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Life in Freshwater

Common Alder (Alnus glutinosa)

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Alder tree at the edge of a lake


IDENTIFICATION: the tree is quick to grow and may reach as high as 20 metres although half that size is most likely immediately around water. This is a native species to the UK and lines all types of waterway, from lakes to canals and rivers. Leaves are very distinctive and called obovate. At the base they are narrow but quickly broadening to a wide end.

ECOLOGY: Alder is very important for several reasons. 1. The extensive, shallow root systems give good stability to the bank. Around the edge of lakes the roots maybe exposed by the waves but the roots again protect the edge of the land reducing erosion. 2. The roots have large numbers of root nodules. These contain nitrifying bacteria which improve the quality of the ecosystem. In addition they are also good emergent platforms for insects around lakes as well as places for protecting vertebrates.

Alder Catkins
 Close up of the dark previous year's fruit and the fresh male catkins liberating pollen; female part dark red

 


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