Study reveals flawed climate change predictions

By James Gamble via SWNS

A widely used method for predicting the impacts of climate change on plant species is flawed, according to a new study.

A tree thought to grow faster in hotter weather actually grew slower, exposing the problem.

American researchers found the ponderosa pine, which was expected to favor warmer weather, actually suffered detrimental effects from the warming climate of the past few decades.

The method used to predict how the tree would fare is therefore flawed, scientists say - meaning thousands of other climate change predictions for plant species may also be wrong.

The climate scientists behind the study suggest this may be because the trees can't adapt fast enough to keep up with the quickly changing climate.

They warned that for ecologists to rely on predictions from this current method, known as the space-for-time substitution, could prove "dangerous."

As our planet's climate heats up and shifts, life on Earth will be forced to either migrate, adapt or go extinct.

For several decades scientists have used the space-for-time substitution to predict how plant species will fare in this changing climate.

But now, a research team from the University of Arizona believes this method could be producing erroneous and misleading results.

The space-for-time substitution method infers that each species occupies a preferred range of climactic conditions.

It's therefore assumed that the individuals growing at the hotter end of that range can serve as an example of what might happen to populations living in cooler locations in a warmer future.

The researchers, along with collaborators at the US Forest Service and Brown University, discovered that the space-for-time substitution method inaccurately predicted how a widespread tree of the Western US, the ponderosa pine, has responded to the last several decades of warming.

The team collected and measured ponderosa pine tree rings from across the region from as far back as 1900, and compared the trees' actual growth to how the model predicted the trees should respond to warming.

They found that the ponderosa pine trees grow at a faster rate at warmer locations.

Under the space-for-time substitution method, this suggests that as the climate warms, it should serve the species favorably.

However, when the researchers used tree rings to assess how individual trees responded to changes in temperature, they found that the ponderosa's were consistently negatively impacted by temperature variability.

The team behind the study, published in the journal Proceedings of the National Academy of Sciences, suspects this happens as the trees simply cannot adapt fast enough to keep up with the fast-changing climate.

Plant population biologist Dr. Margaret Evans, a study co-author and associate professor in the UArizona Laboratory of Tree-Ring Research, explained: "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.

"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."

A tree's rings are a record of the genetics of that specific tree being exposed to different climatic conditions in one year compared to the next.

But how a species responds as a whole is the result of the slow pace of evolutionary adaptation to the average conditions at a specific location, which are different from another location.

Like evolution, migration of better-adapted trees with the changing temperatures could potentially rescue species - but climate change is happening too fast, the researchers said.

The team also investigated how trees respond to rainfall, and confirmed that more water is always better whether you look across time or space.

"These spatially-based predictions are really dangerous," Dr. Evans concluded.

"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.

"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."