Tree-climbing, cranes, chemical knockdown – collecting samples of biological life from forest canopies can be challenging and time-consuming for scientists.

To find out more about who - or what - is living in the canopy, researchers at the University of Duisburg-Essen (UDE) in Germany hit on a brilliant idea. Shortly before forecasted downpours, they place rain samplers beneath the oaks, beeches, pines and larches of the forests where they carry out their work.

As well as microorganisms and small invertebrates, the collected water also contains environmental DNA (eDNA), including genetic information released from organisms through abrasion or excretion. This mixture of beetle, fungus, ant, and oak DNA is subsequently analysed by eDNA metabarcoding.

This method can capture even the smallest trace of genetic information, amplify it, and enable the precise identification of each species present. By comparing DNA analyses, the biologists found that of the 50 species detected in the rain samplers, only seven had been caught as whole specimens.,

"Our results show the potential of eDNA metabarcoding in rainwater as a rapid and minimally invasive method to measure the diversity of invertebrates living in tree canopies," said Professor Florian Leese, whose team focused on the canopies of the Diersfordter Forest and the Great Veen nature reserve in the Lower Rhine region.

The biologists from UDE's aquatic ecosystem research working group also found that species composition varied from tree to tree. Overall they were able to assign 88% of the species detected to a specific tree type.

Although the researchers worked with a small sample size on this occasion, they say the results are convincing.

Till Macher, first author of the research paper published in Environmental DNA journal said, "So, we conclude that our method actually provides a good overview of the biodiversity in tree canopies."