Slow-growing ponderosa pines may have a better chance of surviving mountain pine beetle outbreaks in western Montana as climate change increases the frequency of drought and insects, according to new research from the University of Montana.

Led by UM biological sciences Professor Anna Sala, the team of researchers published its findings this month in the journal Proceedings of the National Academy of Sciences.

The study found that young families of fast-growing ponderosa pines typically survived to maturity better than slow-growing ones. But that wasn't the case when mature trees were affected by a mountain pine beetle outbreak.

In that scenario, Sala said, slow-growing families survived better.

“Our findings explain why natural tree populations maintain a mixture of genotypes with different growth rates,” said Sala. “The study illustrates why the maintenance of genetic diversity is critical to cope with the varying demands as organisms grow and as environmental conditions change.”

The team used a combination of data to show that fast growth in trees may be costly.

Sala said they measured survival after a mountain pine beetle outbreak, when trees were almost 40 years old. They applied long-term data sets on survival and growth rates of more than 4,000 trees planted in 1974 and provided by the Inland Empire Tree Improvement Cooperative.

With these data, Sala said, the researchers were able to show in a long-lived organism that the specific genotypes that survive at any given point in time had changed over time.

Their study shows that under some circumstances, such as high bark beetle densities during an outbreak, fast growth is costly.

The article, "An insect outbreak shifts the direction of selection from fast to slow growth rates in the long-lived conifer Pinus ponderosa" can be accessed online.