Alnus cordata - Italian Alder

Corsican alder is a medium-sized, deciduous tree with very aesthetic heart-shaped dark green, leathery and shiny leaves that remain on the tree for a long time before falling in winter. Native to Corsica and southern Italy, it is found in moist woods at high altitudes and along watercourses, in sunny locations with moist, clayey, and acidic soil, where it thrives alongside chestnut trees. The luxuriance of its dense canopy and its good hardiness mean, it is often planted as a shade tree in squares and as an avenue tree in central and western European cities. This is a fast-growing tree that tolerates poor soils and resists drought better than other alders!

Alnus cordata is a deciduous tree of the Betulaceae family. It is native to the moist woods of Corsica and southern Italy, where it is found up to 1000 metres (3280 feet 10 inches) above sea level, often along watercourses. It has an elegantly slender, slim and conical silhouette. Its bark is initially brown-grey and smooth, then becomes blackish and fissured as it ages. Its 4 - 10 cm (1.6 - 3.9 in) bright green leaves are heart-shaped at the base and pointed at the tip. They persist on the branches for a long time and change little in colour before falling in winter. They are leathery and shiny and the main ornamental feature of this tree. Their undersides are lighter and have brown hairs at the vein intersections. The flowers appear later in this species. From March, pendant, quite bright yellow-brown male catkins, appear. The female flowers resemble dark brown cones, 2-3 cm (0.8-1.2 in) long. Corsican alder grows rapidly to 15 metres (49 feet 2 inches) in 20 years. At maturity, it reaches a maximum height of 25 metres (82 feet) and a width of 6 metres (19 feet 8 inches). The fruits are woody ovoid cones, called strobili, which remain on the tree for one year. They release narrow, winged nuts that are dispersed by the wind and provide an important food source for birds.

Corsican alder needs less water than common or white alder. Its tolerance to limestone is excellent and its hardiness is quite good, down to -20°C (-4 °F). Thanks to its very dense foliage cover, it is suitable for planting to create a shaded area in a large garden. It is particularly lovely planted in groups on slopes or embankments to retain soil, as a windbreak or in a countryside hedge. Combine it with other large tree and shrub species as its dense canopy does not allow for underplanting. Create functional and woldlife-friendly hedges by planting it with fruit-bearing species such as elderberry and rowan.

Alnus cordata is widely used for stabilising limestone soils and revegetating poor and unstable soils, especially in challenging sites such as urban wastelands, slag heaps, and abandoned mines where its extensive, branched root system effectively retains the soil. Like other alder species, it forms nodules containing nitrogen-fixing bacteria, thus restoring this richness to the soil. Its wood is lightweight and rot-resistant. It is easy to grow, but there has been a deadly disease present since the 1980s that causes the decline of alders, transmitted through root penetration, especially when planted near slow-flowing, warm, and poorly shaded watercourses. All affected trees should be pruned to ground level. As a preventive measure, monoculture plantations along watercourses should be avoided. Alnus is loved by wildlife, so protect the collar and trunk from potential nibbling!