Alder (common)
20th February 2012
A sure sign that spring is on its way the emergence of catkins on Alder indicates the awakening of woodlands after winter. A native broadleaved deciduous tree standing at 15 – 25m it is primarily found in wet environments in particular along the banks of streams and rivers. Garnering its Latin name glutinosa from its twigs which may be sticky to the touch. Its flowers are both male and female: males in the form of yellow-brown catkins with females distinctly different in appearance as 6mm red cones.
Alder has a symbiotic relationship with a nitrogen fixing bacterium which forms nodules on its roots from where these make nitrogen from the air available to the tree, receiving in return carbon produced by the tree during photosynthesis. As a pioneer species it is often one of the initial species to colonise a new site and this improvement in soil fertility may aid successive species on the site. As with many pioneer species it is relatively short lived reaching on average 150 years.
Latin name: Alnus glutinosa
Population Numbers: A common UK species occurring across the majority of Europe it is difficult to determine exact numbers.
Where to see and when: From February to early April the Alder is a distinctive sight with yellow-brown catkins contrasting with the red cones of the female flower. At Clouts Wood, a site covered by woodland since the end of the last ice age, the variety of chalk and clay streams and springs dispersed throughout the site make it an ideal habitat for the Alder. Protected from use as agricultural land due to the steep valley sides Clouts Wood is home to a wide variety of wildflowers, fungi, birds and mammals.
What’s being done: While a common species throughout the UK as a native species the Alder plays an important role in woodland and riparian ecosystems. Its preferred habitat of river and stream banks and its deep roots means it plays an important role in supporting river banks, reducing the effects of erosion. Where these roots enter the water they provide shelter for a variety of invertebrates and fish species while its leaves are a food source for the larvae of a number of riverfly species including caddisfly and stonefly larvae.
As a result, whilst the species itself is not of conservation concern it can play an important role in ecosystems vital to many conservation projects. Therefore the correct management of the species and the sites on which is occurs is important. At Clouts Wood, coppicing, which has been recorded on the site since the 1600s, is on-going and is carried out in winter to allow sunlight to reach the woodland floor, thus encouraging the emergence of wildflowers through the spring and summer which are important food sources and breeding sites for a range of invertebrates. Additionally a considerable amount of work is being carried out to remove non-native invasive species and recently over 150 new alder have been planted within a wet part of the reserve to recreate the historic range of the woodland.
