What is Blanket Bog?
Blanket bog on Hangley Cleave, Exmoor – Photo D. Smith
Why does peat accumulate? Prevailing environmental conditions lead to a build up of un-decomposed vegetation which accumulates over time. In the moorlands of Exmoor peat develops due to the following factors:
- Western climatic conditions and elevation on Exmoor means high rainfall, a cool climate and high levels of humidity. All of which contributes to a slow rate of organic decomposition.
- Topography Natural hollows in the landscape fill with water, plant material and eventually fen peat develops. If left alone for long enough raised bogs begin to grow on top of the fen peat.
- Springs and flushes also provide the saturated conditions required for reduced decomposition, peat build-up and mire formation.
Sphagnum hummock in a bog pool on Blanket Mire – photo J. Sabel
Blanket bog vegetation typically overlies deep peat and receives all its nutrients through rainfall. In addition to bog mosses, other widespread plants of blanket bogs are heather, cross-leaved heath, deer grass and cotton grass. For blanket bog to form, water levels need to be near the surface. Where the ground is not so waterlogged, other habitats occur.
Sphagnum Subnitens - Photo J. Sabel
Wet heath vegetation is found on thinner, better drained peat or where management has caused the peat to dry out. This community has many of the same plants as blanket bog, but the bog mosses are less dominant, cotton grass is absent and heather is more widespread. Dry heath and acid grassland are found on drier ground with mineral soils or occasionally very shallow peat.
Typical wet heath plants including Heath Milkwort – photo T. Smith