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Betula

Betula pubescens - white, or downy birch

Although silver birch (B. pendula) has become very popular, to the extent that it has even been called Finland’s national tree, in their own local environment at least as many Finns have come across the white or downy birch, familiar but largely unknown.

Familiar it must be because it is currently the most common tree species in Finland; unknown, perhaps, because it is not easy to distinguish from the silver birch, particularly further north. Birch species hybridise, but distinguishing between these two species is made more difficult by the variability of the white birch. Naturally appearing forms and mutations are numerous, including the red birch (f. rubra), the pole birch (f. columnaris) and shrubby birch (f. fruticosa). An important subspecies is that found on the fells of Lapland, subsp. czerepanowii.

Compared with silver birch, the white birch usually grows on wetter soils, even on peat bogland. It withstands trimming better than silver birch so is used in birch hedges in northern parts, especially in Sweden. Its common use in plantings can be explained by how easy it is to transplant young trees from the wild. White birch is less long-lived than silver birch, but even when old it is a beautiful tree. The trunk remains white longer than that of the silver birch, and its branches don’t usually droop at any stage. In winter the shoots can be used to help in recognition: the white birch has smooth shoots, the silver warty ones; in summer the leaves can help, those of the silver being triangular or diamond-shaped, while those of the white birch are more round.

 

Betula pendula var. carelica - curly birch (or visa birch)

Curly birch (or visa birch) is a genetic variety of  the silver birch (Betula pendula). Its wood has curled grain, called "visa" formation in Finnish, an unusual growth form. At various places on the trunk and branches the bark is noticeably thicker than usual, and parts of the bark appear within the wood itself as brown spots or streaks. The wood is very decorative, at best resembling wooden marble. The visa formation is also visible in the tree’s outward appearance in the form of bumps or pits in the surface of the trunk, excessive localised branching, and exaggerated twisting or narrowing. The formation usually becomes apparent at about 5-6 years old. Similar formations can occasionally be seen in other genera, particularly alders (Alnus) and mountain ash (Sorbus).

The decorative and extremely hard wood of curly birch has been used for centuries by local craftsmen. In the Finnish pavilion at the Paris World Fair of 1900, Gallen-Kallela’s “Iris”-room with its visa furniture and other art treasures were a major attraction. Visa is both valued and valuable timber. Production of top-quality visa-timber requires expertise, and great attention to tree care and thinning.

These days commercial visa birch cultivars may well be micro-propagated but the seedling production was started with seeds from a tree still growing at Punkaharju, near Savonlinna. This was possible because visa formation had been noticed to be an inherited characteristic. 

 

Betula platyphylla var. japonica - Japanese white birch

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The Japanese white birch is the equivalent of the native Finnish species, B. pendula, called white or silver birch. Many experts consider the two as different forms rather than different species. There are distinguishing characteristics: the Japanese tree has larger leaves, there is no droop to the branches, and the bark doesn’t develop like that of the Finnish species, but rather maintains its handsome whiteness into maturity, sometimes with a touch of pink.

In its native range the Japanese white birch is the most economically important of the birches. In the wild it can grow to a handsome 25m, but experience so far in Finland seems to indicate that it will not grow as tall here.

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