Eastern white pines, the most abundant tree species by volume in the region, are under stress from several years of wetter springs unleashing a string of pathogens impacting the trees’ health and growth.
If it the climatic trend continues, it could change the face of the region’s forests and the economic vitality of its timber industry.
The result is obvious to anyone seeing infected white pine stands - needle drop in summer as opposed to autumn, a change that began nearly a decade ago and in some areas has accelerated.
“In the old days, 20 to 30 years ago, it would come and go,” said Kyle Lombard, program coordinator for the forest health section of the New Hampshire Division of Forests and Lands. “We expected it to come and go this time around, but it hasn’t gone yet. It may be here to stay.”
Among those researching the extent of the damage and developing recommendations to landowners and timber managers is University of New Hampshire doctoral student Cameron McIntire, with UNH’s Agricultural Experiment Station.
“One of the most interesting things about these diseases is they are all native,” said McIntire. “It’s uncharacteristic to see native pathogens blowing up like this as opposed to what we normally see with invasive species. Part of the issue is climate-related. They respond to very warm temperatures and very wet climates, which is coincides with what we’ve been seeing in this part of the country.”
Six of the 10 wettest springs on record have occurred in the past decade, according to more than 100 years of New Hampshire data, he said.
That has allowed the four main types of fungal pathogens to do their damage.
Beginning about eight years ago, the pathogens - collectively called white pine needle damage - began impacting the white pines, which are now experiencing maturing and yellowing needles in early spring with needle drop around mid-June instead of during the natural cycle of defoliation in October, according to the UNH study.
As a consequence, nearly 50 percent of the total annual needle drop occurs in early summer when the stands of white pines that are affected cast most of their mature second- and third-year foliage.
Aerial surveys show thinner crowns and up-close inspections have found one or all four pathogens in a tree, and certainly within a stand, said McIntire.
As of result of the summer litterfall, the majority of the mature foliage is shed during the most productive part of the trees’ growing season and they are not able to take in as much carbon for growth.
“Trees aren’t able to assimilate carbon at the same rate they normally would,” said McIntire.
New needles, too, take about four months to fully develop, and during that process they do not photosynthesize at the same rate as mature needles, he said.
Infected trees are also not able to absorb nitrogen - critical to facilitate photosynthesis - from the cast needles in summer.
Eastern white pine stands that are impacted experience anywhere from 25 to 75 percent reduced stem growth, according to the UNH research.
Branch die-back is also a result.
The Eastern white pine makes up more than half a million acres of forestland in New Hampshire.
Of the roughly 30 billion board feet of saw timber, nearly one-third is white pine.
In all, Lombard and McIntire estimate about one-third of white pine stands in the Granite State are infected in some way.
In addition to impacts on the timber industry, which Lombard said has been hit because of reduced growth rates, there are also effects to the larger ecosystem as several wildlife species depend on the trees.
Seeds are consumed by small mammals and birds, and deer and rabbits browse the foliage.
“White pine is certainly a very important tree species,” said McIntire. “Lots of birds rely on it. Bald eagles use it for roosting, and it makes great perches for raptors.”
In Vermont, Josh Halman, forest health specialist for the Vermont Department of Forests, Parks and Recreation, said the impacts to the Eastern white pine were first seen in 2009 and in recent years have become more pronounced.
In the 2016, Vermont mapped and recorded the largest amount of white pine acreage damaged, more than 30,000 acres, he said.
The 2017 damage was down to 16,000 acres, though that is still not a trivial number, said Halman.
“There is a multi-state effort that includes New Hampshire, New York, Vermont and Maine and we are trying to get a better idea of what’s going on across the landscape,” he said. “We will get a more regional picture of this decline, in particular the needle disease.”
If there is an upside, infected trees are at present not showing a significant mortality rate.
“People are concerned the trees are dying,” said Lombard. “They are not immediately going to die. They can handle it for quite a while. Even the heaviest hit areas of the state still don’t show a lot of mortality, even five years later.”
Something needs to break the cycle and it needs to be the right weather, he said.
“Potentially, consecutive dry springs could act to knock back the severity,” said McIntire.
With the white pine needle damage showing no signs of subsiding, the recommendation for landowners and timber managers is to thin stands that are infected or at risk of infection, said McIntire.
The Eastern white pine, which can reach 200 years and older, can grow to a trunk diameter of well over a meter and to an upward of 120 feet, said McIntire.
“It’s certainly taller than anything else in the region,” he said.
Lombard said, “White pine is the king. The whole timber industry in the Northeast is driven by white pine. The volumes and value per acre are so much. That’s why it’s such a concern.”