Hornbeam (Carpinus betulus)

Carpinus betulus, the European Hornbeam, pictured here, is native to Europe and Turkey, more specifically central and southern Europe extending to northern Iran. There are about 30 to 40 species of Carpinus worldwide; Carpinus cardiniana is the American Hornbeam (Blue Beech). The European Hornbeam prefers deep, moist but well-drained soils as long as they are not too acidic. It is tolerant of shade and sunlight. Ecologically it serves as a primary coloniser and also a secondary or understorey tress, for example in mixed oak-hornbeam and mixed ash/beech/hornbeam communities.

Carpinus belongs to the family Betulaceae (the Birch family).

The roots are shallow, even more so than in Beech (Fagus sylvatica). Hornbeam is sometimes confused with Beech, especially larger specimens of Hornbeam.

The wood of Hornbeam is one of the densest and hardest woods and thus it has been used for arrows, spears, yokes for oxen, mill cogs, mallet heads, tool handles and butcher's blocks. It also makes excellent firewood, said not to crackle even when green and to 'burn like a candle', and excellent charcoal. Charcoal from Hornbeam also makes excellent gunpowder.  The wood is white, close-grained, dense, very hard. However, it's uses are limited as although strong it is rigid, lacking flexibility and shrinks considerably on drying and cross-grains make it hard to work. The wood is diffuse-porous (rings can be discerned under a microscope).

The bark is smooth and grey when young but develops longitudinal / vertical furrows in older trees.

The stem of both pollarded and maiden hornbeams is more irregularly shaped than beech and is usually ribbed, fluted and twisted.

The twigs of Hornbeam are brown, often zig-zag and slightly hairy. The angled buds are pale brown to orange. Hornbeams are monoecious, meaning that individual trees are bear both male and female flowers, though some individuals may be predominantly male or female. Male catkins are borne laterally in the axils of leaves of the previous years twigs and reach 3 to 5 cm in length, maturing before the leaves open. There is one male flower per bract (catkin scale) and each lacks sepals and petals and possesses stamens attached to the base of the bract. The anthers are pale yellow and each is bearded at the apex. Hornbeam is wind pollinated.

Female catkins are fewer in number and borne on the end of twigs and reach 2 to 2.5 cm in length as the leaves develop (reaching maximum length some days after the male catkins which open in April). Both male and female catkins are pendant (hanging down). Each female flower has a minute toothed perianth, 3 to 8 of which persist at the apex of the olive-green nut, and a two-celled ovary with two styles and one ovule per cell. A bracteole (secondary bract) subtends each female flower and a bract subtends each pair of female flowers. After the male catkins fall the female catkins develop fruit before the end of May. Each fruit (a nut) is accompanied by a three-lobed winged cupule (bract) and borne in clusters of pairs on short pedicels (3 to 4 cm long) arranged in a spiral and are dispersed by wind. The central lobe of the cupule is 2 to 3 times longer than the two lateral lobes.

Seeds germinate the next Spring, regardless of whether they are sown in Autumn or Spring.

The leaves are typically about 7 cm long and 4 cm wide and deeply ribbed or plicated (folded like a fan) and hairy on the underside. The margins are doubly serrated. They turn brown in Autumn but may remain in winter, especially on trees that have been clipped (e.g. coppiced or pollarded). Different varieties are recognised based in large part on leaf size, for example var. parviflora has leaves only 3 to 5 cm long and occurs in Oxfordshire.

Hornbeams are often said to reproduce vegetatively by suckers, however these are rarely (if ever?) true roots (adventitious shoots from roots) but are rather the result of natural self-layering of lower branches especially in coppiced trees (branches arching downwards to contact the soil at which point they root). The trunk of hornbeams usually branches much lower down than in Beech, however most hornbeams in the British Isles are either coppiced or pollarded and so their natural growth form is seldom seen. Miller Christy (1924) reports that unpollarded hornbeams in woods reach 15 to 20 feet (about 3 to 4 m) before branching and that the finest maiden trees (in Britain) were at that time found in Cobham hall near Rochester, Kent. These maidens reached up to 90' (30 m) tall and were as much as 90 years of age.

The base of the Hornbeam is strongly buttressed by the roots, especially in old pollards.

There has been much debate as to whether the Hornbeam is native to the British isles, as it is often planted. However, Christy (1924) provided a convincing argument for its native status in southwest Britain, with possibly also a native outpost around the Severn basin. Although it thrives well further North, and is cold-hardy, it appears that it's fruit are frost-sensitive.

The Hornbeam prefers light sandy or gravelly soils in Essex and heavy clay soils near the Thames. Pollards in particular sometimes suffer Witches Broom's galls caused by the ascomycete fungus Taphrina carpini (Exoascus carpini).

Young hornbeams are pyramidal in shape, but when mature the canopy is more globular with no definite leader (main) shoot. Hornbeams are faster growing but shorter-lived than beech trees (Fagus sylvatica) and reaches maturity in under 100 years and has a lifespan as high as 150 years (cf. 200 years in Beech).

References

Christy, M. 1924. The Hornbeam (Carpinus betulus L.) in Britain. J. Ecol. 12(1): 39-94.

Price, D. and Bersweden, L. 2013. Winter trees: a photographic guide to common trees and shrubs. FSC AIDGAP.

A useful diagram of carpinus betulus (I would have added the picture here but I don't understand all that faff about USA Public Domain Tags!).

Article updated: 10 April 2020