Satellite data delves into evergreens' slumber

Satellite data delves into evergreens' slumber
Nebraska's Gamon leads study that visualizes changes in trees' photosynthesis

An international research team that includes Nebraska's John Gamon has combined satellite data to detect seasonal change in evergreen trees across northern North America.
Protasov AN | Shutterstock
An international research team that includes Nebraska's John Gamon has combined satellite data to detect seasonal change in evergreen trees across northern North America.

University of Nebraska-Lincoln researcher John Gamon is part of an international team that has shown in new ways how evergreen conifers go dormant in winter.

The study, published this week in Proceedings of the National Academy of Sciences, visualized the dormancy and a spring awakening of conifers using newly available satellite data. The discovery could improve scientists’ understanding of how conifer photosynthetic activity is changing in a warming climate and could provide a way to assess evergreen forests’ role in the global carbon budget.

The international research team examined the photosynthetic activity of evergreens at the University of Alberta and several other locations in North America. To see the previously invisible pigment shifts in green chlorophyll and yellow-orange carotenoids within the trees, the team combined two remote sensory bands captured from satellites -- one designed for ocean color and another for land vegetation.

“The chlorophyll/carotenoid index is a sharper tool to ask questions about the forests,” Gamon said. “It’s suddenly made visible, the invisible.”

Photosynthesis is the use by plants of the energy in sunlight to carry out chemical reactions such as the conversion of carbon dioxide into oxygen. It also produces sugars that feed the plant. Because evergreens, unlike deciduous trees, show to the human eye no obvious signs of greening or browning when their photosynthesis ramps up or slows down, the timing of their activation or deactivation has been difficult to assess. Scientists hope that the new pigment index will help clarify the exact role northern forests play in the global carbon cycle.

The researchers are using this index to examine if the growing season of the northern forests is shifting and how changes impact photosynthetic activity. Specifically, the project is looking at the possibility that an earlier spring may lead to an increase in photosynthetic activity for northern forests. The team is also considering if an earlier growing season could result in more warming and drought that decreases photosynthesis.

Gamon conducted the research in collaboration with scientists from Alberta, the University of Toronto, the University of North Carolina, the University of Maryland, Baltimore County, the University of Barcelona, NASA, and the U.S. Forest Service.

Gamon has been a part of CALMIT, based in Nebraska's School of Natural Resources, since 2015. He specializes in airborne collection of data, which is used to verify remote-sensing information collected by satellites and from the ground. CALMIT resources, including its plane, and research funding at Nebraska attracted Gamon to Lincoln.

His research will include additional studies into the effects of climate change on northern forests through NASA's Arctic-Boreal Vulnerability Experiment program. For more information on remote-sensing research at CALMIT, click here.