Cankers caused by climate

A native fungal pathogen that was once considered relatively harmless has become increasingly damaging to Eastern white pines since the late 1990s, and it appears to be most severe in stressed, weakened trees. Researchers from the University of Maine said that serious damage from the pathogen, Caliciopsis pinea, was first noticed in central New Hampshire, and it is now having a noticeable effect on New England’s forest products industry.

William Livingston, associate director of the UMaine School of Forest Resources, and doctoral student Kara Costanza have been studying how the pathogen affects trees and how severely the trees are impacted. They have also attempted to quantify the damage. After

Canker photo by Kara Costanza

processing 60 white pines from southern New Hampshire and southwestern Maine for lumber, they found 48 percent were infected with the pathogen, and it resulted in a lower grade or value in about 13 percent of the lumber.

By correlating the presence of Caliciopsis cankers with the year when the infections occurred, the researchers determined that climate extremes like drought or significant precipitation events predispose trees to increased damage. They said the pathogen also causes more damage on trees growing in extremely dense stands or in poor soils.

“Dry summers are definitely associated with a lot of canker initiation,” Livingston said. “At one site where we found the worst cankers, it wasn’t drought but when a hurricane came through that corresponded with the onset. Whatever adversely affects the roots seems to do it.”

Trees with the pathogen show considerable stem damage, as the fungus works its way into the bark and kills the cambium.

“White pines produce a resin in reaction to the pathogen, indicating something is killing the tissue inside the tree,” explained Livingston. “We’re finding the fungus is associated with the resin.” A U.S. Forest Service survey of white pines in New Hampshire found 70 percent of stands showed symptoms of stem resin.

A small insect called the white pine bast scale has also been implicated. It feeds on tree stems, which may provide the fungus with access into the trees.

To avoid tree damage from the pathogen, the researchers recommend low density management of white pines. Wider spacing of trees appears to reduce the risk of fungal damage.

“This is not a threat to the supply of white pine, but if you don’t manage your stands, you’re going to have less wood and less quality stands,” Livingston said. “The more the stands can be managed, the less risk you’ll have of damage during dry years or when other stresses hit the trees. Thinning may not stop the fungus, but it definitely decreases the size of the canker.”

The researchers plan to continue monitoring tree damage over time to see if managed stands have fewer problems associated with the pathogen. “We’ve gone through a couple of dry summers, so according to our hypothesis, we should see an uptick of problems,” concluded Livingston. “Our next step is to see if, as we get more extremes in climate, are these problems with white pines going to increase.”

This article first appeared in the spring 2018 issue of Northern Woodlands magazine.