Timber salvaged from New York City buildings reveals ancient climate

Timbers taken from demolished buildings in the city can extend by hundreds of years how far back in time scientists can tell what the climate was.

Old-growth forests once covered the eastern United States, but they were almost entirely decimated by the early 1900s after centuries of commercial logging. Yet wood from those forests survives, much of it tucked behind the walls of New York City buildings. The tree rings on these timbers are sources of historical climate data, which is why researchers are working to recover them. 

At the Tree Ring Lab at Columbia University’s Lamont–Doherty Earth Observatory, a team of dendrochronologists—scientists who study tree rings to determine the dates of past events—is collecting samples of the timbers from demolition sites around the city. They focus on buildings constructed before steel framing became common in the 1920s and 1930s, since most of these structures were built with wood from old-growth forests in the U.S.

Every year a tree grows, it adds new rings that reveal the environmental conditions of the time. In general terms, a wider ring indicates more rainfall in a growing season than a thinner ring. Rarely, in some trees at high elevations, the variation in the size of the rings reflect fluctuations in temperature instead, with wider rings indicating warmer weather.

Mukund Rao, one of the leaders of the Tree Ring Lab project, says that many of the trees used in the construction of New York City were 200 to 300 years old when they were logged over a century ago. That means they sprouted long before the founding of the U.S., in some cases in the 1500s or earlier. Their rings can help scientists fill in gaps in the existing data.

“Having these really old timbers allow us to go further back in time to understand the past,” says Rao. This makes it possible for scientists to put recent changes in climate patterns into greater historical context.

“You can see if the temperatures we are experiencing now are unprecedented or if they are within normal range. Same with a significant drought,” says another project leader, Caroline Leland.

Going back to the source

Much of New York City was built during the latter half of the 19th and the early 20th centuries. According to a 2019 study, the city is believed to be home to more than 14 million cubic meters of old-growth timber, making it the largest repository of this material in the country. That’s equal to almost 75,000 subway cars.

The wood framing for New York’s City older buildings was sourced from different regions along the eastern seaboard. First, builders logged the forests of the Northeast for white pine, spruce, fir, and hemlock. By the turn of the 20th century, many of those forests had been depleted. But the industrialization of logging had made it possible to ship lumber over longer distances, so builders set their sights on the longleaf pine forests of the South. As a result of that uncontrolled logging, just 3 percent of southern longleaf pine forests remain.

A collaboration with Alan Solomon of the Sawkill Lumber Company, a timber salvaging business that remanufactures old wood, has given the Columbia team access to samples from at least 18 different New York City structures. They range from a firehouse in Manhattan to horse stables in Brooklyn. For a wood sample to be old enough to be of interest to the team, it should have at least 150 rings, meaning the tree was at least 150 years old when it was cut.

After collecting a wood sample, researchers first identify the species of tree using the wood’s resin content, the size of the pith (tissue found in the center of a tree) and other anatomical characteristics. Then they process each sample, which involves documenting the width of each ring. 

“This pattern of wide rings and narrow rings tends to be unique to a particular region,” says Rao.

The tree-ring pattern functions like a barcode that can be compared with patterns from other trees, a process known as cross-dating, to determine the wood’s origin. This is another reason why it is ideal for a sample to have at least 150 rings: It allows researchers to confidently pinpoint the region the wood is from.

“If you successfully match those patterns of tree-ring widths, then you can figure out where that sample came from or when that tree was cut down,” says Leland.

Extending climate records

The first timbers the team studied came from the Terminal Warehouse, a massive 1891 building in the Chelsea neighborhood of Manhattan. After determining that the timbers were longleaf pine, the scientists compared their ring patterns to an extensive database and found a match among living trees near the Georgia-Alabama border. The oldest tree from the Terminal Warehouse is believed to have sprouted around 1512.

The researchers have also processed timbers from 211 Pearl Street, a commercial building in lower Manhattan built in 1831. They identified the species as white pine and concluded that the wood came from New York’s Adirondack Mountains. Living tree studies have yielded data for that region going back to 1690, but some of the timbers from 211 Pearl Street were young in the 1530s, making it possible to tell what the climate was like in that region more than 150 years further back than before.

The more tree-ring data the team can gather from different sites, the better, as it enhances scientists’ understanding of not only how climate has changed over time, but also how it has varied by region.

“Combining sites from a network of tree-ring data from different locations will be more valuable for understanding spatial and temporal climate variability,” Leland says.

David Frank, director of the Laboratory of Tree-Ring Research at The University of Arizona, describes this kind of research as “incredibly valuable,” as it allows scientists “to quantify, understand, and more accurately model the Earth’s climate system.”

Frank also notes that “long records are crucial to identify rare, extreme events.”

“If it happened in the past, there is a chance it will happen in the future,” he says.  

Keeping data out of landfills

Each year, some 1,000 buildings in New York City constructed with old-growth wood are demolished or gutted and renovated. The average quantity of wood per building is estimated to be 14 cubic meters. That means that, on average, 14,000 cubic meters of old-growth wood is removed annually.  When this material isn’t salvaged by a company like Solomon’s, it often ends up in landfills, where it releases carbon dioxide as it decomposes, contributing to greenhouse gas emissions.

“Not only is it good for the environment to recover, repurpose, and reuse these samples, but also there's so much scientific value and so much history locked up in these timbers that it would be a shame to lose,” says Leland. 

The timbers are so valuable that Solomon and the Tree Ring Lab team have taken the first steps toward starting a nonprofit aimed at salvaging and repurposing this wood.

“It’s a finite resource,” says Solomon. “Once this material is gone, there is no more record of these forests.”

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