Peat is a largely organic material of plant origin which forms in water basins of various types and sizes, or in very damp environments due to the incomplete transformation of the residual dead plants in anaerobic conditions caused by water saturation. The natural environments where peat normally occurs are known as "bogs". Bogs form mainly in cold wet regions of the Earth (northern Europe, Siberia, Alaska, Canada, etc.) and in particular "niches" in the equatorial belt. In Italy, bogs are relatively rare (about 100,000 hectares of land) and found mainly in closed Alpine valleys where the meteoric water is unable to flow away rapidly or near natural basins, river deltas and low-lying coastal plains. Bog flora and vegetation are highly characteristic and differentiated in relation to the soil and weather conditions where the bog has formed. One classification of bogs divides these particular ecosystems into two main categories: lowland bogs and upland bogs. Upland bogs form in the coldest rainiest regions of Europe, North America and certain areas of the Alps. They are characterised by a high percentage of sphagnum moss, accompanied largely by algae, bryophytes, pteridophytes (Lycopodium, Equisetum and ferns) and small conifers (mugo pine). Lowland bogs usually form in temperate-cold areas with medium to low rainfall (or in the tropics) in lowland marshes, river valleys or near lakes and water-meadows. The typical vegetation of lowland bogs is dominated by hygrophilous monocotyledons (particularly sedges, rushes and reeds) with the more or less sporadic presence of other hygrophilous acid-loving plants including ferns (Osmunda regalis, Thelypteris palustris, etc.) and angiosperms (Hydrocotyle vulgaris). Conifers are not usually present. The peat that forms in lowland bogs is finer than sphagnum peat, more mineralised, slightly acid (sometimes sub-alkaline) and rich in calcium, potassium and sodium salts ("brown" peat).
From the Great Oak you head northwards. After crossing a ditch marking the entrance, you then cross a quite dry zone of peaty terrain colonised principally by the common reed (Phragmites australis) and great fen sedge (Cladium mariscus). This cenosis represents an intermediate stage in evolution of the marsh. In terrain where the water table is near the surface or where flooding is frequent, the marshes evolve slowly and naturally.
Accumulation and annual renewal of vegetation on the ground forms ever denser peaty soils like the one you cross where over time various bushes such as alder buckthorn and willow grow. Lastly, trees put down root and configure a new biotope, the lowland wood.