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Dying pine trees: sea level rise or pine beetles?

October 27, 2017

Several months ago, I asked Evelyn Maurmeyer if she could show me proof in our area of sea level rise. After 40 years of life in Lewes, I haven't noticed any overt change in the kind of flooding on Lewes Beach that comes with occasional moon and storm events. With so much discussion, I wanted to know.

A doctoral scientist with a PhD in geology, Evelyn makes her living delineating boundaries between uplands and saltwater marshes relating primarily to development proposals.

She said she doesn't believe sea level rise caused by global warming is progressing as rapidly as some in the environmental community predicted a few decades ago. But, she said, she doesn't doubt sea level rise, and she pointed to stands of dying loblolly pines on the fringes of Delaware's salt marshes as proof.

Loblollies are native to Delaware and widespread throughout the nation's southeastern forests. Loblolly roots can withstand a certain amount of saltwater. But when the roots' saltwater exposure goes beyond their freshwater exposure, the trees weaken over time and eventually die.

Just a few weeks ago at a party, I was talking to a man knowledgeable about Delaware's forests. I mentioned Evelyn's belief that the gradual sea level rise is starting to kill off loblollies in Delaware's lowest areas.

"It's not sea level rise killing them," he said. "It's pine beetles. The state missed a year spraying for them, and that has taken its toll."

So, is it saltwater or pine beetles killing off stands of loblollies along the salt marsh edges?

Mike Valenti, forestry administrator for Delaware's Department of Agriculture, said it's actually both.

"Pine beetles and rising levels of saltwater are a one-two punch," he said. "Saltwater in the soil, from gradual sea level rise and storm surges that inundate low-lying areas, weakens the trees and makes them more susceptible to pine beetle attack. Stressed trees give off odors - or volatiles - that the insects detect and are attracted to. Healthy trees have chemicals and resins in their systems that provide a defense system to drive out the beetles if they are attacked. But trees weakened by saltwater intrusion have weakened defenses."

The beetles drill into the bark, lay their eggs, and, between the juveniles and the adults, eventually girdle and kill the tree with drilling and channeling beneath the bark. Infestations in a single tree can multiply quickly and then spread to other trees.

Bill Seybold, forest health specialist for the Department of Agriculture, said the state was notified earlier this year about a stand of dying loblollies on a private tract along the edge of the Great Marsh north of Lewes. "It was about 25 acres of trees, and 80 to 90 percent of them were dead or dying from a pine beetle attack," said Seybold. He said he told the landowner about the proper way to salvage-harvest the trees, which usually involves stripping them of their bark, where the beetles live, so as not to carry an infestation anywhere else. "It's a very wet area, so I don't even know if the trees are harvestable," said Seybold. He said the area where these trees were attacked is in a stressful environment, making them more vulnerable to attack. "Saltwater intrusion is a factor, as is storm surge, and the fact that there in an open area along the marsh where it can get very hot."

Valenti said the state does not spray to defend against pine beetle attacks. "It's up to the landowner to take care of affected trees," he said.

"Ten years ago or so, we had about a half-acre of trees in Redden State Forest that were attacked by pine beetles. We cut out the trees, sent them to the sawmills, and also cut a buffer around the trees of about six to seven acres. If you don't stop them, they can really wreak havoc."

Between 1960 and 1990, it's estimated that pine beetles destroyed $900 million worth of pines in the nation's southern states.

Valenti said scientists in Delaware's Department of Natural Resources and Environmental Control acknowledge sea level rise of about three millimeters per year. That equates to about a foot per century. But, he said, the gradual sea level rise is worsened by land that's sinking. That's called subsidence.

"Areas that are just a little above sea level will suffer as time goes by," he said. "That three-millimeter-per-year figure for sea level rise is consistent with world averages measured by hundreds of gauges around the planet. We know it's rising. We just can't do anything about it. Delaware's forest service hopes that the U.S. Forest Service will come in and help by introducing new varieties less susceptible to saltwater. At five or six feet above sea level, it's not a problem."

Seybold said Delaware forest health specialists conduct annual aerial surveys of the state's trees. "We can pick up problem areas as small as half an acre," he said. "Then we can do a ground check for evidence of pine beetles to take action if necessary. We also have four locations in Sussex County where we put out pheromone containers that attract pine beetles if they are in the area. That gives us an indication of what might be going on." But, he said, the aerial survey conducted around June 20 each year didn't pick up the problem at the Lewes tract.

"We haven't seen many beetle outbreaks in the last couple of years," said Valenti, "but we are very aware of saltwater intrusion and its problems in forested areas near the ocean."

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