Alder and Willow are trees which thrive on wet and /or waterlogged soils. Both species will commonly be found along the banks of streams and rivers and wherever poor drainage results in wet soils. A natural process of succession will also lead to wetlands and marshes eventually becoming wet woodland. Wetlands and marshes naturally gradually dry out through siltation and evaporation. As the ground becomes dry enough to support tree growth, Alder and Willow will gradually grow up and replace existing vegetation, leading to the development of wet woodland. Further drying out of the land leads naturally into a drier woodland type dominated by other broadleaf trees such as Oak. The final dominant tree species will depend largely on soil type.  

The picture on the left is typical of wet woodland. Willow often topples over, so that horizontal trunks dot the woodland. Provided the trunk retains even a small connection to the roots, the stem will regenerate new shoots, which grow up into new trunks. Wet woodlands are potentially extremely diverse areas. Willow will support a staggering number of invertebrates (450 species). A great variety of birds are therefore attracted to wet woodland because of the invertebrate bounty on offer. The woodland floor abounds in plants which favor wet soils, such as sedges and rushes. A great variety of mosses and ferns also thrive in the humid atmosphere of the woodland.

In times past, wet woodland would have been common in Britain, particularly on the sides and in the bottom of poorly drained river valleys. Extensive drainage for development of poor, marshy land has meant that wet woodland has become something of a rarity and is one of the habitats selected for conservation action in the Devon Biodiversity Action Plan.

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