Content - Wood diary

Wood diary. When we make our way through European forests and talk with local specialists or farmers, we often make interesting observations. Many of these we record in our wood diary, in order to capture knowledge and facilitate the identification of interrelationships. At this point we would like to share a number of these individual entries with you. 

The flowering process of trees. In May, the power of nature makes itself felt. There is a reason why this month is one of our favourites. 


The flowering process of trees. In May, the power of nature makes itself felt. There is a reason why this month is one of our favourites. 

Often, summery temperatures already begin heralding the most popular season of the year. Our perception is frequently focused on the flowering phase of flowers and shrubs, as well as of fruit trees in the garden. On the other hand, we often miss the flowering of woodland trees. One of the few species of tree in the forest that has showy blooms is the cherry tree, which is frequently found on the edges of woodland. In spring, its white blossom stands out against the sometimes still rather colourless surroundings. 

The flowering of other woodland trees is less conspicuous and mostly hidden away, high above the heads of those venturing into the forest. Whether and to what extent trees flower depends on a large number of factors: the production of flowers is highly dependent on temperature and sunlight or the length of exposure to light. These determine the budding and the time of flowering.

Site quality also plays a major role. This is determined by the area in which the tree grows, exposure, altitudinal belt and, of course, nutrient supply.

When trees grow in unpolluted environmental conditions, they take several years to produce flowers and gain the ability to reproduce. Free-standing specimens produce flowers earlier than trees growing within a stand in woodland.

The role of temperature in the production of flowers has been proven in several species of tree. If higher (above-average) temperatures occur in spring or early summer, more flowers can be expected to form the following year. The temperature required for the flowering stage differs according to the species of tree: early-flowering trees such as hazel and alder do not need as high a temperature as beech, oak, spruce and fir trees which do not begin flowering until early May. 

Reproduction occurs through pollination, meaning that pollen is deposited on the stigmas or ovules either by bees or the wind. Spruce trees have around 200,000 grains of pollen per flower, pine trees 160,000, oak trees 40,000 and beech trees 12,000. A tree’s nutrition plays a special role in the generative process. In general, a full yield of fruits can be obtained if the tree is able to store sufficient reserves the year before. In life-threatening situations, on the other hand, trees may use their final reserves to produce flowers before dying. 

However, to produce a mass of flowers, trees require sufficient water. Another important criterion is the basic temperature at the height of the flowering season. To pollinate flowers successfully, particularly those on fruit trees, bees need an outside temperature of at least +9 °C. 


Round wood storage – wood preservation based on optimum felling time. The moment we separate a tree from its roots, it becomes our responsibility as human beings to retain its value with care and (unless it is firewood) to give it new life by making good use of the wood.


Round wood storage – wood preservation based on optimum felling time. The moment we separate a tree from its roots, it becomes our responsibility as human beings to retain its value with care and (unless it is firewood) to give it new life by making good use of the wood.

The best way to preserve wood is to choose the optimum time for felling. That always means the cold months of the year, preferably from the winter month of November through to the first new moon in March. To obtain smooth, even wood that will not warp during storage, the time of the waning moon is definitely preferable. This is known as moon-phase wood.

Leaving trees as round wood in the forest for a period of time after felling is more an advantage than a disadvantage. If it is clear at the time of felling that heavy snow will delay transportation, for example, a tree must be felled in such a way that it points downhill after felling. The treetop must be lower down than the roots, so the felling direction cannot be chosen at random. If possible, the directional cut must be made on the downhill side of the tree to enable the felling cut to be made on the uphill side and a wedge to be driven into the felling cut, forcing the tree to fall in the right direction. The branches are then simply left on the trunk and only the very top of the tree is removed. Gravity then helps to drain the remaining fluids. Water absorbed from the ground also flows in that direction in the vessels. The tree will then demonstrate an astounding will to survive. It forces the remaining fluids into the branches to try and produce shoots through fruit and soil contact – an astonishing phenomenon. This causes the body of the trunk to dry out further. The heavy waterlogged branches are left behind in the forest once they have been removed. This is a natural way for the wood to dry out and mature.

When the timber is retrieved from the forest the following spring, wonderful results are obtained after sawing: the colour is generally rich and even, according to the type of wood, the goods are not prone to warping and the initial lower moisture content saves a great deal of time in the air-drying process outside the forest. This investment pays off. 

In the past, felled oak trees were often left in shady and sheltered locations in the forest over the summer as cut round wood with the crown pointing downwards. This resting position allowed the varying tannic acid deposits to even out and produce a consistent colour. After cutting during the following winter, this oak had a softer, more homogeneous and less gnarled appearance. Particularly valuable trunks were generally selected for this process. 

Another practice in round wood storage is sprinkling. Today, some oak saw-mills still store their round wood for a whole year's production crown-down. The wood is sprinkled with water throughout, except on days with heavy rain. The effect in the wood itself is basically the same as that achieved by leaving it lying in the forest. The difference is that the water, which constantly permeates it from the higher root end, causes the tannin to be practically washed out. The result in the wood is purely beneficial for all further finishing processes. Nowadays, many companies can barely afford this kind of advance financing since it requires both the obligatory timber depot and an additional large round wood depot.


Slavonian oak. The timber industry is a traditional sector with a long history.


Slavonian oak. The timber industry is a traditional sector with a long history.

The term “sustainabilityˮ was coined in this context – back in 1713 by Hans Carl von Carlowitz in his “Sylvicultura oeconomicaˮ. This was a manifesto calling for the responsible handling of resources. It demanded that trees should only be felled at a rate at which they can grow back.

The raw material itself has not changed since then – but the variety of its uses has certainly increased. Its properties are fixed and must be accepted. Using intelligent forest management, however, trees can be influenced in their growth right from the beginning and thus optimized for their intended usage. 

While many new and innovative products now exist in the composite wood field, which can be precisely defined with norms, the field of solid wood is largely excluded from technological developments. However, it does offer different processing options to suit the needs of those working the wood.

Such processing steps include the popular steaming method – particularly for walnut trees, beech trees and elms, but also increasingly for oak and ash. 

The steaming process – “boilingˮ fresh wood – gives oak its colour and also reduces much of its inherent tension. The substances derived from air and sunlight, which are stored in the wood as nutrients in the form of glucose, are transformed during the process. The sugar turns a reddish colour.

When this combines with the green tannic acid or tannin stored in the heartwood, it ultimately develops a beautiful dark brown earthy hue which is similar to that of 1,000-year-old oak.

Historically, Slavonian oak was the result of an intelligently implemented reform policy during the reign of the Imperial-Royal Austro-Hungarian monarchy in the mid-18th century. Empress Maria Theresia had the marshy areas of the Pannonian Plain drained through the systematic planting of trees. The area encompasses eastern Croatia (Slavonia), southern Hungary and parts of Romania (Banat). The forestry law, which still applies in Croatia today, was laid down by the Empress. She planted large stands of oak and ash on the flood plains of the Drava and Save rivers and as far as the vast Danube plain. She thus succeeded in generating the necessary agricultural land for the future by cleverly creating woodland to initiate the natural draining of the marshes. 

The pedunculate and sessile oaks which grow there today, and their hybrids, possess special features: distinctive shallow roots owing to the high groundwater levels, as well as a uniform light base colour and even annual rings. This is why the trees are now known as world-famous “Slavonian oakˮ which, born out of necessity and created through clever planning, still safeguard the livelihood of the current generation.

These oak trees, which grow further south than those in the enormous oak forests of Central Europe and are therefore exposed to more sunlight, protect themselves with a pronounced crown. In large forests, they can thus create the climate necessary for the following generation of young plants to thrive. 


Crab apple. Over the past few weeks, the cultivated landscapes have awoken from their winter slumber.


Crab apple. Over the past few weeks, the cultivated landscapes have awoken from their winter slumber.

There is a first hint of green and the first trees are in bloom. In the plant kingdom, the time of growth and reproduction is beginning. The cultivated landscape shaped by human activity is subject to constant change: new species, known as non-native invasive plants, are introduced indirectly or deliberately planted, for example. Other older species, on the other hand, which have been a feature of our man-made landscapes for millennia, are disappearing. 

One such tree from cultures long past is the crab apple (Malus sylvestris). The oldest discovered remains of the fruit are estimated to be 6,000 years old. Remains are also found now and then on the sites of prehistoric pile-dwellings, Linear Pottery culture dwellings and in graves in Central Europe. Contiguous populations of this species have not existed for many years and the impact of hybrids and naturalized species, cultivated apples, is a challenge for the crab apple – even to the extent of suppressing it altogether. 

The natural distribution area of the crab apple ranges from Europe to western Asia, although the southern and eastern limits of its distribution are not clearly defined. It is mainly found in low-lying areas of Central Europe. In the Alps, the crab apple grows up to an altitude of 1,100 metres above sea level. It prefers water-meadows and damp woodland edges. Since these natural habitats have drastically declined owing to human interference, the crab apple population is under threat. The crab apple is found scattered in riverside forests, in hedgerows and copses, where it favours fresh, nutrient-rich and alkaline-rich, mainly deep loamy and stony soils and needs a damp, warm climate.

To spread, it requires a high stand density. 

The distance which pollen can be transported ranges from a minimum of 6 m to a maximum of 10.7 m. 

A study by the Federal Office for Agriculture in Germany showed that the number of crab apple trees in close proximity to the mother tree has a great influence on the distance which pollen can be transported. If only four or fewer trees stood within a radius of 250 m of the mother tree, for example, pollen was transported an average distance of 950 m. The number of hybrids was also highest among the young trees there. If, however, more than 20 crab apple trees were found within a radius of 250 m of the mother tree, pollen was carried only 30 m on average and none of the seedlings had been pollinated by a cultivated apple tree. An increase in stand density results in a greater number of flowers, meaning that bees are able to find sufficient nourishment even within a smaller radius. Pollination between neighbouring trees is facilitated and the distances which pollen is carried are shorter. The risk of producing hybrids with cultivated apple trees is also lower. In stands with just a few individual specimens, on the other hand, it is likely that ever more hybrids will be found among the naturally occurring young trees and that these will supplant the “trueˮ crab apple in the long run. 

It is interesting to note, however, that even scientists cannot agree on how to distinguish the crab apple from other species. The original variety of cultivated apple is probably Malus domestica, although a hybrid of various species is possible. On the other hand, recent genetic research has shown that the domesticated apple is descended from the Asian wild apple (Malus sieversii). 

It is extremely difficult to differentiate between the crab apple and wild varieties of cultivated apples. It is even debatable whether the crab apple (Malus sylvestris) actually still exists at all or whether it is basically a wild variety of the cultivated apple. What is interesting about nature is the encouraging fact that something new can develop and that the plant world is also clearly able to adapt. Losing something should be a lesson to us and gaining something a gift.

The reddish-brown heartwood of the crab apple tree is prized by artisans and woodturners in particular, but is also used for exclusive individual items of furniture. Owing to the limited availability of wood with usable dimensions, it cannot be processed in large volumes.


Tannin marks. How patches of discolouration appear on oak.


Tannin marks. How patches of discolouration appear on oak.


Oak is one of the most popular types of wood in Europe today. Although it grows in many places and is usually easily available, the production of oak is currently reaching its limits. Certain ranges are already sold out in the large sawmills, and the price of sawn oak is rising.

As a consequence of this high demand, the prolonged outdoor storage period of the stacked boards is being drastically shortened so that the wood can be processed as quickly as possible. It also used to be common for the oaks freshly felled in winter to be left to lie in a dark, damp place until the next summer. This is not the case today. These periods would serve to distribute the tannic acid (tannin) released in the wood moisture evenly throughout the heartwood, as unevenly distributed tannin causes irregular discolourations. In addition, the summer rain would disperse excess tannin, revealing the oak's natural light-brown colour beautifully.  

Sudden changes in weather also influence the acid distribution. While we have accustomed ourselves to frequent and sudden changes in the weather, from damp and wet, to dry, and even somewhat warm, oak does not fare so well under these fleeting conditions. It is becoming increasingly common for small cracks to form on the surfaces of outer boards if there are strong, dry winds in February. As the dry air quickly removes the moisture, the tannin present in the water also appears, adhering to the surface of the board as the water evaporates. The discolouration of the visible surface often also exhibits an inconsistent depth of between 2-15 mm.

This cloudy discolouration is barely noticeable on a freshly sawn board. The negative effects only become apparent when the boards are planed. The newly visible surfaces now look striped or checked, with alternating large and small patches of lighter and darker colour. This makes the wood rather unsightly.


Drying wood. Cracking and warping of furniture as a result of incorrect drying. 


Drying wood. Cracking and warping of furniture as a result of incorrect drying. 


Anyone who works with solid wood will inevitably have to deal with the topic of wood drying out. There is an interplay between wood as a material and the room climate - the wood adapts its moisture content to the ambient temperature and humidity, resulting in changes in its shape. Cold, dry winter weather causes wood to contract, while humid summer heat causes it to swell. Heating and ventilation therefore also affect wood's volume.

An oak tree can store moisture amounting to around 30 percent of its mass in its cell walls. If the wood is used indoors in a place that is protected from the elements, well ventilated and well heated in winter, the average moisture content should, however, only amount to 9 percent - with a fluctuation range of ±3 percent. When the moisture content is reduced from 30 to 9 percent the oak loses around one tenth of its volume. If this drying process takes place too quickly, damage soon manifests itself: warping, interior cracks and surface cracks. 

Two aspects are important for avoiding damage to wood over the long term. One is the moisture content required for the relevant purpose and the other is the type and duration of the drying process. In unheated rooms, the wood's moisture content should be around 15 percent on average. In rooms with low-level heating, the mean can be 12 percent, and well-heated rooms require 9 percent. In Alpine countries, particularly at altitudes of over 700 metres, these figures are lower. In February, a dry wind blows over the Alps, and the air in homes there is often too warm and dry. In Switzerland, these conditions have resulted in a widespread view that wood must always be dried to 8 percent. 

In order for green wood to be used at all, moisture has to be extracted. A shortage of storage space and the need to turn inventories over quickly for reasons of profitability mean that wood is often force-dried in vacuum kilns or drying kilns. This very fast process in an extremely dry and unaccustomed climate "stresses" the wood. Moreover, when dried to a moisture content of less than 11 percent, the diffusion resistance increases exponentially: the moisture is forcibly removed from the wood with a disproportionately large amount of drying energy.  

A gentler processing method involves gradual air-drying in the timber store. The moisture content in the cut wood declines to 12-16 percent over a period of two to four years. Thereafter it need only be briefly kiln-dried to a level of 10-11 percent. For solid wood tables, mature, well-stored wood with a moisture content of 11 percent is more suitable than green wood, which is dried intensively in a short time in kilns. It is relaxed and barely works any more, provided that the ambient climate is conducive to this 11 percent. If the wood was dried to harshly it will be "thirsty". This thirst corresponds to the need of the dried wood to return to the equilibrium humidity (moisture content in balance with the environment), i.e. to absorb moisture.

The greatest damage occurs with wood that is over- rather than under-dried. The decisive factor is always the place or the room temperature where the wood will be used: if the wood's moisture content is in line with that of the environment it will not absorb or desorb any water; the wood will not work and no cracks or warping will appear.

When measuring the moisture content of cut wood, it is important to note that there will be a humidity differential across the width of the plank as well as from the root to the crown. In other words, depending on the point on the plank or trunk where the measurement is taken, the moisture content will vary. A mean level is thus calculated from the highest and lowest levels. This is not a fixed value; instead it adapts to the climate at the location where it will be used. It therefore makes sense to process wood with a moisture content that best suits the intended purpose instead of purchasing it with a standard 8 percent moisture content.


Interplay of colour in the forest. It is actually the reduced power of the sun that enables fruit to ripen in the autumn. 


Interplay of colour in the forest. It is actually the reduced power of the sun that enables fruit to ripen in the autumn. 


"Herbst", the German word for autumn, originally meant "harvest time". Indeed, it shares the same etymology as "harvest" – as well as "carpere", the Latin for picking. In the United States, autumn is of course "fall", a seasonal reference to falling leaves, whereas its Germanic equivalent still means "harvest" in an agricultural context.

As the sun's power wanes in autumn, the sap in a deciduous tree will flow back to the trunk and roots. Notably, the production of chlorophyll that gives leaves their green colour decreases as a result. Carotenoids and/or anthocyanins that were already present in the leaves during the summer subsequently take over the reins – and nature's joyful display of autumn colours can begin

Once they are active, these pigments flow down the trunk with the sap, whose colour and composition change to reflect the turning season. This, in turn, has an effect on evaporation from the tree's foliage, with the colour and smell of the sap helping to repel autumn insects from the tree.

As the leaves increasingly lose moisture, they will gradually roll up and deform. This means more and more direct sun for the tree's seeds and fruits, thus allowing them to grow to full ripeness. Then it's time for picking – or "carpere".


The sessile oak. Tree of the Year 2014 and questionable pieces of advice.


The sessile oak. Tree of the Year 2014 and questionable pieces of advice.


The sessile oak (Quercus petraea) – also referred to as the durmast oak – was chosen as tree of the year for 2014. It is deciduous, grows to a height of 25 to 30 – sometimes even 40 – metres, and can measure up to two metres in diameter. A sessile oak's taproot is extremely sturdy and strong. The tree can live for 800 to 1,000 years.

The pedunculate oak is a very similar species that also tends to grow in places where the sessile oak is indigenous. The difference between the two is that the sessile oak's acorns are stalkless, i.e. "sessile".

Oak trees are quite frequently hit by lightning. Not only is this due to their taproots being in contact with the groundwater, but also because they often stand in splendid isolation in the middle of meadows or squares. According to a saying in German, you should "flee the oak and seek the beech" – which, in point of fact, is still the last thing you should do if you find yourself out in the open during a storm. A lightning bolt will normally run down the outside of a beech tree's moist bark – to hit the very spot you may have chosen for shelter. Beeches may rarely bare visible scars from electrical storms, but by no means are they immune from lightning strikes.


The noble oak. When the fruit and bark of the oak were more important than its wood. 


The noble oak. When the fruit and bark of the oak were more important than its wood. 


The oak plays an important part in mythology. Celts, Teutons, Romans and Greeks alike associated the tree with the gods. Oaks embody steadfastness, power and strength, while their leaves – which symbolize endurance – can be found to this day on many coins, heraldic bearings and certificates.

However, the oak's deep roots in the lives of early civilizations were not merely of symbolic nature. The tree used to be more widespread back then as well as a major source of nutrition for humans and animals. For centuries, oak forests were primarily harvested for their fruit and bark. Less importance was attached to woodcutting.

Peeled and dried at 20-year intervals, oak bark was used as an agent for tanning and dyeing animal fur. The acorn was very popular because it was the most important constituent of pig feed and therefore helped to produce lean meat and tasty bacon. The pastures and forests used for fattening pigs were subject to strict laws, and the value of oak forests was calculated on the basis of the number of pigs grazing there.

During the two world wars of the 20th century, the acorn again became an important source of nutrition for humans as a coffee substitute.


Warm January. Why there are now hardly any usable old walnut trees left in Switzerland.


Warm January. Why there are now hardly any usable old walnut trees left in Switzerland.


Our wood trade experienced an unusually warm winter this year. Although we still associate January with frost, ice and snow, the trees in our local climes start to adjust to the changing conditions and develop a strong barks to avoid freezing completely.

An old farmer in our village recently told me that the situation during the winter of 1956 was quite similar: "January was very warm – in excess of 15 degrees – so the walnut trees began shooting. Temperatures then plummeted in February, remaining extremely low for four weeks. Virtually all the walnut trees died. The few that survived all bore those telltale frost rings, so the wood was unusable."

I am very conscious of what happened as a result of that exceptional winter. Switzerland hardly has any more old walnut trees worth using – although it wasn't the only country to be affected.

Walnut trees used to line the entrances to many a stately farm. They have now vanished in many places, yet the tree itself still occupies a fond place in many people's hearts.