uni'wissen 02(4)-2011_ENG

sary or not. Rather, we are looking for concrete patterns,” explains Prof. Dr. Markus Weiler, Di- rector of the Institute of Hydrology. “What inter- ests us is a naturally occurring extreme drought. We thus need an extremely low level of precipita- tion for the experiment.” In order to simulate such climatic conditions, the research team built half-open roofs of various sizes under the crown growth in their experimental plots. The project was launched at the beginning of 2011. In the spring the original state of each plot was documented, and in the summer the roofs were built. In order to enable a direct compari- son, the team left control plots in which every- thing remained untouched. The three research groups are all – each within the context of their own discipline – investigating the impact extend- ed drought has on the forest ecosystem. Weiler and his team, for instance, are studying how the soil structure changes: Will there be cracks in the ground or more water-repellent material? Will the flow paths along the roots change? And will the drought influence the transpiration of plants, i.e., how they give off water vapor? In or- der to answer these questions, the team needs sensors. They have placed 25 of them in the ground and in the trees of each plot. Among oth- er things, the sensors measure the amount of precipitation, the air and soil temperature, the moisture content of the soil, and the flow of sap in the trees. “The point is not to make predic- tions,” says Weiler. “We want to find out how so- ciety could react to climate change for its own protection.” Less Diversity, More Ticks? Prof. Dr. Michael Scherer-Lorenzen would like to conduct research at the covered plots in the exploratorium in a second project phase starting in 2014 in order to answer further questions: How great is the impact of diversity and drought on the nutrient intake of the plants? And which plants complement each other best? The Univer- sity of Freiburg biologist already participated in the Jena Experiment begun in 2002, which found evidence for a relationship between changes in biological diversity and important ecosystem functions. “We don’t just want to determine the role biological diversity in the forest plays for the functioning of ecosystems; we also want to quan- tify its goods and services,” explains Scherer- Lorenzen. What the Jena Experiment found is that “species-rich meadows can recover more quickly from severe drought and are less sus- ceptible to drought when there is too little pre- cipitation several years in a row.” In addition, in many cases mixed forests have a higher produc- tivity than monocultures. Productivity refers to the production of biomass that can later be har- vested and sold. On the meadow this means hay, in the forest wood. There are many – sometimes unusual – ways to approach the topic of biodiversity: For a proj- ect scheduled to begin in 2012, Scherer-Loren- zen has joined forces with medical researchers at the university. Using the example of Lyme dis- ease, they aim to provide evidence for the con- Covered up: The researchers are simulating drought in the ­forest with half-open roofs under the treetops. The picture shows how the roofs are built. 34