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Examining forest health by foliar analysis

The long-term Forest Ecosystem Research (Langfristige Waldökosystem Forschung) is a project run by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), which aims at monitoring the effects of air pollution and climate change on Swiss forests. One aspect is the foliar analysis, which is carried out every two years. It consists of the chemical analysis of tree leaves and needles of five to six trees of the dominant tree species per site, with the goal of identifying nutrient deficiencies or imbalances at the study sites.

Looking at oak leaves with various discolorations caused by fungal infections and aphids together with my supervisor M. Schmitt.

My experience

The internship consisted mostly of lab work and few field days. Leaf branches were harvested from the dominant tree species at the project sites in August 2021, and then brought to WSL for foliar analysis. There, discolorations due to fungal infections and insect traces on beech, oak, and hornbeam were analysed. Symptoms were recorded to characterise the overall tree health at the respective sites. Subsequently, leaf samples were collected, then weighed, the leaf area scanned, dried, re-weighed, milled, residual water content measured, samples weighed into tin capsules, and sent for chemical analysis at the central lab. 

All work was completed within the Forest Soils and Biogeochemistry research unit at WSL. I experienced a pleasant and collegial atmosphere, where I was trusted to work independently very quickly. Still, everyone was available to provide help, if asked. No special skills are needed for this internship, although a general background in environmental sciences and the ability to work independently is expected. Additionally, previous lab experience is appreciated. However, knowledge about the diseases affecting trees in Swiss forests is not implied and can be acquired during the internship. 

Organisation of the internship

Generally, internships are announced via the official portal. However, I organised this internship via an ETH professor since I was looking to find work for a specific time frame. Hence, I would recommend to first check the available positions, before asking directly. From my experience, the people at WSL are very friendly and accommodating: If they have enough work and funding for an internship, they will gladly organise the employment.

Lisa Maria Pirisinu

Weiterführende Informationen



Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft (WSL)


Zürcherstrasse 111
CH-8903 Birmensdorf


Max. 6 months, depending on the internship


Paid, WSL salary key


For any questions you can contact me.