The hidden worlds in tree crowns

The next time you walk through the woods, take a look at the treetops high above. What’s up there?

A team of researchers in Europe wanted to find out, so they clambered up and surveyed the lichens and mosses on the tree crowns. Their conclusion: Scientists who catalogue only the species within easy reaching distance are missing out on a lot of the forest’s biodiversity.

When researchers want to estimate the number of lichen and moss species in a forest, they usually collect samples from the first two meters of tree trunks. Species at the treetops “are rarely investigated, especially for forests in temperate Europe,” the authors write in PLOS ONE.

So the team visited 30 plots of Norway spruce, Scots pine, and European beech in Germany and surveyed the lichens and bryophytes (a group of plants that includes mosses). First, they looked at the first two meters of trees and shrubs and at rocks, dirt, and dead or fallen wood. Next, the researchers climbed one tree in each plot and searched about 70 percent of the crown, scouring the branches “until no more new species were found.”

Overall, they catalogued 187 lichen and bryophyte species. About two-thirds of the species didn’t grow on the ground; the remaining ones were found on rocks, deadwood, and detached branches and twigs.

The team would have missed 54 percent of the lichen species and 20 percent of the bryophytes on each tree if they hadn’t surveyed the crown. And they would have overlooked 38 percent of the lichens and 4 percent of the bryophytes on each plot.

The study suggests that to properly estimate biodiversity, researchers need to set their sights higher. But if climbing the trees isn’t feasible, they could take crown samples from trees that have fallen or been cut down.Roberta Kwok | 20 December 2013

Source: Boch, S. et al. 2013. Up in the tree — The overlooked richness of bryophytes and lichens in tree crowns. PLOS ONE doi: 10.1371/journal.pone.0084913.

Image © Kuttelvaserova Stuchelova | Shutterstock