Trees have an amazing ability to adapt to new climates

Although tree species appear to prefer certain climates, their true preferences are often obscured by species interactions and dispersal limits.

During a recent yearlong sabbatical, Daniel Laughlin led a study that revealed trees can thrive in temperatures beyond their current habitats. 

Trees tolerate a range of climates 

“We were amazed. The result was crystal clear, and that doesn’t always happen in ecology,” said Laughlin, a professor in the University of Wyoming Department of Botany. 

“We found that tree species could grow and survive at one common moderate temperature, even though many species are only found in either cold or warm environments. In fact, many trees could expand their ranges by more than 25 percent based on their potential temperature tolerances.”

Laughlin is the lead author of a paper titled “Trees have overlapping potential niches that extend beyond their realized niches” published in the journal Science. 

How trees respond to climate change 

Co-authored by Brian McGill, a professor in the School of Biology and Ecology at the University of Maine, the study aims to understand how species respond to rapid climate changes by examining occurrences of North American tree species in arboreta worldwide to measure their tolerance to extreme temperatures.

The researchers quantified the realized and potential thermal niches of 188 North American tree species to test the architecture of niches on a continental scale. 

The study included 23 tree species native to Wyoming, such as the Engelmann spruce, the subalpine fir, and the ponderosa pine.

Trees and their potential niches 

According to Laughlin, the realized niche of a tree species is where it is found in nature, while the potential niche includes areas where it could survive but does not due to competition or dispersal limitations. 

For example, the Engelmann spruce, typically found in high-elevation subalpine forests, could also survive in warmer, lower elevations but is outcompeted by faster-growing species like cottonwoods.

The study revealed that tree species at thermal extremes occupy less than 75% of their potential niches, with species’ potential niches overlapping at a mean annual temperature of 12 degrees Celsius (approximately 55 degrees Fahrenheit).

Competition with other tree species 

“When we walk in the woods, we see with our own eyes that tree species occur in distinct places. This is a core tenet of ecology,” Laughlin explained. 

“However, where species are actually found in nature is a fraction of their potential distribution because competition with other species and dispersal limitation constrain where they actually occur.”

The findings challenge a core assumption of current methods for predicting species distributions, highlighting the need for ecologists to quantify the full range of environments tolerable to plants.

“This is a critical missing piece of information for predicting how they respond to a warming world,” Laughlin said.

Fundamental temperature tolerances of trees 

The results suggest that tree species will have varied fates with climate change. Cold-tolerant trees like Engelmann spruce may not need to move, while warm-tolerant species like live oak will need to migrate.

“North American tree species have been navigating changing climatic conditions for millions of years. We know that, over long time spans, trees have moved across the continent to track suitable climate conditions, but we don’t know how this will play out over the next few decades and centuries,” Laughlin said. 

“For example, the climate in Laramie may soon be suitable for trees from the Southwest that are adapted to warmer conditions, but we are uncertain about which species will arrive first.”

“Understanding the fundamental temperature tolerances of trees is an important first step to improving our predictions of how tree species’ ranges will shift over time.”

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