Dr. Malcolm Cleaveland stands at the base of an ancient bald cypress along the Blanco River in Wimberley. In a camera lens, he is dwarfed by a giant tree that was alive a half century before Columbus sailed to the Americas. To be more precise, this particular bald cypress dates back to 1426 or earlier.
Cleaveland is a retired professor of geosciences and a paleoclimatologist at the University of Arkansas Tree Ring Laboratory. Even in retirement he is still known by others in his field as the “Climate Detective.” He agreed to travel from his home in Fayetteville last month to spend a day in the Texas Hill Country to deepen my understanding of his work and what it teaches us about the history of drought in Texas.
Most public policy debates about water and drought in Central Texas start with the “historic drought” of the 1950s, based on rainfall records dating back to the late 19th century. As Cleaveland’s work shows, a reliable 500-year record of drought is stored inside the region’s oldest living trees.
How do we know the Wimberley bald cypress, still healthy with a massive trunk and towering crown, will be 600 years old soon? Cleaveland studies the tree rings of the hemisphere’s oldest living trees by extracting long, thin cores the width of a pinkie finger that leave the tree undamaged and give scientists a year-by-year record of growth and rainfall over the long life of the tree.
Reading tree rings is both art and science. One of Dr. Cleaveland’s significant contributions to the field was refining how to read a tree-ring core where severe drought so inhibited growth in a given year there is no record of a ring above the cellular level. The core work is done afield as scientists scour the landscape for the oldest living trees and once found, make an extraction. The analysis occurs back in laboratory where the cores are finely sanded, and then carefully studied and dated under microscopic inspection.
Cleaveland and his colleagues, notably Dr. David Stahle, director of the Tree-Ring Lab at the University of Arkansas-Fayetteville, have pushed back the drought record to a time before European settlers arrived in the New World. Scattered indigenous populations were the sole occupants of the Southwest, yet periodic, sustained drought was a reality, long before growing populations brought added pressure to the water supply.
“Dave taught me a lot of what I know about dendrochronology, and he is simply the best in the world at working out the dating of difficult material, that is, slow-growing samples with a lot of missing and false rings,” Cleaveland said. “For example, he worked out a bald cypress chronology in Mexico back to the 700s when no one else who tried could date it before the 1500s.”
Dr. Todd Votteler, the executive manager of science, intergovernmental relations, and policy for the Guadalupe Blanco River Authority, first invited Cleaveland to the Texas Hill Country to help establish a better understanding of drought and the corresponding need for enhanced water conservation and management. Beginning in May 2009, the Environmental Science Institute at the University of Texas at Austin partnered with the GBRA and the University of Arkansas Tree Ring Lab to study and reconstruct the drought history of Central Texas. Thus began the hunt for the region’s oldest trees and the secrets they held in their cores.
“We initiated this study at a time when there was discussion in the water management community that maybe the drought of the 1950s was an aberration, a one-in-every-1,000-years occurrence, and therefore we might not have that much to worry about,” Votteler recalled. “We knew better, but realized we needed evidence. This study has gone a long ways toward eliminating that viewpoint.”
Cleaveland said the research quickly established that the ’50s drought was not the “drought of record.”
“When you study the historic record you see there were multiple 10-year droughts worse than the so-called ’50s drought of record,” Cleaveland said. “There was a period in the 1500s and another in the late 1600s that make the 1950s look wet. You’re going to have a least one major drought every century if you study the data.”
Over the last five years, Cleaveland, Votteler and other researchers have sleuthed their way through Central Texas in search of the oldest living trees, taking core samples for later study at the university’s tree-ring laboratory.
The study has reinforced the fact that the biggest trees are not necessarily the oldest trees, which often annoys landowners and others who tend to exaggerate the age of trees based on height, girth and local legend. One landowner who leads guided tours of his property for profit told Cleaveland and Votteler that a legendary live oak tree on his land was more than 1,000 years old. A core sample revealed that the massive oak was less than 200 years old. The landowner was not happy to receive the news and, unwilling to accept the study results, continued to tell visitors the tree dated back to the start of the last millennium.
“Some of the oldest trees we’ve seen are narrow and twisted and shrunken looking,” Cleaveland told me. “Some of the big ones are not so old.”
To start our day afield we paid a visit to San Antonio conservationist Bill Lende at his 521-acre Cibolo Preserve east of Boerne, which he established as a natural habitat laboratory and to preserve the constant flow of water in Cibolo Creek. An innovative agreement reached with the City of Boerne in 2010 guarantees a minimum daily flow of 410,00 gallons of water into Cibolo Creek where it enters the Preserve and then recharges in the underground Trinity Aquifer, which helps preserve the local water table for Kendall County ranchers and others with pumping permits.
We made our way along the creek until we reached a stand of tall bald cypress where University of Texas graduate research assistant Richard Casteel took a core sample from one towering tree. Watch this video of Casteel extracting the core sample, and Cleaveland examining it afterwards.
After looking at the sample, Casteel quickly declared the tree to be “young.” How young? I asked. “Only about 150 years old,” he replied.
With floods having brought down some of the Preserve’s oldest bald cypress trees more than a decade earlier, the team examined some of the trunks Lende keeps stored on higher ground. We quickly grew distracted by the Preserve’s most extraordinary geological feature, a narrow limestone canyon that exposes a large caprinid reef formed more than 110 million years ago.
The formation is characterized by enormous swirling sinkholes, curving rock faces and walls embedded with tubular bivalves called caprinids, some 8-10? long.
Lende and his Preserve Docent J.W. Pieper are accustomed to hosting visiting scientists and researchers. The University of Texas at San Antonio, the Cibolo Nature Center, and Texas Parks & Wildlife regularly conduct research at the Preserve. As noon approached, they led us into Boerne for lunch at the Cypress Grille, where we enjoyed the best buffalo burger I’ve ever eaten. Afterwards, we drove to Guadalupe River State Park to examine an old bald cypress there, but continuing roadwork prevented us from reaching it.
We made our way to Wimberley to visit the oldest tree the team has core sampled in Central Texas, the 1426 bald cypress.
“It’s probably older,” Votteler said. “I don’t think the tool we used to extract the core sample was long enough to actually reach the center of the tree, but where it did reach we dated back to 1426.”
We didn’t repeat the core sample extraction at the tree, which is set amid a stand of other old bald cypress, their high canopies, an absence of lower limbs and slightly twisted main trucks all evidence of great age. The core sample process doesn’t harm the trees — the small hole, or wound, quickly grows over and seals itself — but it somehow seemed disrespectful of a living organism so old to sample it again for the sake of a story. We agreed not to disclose the location of the tree, and the landowner proudly retrieved a bronze plaque that Cleaveland held for a photograph commemorating the 2009 discovery of the tree’s age.
“We knew it was an old tree, and that all the trees along the river here are quite old,” the landowner said, “but we had no idea it was this old until the study was done.”
When Cleaveland and Votteler and other members of the team combined the Central Texas tree ring data with data gathered in Mexico and West Texas, a drought record emerged reaching back to A.D. 800 in Mexico that showed four megadroughts that lasted 15-30 years each, and at least one major drought per century in Central Texas. Their work was published in a 2011 edition of the Texas Water Journal in a research article entitled Extended chronology of drought in South Central, Southeastern and West Texas.
Readers who wish to delve more deeply into the science of tree ring study can access the International Tree-Ring Data Bank maintained by the National Climate Data Center. The region’s growing population and relentless conversion of undeveloped ranchland into subdivisions is placing even greater pressure on scarce water resources. What Cleaveland’s data tells us about climate change and drought is essential for policymakers and the public as we construct water conservation and management models for the future.
Drought periods are becoming more frequent, are lasting longer, and are more intense. Recent wildfires are one measure of the effects of such change. Policymakers must weigh environmental concerns against development demands, a major political challenge for any officeholder. The old trees tell us what we already should know and accept: Drought is an inescapable part of life in the Southwest. It’s been that way for centuries.
*Featured/top image: A cross section of a bald cypress displays the rings used to calculate its age. Photo by Robert Rivard.