of the last active blanket bog systems in Western Europe) extends into the park, and is home to a number of protected plant and animal species.
Because bogs are acidic, oxygen- and nutrient-poor habitats, only certain plants can grow in them successfully. For example, the stem of bog cotton acts as a ‘snorkel’, bringing oxygen down to water-logged roots. As an adaptation to the low nutrients, some bog plants are even carnivorous. Sundews, bladder-worts, and butter-worts use a variety of means to attract, trap, and consume insects. (Very sci-fi!)
Although bogs are quite nutrient-poor, a wide variety of animals can be found within them. Hares, which prefer an open habitat, are a common resident. Several rare (and protected) birds, such as hen harriers, merlins, peregrine falcons, and golden plover nest in bogs. Additionally, many invertebrates, including dragonflies, damselflies, beetles, and spiders live in the bog environment.
Bog snorkelling, a uniquely Irish sport has gained popularity in recent years. It consists of a timed swim without the use of arms or hands, of 120m length, along a bog-drain, using a snorkel and flippers. There are even championship bog snorkellers.