New in Forensics: Using Plants to Find Dead Bodies

(Courthouse News photo / Chris Marshall)

(CN) — Can plants help direct search teams to find a missing body in the forest? Scientists believe so, based on an array of changes to the surrounding soil caused by nutrients released during decomposition.

Nitrogen stimulates production of chlorophyll — a chemical that converts sunlight to energy and gives plants their rich green color — which in turn leads to increased foliage growth. The average human body contains nearly 6 pounds of nitrogen and would decompose onto 9 square feet of soil, aptly named “cadaver decomposition islands.”

At those concentrations nearby plants would receive 50 times their recommended amount of nitrogen fertilizer, resulting in either far greener and foliage-dense plants, or nitrogen-burned leaves, depending on the soil’s drainage. Either way, such a difference should be readily apparent.

Researchers studied these corpse-induced changes to the surrounding soil to determine if they could help track missing cadavers in a study published Thursday in the journal Trends in Plant Science.

“The most obvious result of the islands would be a large release of nitrogen into the soil, especially in the summertime when decomposition is happening so fast,” said author Neal Stewart Jr., a professor of plant sciences at the University of Tennessee, in a statement. “Depending on how quickly the plants respond to the influx of nitrogen, it may cause changes in leaf color and reflectance.”

Healthy plants reflect more light than nitrogen-starved plants, which is measured with a tool called a refractometer. A refractometer measures sugar levels in leaves by gauging the amount of light they reflect — the more chlorophyll in a leaf, the more reflective it is. Farmers regularly use refractometer-equipped drones to inspect vast swaths of cropland, and researchers hope these same tools could be harnessed to find the remains of missing persons in forested areas.

“In smaller, open landscapes foot patrols could be effective to find someone missing, but in more forested or treacherous parts of the world like the Amazon, that’s not going to be possible at all,” Stewart said. “This led us to look into plants as indicators of human decomposition, which could lead to faster, and possibly safer body recovery.”

The University of Tennessee operates an anthropology research facility affectionately known as the “Body Farm.” It’s here that researchers study the connections between plants and decomposing bodies under varying conditions. The goal is to assess how changes in the surrounding soil’s nutrient concentration affects different plant species to determine how these changes can be identified to aid search teams on the ground.

Because humans won’t be the only creatures to die in a given forest, a major hurdle for researchers will be determining exactly which metabolites are released when a human body decomposes, in what amounts and what specific effect that has on various plant species. They then need to compare the results with those taken from other forest critters so that a dead animal isn’t mistaken for the person being sought. Stewart explained that deer will be the most common contender throughout the United States, as smaller animals give off less of a signal than humans.

“We’re doing something that nobody’s done before,” Stewart said in an email.  “We don’t know what sort of plant/spectral signatures we’re going to find, and then how generalizable they will be among plant species.”

Researchers may one day be able to identify individual bodies based on their lifestyle, according to Stewart. A frequent smoker, or a person with a career in manufacturing, for example, may have elevated levels of cadmium in their body which is readily absorbed by plants and could be detected from afar. He acknowledged, however, that’s a bit farfetched at the moment.

Forests cover 31% of Earth’s land mass, and scores of individuals go missing every year while hiking through the great outdoors. In regions with ongoing conflicts it can be impossible to send a team tromping around densely wooded areas. By determining what changes in the landscape are prompted by a decomposing human body, researchers could potentially transmute this massive obstacle into a valuable resource.

“The research that we’ve started this June is an interdisciplinary project that spans from anthropology to plant and soil biochemistry — very broad scale of topics — which is likely going to be challenging to integrate,” Stewart added. “But if we’re successful, it will be very exciting too. I hope that our findings can be used for humanitarian purposes as well as those in law enforcement.”

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