Forensic botanists: The science of using plants to find bodies

In life, humans impact our natural environment pretty much constantly. So too, it is in death.

After death, our bodies decompose, releasing certain chemicals, and, if our body is laid to rest on the ground, these chemicals alter the state of the surrounding plants. These traces of humanity are faint echoes of our former selves, but by studying decomposing bodies, scientists hope to one day use these clues in the search for missing people.

In a new study, a team of researchers lay out the potential of 'forensic botany' – a new understanding of plant chemistry that could make search-and-rescue missions both faster and more accurate.

In the United States, 100,000 people go missing every year, the authors of the new study say. And when search teams hunt for human remains, logistical issues can slow the process. Searching on foot can be arduous, and tree cover can block the view for aerial searches.

But the researchers say their method turns that problem into an asset.

Through this work, the researchers are working to determine whether that effect is visible — whether it changes the color of the leaves, for example, or how reflective they are, or which plants thrive.

The research was published on Thursday in the journal Trends in Plant Science.

A prime candidate for tracing remains is nitrogen, which is associated with increased chlorophyll. Decomposing bodies add nutrients like nitrogen to the ground, changing the chemistry of nearby plants. A surge in the nutrient could cause a "greening" effect on tree leaves.

Body farm — To study how decomposing humans alter their natural environments, researchers are using a curious academic resource at the University of Tennessee: its so-called "body farm."

The farm, part of UT's Anthropology Research Facility, is a 1.3 acre space where human remains are studied under different conditions, to see how they interact with the environment.

At the facility, researchers call to the area that surrounds a body as a "cadaver decomposition island." Along with environmental factors, human biology influences the chemical and microbial composition of that island.

The process creates a “necrobiome” where plants may grow differently. Plants that can respond quickly to a changing environment, like exotic invasive plants, may prosper on cadaver decomposition islands, the authors of the new study posit.

Human remains are different from other large mammals because of molecules called metabolites, which are specific to our bodies. Scientists at the body farm are working on understanding how cadaver metabolites affect plants. That information could allow researchers to scan treetops for certain colors or signs of leaf reflectance, using those markers to find human bodies.

"With plants acting as environmental sentinels, forensic investigators can make better-informed decisions that maximize scarce resources and keep ground teams safe in conflict zones," the study authors write.

Future of forensics — The information gleaned in the lab could one day be used by search teams looking for human remains. In the future, scientists hope to use clues from plants to improve rescue missions, making them both more efficient and even potentially safer.

"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," senior author Neal Stewart Jr., a professor of plant sciences at the University of Tennessee, said in a statement.

Eventually, the research team said findings could be paired with technology that helps identify plant phenotypes from drones. In theory, that would lead searchers closer to finding remains in hard-to-reach areas.

You can "think of the signals more like a check engine light," Stewart said. "If we can quickly fly where someone may have gone missing and collect data over tens or even hundreds of square kilometers, then we'd know the best spots to send in a search team."

Putting together the technology to create this kind of system is long off. However with the new paper, the researchers"discuss the prospects of using plants to pinpoint human decomposition," while experiments are underway at the body farm.

Abstract: In the U.S., 100,000 people go missing every year. Difficulty in rapidly identifying sites of human decomposition complicates recovery of bodies, especially in forests. We propose that spectral responses in tree and shrub canopies could act as guides to find cadavers using remote sensing platforms for societal benefit. Forests cover 31% (~4 billion hectares) of the earth’s land mass and much of the temperate and tropical latitudes where the majority of people inhabit. There are many instances in which people seemingly “disappear” in forested areas; many missing persons are presumed to be dead. A search for missing bodies initially begins with pedestrian surveys, aerial photography, and cadaver dog teams. However, when search areas are expansive and in rough terrain, ground based search is challenging-to-prohibitive. Moreover, regions with ongoing conflicts may be unsafe for forensic teams to enter altogether. While remote sensing of decomposing human bodies is certainly feasible, locating bodies can be extraordinarily difficult under forest canopies. Taken together, these obstacles often make human body discovery and recovery nearly impossible. Without a body, criminal prosecution is hindered, war crimes are unaccounted for, human rights violations go unpunished, and victims’ families suffer prolonged emotional distress.