Exceptional trees

The beech: emblem of the Sonian Forest

Grote_en_kleine_beukImpressive, bolt upright beech trees reaching high into the sky: that’s what the Sonian Forest is known for. The Sonian Forest is certainly entitled to its nickname: the beech cathedral.

Nowadays, 70 percent of the Sonian Forest consists of beech trees. That dates from the time of the Austrian Habsburgs (1714-1795). The young Austrian landscape architect Joachim Zinner organised beech plantations on a massive scale. To this day, these form the majestic beech cathedral. Beeches older than 200 years are no exception. Beech wood was once used to make charcoal. Moreover, it is very suitable for furniture and toys because the wood is hard and does not splinter.

Beech nuts are a delicacy for many forest animals: deer, squirrels, mice. Yet a beech forest also has disadvantages. The dense foliage of the beech lets little light through. This hampers the germination of young seedlings. The fallen leaves do not decompose easily. As a result, the undecomposed humus piles up and makes the soil acidic.

Superman of the forest: the oak

eikThe oak is one of the most impressive trees of the forest, the favourite of walkers because of its powerful appearance, and at the same time the darling of the woodcutter because of its fixed value on the timber market.

Even someone who is not a nature specialist can recognise the oak with his eyes closed. It is a majestic tree that is over 30 metres high and can be up to hundreds of years old. The crown of the oak is widely branched, its trunk is stocky. In older trees, the grey-brown bark blackens and splits. The oak is a natural world in itself: the oak processionary caterpillar is not the only species fond of its trunk; between the ridges of bark and in the foliage, caterpillars and larvae, bugs and beetles,ants and spiders abound. The oak is also loved by squirrels and jays, deer and wild boar, who are all after the acorns. Oaks come in many varieties. Typical for our region are the pedunculate oak and the sessile oak. In Southern Europe there is much more variation, with the Turkey oak, the Hungarian oak, the Iberian cork oak, the Holly oak and the Kermes Oak. The Americans divide their many oak species traditionally into a white and a red group. The latter group includes, amongst others, the ‘American oak’, which has also been planted in Europe in many places.

The waning popularity of the American Oak

vilda_Zaailingen_van_Amerikaanse_eik_A5_22412_Jeroen_MentensAs a result of its rapid rate of growth, and therefore its profitable timber yield in a relatively short period of time, the American oak was imported from the north-east of America to our shores in the beginning of the 19th century.

Today, it has become a less welcome guest in the forest. The fallen leaves of the American oak form a thick layer of humus which decomposes with difficulty. As a result, the soil acidifies, which inhibits the growth of many native species. So under the wide crown of the American oak, you find only … more of its own seedlings. Therefore, during felling campaigns, the American oak is more likely to be targeted than an indigenous tree.

Yet, this tree does not deserve to be completely eradicated. Because squirrels and bats greatly prize a cosy nesting hole high up in a tall, old American oak.


The prickly bur of the Sweet Chestnut

Bolsters_van_Tamme_kastanje_Jeroen_Mentens-1Originally, the sweet chestnut was a native of the Mediterranean. Since the 16th century – as evidenced by tapestries from Brussels – the sweet chestnut has been growing in small numbers in numerous locations within the Sonian Forest. Its wood is exceptionally tough, elastic and durable. Tannins arm the wood against humidity and fungi. Chestnut wood is very durable. Even untreated, it remains uneroded for years. This makes it particularly suitable for agricultural fencing poles or garden fencing.

The fruits of the sweet chestnut are easily confused with the horse chestnuts with their bitter and inedible nuts. To play it safe, the sweet chestnut holds three pointy chestnuts, close together, in its bur covered with spines. In the horse chestnut bur, you will only find one perfectly round fruit.

Elegant representative of the olive family: the ash

Vilda_78533_Gewone_es_Lars_SoerinkThe ash is a tall tree, with slender ascending main branches. It bears opposite compound leaves, consisting of from nine to thirteen irregularly toothed, almost sessile leaflets. In winter, it is easily recognisable by its black, velvety mitre-shaped buttons. Fruit-bearing ash trees retain their small winged nuts, called samaras, for a long time after the leaves fall off. They hang in dense bundles spread out over the entire crown.

The ash seeds easily and grows rapidly on richer, moist soils. The ash holds up well in the forest, once it has conquered its place on the ‘upper deck’ because, as a mature tree, it does need light. You will find it even more often in hedgerows, and it also does well in country roads and lanes. Typical for parks and gardens yet again is the beautiful weeping form, which is propagated by grafting.

Ash is pliable and resistant to shocks. It is therefore used for manufacturing axe and spade handles and also for gym equipment.

The Maple feels at home in the Sonian Forest

Gewone esdoorn; acer pseudoplatanus; Common mapleThe maple has a misleading name in Dutch, where its name is “esdoorn”, literally ash thorn. In fact, it does not belong to the family of the ash tree, and it has no thorns. So how do you recognize it then? By its hand-shaped leaves, its smooth, thin bark and its fruit, which you can twirl like a helicopter, thanks to its wings.

Especially in this area, it is the Sycamore maple that is widespread. The Norway maple, with its pointy, divergent leaf lobes, can be easily confused with the Platanus (plane tree), which can also be spotted all over our forests. On the other hand, the smaller Field maple, with its smaller leaf, is much more uncommon. In the arboreta, especially in the one in Tervuren, you can still find many other exotic maples. In the autumn they guarantee a beautiful play of colour.

In the Sonian Forest, which is composed of 70 percent beech, the Sycamore maple, at 2 percent, is the fourth most populous species of deciduous tree after the English oak (13%) and the Sessile oak (2%). In the future, it will become more prevalent since it naturally propagates easily and as a young tree can tolerate shadow well. That is great news for the biodiversity in the forest, because the dead wood of the maple attracts many types of rare fungi, lichens and mosses.

The alder: about alder cones and alder wet woodland

Vilda_29576_Blad_van_Zwarte_els_Rollin_VerlindeThe alder can be recognised from afar in the winter by its tight, somewhat tangled profile, with fine branches, adorned with many long, hanging, male catkins and smaller, upright, female catkins. After pollination, the female catkins form a sort of cone, the so-called alder cone, which becomes entirely woody and remains hanging on the tree long after the seeds fall. The black alder, which to us is the most common, has an opposite, ovate, double serrated leaf that is blunt and often notched in a u-shape at the top. The leaf of the rarer white or grey alder is more pointed at the top and felt haired on its underside. The black alder thrives in a wet location and is a typical species for areas with brooks and springs. Also on nutrient-poor and peaty soils it takes well thanks to its nitrogen-binding root tubers. One often finds it there together with the downy birch. On loamy soils, the alder often grows together with the ash.

Throughout the centuries, alder forests were mostly managed as coppice woods, because after coppicing, the new shoots easily sprout again and thus continuously provide timber for firewood and domestic use. That’s why one encounters so many multi-stemmed alders. Alder wood in contact with the air is not very durable, but it is useful for underwater structures. It is therefore often found in the walls of wells. One peculiarity is that the freshly sawn timber immediately turns a bright orange colour.

The pristine birch

Vilda_16972_berken_op_Gosson__Rollin_VerlindeIn summer and winter you immediately recognise the birch by its often bright white bark, often speckled with black diamond shaped spots. The birch is a pioneer species par excellence. In July-August, the seeds are separated from the catkins to be carried away on wings by the wind. A birch germinates and endures in the worst possible soils, even in the gutter or between the cobblestones.

In Europe we distinguish four different types of birches. Especially the silver birch feels at home in the Sonian Forest.



Delicious nuts: the hazel

Vilda_78529_Hazelaar_Lars_SoerinkIf there is one tree that is truly indigenous, it is the hazel. It colonised our region long before Belgium even existed. After the ice age, it was one of the first trees that formed woods here again. Archaeologists, by digging up large numbers of shells around settlements, have demonstrated that even our ancestors sometimes fancied a hazelnut. No wonder: the nuts are packed with fats and proteins and certainly helped prehistoric man to withstand the harsh winters.

The hazel is our earliest spring bloomer. Ornamental hazels distinguish themselves by curly twigs or reddish tinged leaves. The many twigged bush could use some shade, but has a difficult time under dense foliage. It can thus survive better in coppiced woods. It can be recognised by its large, nearly round leaves that are somewhat reminiscent of the large-leaved lime. But thanks to the double serrated edge and short tip at the top of its leaf, you can easily distinguish it. Its pliable wicker lends itself well to the heavier braided work, such as in braided walls.

The elm, an endangered species?

Vilda_53547_Iep_Jeroen_MentensIn prehistoric times, elms were an important part of the Atlantic primeval forest in the Low Countries. With the advent of agriculture, their share among the indigenous trees gradually decreased. The foliage was used as animal feed; the hard wood was especially popular with furniture-makers and wheelwrights. Since elm disease struck in the early nineteenth century, the number of elms has greatly declined.

The leaf of the elm is a bit like that of the hornbeam, but the leaf edge is double serrated and the elm leaf has a typical oblique leaf base, so that one side is set lower on the short stalk than the other. The fruit is also easy to recognise: a flat nut, embedded between two membranous wings. The three native species – the smooth-leaved elm, the wych elm and the fluttering white elm – are a little harder to distinguish from each other. Twigs of the smooth-leaved elm often have corky bands. In the case of the fluttering white elm, the flowers and the fruit have stalks.

The elm disease is caused by a fungus transferred by the large elm bark beetle. In an infested tree, the part above ground dies within a short time. The smooth-leaved elm can re-grow from root storage; the wych elm propagates itself almost exclusively by seeding and is therefore particularly vulnerable to the disease. The fluttering white elm is most resistant to beetle infestation because of its strong bark. The elms are not really threatened with extinction, but large, mature trees have become very rare.

The medlar: rare delicacy


Just like the chestnut, the medlar is a fruit tree which was imported into our region in Roman times from the east and which has maintained itself in our forests. Unlike the chestnut, the medlar is rare. It produces flowers and fruit, but the seeds germinate with great difficulty. It also grows very slowly. It usually occurs as a shrub, but it can also grow into to a small tree. You can find the species in old, light forests, forest edges, hedgerows, thickets and hedges.

The fruit is only edible when it has become overripe. Some nature lovers believe that you must allow medlars to rot before the tender flesh can be sucked from the rough rind. Not everyone is mad about that, but in any case you can make a delicious jelly from the pulp. Medlars were especially popular in the nineteenth century. In Flanders, four cultivars are known. Cultivated medlars can be distinguished from the wild species by their larger leaves and fruit. The cultivars were often grafted onto rootstocks of wild medlar or of the related hawthorn.