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Last month, Michele Francis, an environmental scientist at Stellenbosch University in South Africa, relocated to central Connecticut only to discover that her new home showed signs of termite damage. When an exterminator suggested setting out traps, Dr. Francis demurred. “I wondered if I could persuade the termites to eat the trees around my house rather than the house itself,” she said. “I hold termites in high esteem.”
Her appreciation for termites stems from a project that she recently oversaw in Namaqualand, a region of desert scrubland along the west coast of South Africa and into Namibia. There, some 27 percent of the landscape is covered with low, sandy mounds that were built by the southern harvester termite, Microhodotermes viator. Inside the mounds are vast labyrinths of chambers, tunnels and nests that extend up to 11 feet underground. The locals call them heuweltjies, which means “little hills” in Afrikaans.
Three years ago, Dr. Francis and her field research team set out to find why the groundwater along the Buffels River in Namaqualand was saline. “The groundwater salinity seemed to be specifically related to the location of these heuweltjies,” she said. The investigators reasoned that radiocarbon dating could pinpoint when the minerals stored in the termite mounds had seeped into the groundwater.
The investigators were surprised to find that the heuweltjies were far older than any active termite structures known to exist. As detailed in a paper that the researchers published this spring in the journal Science of the Total Environment, one of the three mounds selected for dating has been continually occupied by termite colonies for 34,000 years. It is more than 30,000 years older than the previous record-holder, a mound in Brazil built by a different termite species.
Termites are masterful soil engineers capable of erecting cathedral-like edifices out of dirt, saliva and feces. To create and maintain their homes, they become miners, masons, scaffolders, plasterers and roofers. Working together, they don’t just build simple nests; they install air-conditioning, central heating and even security devices. In Namaqualand, the termite activity over thousands of years has resulted in the formation of a hard layer of calcite (the same mineral that limestone is made of), which protects the colonies against predators that are strong diggers, such as aardvarks.
“When we dig a soil profile that breaks any part of the mound, we see that the termite soldiers and workers switch into a sort of emergency mode and appear almost instantly,” Dr. Francis said. “The soldiers guard the tunnels and the workers do the repair work. Unlike ants, which run out of their nests en masse and bite, termites are amazingly efficient.”
Termites eat, process and excrete organic matter, enriching the quality of the surrounding soil. “Their mounds increase the depth, nutrient and moisture status of the soils, which results in the mounds often supporting more vegetation than the soils surrounding the mounds,” said Catherine Clarke, a soil scientist at Stellenbosch University who collaborated on the new study. “So they increase the productivity of semiarid landscapes and likely make these landscapes more resilient to climate change.”
Robert Pringle, an ecologist at Princeton University, said that termites can move astonishing quantities of soil and change the hydrology of entire ecosystems, generally making those networks more productive and more resilient to drought and other disturbances. The new study, he said, underscored what Dr. Francis called the substantial, if poorly understood, role that southern harvester termites play in offsetting climate change by reducing the amount of carbon emitted into the atmosphere.
Termites bring twigs and other dead plants back to their mounds and deep into the soil. Some of this plant matter is consumed by microbes and released back out to the atmosphere as carbon dioxide. But some remains inside the mound as organic carbon, eventually ending up tightly bound to soil minerals. Locked away from decomposers, this carbon can be stored for thousands of years. In a 2023 paper, Dr. Francis and her colleagues estimated that each termite mound in Namaqualand could harbor about 15 tons of carbon.
Some of the carbon brought into the mound is converted into white calcite minerals by microbes. Because this traps carbon in a mineral form, it is sequestered for much longer than if the carbon remained as organic matter. In addition, the calcite can react with carbon dioxide in the atmosphere to form dissolved carbonate ions which can be channeled through the termite burrows into groundwater and subterranean aquifers.
As a consequence, the carbon dioxide is not returned to the atmosphere but moved to the groundwater as a permanent reservoir. “Even though Namaqualand is a dry area, it does experience occasional floods,” Dr. Francis said. The region was wetter during prehistoric periods of global cooling, which is when the mounds were formed and many of the soil minerals that contained carbon were transported downward into the area’s aquifer. “This makes the groundwater salty and not that suitable for use, but is a good carbon sink,” Dr. Francis said.
Dr. Pringle, who was not involved in the study, agrees. “Termites undoubtedly play a major role in carbon sequestration and storage,” he said, “as they do in almost all aspects of African savannas, grasslands and woodlands. It is nice to see the growing interest in understanding exactly how they do that.”
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