What does the succession of a forest sound like?

And, why does it matter what the succession of a forest sounds like?

It matters because our ears are especially attuned to finding patterns, and through the sonification of datasets, scientists (and everyone else) may better understand large amounts of data, or complex data sets—such as variations in the composition of tree species in a forest that stretches 300 miles.

Ecologist Lauren Oakes, a researcher at Stanford University, sampled forest stands in the Alexander Archipelago off the coast of Alaska. This archipelago is known for its isolation, heavy rain, and ancient forests composed of hemlock, pine, spruce, and yellow cedar (Callitropsis nootkatensis).

A forest in southeastern Alaska affected by yellow-cedar decline. Photo: Lauren Oakes

The yellow cedar was the focus of her study—yellow cedars on the Alexander Archipelago are dying off as less snowpack has exposed the tree’s shallow roots to freezing temperatures. She and her field crew observed that on the southern stretch of the islands, a few very old yellow cedars remained, but there weren’t many young yellow cedars to replace them and those trees are being outcompeted by other conifers.

To communicate what she’d seen, Oakes did what a lot of us do: she created bar graphs, charts, and scatterplots to represent the data. But she also partnered with a fellow Stanford scholar, Nik Sawe, who put the data to music (listen here, one clip that’s roughly 3 minutes), after assigning each of five species of trees a particular instrument:

• Yellow cedar: piano
• Western hemlock (Tsuga heterophyllia): flute
• Shore pine (Pinus contorta): clarinet
• Mountain hemlock (Tsuga mertensiana): violin
• Sitka Spruce (Picea sitchensis): cello

Each note represents a tree. The pitch of each note, and how hard it is hit, correlate with the tree’s height and diameter. This creates a soundscape of the forest. The composition moves from the northern end of the Alexander Archipelago, where a fair number of yellow cedar still grow, to the southern end of the string of islands, where relatively few remain. This means the early portion of the soundscape is dominated by piano, but by the end flute has nearly entirely replaced piano.

For some, this sounds like hope. But when Sawe removes the flute, clarinet, and strings from the piece (listen here, second recording on the page) the dropped notes (representing dead trees) become more evident, and it’s critical to note that the “species solo” ends with several seconds of silence (aka dropped notes).

Those of us who do the work of helping people to understand complex datasets, sonification of data may well be something we should champion. This can help us see patterns we’ve missed, and can make complex ideas more accessible to the public or our clients. Part of what I particularly like about Sawe’s work to sonify Oake’s data is that it’s not just created as a series of notes (some sonified data is truly hard to listen to); instead it sounds like an orchestra.

Interested in learning more about Sawe’s process? Outside Online writes about the collaboration between Oakes and Sawe, with a particular focus on the work Sawe did on the project.