Tree Sounding

How do we gain access to tree-ness? How are symptoms diagnosed from within the inaccessibility of a tree–its history, its girth, etc? These are some of the broader landscape forensic questions we have been asking throughout the term.

This past week we worked with the German physicist, inventor, and tree expert Frank Rinn to begin to map the interior of a tree using sound.

Yup, sound.

Frank has invented and manufactures a system for sonic tomography–the measurement of a tree’s cross-sectional density by means of sound-waves. 

With a girdle of 15+ sensors, the tree is sounded in a sort of arboreal perambulation–where each sensor is lightly tapped 5 times as the propagation time of the sound wave is  measured at each of the other sensors. The resulting measurement is a map of the speed of sound through the medium of the tree.

Each vector in the chart to the left measures the relative time it took for the sound wave to reach a corresponding sensor. The resulting diagram of greens, oranges, yellows, pinks, and reds, is simply a visual coding of speed–with green being relatively fast, and red/pink being relatively slow (or nonexistent).

This set of measurement is then interpolated to form a density map on in the tomogram on the right. Here, a visualization of the wood density–and, perhaps, through experience in interpretation, strength–is charted in a communicable form.

As Frank is quick to point out that, while this tomographic system certainly communicates fundamental scientific information about the trees in question, this sort of imagining is fundamentally a political tool. In the politics of the visible, and in the politics of urban street-trees in particular, the ability to communicate the non-visible, the subcutaneous, allows urban foresters an immediate way to construct a slightly more informed landscape public.

At stake in this sort of measurement is the politics of diagnosis. Landscape is uniquely interpretable as a symptom: a symptom of ecological pressures, historical processes, and design intents. The traces of these (geo)histories, embedded as they are within the body of the tree, provide symptoms that can be diagnosed through a range of landscape forensic activities. Much of what we have been up to in this course is exactly this. Landscape forensics as method.