Fens occur extensively in boreal-subarctic and cool temperate regions. Like peat bogs, with which they may form mosaics, they have waterlogged organic soils, but they are rich in mineral nutrients and typically neutral or alkaline in pH. The vegetation comprises a low diversity of small plants, fungi and brown mosses, but woody plants are generally absent. They support insects, specialised frogs and some birds. Shallow standing water or permafrost may be present.