Using new technology, researchers can watch as trees grow, shrink, drink, and breathe. Illustration by Christelle Enault
When we start reading about using transducers to create precision dendrometers to see how a tree grows in Brooklyn, we know we are out of our league. But surprisingly readable, this story tells why it is important to be able to measure tree growth in real time:
One morning earlier this summer, the sun rose over Brooklyn’s Prospect Park Lake. It was 5:28 a.m., and a black-crowned night heron hunched into its pale-gray wings. Three minutes later, the trunk of a nearby London plane tree expanded, growing in circumference by five-eighths of a millimetre. Not long afterward, a fish splashed in the lake, and the tree shrunk by a quarter of a millimetre. Two bullfrogs erupted in baritone harmony; the tree expanded. The Earth turned imperceptibly, the sky took on a violet hue, and a soft rain fell. Then the rain stopped, and the sun emerged to touch the uppermost canopy of the tree. Its trunk contracted by a millimetre. Then it rested, neither expanding or contracting, content, it seemed, to be an amphitheater for the birds.
“I wonder about the trees,” Robert Frost wrote. Monumental in size, alive but inert, they inhabit a different temporality than ours. Some species’ life spans can be measured in human generations. We wake to find that a tree’s leaves have turned, or register, come spring, its sturdier trunk. But such changes are always perceived after the fact. We’ll never see them unfold, with our own eyes, in human time.
To understand how trees transform, dendrochronologists, researchers who study change in trees, have developed a few techniques. They cut trees down to analyze their rings, which have been created by the seasonal formation of new cells, but this terminal strategy can provide only a static overview of the past. They “core” living trees, using bores to extract trunk tissue; this technique, however, can stress trees and sometimes, though rarely, wound them fatally. They measure tree girth with calipers and tape—a less invasive means of studying growth that is also frustratingly intermittent.
Once we had read to this point the following paragraph led to an image search. What does this thing look like? The story did not show it, only described it, so our image search led here:
Figure M1 Collection of point dendrometers (natkon.ch). The carbon frames are either T-shaped (for large stems) or O-shaped (for small stems or branches) and are anchored in the stem with stainless steel rods. Up to three sensors are attached to the different type of frames in order to measure different expositions at the stem or to measure stem radius fluctuations over bark and on the xylem separately.
And those images helped the following make a bit more sense:
In the early two-thousands, a new technique emerged that changed the field. It relies on low-cost transducers: equipped with a tiny spring, a transducer—which converts, or “transduces,” physical motion into an electrical signal—can rest on the bark of a tree, sensing and logging tiny changes in pressure. Instruments that use this approach, known as precision dendrometers, allow scientists to do something entirely new: watch how trees change and respond to their environments on an instantaneous scale.
This spring, I walked along the eastern edge of Prospect Park Lake with Jeremy Hise, the founder of Hise Scientific Instrumentation, a company that sells affordable precision dendrometers to scientists, students, and members of what Hise called the “D.I.Y. makerspace.” Bearded and affable in jeans and a blue sweatshirt, Hise explained that his dendrometers could now deliver their measurements wirelessly to a cloud-based platform called the EcoSensor Network. Users of the network can monitor a tree’s growth, generate graphs, and correlate them with meteorological data. Together with Kevin Griffin, a professor of earth and environmental sciences at Columbia University, Hise is planning to build the largest network of dendrometers in the world, generating millions of data points each year. “We’re looking to be the Weather Underground of trees,” Hise said.