As a wet meadow matures it begins to fill in with vegetation and as this decomposes the soil thickens creating high spots (
hummocks) above the water. Shrubs and small trees begin to grow on these. Shrub swamp water comes from run-off, streams and rivers and the water moves in and out of the swamp throughout the year. Consequently, they tend to be drier than wet meadows or forested swamps and permit water intolerant plant species to grow on the hummocks. Shrub swamps typically occur on organic soils, such as
muck and shallow
peat soils. Common plants found in the shrub swamps of
North America include
alders,
willows,
elderberry and
highbush blueberry. ==Types==