Grasslands are among the most biodiversity-rich ecosystems, including various communities of animals, plants, and other species. Unfortunately, though, they are exposed to the adverse impacts of climate change.
According to a study led by Dr. “Kai Zhu”, Associate Professor of Environment and Sustainability at the University of Michigan, and Dr. “Yiluan Song”, Postdoctoral Fellow at the Michigan Institute for Data Science, the adaptive capability of the native grassland communities is threatened by rising temperatures and droughts caused by reduced rainfall, leading to the invasion of alien species, which in turn causes a disturbance to the ecosystem.
The study, published in Nature Ecology & Evolution on October 16, 2024, reveals that climate change is rapidly shifting grassland communities in the California Floristic Province (CFP) faster than forests. These findings can be generalized to the grasslands worldwide.
We reached out to Drs. “Kai Zhu” and “Yiluan Song”, for an interview. Here is the text of the interview:
1- Why was your research curious about exploring the impacts of climate change specifically on grassland communities?
There are two main reasons. On the one hand, it has been widely shown that forest communities exhibit lagged responses to climate change in terms of community composition. By focusing on grasslands, we hoped to uncover whether certain terrestrial plant communities are more sensitive to climate change than others. We hypothesized so because grassland communities are dominated by short-lived species that are directly exposed to macroclimatic changes. On the other hand, grasslands in regions like the California Floristic Province (CFP) are highly dynamic and often heavily invaded. It is important to study their vulnerability and resilience under climate change to inform conservation and restoration.
2- Could you explain the approach utilized in the study?
We compiled species' relative abundances across 12 observational sites and in three global change experiments. We estimated the climate niches of each species, which represent their preferences for temperature and precipitation. With the relative abundance and climate niche data, we calculated the community temperature index (CTI) and community precipitation index (CPI). These community-level indices allowed us to quantify shifts in community composition along temperature and precipitation axes, referred to as thermophilization and xerophilization. This approach provided a direct and intuitive measure of how communities respond to warming and drying over time and under experimental conditions.
3- How does climate change induce the rapid response of grassland communities?
We observed that under warming and drying in the CFP, species associated with warmer and drier climates tend to increase in relative abundance or appear in communities, while species associated with cooler and wetter climates tend to decrease in relative abundance or disappear from communities.
There are a few reasons that make grassland communities highly responsive to climate change. First, grassland communities consist largely of short-lived species that are annual or perennial. In addition, grass species in this area with the Mediterranean climate undergo seasonal dormancy in the dry summers, further accelerating abundance changes. These life history traits allow for more immediate shifts in relative abundances in response to environmental changes.
Second, while forests create microclimates under the canopy that buffer the effects of macroclimatic change, grasslands are more directly exposed. Furthermore, grasslands, especially those in the CFP, are often heavily invaded by non-native species, many of which are adapted to warmer and drier conditions and grow rapidly in abundance.
4- In what ways does this impact the biodiversity of the grassland communities?
On a species level, these shifts reflect the decline of cooler and wetter species, many being native species, as well as the increasing dominance of warmer and drier species, many being non-native species. On a community level, the change in the combination of species might alter species interactions and ecosystem functioning.
We hope that our work not only raises awareness for climate change mitigation but also informs conservation and restoration efforts, such that we can protect and design grassland communities intentionally with future climates in mind.
5- What are the anticipated outcomes in light of the worsening global warming?
As global warming intensifies, we anticipate that grassland communities will continue to experience rapid compositional shifts. However, this responsiveness may be constrained by the climate niches of species available, especially as we see unprecedented combinations of temperature and precipitation.
Beyond grasslands, our work suggests that terrestrial plant communities will undergo diverse pathways under climate change. The term “climatic debt” describes anticipated biodiversity changes as a delayed response to climate change. We show that grassland communities are shifting in composition and paying off their climatic debts continuously, but for forest communities that accumulate climatic debts, we might expect abrupt reshuffling in the future.
