Green Blog: Capturing Climate Change Digitally

The changing palette of colors in a forest signals more than the arrival of a new season. For those who know how to look, the colors also reveal how much carbon dioxide the trees are absorbing from the atmosphere during photosynthesis, a new study suggests. By analyzing thousands of photographs of a forest canopy less than 40 miles outside London, the researchers were able to estimate carbon uptake over a two-year period based on the leaves? hues.

Forests play a vital role in mitigating the effects of climate change by taking up carbon dioxide and storing it in leaves, stems and roots. In the United States, forests absorb and store some 750 million metric tons of carbon dioxide annually, or about 10 percent of the country?s carbon dioxide emissions, the Forest Service says.

But as climate change shifts the timing of seasons, buds are bursting sooner, and ecologists are working to understand how this affects forests? ability to absorb carbon dioxide.

?Reliably predicting CO2 flux isn?t easy,? the study?s lead author, Toshie Mizunuma, a doctoral researcher at the University of Edinburgh?s School of GeoSciences, said in a statement. ?It varies a lot due to changes in weather and alterations in forest metabolism caused by pests and diseases.?

To better understand the relationship between carbon uptake and canopy color, Ms. Mizunuma?s team set up a pair of digital cameras in Alice Holt Forest, a former royal hunting ground that now has a 220-acre research plot within a commercial oak forest. The researchers, whose work appears in the latest issue of the peer-reviewed journal Functional Ecology, positioned an outdoor Webcam to view the canopy horizontally.

They set up a second camera with a fisheye lens trained downward on the canopy from atop an instrument tower. Each camera took a photo every 30 minutes during daylight for two years, capturing a total of 38,000 images, and the researchers analyzed the four photos snapped each day around midday.

Studying the timing of when trees sprout their first leaves in the springtime, flower and finally shed their leaves in the autumn, is considered one of the simplest ways to monitor how trees are responding to climate change. But the work, known as phenology, has traditionally required visits to the same tree in the same spot at least once a day, sometimes more, Ms. Mizunuma wrote in an e-mail. These manual observations are ?often impractical,? she said. Accessibility to the target trees may be limited, and ?monitoring may be biased by observers.?

More recently, remote monitoring via satellite has offered a less labor-intensive alternative, but clouds often get in the way and the area captured is so large that woodland images are often muddled with adjacent land, Ms. Mizunuma said. And in a study published this year in the Proceedings of the National Academy of Sciences (PNAS), scientists at Colorado State University and Duke University called for correction of the models now used to estimate carbon uptake based on remotely sensed greenness.

Carbon uptake by trees of nearly two dozen species dropped off weeks before leaves began to change color and to fall in the autumn, they found, suggesting that trees may sequester as much as 3 percent less carbon dioxide globally than previously thought.

This latest paper joins a growing body of research comparing direct measurements of carbon exchange in various landscapes with measures of reflected light, said Dennis Baldocchi, a professor of biometeorology at the University of California, Berkeley, who is unaffiliated with Ms. Mizunuma?s team.

?Many of us are interested in providing ground truth? for the estimates of photosynthesis produced by satellites in space, he explained. In recent years, he said, researchers have increasingly used digital cameras or narrow-band spectrometers at instrument towers like the one in Alice Holt Forest. More than 500 such towers now form an international network created in the 1990s to measure carbon fluxes directly over the long term. The idea of using numbers extracted from digital images to detect a vegetation index originated in the laboratory of Andrew Richardson, a physiological ecologist at Harvard, Dr. Baldocchi said.

Ms. Mizunuma suggsted that digital cameras could combine the best of both worlds in that they provide unobstructed images that can be quantitatively analyzed at a far lower cost than previous methods. Her team extracted several parameters from the photos and mapped them against data collected at the site by the instruments on the tower.? ?Of all the expressions of canopy color, hue is the one that seems to have the greatest utility,? the researchers write.

The rise of carbon dioxide uptake in the spring and the decline of uptake in the fall approximately dovetail with the greenness and hue of the leaves. Carbon uptake peaked when the leaves were dark green, suggesting that ?hue can be a useful proxy for photosynthesis,? Ms. Mizunuma said. The authors note, however, that further research is needed at other sites ?to explore whether such a good relationship always exists, as it may be site- and time-specific.?

It?s certainly worth finding out, Dr. Balodocchi said. Exploring hue in this context ?may give us another way to try and upscale carbon fluxes with cheap cameras,? he said. ?This is a good way to produce citizen science and study phenology well, too.?

?We have years of photos at our sites with flux data, he said, ?so it it s a good idea to test.?

Ms. Mizunuma said that experts still do not understand what controls the timing of leaves? sprouting in the spring and falling in the autumn. What is needed, she said, is a cheap and simple way to gather data over the long term, and digital cameras could hold the key.

Indeed, as digital camera technology has improved and prices have dropped, scientists have begun to harness them for a broad range of research projects, sometimes calling on Internet users to help analyze thousands of images.

Researchers with the Zooniverse project led by the University of Oxford and Adler Planetarium, for example, have set up more than 220 camera traps throughout Serengeti National Park in Tanzania. Visitors to the Snapshot Serengeti website, launched this month, can help identify the animals.

As Chris Lintott, the Zooniverse project?s director, explained to PRI?s ?The World,? ?The cameras allow us to carpet the whole place.?

Meanwhile, in Greenland, the Himalayas in Nepal, Alaska and the Rocky Mountains, the Extreme Ice Survey has set up 34 cameras at 16 glaciers to track changes in the ice, seeking to give a ?visual voice? to the landscape.

According to Ms. Mizunuma, digital cameras could also be used to visually monitor the spread of tree diseases, and similar setups could be invaluable in monitoring how vegetation responds to environmental change. ?It is a well-known fact that positive response often turns into negative response at a certain point,? she said, noting that leaves sprouting earlier in the year may expand the carbon-uptake period, but then increase the risk of frost damage.

As a result, she said, ?long-term observation is crucial to understand how plants respond to climate change.?

Source: http://green.blogs.nytimes.com/2012/12/27/capturing-climate-change-digitally/?partner=rss&emc=rss

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