A new study involving researchers at the University of Arizona suggests that climate is changing faster than trees can adapt. The discovery provides a "warning" for ecologists studying climate change. As the world heats up and climate shifts, life will migrate, adapt, or become extinct. For decades, scientists have used a specific method to predict how species will fare during this period of upheaval. However, according to new research, this approach may produce misleading or erroneous results.
Flaws in forecasting methods revealed
Researchers at the University of Arizona and members of their team at the U.S. Forest Service and Brown University found that this method, often called the "space-time proxy method," failed to accurately predict how a widespread tree species called conifer in the western United States has actually responded to climate warming over the past few decades. It also means that other studies that rely on space-time proxies may not accurately reflect species' responses to climate change in coming decades.
The team collected and measured tree rings from pine and cypress trees in the western United States as far back as 1900, and compared the trees' actual growth with model predictions of how the trees would respond to a warming climate.
"We found that the space-time substitution method produced predictions that were wrong in terms of whether they would respond positively or negatively to climate warming," said Margaret Evans, co-author of the paper and an associate professor at the University of Arizona's Tree Ring Research Laboratory. "This method believes that conifers should benefit from climate warming, but in fact they are affected by climate warming. This is dangerously misleading."
Their findings were published in the Proceedings of the National Academy of Sciences on December 18. U.S. Forest Service ORISE researcher Daniel Perret is the lead author and received training in tree ring analysis at the University of Arizona laboratory through the school's summer field methods course. The research was part of his doctoral thesis at Brown University with Dov Sax, professor of biogeography and biodiversity.
Inaccuracies in space-time displacement
The principle of space-time displacement: Each species has its preferred range of climatic conditions. The scientists hypothesized that individuals growing at the hotter end of the range could serve as an example of what might happen to populations in cooler sites under future climate warming.
The team found that coniferous trees grow faster in warmer locations. According to the space-time substitution paradigm, this suggests that as the climate warms, things should get better at the cold edge of the distribution.
"But looking at the tree ring data, that's not the case," Evans said.
When the team used growth rings to assess how individual trees responded to changes in temperature, they found that coniferous plants were consistently negatively affected by changes in temperature. If it's a warmer-than-average year, their growth rings will be smaller than average, so warming is actually bad for them, and that's true everywhere.
The team suspects this is happening because trees are unable to adapt quickly to a rapidly changing climate.
A tree and all its growth rings record the tree's genetics under different climate conditions from one year to the next, Evans said. But how a species responds as a whole is the result of slow evolution adapting to average conditions that differ from one location to another. Like evolution, the migration of better-adapted trees as temperatures change has the potential to save species, but climate change happens so fast.
Effects of Rainfall and Final Thoughts
In addition to temperature, the team also studied how trees respond to rainfall. They confirmed that more water is always better, both in terms of time and space.
"These space-based predictions are really dangerous because the spatial patterns reflect the endpoints over long periods of time during which species have had a chance to evolve, disperse, and ultimately adjust themselves across the landscape. But that's not the case with climate change. Unfortunately, trees are finding themselves in environments that are changing faster than they can adapt, which really puts them at risk of extinction. This is a warning to ecologists," Evans said.
Reference: "Species' responses to spatial climate variability do not predict their responses to climate change", author: Daniel L. Perret, Margaret E. K. Evans, and Dov F. Sax, December 18, 2023, "Proceedings of the National Academy of Sciences".
DOI:10.1073/pnas.2304404120
Compiled source: ScitechDaily