TUCSON, Ariz. — There are flaws in a commonly used method for predicting the impacts of climate change on plant species, a new study explains. Contrary to expectations, the ponderosa pine, a tree previously thought to thrive in warmer weather, has actually suffered adverse effects due to the recent warming climate.
Researchers from the University of Arizona, the U.S. Forest Service, and Brown University are now challenging the reliability of the widely used “space-for-time substitution” method. This method, which has been instrumental in climate change predictions for decades, is based on the assumption that species occupying the warmer ends of their climatic range can indicate the future response of species in cooler areas under a warming climate.
However, the study, published in the journal Proceedings of the National Academy of Sciences, reveals that this approach may lead to inaccurate predictions. The research team analyzed tree rings of the ponderosa pine across the Western U.S., dating back to 1900, to compare the trees’ actual growth against predictions made by the space-for-time substitution method. While this method predicted increased growth rates in warmer conditions, the actual tree ring data indicated a consistent negative impact from temperature variability on the ponderosa pines. The findings suggest that these trees, and potentially other species, are unable to adapt quickly enough to the rapidly changing climate.
This revelation raises concerns about the reliability of thousands of other climate change predictions made using this method. The researchers warn that ecologists relying on these predictions could face significant risks. The study highlights the urgent need for alternative approaches to predict the responses of plant species to a changing climate, emphasizing the potential consequences of migration, adaptation, or extinction of life on Earth.
“We found that space-for-time substitution generates predictions that are wrong in terms of whether the response to warming is a positive or negative one,” says Margaret Evans, a co-author on the paper and an associate professor in the UArizona Laboratory of Tree-Ring Research, in a university release. “This method says that ponderosa pines should benefit from warming, but they actually suffer with warming. This is dangerously misleading.”
Dr. Evans adds that though the ponderosa should be thriving in the warmer climate according to the space-for-time method, “in the tree ring data, that’s not what it looks like.”
“If it’s a warmer-than-average year, they put on a smaller-than-average ring, so warming is actually bad for them, and that’s true everywhere,” Evans explains.
Tree rings provide a record of how the unique genetics of a specific tree react to varying climatic conditions from one year to the next. However, the response of a species as a whole is shaped by the gradual pace of evolutionary adaptation to the average conditions of a specific location, which differ from those of other locations.
The researchers noted that similar to evolution, the migration of trees better adapted to changing temperatures could potentially aid in the survival of species. However, they emphasized that climate change is occurring too rapidly for this to be a viable solution.
Additionally, the team conducted research on how trees respond to rainfall. They confirmed that increased water availability is consistently beneficial, regardless of whether it is examined over time or across different geographical areas.
“These spatially based predictions are really dangerous, because the spatial patterns reflect an end point after a long period of time when species have had a chance to evolve and disperse and, ultimately, sort themselves out on the landscape,” Evans concludes.
“But that’s just not how climate change works. Unfortunately, the trees find themselves in a situation where change is happening faster than the trees can adapt, which is really putting them at risk of going extinct. It’s a word of caution for ecologists.”
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South West News Service writer James Gamble contributed to this report.
