Matt Bekker, a Brigham Young University scientist, analyzed timbers from beneath the choir section in the west end of the Tabernacle during the domed building's 2005 renovation. Their annual growth rings indicate a severe drought was under way in the Salt Lake Valley when Mormon pioneers arrived in 1847, according to his findings published in the current edition of Tree-Ring Research, an academic journal on the science of dendrochronology, or tree-ring dating.

"We know 1847 was a dry year because they were here and having a hard time getting agriculture set up," Bekker said. But thanks to his findings, historians now know the years 1846-48 were among the driest in the preceding century and half, throwing a new light on the challenges faced by Utah's first Anglo settlers.

Dendrochronology often relies on living trees to help document past climate patterns, but old trees have become increasingly scarce.

"Historic buildings can be an important resource for old wood because there just aren't trees in the vicinity," said Steve Leavitt, of University of Arizona's Laboratory of Tree-Ring Research. "Wood from churches in Europe has helped construct climate chronologies going back hundreds of years."

Salt Lake City's 250-by-150-foot Tabernacle, one of Mormonism's most sacred buildings, was built from locally gathered materials between 1863 and 1868, just before the arrival of the railroad. When The Church of Jesus Christ of Latter-day Saints invited him to sample the Tabernacle's old wood, which was being replaced with steel beams, Bekker's purpose was to learn about the unhewn timbers themselves. He and research partner David Heath wanted to know whether they were salvaged from other structures, particularly the open-sided "boweries," Mormons built upon their arrival.

Of primary concern was what the wood would reveal about construction practices and the history of alternations to the building. But the 140-year-old tree trunks also provided an unprecedented opportunity to study historic weather patterns.

Bekker, an assistant professor of geography, cut cross sections and took core samples from 28 timbers to expose their patterns of annual growth rings, enabling him to build a 162-year climate chronology dating back to 1702.

To determine the year the trees were cut, he correlated their ring patterns with samples from old trees growing in northern Utah. Lining up where these patterns overlapped, Bekker determined many of the trees were cut in 1863, the year the Tabernacle's foundation was completed. Fifteen rings in from these timbers' outer edges, Bekker observed a cluster of narrow rings, documenting a severe drought from 1846 to 1848. These were the sixth, 10th and 16th narrowest bands in the entire chronology, indicating the Mormon experiment in the desert was launched during an extraordinarily dry period.

Bekker was surprised to discover five of his 28 timbers came from trees that died before the pioneer's 1847 arrival, indicating they harvested dead trees.

"In this desert environment, the settlers would not overlook the dead trees," Bekker said. "In fact, there may be advantages to using postmortem timber because you don't have to take bark or twigs off and it's already dried so it's not going to warp any more after you cut it."

bmaffly@sltrib.com