Bogbean and sweet gale are often pioneers on sphagnum mats. Leatherleaf and other species such as bog Labrador tea follow. The limit to bog formation is reached where vegetative evapotranspiration rates are higher than the bog water-holding capacity. Lake-fill bogs have vegetation zones corresponding to successional stages. Tree growth is most dense around the outer edges.
Shrubs form a ring along the interior edge of the trees.
In the center sphagnum and other mosses and sedges form dense mats. There may be areas of open water. Paludification is the creation of a peatland by the drowning or submergence of upland habitats. With a rise in the water table, roots of upland plants are suffocated and peat begins to accumulate. Trees initially colonize open bogs by seed, but tree cover increases in conifer bogs largely due to layering.