Raised bog

In raised bogs, the water table level is elevated  by a few centimeters to metres above that of mineral rich ground water of surrounding areas and consequently there is an ombrotrophic (rain-fed) nutrient regime. The peat layer is often several metres thick and mainly composed of Sphagnum remains, highly water saturated with the water table close to the surface. High acidity (pH < 4.5) and low mineral content characterize the peat and pore water. Typically there is a pattern of alternation between micro  habitats (hummocks, lawns, carpets, hollows) that relate to topography, hydrology and peat formation. Hummock-hollow patterning can be irregular in flat plateau bogs, where hummocks remain low. In concentric and eccentric raised bog complexes, hummock-hollow patterning shows a distinct orientation perpendicular to the slope and water flow. Open water pools of secondary origin, i.e. developed on the peat after hummock ridge formation, are often found and provide important aquatic microhabitats. Raised bog habitats are most typical in central parts of raised bog complexes (EUNIS habitat X04) but they are also found in mixed complexes with D3.2 Aapa mires. Mire complex patterns may also be completely missing and often raised bog habitats are found as small undrained remnants of historically degraded bog complexes. Raised bogs differ from D1.2 Blanket bogs by being restricted to basins rather than blanketing over variable terrain. The lagg zones of raised bog complexes are considered under D2.2a Poor Fens.

Trees (Pinus sylvestris, Betula pubescens) are found only sparsely on hummocks and Sphagnum mosses dominate the ground layer of vegetation. In hummocks, Sphagnum fuscum is the most characteristic species, especially in boreal and continental areas. Other typical hummock species are S. rubellum, S. magellanicum, S. capillifolium, S. angustifolium, Dicranum bergeri  and Polytrichum strictum. Dwarf-shrub species Andromeda polifolia, Betula nana, Calluna vulgaris, Empetrum nigrum, Erica tetralix, Ledum palustre, Vaccinium microcarpon, V. oxycoccos, V. uliginosum are characteristic on hummocks, while only few herbs (Drosera rotundifolia, Rubus chamaemorus) and sedges (Carex pauciflora, Eriophorum vaginatum) are found. The wet hollows may have continuous carpets of Sphagnum or sometimes muddy peat surfaces void of mosses or with some cover of hepatics or Warnstorfia fluitans. Typical species include Sphagnum cuspidatum, S. balticum, S. jensenii, S. majus, S. tenellum among mosses and Carex limosa, Scheuchzeria palustris, Rhynchospora alba among vascular plants. Also forest mosses like Pleurozium schreberi, Hylocomium splendens, Dicranum polysetum and lichens like Cladonia spp. and Certraria islandica are found on hummocks.

Raised bogs are widely distributed from central European mountain areas to north-boreal regions, being most prominent in the hemi-boreal to south-boreal zones. The pattern of dominance and features of micro-habitat patterning vary over different climatic zonation belts.

Indicators of good quality:

• Under natural conditions, the water table is close to surface in hollows and it can be readily observed in small pit dug in peat surface except during prolonged drought.
• There is a gradual and logical continuum between dominant vegetation and the composition of recently (decades to centennial) formed peat, indicating that modern vegetation is forming typical Sphagnum peat.
• Species composition differs between hummocks and hollows in a regionally characteristic way and there are no large patches of lichens or hummock mosses such as Polytrichum strictum in the hollows.
• Ombrotrophic and acidophilic Sphagnum mosses and other characteristic species comprise substantial elements in vegetation.
• Number of species or diversity indices of vegetation are not good indicators since raised bogs are naturally species poor habitats, while harboring unique species assemblages.
• Occurrence of trees is limited to scattered individuals on hummocks. Drainage ditches are one main factor to cause decline of quality of raised bogs but their occurrence alone does not always indicate poor quality.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats