Grey Alder

Tree full of catkins

In early spring, sometimes as early as February, the white alder becomes laden with catkins - male inflorescences full of pollen - this is what makes the white alder so attractive. The female inflorescences remain unremarkable. In the summer three generations of female fruit hang in the tree: small green fruits, larger green alder fruits and the brown, woody, cone-like alder fruits. If the brown alder fruits have opened, the seed has been shed.

The upper surface of leaves are dull green, the lower surface is a greyish colour due to the covering of short hairs that become more concentrated at the tip. If the leaf tip is rounded, there is a high probability that the tree is bearing characteristics of the closely related black alder. Wind pollination allows for 'free movement’ of pollen and so hybrids between black and white alder are therefore common.

Incana means dull or grey - this refers both to the underside of the leaf and also to the bark, which is remarkably smooth and light (silver) in colour. The trunk is straight with the branches usually growing obliquely upwards. The overwintering buds are not sticky. The natural range of white alder lies well above the Arctic Circle and includes Central Europe, Russia, the Caucasus and northern Iran; it is not native to the Netherlands. This species naturally prefers cool to cold climates and relatively dry ground, and can reach altitudes of about 200 m higher than the black alder. Although it is a highly adaptable species it cannot tolerate sea wind. It is a pioneer tree through its capacity to improve the underlying soil. It is not very long-lived and usually grows to between 100 to 125 years.

Alders have rapidly decomposing leaves and within their roots there are special nodules that contain a bacterium that fixes nitrogen. The fixed nitrogen is subsequently used by both the white- and the black alder hosts.