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Humboldt Field Research Institute

Posted July, 1995

Basketmaker's Tree May Also Have Important Climate Message

Maine's brown ash trees, long valued by Native American basketmakers, may also carry an important message about the state's climate, according to University of Maine researchers working to understand the species' recent decline.

William Livingston and Alan S. White, associate professors of forest ecosystem science, graduate student Annie Hager of Old Town, and David Hobbins on sabbatical leave from UM - Fort Kent have been analyzing tree rings, looking for pest damage and sifting through weather data in an attempt to explain why so many trees have dead branches and reduced growth rates.

These symptoms are collectively known as dieback and are similar to what happens to lawns during periods of no rain.

In a 1993 survey, the Maine Forest Service found that more than 30 percent of brown ash trees studied had suffered more than 80 percent dieback. The Service concluded that "brown ash in Maine has been and continues to be in a state of severe decline throughout the state."

"Surprisingly the survey found that most trees were surviving the dieback," Livingston says. "The basketmakers first noticed in the late 1980s that branches on many brown ash trees had died. However, they are very concerned about the health of the brown ash because the brittle wood from unhealthy trees cannot be used for making baskets. Also, it was not known if the problem would continue to spread and cause more damage."

In response, UMaine researchers developed a cooperative research program with the Forest Service and the Maine Indian Basketmakers Alliance. The Service selected 22 trees to study at each of six sites located in central, Downeast and northern Maine where information was also available on weather and streamflow.

Although the mystery of what's causing the dieback has not been completely solved, the project has shown that:

• for the last century, brown ash stands have gone through numerous episodes of decline, most notably in the '20s, '50s and '70s;

• the most recent decline is more extensive than previous episodes and began in 1985 in central Maine and spread north in 1987;

• insect and microbial pests, air pollution and pesticides have been ruled out as the cause of such a statewide phenomenon;

• the most likely causes are weather related and include spring droughts and excessively wet winter conditions followed immediately by freezing temperatures;

• ironically, dieback is more extensive in larger trees on wetter sites, while trees on drier sites had few symptoms;

• tree rings from the past several years show the beginnings of recovery.

In general, brown ash tends to grow slowly in swampy areas and along riverbanks. It does not compete well against faster growing species on drier land and makes up less than one percent of the Maine forest. A denizen of the far north, brown ash does well in Quebec where little decline has been reported. (Dieback has been reported in New Brunswick.)

"Brown ash appears to be a good indicator of Maine's climate," suggests Hager. "It doesn't do well under warmer and drier conditions, and if the climate changes in that direction, brown ash could eventually be one of the first tree species eliminated in Maine."

Hager conducted the tree ring analysis by precisely measuring the thickness of each year's growth for all 22 trees at each site. She entered each measurement into a computer and then looked for environmental factors associated with either growth or decline.

Hager found that wet summers followed by dry falls tend to benefit the tree, most likely by encouraging root growth. However, dry springs are associated with periods of decline.

"Brown ash is very sensitive to changes in the water table," Livingston explains. "The roots need oxygen, and if the water table is too high, they can't develop. On the other hand, if the water table drops too low, they can be starved for moisture."

By tracking growth and decline over the years, Livingston showed that periods of decline have become more frequent in the past two decades. While spring droughts were a factor during the mid-1980s, they did not explain previous declines. Clearly, other factors were involved.

"We looked for other types of stress that could affect the trees, some type of triggering event that would start the cycle of decline," says Livingston. "We made graphs of daily and monthly precipitation, streamflow and extremes. We found that years of decline tended to be preceded by high water in December, but it wasn't clear why that would be a problem. After all, the trees are already dormant by then. The roots aren't developing and don't need oxygen."

"Then we looked at what was happening with temperatures after those December floods. We thought that perhaps ice could damage the trees. The soil could also freeze and break the roots."

Livingston found that subfreezing weather with little snow fall after a wet December was the most common event preceding cycles of decline. "We don't think that these events are enough to cause the dieback by themselves. They may just make the trees more vulnerable to drought."

One of the project's unresolved mysteries concerns the relationship between periods of reduced growth and the onset of dieback symptoms. "We've spent a lot of time arguing about that," says Hager. "You would think that people would have noticed bare branches and poor wood quality during past period of decline, but that's not so."

"The State Forest Commissioner's reports from the mid-1950's mention brown ash dieback but not on a wide scale. But I'm not convinced that this means dieback wasn't occurring back then. I've asked a few of the older basketmakers and foresters if they remember other times when the trees may have been in decline, and they have told me that the trees often look pretty ragged. It's possible that past declines could have been overlooked," Hager adds.

"There has been a recent revival of basketmaking, and people may just be more aware or more worried now than before. It could also be that this is the first time dieback has occurred all over the state at the same time."

The research team will continue to monitor the health of brown ash in 11 more stands this summer. "We need to know if our findings hold up in other stands," says Livingston.

The brown ash project is a good example of collaboration among public and private interests, says Livingston. The basketmakers first brought the problem to light, and staff working for the Maine Forest Service made the initial survey. Coordinated by Henry Trial of the Forest Service, the survey was conducted by F. Michael Skinner of Island Falls, Gralyn Smith of Greenville, Everett Cram of Medway, David Stewart of North Bridgton and Jonathon Connor of Stillwater.

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