DRONES: GETTING ABOVE THE FOREST TO SEE THE TREES
With a buzz the drone lifts off into the air, whizzing into the tree canopy with a digital camera strapped onboard. Its mission: record the progression of autumn colors in the trees. Yellow, gold, orange red: they all have meaning. So does green.
For researcher Stephen Klosterman, a drone is a useful way to explore the seasonal progression of the tree canopy, acres at a time. It’s cheaper than hiring a plane, and very efficient. With one drone flight Klosterman can survey about 10 acres of his research plots at the Harvard Forest in just six or seven minutes. It cruises along at about 11 miles an hour, at just under 400 feet.
The drone-mounted camera can take sharp photos of the tree canopy, at nearer proximity than satellite images. Not that drone research is without its hazards. Wind is a foe, and even clouds; intermittent sun bedevils the exposure setting of the camera. The Harvard Forest Woods Crew has fished his drone out of the tree tops a time or two after a mishap with a wind gust: “There is always the possibility,” Klosterman said, “of turning a remote control helicopter into a remote control hedge trimmer.”
This is high tech science, with blue tarp accessories. “Hand me those would you?” Klosterman said, pointing to four rocks on the ground, and placing them at the corners of the tarp to weigh it down, creating a tidy improvisational launch pad. He readied his joystick controls and calibrated the camera’s color balance, checked its batteries, then urged me to stand back, as the drone’s blades started to whir.
It’s a cool little gizmo, no doubt about it, but that’s not what attracted him to using a drone for his biological research, Klosterman said. It’s the value of the pictures he can gather with it, cruising large swaths of forest to document the seasonal change of the canopy.
Observation of phenology — the regularly occurring seasonal changes in nature, such as budding trees, leaf color and drop — is a very old practice, and comprises what may be biology’s oldest written record. From the Marsham family recording the signs of spring at their country estate in 18th century England, to monks logging the bloom time of cherry blossoms in Kyoto since the 9th century, all kinds of people for all kinds of reasons have long observed the stately procession of the seasons in the world around them. Today scientists have not only new tools, but also new interest in observing the rhythms of nature, as climate change resets the planet’s seasonal clock.
Klosterman works in Associate Professor Andrew Richardson’s lab at Harvard’s Department of Organismic and Evolutionary Biology. A physiological ecologist, Richardson deploys everything from a weekly boots-on-the-ground survey of trees every spring and fall by Harvard Forest field phenologist John O’Keefe, to Klosterman’s drone, and even surveillance cameras to keep a watch on the canopy at the Harvard Forest. Richardson deploys five so-called PhenoCams at the forest to beam back images of the canopy every half hour, from dawn to dusk, year round – thousands of images, uploaded to an online database.
Those cameras are part of a network of 80 PhenoCams that together comprise a continental-scale, virtual observatory Richardson is creating with a team of scientists under a National Science Foundation grant. The cameras document the seasonal transitions of all types of landscapes, from Alaskan tundra to the forests of New England.
I hooked up with the Richardson Lab last year, while a fellow in the Knight Science Journalism program at MIT. I watched as Andrew and lab post doc Don Aubrecht used their recreational rock and ice climbing chops to ascend a 130-foot high instrument tower, to install more gear alongside one of the PhenoCams aimed at their research plot. I’ve also been along for some of Klosterman’s drone flights, many lab tree coring expeditions, and walked O’Keefe’s tree survey with him through two falls and a spring. We’ll go out again on another round come March or April.
What a survey: O’Keefe has been closely observing the same trees at the Harvard Forest for 25 years, carefully recording their bud burst, leaf growth, color and drop in detailed weekly observations throughout spring and fall.
In addition to trees, he watches the emergence of native plants, mushrooms, stream flows, and a vernal pool on his route. He listens for the first call of wood frogs, and notes the first frost. His notes, penciled on a clipboard as he walks his approximately 3 mile survey route, provide the fuller biological story behind the seasonal changes documented by the drone and the PhenoCam.
All of these observational methods are stronger together. Adding the drone and PhenoCam to John’s ground survey provides scale –a look at the forest for the trees. And John’s observations provide a way to verify, from the level of individual plants, just what the bigger picture is saying.
In a paper published last year in Nature Climate Change author Trevor Keenan, Richardson and other scientists last July revealed Northern forests in the past two decades are cranking harder and using water more efficiently as temperatures warm and the level of C02 in the atmosphere increases. This suggests a shift in the workings of trees, with profound implications for everything from water cycling, to climate. (Keenan, T.F., D. Hollinger, G. Bohrer, D. Dragoni, J.W. Munger, H.P. Schmid, and A.D. Richardson. 2013. Increasing forest water use efficiency as atmospheric CO2 levels rise. Nature, 499: 324-327.) Other work at the Harvard Forest also documents an increase in growth by red oak over the same time period. O’Keefe’s phenology surveys, going back even further, document on average earlier springs, and later falls.
Seeing is believing. Whether from a drone, a camera in a tower, a weekly walk, or analysis of the data all these provide, the evidence coming in over time is clear. Climate change is resetting the seasonal clock, and jacking the works of the trees and the forest.
Last year, the first frost arrived at the forest in late October. For most of the 20th century, first frosts came in September. In the 50-year record, the record-latest frosts all occurred in the last 12 years. This year, I didn’t see the first glint of frost on the grass, or crack ice on the puddles until O’Keefe and I took our weekly survey walk on November 4.
The phenological research of the Richardson lab also communicates the story of a changing world not only to scientists, but to the public in a way that equations and computer models do not. It’s a familiar, deeply human practice, with a new, urgent relevance. Trees have important things to say in a language anyone can understand of wood, leaves, and seasonal time. They hold out too an invitation to wonder and delight, and engagement in our planet’s unfolding story.
“Observing nature is something everyone can do, and relate to,” Klosterman said. “Yet at the same time, it holds a lot of mystery, and room for a lot more understanding.”