Plants could help investigators find dead bodies. Botanists believe the sudden flush of nutrients into the soil from decomposition may affect nearby foliage. If scientists can understand those changes – for instance, on leaf colour – they may be able to identify where remains are buried simply by studying aerial images.
“If we’re able to use the plants as sensors, at least first as indicators or crude indicators, we can identify whether a missing body may be close by,” says Neal Stewart Jr at the University of Tennessee.
Teams looking for human remains often rely on aerial searches, but these are difficult if a cadaver is buried in a forest. Although pedestrian surveys or teams of trained dogs can help in these situations, such searches are impractical in huge forests or war zones.
Forensic anthropologists at the University of Tennessee have been training members of the FBI for 20 years, including in rudimentary “forensic botany”. Anecdotal evidence suggests that visual signals can appear in the leaves of trees and shrubs growing near a body. For instance, a body can affect the mix of plant species growing nearby and plant leaves may be visibly darker, indicative of higher nitrogen uptake.
Now, the plan is to explore those botanical effects more thoroughly at a “body farm” at the university, where researchers study the way cadavers decompose.
“We’ve actually built a whole plant imager that can analyse fluorescence signatures,”
says Stewart. “But the first steps are going to be very fine scale, looking at individual leaves and measuring how their reflectance or fluorescence changes over time when plants are near human remains.”
The average person in the US contains roughly 2.6 kilograms of nitrogen, much of which is released and converted into ammonium when their body decomposes. That may see nitrogen in the soil spike to levels up to 50 times higher than when a typical fertiliser is added. This can increase soil toxicity or alter leaf fluorescence or reflectance.
“That is why this study is exciting, as we can quantify exactly what is happening in the foliage with hyperspectral and chemical analyses even if we can’t see a physical change,” says team member Dawnie Steadman, also at the University of Tennessee.
Currently, the research is at an early stage. The team is focusing on plants growing at the body farm, which are predominantly Amur honeysuckles, an invasive plant found across much of the eastern US. The results may be translatable to different climatic zones and ecosystems, but the team is unsure how effects can be generalised between species.