Climate change has many different facets, which can have different effects depending on the location. For example, increasing temperatures may bring a decrease in biodiversity to already dry sites, while a similar increase at a rather wet and cold site may lead to an increase in biodiversity. What is likely to change fundamentally, however, is the composition of communities. Recent global studies show that ecological communities are becoming more similar over time; this is referred to as "homogenization". Moreover, the consequences of climate change always depend on how fast the climate is changing and whether local communities can adapt and spread species. If the change is too rapid, species will not "catch up" and may become extinct, at least locally.

Biodiversity is primarily threatened by extreme climate events, such as droughts and floods. It is therefore not so much the slow changes in temperature, but the increase in extreme events that accompany them, that leads to extinction events. After all, we have been able to observe in recent years how nature has suffered from the recurring dry summers. If individual species are lost, this can result in a whole cascade of further extinction events, because all species are linked to each other by a multitude of interactions. Alexander von Humboldt already pointed out this network of biological diversity. Our studies show that, for example, the local loss of plant species causes insect species to disappear as well, and that fewer invertebrates and microorganisms are found in the soil. This in turn has an impact on animals that depend on these insects, such as birds, and so on.

Earthworms have been used as so-called bioindicators for some time. This means that the presence of earthworms can provide information about how healthy a soil is, how well natural decomposition and mineralization processes take place, how heavily fertilized and polluted soils are, and how much they are tilled. These natural decomposition processes are central to the functioning of our ecosystems and determine how well nutrients are made available and how plants can grow. In addition, earthworms are often representative of other soil animals and microorganisms because, as so-called "ecosystem engineers", they promote the biodiversity of these organisms. Earthworms structure the soil environment, work plant material into the soil, create a system of tunnels, and thus have a major impact on other soil organisms.

Predictive models are playing an increasingly important role in biodiversity research. They allow us to clarify what consequences our past, present and future actions will have on biodiversity and to take appropriate countermeasures. We are continuously working to improve these models by identifying the important control variables for different plant, animal and microbial species. There is still work to be done, of course, but we cannot wait to take countermeasures until we have a suitable model for each species, because by then it will already be too late to take any. For soil biodiversity, we therefore initially focused on earthworms and were able to show that a changing climate will have a major impact on soil animals. Such predictive models are therefore of great and growing importance in nature conservation and policy advice.

There is still a lot of biodiversity to be explored in the soil; it is therefore often referred to as a "black box". With the knowledge generated, we can then better understand why which species communities occur where and how they function. The next step should be for biodiversity researchers to offer solutions to help us conserve and protect this diversity so that we can manage ecosystems in a sustainable way. For this, it is important to prepare and present the scientific findings to decision-makers and the public in an understandable way. We are part of the ecosystems on which we depend, for example, to produce food and to have clean water and air - this understanding should guide our actions.

Interview: Beatrix Boldt