In 2017, the Bighorn National Forest experienced a relatively healthy year with sustained improvements in the management of some of the threats to forest health, a report compiled by the USDA Forest Service concluded.
Kelly Norris, Buffalo district forester, agreed with the report’s assessment.
“Overall, we’ve had a pretty good year. There have been no major outbursts or anything that would be a real threat we would immediately need to mitigate,” Norris said.
She added that the environmental factors that contribute to forest health have remained stable as well.
“We’ve had pretty good moisture over the last couple of years; we’ve seen our snowpack stay above 100 percent,” Norris said. “So we aren’t seeing anything drastically changing in our environment, but that’s not to say that’s not going to happen.”
There are still diseases and insect infestations throughout the forest, however, and while some of those threats improve each year, some pose long-term concerns to forest health.
The report noted that subalpine fir deaths, which have been a concern over the past 20 years, were down in 2017, sustaining a trend of decreased fir deaths since 2012. The report also showed that the western balsam bark beetle was the most common cause of death among subalpine firs, which Bernie Bornong, the resource staff officer for the Bighorn National Forest Service, said was evidence the trees’ lifecycles were occurring naturally.
“As the trees get older and larger, they become more vulnerable to the bark beetle,” Bornong said. “The trees and the beetle kind of go back and forth. After [trees die], they are replaced by younger and stronger trees that, as they age, become susceptible to disease, just like humans… that’s part of the natural cycle.”
Dwarf mistletoe, a parasitic plant that stunts the growth of trees and causes them to develop abnormal growths, has also seen a marked reduction in the last five years, according to the report. The plant spreads by inducing the host tree to drop seeds on younger trees in the understory, so treatments that remove infected trees have proven to be effective.
Bornong noted, however, that these treatments were confined to areas that have been identified as crucial to timber production, which is only a fraction of the forest.
“There’s about 700,000 forested acres in the Bighorn and there’s dwarf mistletoe all through that,” Bornong said. “And in 100 years, the forest management of the Bighorns has treated maybe 100,000 acres total.”
The most concerning threat to the Bighorn’s health, Bornong said, is a disease called white pine blister rust. It is not native to the United States, which means the trees do not have inherent resistances to it. Bornong said disease spores were brought to the continent, accidently, with European nursery transplants around 1900 and have spread through wind or birds over the last century. Though he does not know exactly when the disease made its way to the Bighorns, Bornong said it has been spreading in the forest for the past several decades.
“I would say way more than half, and maybe pushing 80 or 90 percent, of the limber pine in the forest have white pine blister rust,” Bornong said. “It’s become pretty widespread.”
Trees in the forest could adapt naturally to resist the threat, but Bornong said forest management is also working on genetic breeding efforts to introduce more resistant trees into the forest. Those efforts require forest service staff to identify trees that appear to be more resistant to the disease and collect their pine cones and send them to a nursery where a geneticist can test to see if certain stock is in fact more resistant. One concern on the horizon is the presence of the mountain pine beetle in the forest. Bornong said that beetle has caused “historic” damage to pine forests in the western United States and parts of Canada, but Bighorn has, so far, resisted that kind of damage. But that does not mean the forest is protected from the threat going forward.
“About a third of the Bighorn burned in the late 1800s, and lodgepole pine doesn’t really become susceptible to mountain pine beetle until about age 100,” Bornong said. “So there’s a lot of the Bighorn that is coming online very soon. That could be the reason, that our forest is just a little bit younger and we will see that epidemic occur in the next few decades.”
Norris also said that forest management will have to start tending to the long-term health of the forest.
“Our forests are looking good but our forests are, on average, over 125 to 130 years old,” Norris said. “And as we start to see drier climates, less moisture and warmer temperatures, that will stress our trees. And something has got to give in that. In the future, I think we could start to see some large-scale die-offs. We just haven’t seen that yet.”
Those concerns are unlikely to manifest themselves in 2018, but forest managers will continue looking ahead to ensure a healthy future.