ALNUS GLUTINOSA, the COMMON ALDER, BLACK ALDER, EUROPEAN ALDER or just ALDER, is a species of tree in the family Betulaceae , native to most of Europe, southwest Asia and northern Africa. It thrives in wet locations where its association with the bacterium Frankia alni enables it to grow in poor quality soils. It is a medium size, short-lived tree growing to a height of up to 30 metres (100 ft). It has short-stalked rounded leaves and separate male and female flower in the form of catkins. The small, rounded fruits are cone-like and the seeds are dispersed by wind and water.
The common alder provides food and shelter to wildlife, with a number of insects, lichens and fungi being completely dependent on the tree. It is a pioneer species, colonising vacant land and forming mixed forests as other trees appear in its wake. Eventually common alder dies out of woodlands because the seedlings need more light than is available on the forest floor. Its more usual habitat is forest edges, swamps and riverside corridors. The timber has been used in underwater foundations and for manufacture into paper and fibreboard, for smoking foods, for joinery, turnery and carving. Products of the tree have been used in ethnobotany , providing folk remedies for various ailments, and research has shown that extracts of the seeds are active against pathogenic bacteria.
* 1 Description * 2 Taxonomy * 3 Distribution and habitat * 4 Ecological relationships
* 5 Cultivation and uses
* 5.1 Timber * 5.2 Tanning and dyeing * 5.3 Other uses
* 6 Health
* 7 Details of
Foliage Male inflorescence (left) and mature cones (right)
The leaves of the common alder are short-stalked, rounded, up to 10 cm (4 in) long with a slightly wedge-shaped base and a wavy, serrated margin. They have a glossy dark green upper surface and paler green underside with rusty-brown hairs in the angles of the veins. As with some other trees growing near water, the common alder keeps its leaves longer than do trees in drier situations, and the leaves remain green late into the autumn. As the Latin name glutinosa implies, the buds and young leaves are sticky with a resinous gum.
The species is monoecious and the flowers are wind-pollinated; the slender cylindrical male catkins are pendulous, reddish in colour and 5 to 10 cm (2 to 4 in) long; the female flowers are upright, broad and green, with short stalks. During the autumn they become dark brown to black in colour, hard, somewhat woody, and superficially similar to small conifer cones. They last through the winter and the small winged seeds are mostly scattered the following spring. The seeds are flattened reddish-brown nuts edged with webbing filled with pockets of air. This enables them to float for about a month which allows the seed to disperse widely.
Unlike some other species of tree, common alders do not produce shade leaves. The respiration rate of shaded foliage is the same as well-lit leaves but the rate of assimilation is lower. This means that as a tree in woodland grows taller, the lower branches die and soon decay, leaving a small crown and unbranched trunk.
Within the genus Alnus, the common alder is placed in subgenus Alnus as part of a closely related group of species including the grey alder, Alnus incana , with which it hybridizes to form the hybrid A. × hybrida.
DISTRIBUTION AND HABITAT
The common alder is native to almost the whole of continental Europe
(except for both the extreme north and south) as well as the United
The common alder is most noted for its symbiotic relationship with the bacterium Frankia alni , which forms nodules on the tree's roots . This bacterium absorbs nitrogen from the air and fixes it in a form available to the tree. In return, the bacterium receives carbon products produced by the tree through photosynthesis . This relationship, which improves the fertility of the soil, has established the common alder as an important pioneer species in ecological succession .
The common alder is susceptible to Phytophthora alni , a recently evolved species of oomycete plant pathogen probably of hybrid origin. This is the causal agent of phytophthora disease of alder which is causing extensive mortality of the trees in some parts of Europe. The symptoms of this infection include the death of roots and of patches of bark, dark spots near the base of the trunk, yellowing of leaves and in subsequent years, the death of branches and sometimes the whole tree. Taphrina alni is a fungal plant pathogen that causes alder tongue gall, a chemically induced distortion of female catkins. The gall develops on the maturing fruits and produces spores which are carried by the wind to other trees. This gall is believed to be harmless to the tree. Another, also harmless, gall is caused by a midge, Eriophyes inangulis , which sucks sap from the leaves forming pustules .
The common alder is important to wildlife all year round and the seeds are a useful winter food for birds. Deer, sheep, hares and rabbits feed on the tree and it provides shelter for livestock in winter. It shades the water of rivers and streams, moderating the water temperature, and this benefits fish which also find safety among its exposed roots in times of flood. The common alder is the foodplant of the larvae of a number of different butterflies and moths and is associated with over 140 species of plant-eating insect. The tree is also a host to a variety of mosses and lichens which particularly flourish in the humid moist environment of streamside trees. Some common lichens found growing on the trunk and branches include tree lungwort ( Lobaria pulmonaria ), Menneguzzia terebrata and Stenocybe pullatula, the last of which is restricted to alders. Some 47 species of mycorrhizal fungi have been found growing in symbiosis with the common alder, both partners benefiting from an exchange of nutrients. As well as several species of Naucoria , these symbionts include Russula alnetorum , the milkcaps Lactarius obscuratus and Lactarius cyathula , and the alder roll-rim Paxillus filamentosus , all of which grow nowhere else except in association with alders. In spring, the catkin cup Ciboria amentacea grows on fallen alder catkins.
As an introduced species, the common alder can affect the ecology of its new locality. It is a fast-growing tree and can quickly form dense woods where little light reaches the ground, and this may inhibit the growth of native plants. The presence of the nitrogen-fixing bacteria and the annual accumulation of leaf litter from the trees also alters the nutrient status of the soil. It also increases the availability of phosphorus in the ground, and the tree's dense network of roots can cause increased sedimentation in pools and waterways. It spreads easily by wind-borne seed, may be dispersed to a certain extent by birds and the woody fruits can float away from the parent tree. When the tree is felled, regrowth occurs from the stump, and logs and fallen branches can take root. A. glutinosa is classed as an environmental weed in New Zealand.
CULTIVATION AND USES
Infrutescence and Achenes
The common alder is used as a pioneer species and to stabilise river
banks, to assist in flood control, to purify water in waterlogged
soils and to moderate the temperature and nutrient status of water
bodies. It can be grown by itself or in mixed species plantations, and
the nitrogen-rich leaves falling to the ground enrich the soil and
increase the production of such trees as walnut ,
On marshy ground it is important as coppice-wood , being cut near the
base to encourage the production of straight poles. It is capable of
enduring clipping as well as marine climatic conditions and may be
cultivated as a fast-growing windbreak . In woodland natural
regeneration is not possible as the seeds need sufficient nutrients,
water and light to germinate. Such conditions are rarely found at the
forest floor and as the forest matures, the alder trees in it die out.
The species is cultivated as a specimen tree in parks and gardens,
and the cultivar 'Imperialis' has gained the Royal Horticultural
Award of Garden Merit
The wood is soft, white when first cut, turning to pale red; the
knots are attractively mottled. The timber is not used where strength
is required in the construction industry, but is used for
paper-making, the manufacture of fibreboard and the production of
energy. Under water the wood is very durable and is used for deep
foundations of buildings. The piles beneath the
TANNING AND DYEING
The bark of the common alder has long been used in tanning and
dyeing. The bark and twigs contain 16 to 20% tannic acid but their
usefulness in tanning is limited by the strong accompanying colour
they produce. Depending on the mordant and the methods used, various
shades of brown, fawn, and yellowish-orange hues can be imparted to
wool, cotton and silk.
It is also the traditional wood that is burnt to produce smoked fish and other smoked foods, though in some areas other woods are now more often used. It supplies high quality charcoal .
The leaves of this tree are sticky and if they are spread on the floor of a room, their adhesive surface is said to trap fleas.
Chemical constituents of
Pollen from the common alder, along with that from birch and hazel , is one of the main sources of tree pollen allergy. As the pollen is often present in the atmosphere at the same time as that of birch, hazel, hornbeam and oak, and they have similar physicochemical properties, it is difficult to separate out their individual effects. In central Europe, these tree pollens are the second most common cause of allergic conditions after grass pollen.
The bark of common alder has traditionally been used as an astringent
, a cathartic , a hemostatic , a febrifuge , a tonic and a restorative
(a substance able to restore normal health). A decoction of the bark
has been used to treat swelling, inflammation and rheumatism, as an
emetic , and to treat pharyngitis and sore throat . Ground up bark
has been used as an ingredient in toothpaste, and the inner bark can
be boiled in vinegar to provide a skin wash for treating dermatitis,
lice and scabies. The leaves have been used to reduce breast
discomfort in nursing mothers and folk remedies advocate the use of
the leaves against various forms of cancer. Alpine farmers are said
to use the leaves to alleviate rheumatism by placing a heated bag full
of leaves on the affected areas.
In a research study, extracts from the seeds of the common alder have
been found to be active against all the eight pathogenic bacteria
against which they were tested, which included
DETAILS OF ALDER STRUCTURE AND GALLS
Trees in winter, Germany *
Black alder in Ås , Norway *
Black alder defies harsh conditions in the Swedish archipelago
* Trees portal
* ^ Participants of the FFI; IUCN SSC Central Asian regional tree
Red Listing workshop, Bishkek, Kyrgyzstan (11–13 July 2006) (2007).
IUCN Red List