Sherlock Holmes and Lake Iffig

Environmental scientist Christoph Schwörer is piecing together vegetation history with the help of sediments from alpine lakes. And using data from the past, he’s also simulating the future tree line.

This took some detective work. How else could Christoph Schwörer have used fungal spores to prove that 7,000 years ago, people from the Valais crossed the Schnidejoch with their goats and sheep to reach the Bernese Oberland? The solution to the puzzle: The specialist in vegetation history discovered traces of Sporormiella in a sediment core from Lake Iffig near the Schnidejoch pass. That’s a fungus that grows especially well on cattle dung. Schwörer also found charcoal particles, a hint that the shepherds burned down the forest to create more pastures for grazing.

But what was it that suggested that it was people from the Valais – on the other side of the pass – rather than people from the much closer Bernese Oberland who let their herds graze at Lake Iffig? Christoph Schwörer whips out a pollen diagram showing how so-called “cultural indicator species” have changed around ​​Lake Iffig.

“In cold phases, when the glaciers advanced and the Schnidejoch was no longer passable, less fungal spores and charcoal particles appear in our sediment core,” is the environmental detective’s tidy explanation. As Sherlock Holmes would say, “Elementary, my dear Watson”.

Interdisciplinary cooperation

This evaluation of Lake Iffig’s environmental archive is part of a scientific publication written by Christoph Schwörer together with archaeologist and OCCR member Albert Hafner. The combination of climatic and vegetation reconstructions along with archaeological discoveries from the Schnidejoch led to the following jointly developed hypothesis: Valais was settled before the Bernese Oberland. But the mountainsides were covered in forest, with the best options for grazing above tree line. So the shepherds walked over the relatively easy Schnidejoch pass to take advantage of the additional grazing opportunities on the northern side of the Alps.

Christoph Schwörer first became acquainted with Lake Iffig while pursuing his doctorate. After completing his master’s degree in environmental sciences at ETH Zurich, he did his PhD thesis – “Drivers of Holocene Vegetation Dynamics in the Northwestern Swiss Alps” – at the Oeschger Centre. For this work he took an eight-metre-long sediment core from the lake near Lenk.

“With some luck, the oldest sediment can be traced back to the end of the last Ice Age, when the alpine lakes formed,” explains the climate researcher. Thus sediment cores from these lakes represent a climate and environmental archive that goes back 12,000 years.

Now Christoph Schwörer and his colleagues from the OCCR Research Group for Terrestrial Paleoecology are getting this archive to talk as they search for pollen in the sediments as well as remains of trees washed from the lake’s surrounding areas, including seeds, needles, leaves and bud scales.

“If we find many plant remains of a certain kind, we can assume that the forest was populated with that type of tree.”

Vegetation model as a time machine

However, Christoph Schwörer doesn’t just want to find out how the composition and spread of the plant species has changed over the past millennia. He is particularly interested in the future. For this purpose, he uses a vegetation model developed at the ETH Zurich – which he feeds with reconstructed data from the past.

“The model serves as a kind of time machine,” he explains. “If it is able to show the effects of the temperature fluctuations over the past 12,000 years, we can also project the future effects of climate change on the vegetation.”

The Bernese researcher is very familiar with the so-called LandClim model. He worked with it during his two-year stay at the University of Oregon in Eugene, where he did his Swiss National Science Foundation (SNSF) Early Mobility postdoc. In his second postdoctoral position at the Oeschger Centre, he is currently developing a very local but more precise view of future vegetation by means of model simulations. In one of his studies, he has simulated changes in the species composition and in the tree line around Lake Iffig until the year 2500 – and this within a radius of five kilometres and practically tree by tree. The simplified conclusion of this simulation: The tree line will rise considerably, and beeches will expand at the expense of spruces. But according to Schwörer, there will be fewer meadows and fields in the alpine vegetation zone, as some plants have a problem. They cannot survive at high altitude. The reason? The increase in temperature is much too rapid for humus to form on the rocky subsoil.

Christoph Schwörer is striving for an academic career. So for his next step on this challenging path, he’s applying to the SNSF for an Ambizione project. For this research project he hopes to examine alpine sediment cores with unrivalled thoroughness.

“Since the lake bottoms have a maximum temperature of 4°C, the DNA is preserved in plant remains. After the last ice age, plants were forced to shift their distributions due to climatic changes. I want to find out what happens to genetic diversity during these times.”

(December 2016)