Walnut Tree (Juglans regia)
Family: Walnut family (Juglandaceae)
Type: Walnut (Juglans)
The tree of the year in Germany is annually chosen by the Kuratorium "Baum des Jahres" (site available in German only).
The tree of the year 2008 is common knowledge by the economical use of its fruits. The kernels of the fruits, which indicate their maturity by a shell becoming brown and cracked, are known as walnuts and are commercial everywhere. Traditionally, the fruits of the walnut family were classified as drupes in the botany. But the walnut is indeed a nut, as a diploma project at the Ruhr University Bochum showed, as the German Scientific Information Service pointed out: The shell proves that the walnut is really a nut. A nut is an indehiscent fruit with a seed and a tough shell. This is formed out of the carpels and doesn't open by itself.
The leaves of the walnut are especially rich of tannin, that is to say they decompose slower than other foliage and might not be all that tasty for insects. Walnut trees are furthermore said to disperse flies, thats why they were frequently used for a shady seat in the inner yards of farms (beside the dunghill necessary there).
The tree of the year 2008 reacts very variably to cutting measures at different dates. If it's cut in spring, a very intense and enduring gummosis begins. This effect is often described as 'to bleed out' by unbiased spectators. The gummosis can't be stopped with means, but ends after considerable time independently by wound healing. In order to avoid these unpleasant effects, cutting measures can happen in summer around Midsummer's Day (temporally together with the crop of the sweet cherry). Here the wound healing is way faster and the 'bleeding out' is neglectable.
Allelopathy and Walnut Varieties
The walnut is gladly exemplified to explain allelopathy. In the green organs, a glucoside is composed which is converted to juglone after release. This affects numerous plant species germ- and growth inhibitingly. Thereby the walnut avoids a settlement of competitors in the close environment of the stem.
Solely in Germany there are more than 100 species which differ in nut shape, yield, frost-resistance or other features. Further famous instances of this group are the black walnut (Julgans nigra) and the butternut (Juglans cinerea), which were imported from North America to Germany.
The home of the walnut is the eastern Mediterranean area and the Balkan Peninsula plus Middle East and Central Asia. You can find it in moist ravine forests of the mountains and it grows in the northwestern Himalaya in heights of up to 3300 m above sea level.
The contemporary areal distinction is difficult because the walnut has been grown since the Neolithic Age. So, its current dissemination is deeply characterized by the cultivation as a fruit tree: The walnut was naturalized by the Romans in large parts of Southern, Western and Central Europe. In Central Europe it occurs in sophisticated form on farms, in gardens or as isolated tree in the meadow as a rule. Occasionally it is to be found overgrown, especially in alluvial forests of the Rhine and the Danube. Although the walnut is to be found up to 1200m in the Alps, it rarely grows on habitats above 800m above sea level.
Because the tree of the year 2008 is very sensitive to winter's cold and late frosts, it is often to be found in winter-mild locations with low precipitation like in wine-growing areas. The walnut grows especially well on profound, fresh, nutrient-rich, calcareous loamy and clayey soils.
An additional spread as a forestry tree species has, despite the valuable wood, hardly occured until now, as the walnut is classified as a competitive weak light tree species, although shadow tolerant in its youth, and consequently only conditionally incorporatable into common silviculture drafts.
Cultivation in Forestry
The growing of the walnut tree occurs for the main part because of the crop yield. Whereas also the wood is very coveted and is one of the most expensive woods, it is tried to be used silviculturally since the end of the last century. Forestry use requires fast- and straight growing planting material, which is currently not in trade in this form. The propagation in populations constrains the crowns, what indeed leads to a lower crop yield, but helps to attain longer stem sections free of knots. Trees growing in competition may become up to 10 m higher than single trees. Related to the production of high grade wood, the walnut (♂) was interbred with the black walnut (♀). The Juglans x intermedia, which has developed out of that, is said to have a shafty treetop and to be fast-growing.
Usage of Walnut Wood
The wood of the walnut tree is a coveted precious wood, its usage is confined to valuable objects. As it normally only arises as a byproduct at the felling of fruit trees and an aimed cultivation for the wood production is only existing rudimentally, a stop is often put to its usage. That walnut trees are often lifted including the rootstock, is not attributed to its shortage however. The bottommost tree parts, partially reaching till into the earth, are bulbically thickened and are suppliers for the most valuable vein veneers, also called root veneer, and among others car fittings. Furthermore, the wood is used for turneries, carvings and rifle stocks.
The Caucasian Wingnut, a deciduous tree species from the type of wingnuts, belongs to the walnut family, too. The Caucasian Wingnut delivers one of the most valuable veneerings for the furniture industry. The fine, but very distinct dark draft often forms gorgeous patterns.