Forest liming

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Forest liming near Siegen in October 2013

Under a Waldkalkung (also Forstkalkung) refers to the introduction of carbonate of magnesium lime in very strong soured forests to there gently the pH to increase the forest floor and counteract thus a forest soil acidification. An intact mineral soil should have pH values ​​above 4.5.

In order to counteract the strong soil acidification , liming has been carried out in German forests since 1980 . For each location, examinations should be carried out in advance and samples analyzed to see whether liming makes sense or not. For forest liming, carbonic acid magnesium limes with a magnesium content of more than 15 percent are usually used in order to increase the magnesium supply and base saturation in addition to improving the pH value.

Causes of forest soil acidification

The main cause of the strong acidification of forests and the resulting damage to ecosystem functions was and is the entry of acids with rain, also known as acid rain . They come from immissions from traffic, agriculture, industry and the combustion of fossil fuels such as coal and oil. Since the beginning of the 20th century, these have led to an increase in acid values ​​in non-calcareous soils by a factor of 100 to 250 on average. Although the sulfur inputs have decreased in the meantime, the acids continue to accumulate in the soil. As a result, the natural buffer systems of the soil are exhausted in the long term and the biological diversity in the forest floor is also reduced.

Especially in their upper layers, the soils of many forest locations are strongly acidic and poor in basic components. The acids damage, among other things, the fine root system and thus reduce water absorption and the stability of the trees.

How lime works in the forest floor

The lime spread in the forest neutralizes the acid in the soil and helps to stabilize the pH value of the forest soils. The acid rainwater is neutralized as soon as it comes into contact with the lime. After its dissolution, the lime also provides the elements calcium and magnesium as nutrients. It increases the content of exchangeable calcium (Ca 2+ ) and reduces the leaching of harmful aluminum (Al 3+ ) and manganese (Mn 2+ ).

By improving the pH value and the physical properties of the soil, microorganisms, earthworms and many other soil organisms get better living conditions. This results in increased biodiversity and soil fertility. Soil aeration, water storage and nutrient mobilization are improved.

Suitable types of lime

Carbonate, dolomitic magnesium lime is used almost exclusively for forest liming, because it combines the slower solubility and pH improvement desired in the forest with a high supply of magnesium. But dolomitic lime also provides the soil with sufficient calcium. Both elements serve on the one hand as nutrients and on the other hand to improve the base saturation and the soil structure. The lime, which is brought out by helicopter, looks almost like sand because it has a grain size spectrum of fine sand and is earth-moist. The carbonic acid magnesium lime that is released is harmless to humans and animals.

Types of lime application

The forest liming takes place mainly in autumn and winter. In spring and summer there is normally no liming so as not to disturb the animals in the forest. In some federal states, forest liming can begin as early as late summer. Today the forest is almost exclusively whitewashed from the air with modern helicopters. GPS-supported digital maps show the pilot in the helicopter exactly which areas of a forest area are to be limed and which are left out (e.g. bodies of water, sensitive nature conservation areas). This technique enables precise liming to be carried out. Therefore, only small distances to the surfaces that are not to be limed are required.

In addition to liming from the air, blowing devices are also used. These are vehicles that blow the lime into the forest from the forest paths and back alleys.

Lime amounts applied

In Germany, the usual amount of three tonnes of lime per hectare has been applied for many years, because this amount neutralizes the acid input for about ten years on average. In the period from 1980 to 2012, an average of around 300,000 t of lime was applied in Germany. Thus, an average of around 100,000 hectares (ha) of forest was limed per year. This corresponds to about one percent of the German forest area of ​​11.42 million hectares. In the opinion of the industry association, an annual liming requirement of approx. One million tons or an annual forest area of ​​approx. 330,000 hectares would make sense in order to achieve a noticeable and sustainable improvement of the forest soil to reach.

Individual evidence

  1. ↑ Forestry experimental and research institute Baden-Württemberg: Leaflet 54/2013 - Regeneration-oriented soil protection liming
  2. ^ Fritz Scheffer - Paul Schachtschabel: Textbook of Soil Science , 1998, p. 113
  3. ↑ Lime Colloquium 2013
  4. ↑ Selected results of the third national forest inventory
  5. ↑ Information brochure on the subject of forest liming

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