The Birch family (Betulaceae) is comprised of 6 genera worldwide all of which, contain trees or shrubs. Of these 3 genera are represented in the wild in Scandinavia, the Silver birch (Betula pendula) the Downy birch (Betula pubescens) and the Dwarf birch. (Betula nana) The dwarf birch is mainly confined to the Tundra and mountainous regions of Europe, the downy birch can dominate the landscape up to the tree-line, whereas the silver birch is found at lower altitudes.
B. pendula is able to reach 15 to 25 m in height with a slender trunk usually under 40 cm diameter. The trunk’s bark at first is brown, but changes to white as the tree develops. Branches are long and hang down, hence it’s common name ‘The weeping Birch’, leaves are short with slender stalks 3 to 7 cm long, they are triangular with broad wedge-shaped bases and slender pointed tips, the foliage pale to medium green has a paper feel to the touch.
B. pubescens commonly known as ‘The downy Birch’ attains a height of 10 to 20 m with a slender crown and a trunk up to 70 cm with smooth, but dull grey-white bark finely marked with dark horizontal lenticels. The branches unlike B. pendula do not hang down they radiate outwards and slightly upwards. The leaves are ovate-acute, 2 to 5 cm long and 1.5 to 4.5 cm broad, with a finely serrated margin and have a velvet or hairy feeling to the touch.
B. nana is a monoecious shrub growing up to 1 to 1.2 metres tall, the bark is non-peeling and shiny red-copper in colour. The leaves are rounded, 6–20 millimetres in diameter, with a blunt toothed margin and are a darker green on their upper surface. Leaf growth occurs after the snow has melted turning red in autumn. The wind-pollinated fruiting catkins are erect, 5–15 millimetres long and 4–10 millimetres broad.
Used – Research has shown that sap from birch, which contains Xylitol, fructose and glucose, amino acids, vitamin C, potassium, calcium, phosphorous, magnesium, manganese, zinc and high in polyphenol antioxidants that are known to protect body cells against damage from molecules and free radicals. According to research and other such findings, polyphenols safeguard an individual person from several conditions that include type 2 diabetes, Alzheimer’s, heart disease, certain types of cancer and Parkinson’s. The properties of birch sap are considered health-beneficial and has been widely consumed by people of Scandinavia, Russia and North America.
Birch trees provide the predominant hard wood source in northern Europe, and some varieties of the silver birch produce highly priced veneers and decorative wood furniture. The downy birch is used for construction, plywood, wood flooring, furniture, shelves, coffins, pulp and fire wood. The dwarf birch secretes a yellow fungus from the wood and when processed is called Moxa, according to some sources it is regarded as an effective remedy in painful diseases. The yellow dye collected from the leaves is used as a hair conditioner and treatment for dandruff.
Abused – Apart from the many benefits mentioned above, the birch species arguably gets more than its fair share of abuse for example, it is constantly under attack from animals, insects and fungal infection. Scandinavia is riddled with herbivores that constantly feed on birch, for moose it is a smörgåsbord (Swedish for buffet) who can devour large swathes of bark leaving bare wood open to attack from fungi and wood boring insects, whilst smaller creatures deer, will strip the foliage bare especially on young trees.
Consider the bronze birch borer (Agrilus anxius) an insect native to North America found in the southern portions of all Canadian provinces and in the northern United States from Maine to Idaho, Colorado, and Utah; is now found in Russia and Europe. Although it prefers to attack weakened trees it will attack healthy specimens as well with devastating impacts on forest ecosystems.
Adult beetles are small with a flat head and elongated bodies. They range in colour from olive green to black with bronze reflections and are approximately 6.4 to 12.7 mm long with the females being larger than males. The eggs are initially white but turn yellow as they mature, their shape is oval and are 1.5 mm long by 1 mm wide. The larvae are white, legless and have flattened elongated bodies about 12.7 to 15.2 mm long with a small enlargement in the second thoracic segment and two brown spines extending from the last segment of the body. This insect is considered a serious pest to birch species. The adults cause minor damage by feeding on the leaves, but the main damage is caused by the tunnelling larvae interrupting the flow of sap reducing tree growth causing mortality.
Although the bronze birch borer is a major pest there are other insects that cause havoc for example, the Birch leaf miner (Fenusa pusilla) attacks all birch species, Aphids (Aphis gossypii) a very common insect pest that will swarm over and devour the leaves of all species of birch. The Forest Tent Caterpillar (Malacosoma disstria) a major player in foliage destruction. Of course there are other insects considered as pests; white grubs, weevil larvae, and wire worms.
All Birch species are susceptible to fungal attack for example, Birch dieback a disease that causes branches in the crown to die off causing stress that may result the tree’s demise. The pathogenic fungi (Melanconium betulinum), (Anisogramma virgultorum) and (Marssonina betulae) were found in association with affected trees. Birch dieback usually attacks trees that are under stress for example, exposure to phenoxy herbicides used to control broad-leafed weeds, drought and winter kill.
Indications that all is not well are; firstly the foliage becomes scant and turns yellow a sign that chlorosis is present, another indication is leaf tips and new shoots start to curl wither and drop. Secondly small branches or twigs become barren as new leaves fail to develop. As the disease spreads whole branches may die as well as parts of the crown, the lower parts of the tree may develop densely bunched foliage; the tree usually dies within three to five years of the development of symptoms.
Unloved – why is this? – in bonsai the birch tree is not a popular species although it is found in some collections. Is it because of its susceptibility to the many pests and disease that it is prone to, which might affect other tree species in a collection. In short the answer is no, because all plants can be attacked by some form of fungal disease, insect infestation, poor incompatible soil mediums, drought or excessive watering.
There are a number of reasons why it is unloved (a) because of its nature for example, birch are prolific in their release of pollen, which for many sufferers of hay fever and asthma are susceptible, hence people with these afflictions avoid the species altogether. (b) Another possible reason is that unlike many deciduous and coniferous species that can be shaped into various forms like their wild counterparts, birch in their natural setting are mainly formal uprights. Nonetheless, there are exceptions to the rule where in the wild some trees have had their natural shape altered drastically, due to some catastrophe.
However, much depends on you the artist/designer – the old rules are not set in stone, they are but mere guidelines. If you are a traditionalist then hear the words of master bonsai horticulturist John Yoshio Naka who stated “Don’t turn your tree into a bonsai – turn your bonsai into a tree.” Alternatively if you are a free spirit akin to Paul Jackson Pollack the American abstract painter, then you can do what you like. The full article on this topic ‘Different Perspectives’ can be found on this site the date is May 14th 2017.
In the green container shown below are a number of birch saplings, the result of seeds blown in to my bonsai area from the adjacent forest that are now in their 3rd year of growth; a mixture of B. pendula and B. pubescens. Initially the idea was to grow a birch forest, but idea was shelved, because it is highly unlikely to find these two species in close proximity, hence the overall composition would be incorrect. The two larger saplings in the centre were originally intended as a twin trunk design (Sokan) and were shaped but, all the others are in their natural state. These saplings when in leaf will be separated into their individual species and like the Sea buckthorn in the previous article they too will be given away. Until next time, BW, Nik
N.B. As you will have noticed this article is numbered as 50, hence forth all articles will be numbered in numerical order to assist in keeping an uncomplicated filing system diminishing the time searching the archives.