Functions of forests
Sustainably managed forests fulfil a range functions to the benefit of both man and nature. Forests are not only important as suppliers of wood, but also especially as protectors of soil, water, and climate, as well as flora and fauna. As areas for recreation and relaxation for human beings, forests are indispensable.
Practical uses of forests
The main use to which forests are put is the production of wood, a most valuable resource. Germany’s latest national forestry inventory from 2006 shows annual growth in wood of around 95 million m³, compared with a statistically recorded annual harvest of around 48 million m³ on average over the last five years. In addition, forests also supply berries, mushrooms, herbs and game for hunting.
Wood is one of the oldest and most important materials known to man. Annual wood production still exceeds the amounts of steel, aluminium and concrete. The FAO’s 2005 estimate for the volume of above-ground woody biomass accumulated in the world’s forests was 422 billion tonnes. Every year 3.2 billion m³ of raw timber are currently being harvested, almost half of this in the tropics. The highest annual intensity of harvesting, however - 2.3 m³ per hectare - takes place in Western Europe. Almost 50% of the global wood supply is used as fuel – mainly in tropical countries, where energy production is still the most important use for wood. In western Europe, only about a fifth of the proportion of wood felled is used as fuel.
As a resource, wood is rapidly gaining importance as its production is almost CO2 neutral, it is compatible with ecological and sustainable commercial practices, it can be worked with a low energy requirement and the material can be used in its entirety.
In its 2006 wood market report, The Federal Ministry of Food, Agriculture and Consumer Protection gives the following figures for the most important timber species for Germany: spruce (incl. fir and Douglas fir) around 37 mill. m³ – approx. 60 % of the entire 62 mill. m³ harvest –, pine (incl. larch) around 12 mill. m³, beech; around 10 mill. m³ and oak; around 2.5 mill. m³ – with an increasing tendency in each case. About 80 % of the entire harvest consists of coniferous wood.
Protective functions of forests
As the extensive network of tree roots prevents water and wind, but also rockfalls and landslides from eroding the soil, forests are an important erosion protector, particularly on slopes and hill or mountain sides. This protection is afforded more by deciduous trees than coniferous trees as their root penetration is more intensive. An important function particularly in mountain regions is avalanche protection. The occurrence of avalanches is greatly reduced and a forest can break the force of an avalanche already in motion and trap a huge proportion of the snow masses.
As a forest floor, like a huge sponge, can retain huge amounts of water – up to 200 l per m² – and prevent the water running off on the surface, forests make a significant contribution to water conservation. If saturation point is reached, the water filters through the soil and increases the volume of accessible ground water. Meltwater and rainwater seep away slowly and are filtered in the soil to become pure ground water.
Forests ease daily and annual temperature fluctuations, raise humidity and increase dew formation. Due to reduced exposure to sunlight and greater humidity than in the open, forest air in summer is mostly cooler than in open country and cooler again than in cities. Large expanses of forest near cities can have positive effects on the climate, as the temperature differences lead to a constant exchange of air.
The emission protection function describes the forest’s ability to filter aerosols of all kinds, dust particles and radioactive substances out of the air. This filter effect is governed mainly by the leaves. For instance, 1 hectare of spruce forest can filter out 420 kg of dirt particles, whereas a similar sized bare beech wood in winter only manages 240 kg. A 100-year-old oak tree filters a ton of dust out of the air every year: the dust settles on the surface of the leaves and is washed into the ground with the next rainfall. Gases are mainly absorbed when treetops are moist and the gases can dissolve in rainwater. Due to the temperature differences already mentioned, cleaner air of much better quality then flows into the residential areas. The forest’s emission protection function also includes protection from noise, as trees form a barrier to noise from traffic, industrial estates and sports facilities.
And finally, forests also contribute to species protection. Many animals, plants and fungi have adapted to their forest habitat. A fully grown oak tree, with a height of 30 – 50 metres and up to 250,000 leaves, can accommodate up to 300 species of insect: beetles, butterflies, plant bugs and many, many more.
For the many recreational users, the forest is perceived mainly as unspoiled nature. According to surveys, it is still the most popular metaphor for nature itself. It offers visitors peace, relaxation and a healthy climate for recuperation – for many, it is a “balm for the soul”.
However, in recent years, there has been a change from pure relaxation to activity. Forests are now attracting the joggers, mountain bikers, climbers, paragliders, inline skaters, cyclists, etc., though hiking and walking are still the main activities.
So to keep the peace between the various factions, many places have well sign-posted bridle or cycling paths, mountain bike and Nordic skiing trails. The recreational spectrum is rounded off by play and barbecue areas, keep-fit paths and adventure walks.