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Data series up to 130 years old provide answers for tomorrow's forests

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“To create a sound basis for forestry to its fullest extent” was the mission given to the predecessor of WSL, the ‘Central Station for Experimental Forestry’ in 1885. From the outset, this included researching open questions on the development and management of Swiss forests and communicating the findings to forestry practitioners.

To fulfill this mission, WSL still carries out numerous series of experiments on the growth of the most common tree species and forest types. It operates 390 permanent plots in Switzerland, covering a total area of 132 hectares, which is about as large as 180 football pitches. Researchers measure the growth in trees’ diameter and height, and record dead individuals and the intensity of silvicultural interventions. The plots represent very different types of forest: most on the Central Plateau are covered with beech and Norway spruce, and others with oak; chestnut trees dominate in the Southern Alps; while larch and Swiss stone pine trees are more common in the higher mountain areas.


In the Pre-Alps and the Jura, the WSL collects data from so-called ‘plenter forests’ (literally ‘plent forests’), in which foresters regularly harvest only a few of the largest trees. “The data set, which is more than 100 years long, is one of the most valuable in the world for such mixed forests,” says David Forrester, a researcher in the Research Group ‘Stand Dynamics and Silviculture’. The findings from this research help foresters and forest owners to optimally control the incidence of light in plenter forests, in which tree species that need light, such as Norway spruce and beech, and those that are shade-tolerant, such as silver fir, both grow.

A treasure trove for answering new questions

“Our long-term data series, obtained from more than 450,000 individual trees, show how trees react to external influences,” says David. This enables researchers to inform foresters about, for example, which tree species mixtures are most suitable for producing high-quality timber and ensuring that forest management is sustainable and as close to nature as possible. Or they may explain where and how mountain forests provide protection against avalanches and rockfall. “The impact of climate change on forests managed in different ways is a typical example of an environmental change that raises new questions for forestry,” says David. (Reinhard Lässig, Diagonal 1/19)