Water is a scarce resource in many ecosystems on Earth. This scarcity will likely increase with climate change. This, in turn, could lead to a considerable decline in plant diversity. Using experimental data from around the world, scientists from the Helmholtz Center for Environmental Research (UFZ), the German Center for Integrative Biodiversity Research (iDiv) and the Martin Luther University in Halle-Wittenberg (MLU) first demonstrated time that the plant biodiversity of arid zones is particularly sensitive to changes in precipitation. In an article published in Nature communications, the team warns that this may also have consequences for people living in affected areas.
How will climate change affect Earth’s ecosystems? How will biodiversity change in different regions? Such important questions about the future are difficult to answer. To do this, it is important to know how individual species and their communities will react to changes in precipitation conditions, for example. But despite many scientific experiments in the world, we do not have synthetic and comprehensive answers to these questions. For example, the experiments differ considerably in their methodology, for example whether they add small or large amounts of water. “These studies use different methods and are located in different regions of the world,” explains the first author, Dr. Lotte Korell, biologist at UFZ. “And these studies give conflicting results in many cases.” With her colleagues, she therefore set out to gain a general understanding of the data collected around the world. The focus was on how an increase or decrease in precipitation affected the plant diversity of terrestrial ecosystems.
In their search, she and her team found 23 usable publications, which presented the results of 72 field experiments. With this data, they calculated various statistical variables that provided information on the biodiversity of individual sites and related it to increasing or decreasing amounts of precipitation.
“However, in such experiments, biodiversity depends on many factors,” says Professor Tiffany Knight, the latest study author and environmentalist at UFZ, iDiv and MLU. For example, the size of the experiment plays an important role. If you focus on a single experimental plot, then you might see dramatic effects of treatments on biodiversity, as plots with less water have fewer plant individuals growing there, and therefore fewer species. However, at least one individual of each species could be found on a larger scale, and therefore a lesser effect of the treatment on biodiversity. Indeed, the researchers found that increasing drought has a larger effect when viewed at a small scale compared to larger spatial scales. “So, to draw the right conclusions from the data, you need to take into account both local climatic conditions and the spatial scale of the experiments,” says Knight.
In this way, the researchers identified a clear trend. In arid areas of the world, changes in precipitation levels have a much greater effect than in more humid regions.
Dry ecosystems currently occupy about 40% of the Earth’s land surface. It is not easy to predict what awaits these areas in a context of climate change. Although climate models predict increased precipitation in some dry regions, water scarcity is likely to worsen in most of them.
According to the study, plant diversity should increase where it becomes wetter. This is probably because the seeds of the species found there may have a better chance of germinating and establishing themselves.
However, given the expected expansion of drylands, this effect is likely to benefit only a relatively small number of regions. According to the authors, this would lead to a notable decline in plant diversity. “Although plants have adapted to the challenges of their habitats over long periods of time,” Korell says, “at some point, even the most resilient survivor reaches their limits.” And with each species that dries up and can no longer germinate, biodiversity is reduced.
This could be bad news not only for ecosystems but also for people living in drylands. After all, they make up about a third of the world’s population. Many of these people struggle to make a living off the land under the most difficult conditions. If biodiversity decreases with rainfall, this will likely become an even greater challenge. For Korell and his colleagues, this is another pressing argument for slowing climate change. “It is also important to protect drylands particularly well,” explains the researcher. The more these sensitive ecosystems are subjected to the pressure of overgrazing and other stressors, the more likely climate change is to affect plant diversity.