A region of badly drained permanently wet land that is subject to high rainfall and has a persistently moist atmosphere. These conditions result in a *climax
community with no trees. The most common plants are bog mosses (Sphagnum), cotton grasses (Eriophorum), ling (Calluna vulgaris), cross-leaved heath (Erica tetralix), bog myrtle (Myrica gale), rushes (Juncus), and sedges (Carex). Bogs are commonly found in upland and western areas of temperate regions. There are three main types. Blanket bog consists of acid peat formed from the remains of the bog plants. It is variable in thickness and the high acidity (pH 3.0-4.5) is caused by the continuous flow of water through the peat. This washes out any bases and prevents minerals from the underlying rocks reaching the plant roots. Thus the organic acids are not neutralized and the peat is poor in nutrients (oligotrophic). Blanket bog can form over limestone. Raised bogs develop from *fens
. Rain water leaches nutrients from the upper layers of the fen peat making it acid. This favours the growth of bog plants and prevents the growth of trees. As the bog plants become established more peat forms, especially in the central regions, resulting in the centre being raised above the periphery. Valley bogs form in regions, such as the glens of western Scotland, receiving runoff and spring water from surrounding mountains.