When dry periods last for several years and are particularly severe, many ecosystems lose some of their ability to stay productive. A new international study published in Science, in which Innsbruck ecologist Michael Bahn participated, shows that repeated extreme droughts significantly slow the recovery of grassland and shrubland ecosystems
Severe droughts not only affect plant growth in the short term, but can also alter the functioning of entire ecosystems. This is the conclusion of an international team that carried out coordinated field experiments on six continents to understand how prolonged water stress affects vegetation. The researchers also investigated the consequences for the global carbon cycle, as grass- and shrub-dominated landscapes cover roughly 40 percent of the Earth's land area and play a central role in regulating it. "Our data show that the intensity of drought is crucial, and that the impact becomes much stronger when extreme droughts occur repeatedly," says Michael Bahn , head of the Functional Ecology research group at the University of Innsbruck.
As part of the International Drought Experiment (IDE) - a global network of more than 170 scientists - rainfall was experimentally reduced in grassland and shrubland plots. This allowed the team to track how drought duration and intensity affect plant productivity. The results were striking: after four consecutive years of extreme drought, vegetation growth was on average 2.5 times lower than in the first dry year. Severe and repeated droughts led to a marked decline in above-ground biomass, while ecosystems exposed to moderate dry spells often showed signs of stabilization.
Implications for Europe and Austria
Bahn points out that these findings are also relevant for Europe and Austria. "We are already observing that drought events are occurring more frequently and with greater intensity, especially in drier regions in the East and South of Austria, as well as in parts of the Alps, such as the Tyrolean Oberland," he explains. Even if total precipitation remains roughly the same in the future, rising temperatures will lead to increased evaporation and drier soils. This will put more pressure on vegetation and increase the risk of crop failures. "Grasslands are an important foundation for European agriculture and play a key role in climate protection by storing large amounts of carbon. As droughts become more intense, these ecosystems are weakened, affecting biodiversity, water resources and the global carbon cycle," says Bahn.
Climate protection measures as the key
"The more successfully we limit the overall rise in temperature, the lower the risk of frequent and severe droughts," says Bahn. "Climate protection measures are therefore a direct way to maintain the resilience of ecosystems."
The study provides a solid basis for predicting how climate change will affect natural and agricultural ecosystems and for developing effective adaptation strategies. It also highlights how closely ecological stability and human well-being are connected - from carbon storage and biodiversity to water supply and agriculture. Understanding these links will be crucial to mitigate the long-term effects of increasing drought.
Publication: Drought intensity and duration interact to magnify losses in primary productivity.
T. Ohlert et al. Science (2025). DOI: 10.1126/science.ads8144
