Structure of Tree Canopies an Important Factor in Infrared Reflection

A new finding challenges the assertions that forests tree leaves, rich in nitrogen, may aid in reflecting infrared radiation. According to the new finding, it is not the leaves but the structure of tree canopies that plays an important role in infrared reflection.

The recent studies have observed a strong association between the concentration of nitrogen in forests and infrared reflectance measured from aircraft and satellites.  This reveals a previously overlooked role for nitrogen in regulating Earth's climate system.

The authors of the new finding, professor Philip Lewis and Dr Mathias Disney (UCL Geography), highlight the fact that the association between nitrogen levels of the leaves and infrared reflection is false. They show  that forest canopies determine the ability to reflect infrared light.

The study claims that the nitrogen-rich leaves are worse at reflecting infrared radiation. It is the complex arrangement of the trees with radically different arrangements of leaves within a forest that basically camouflage this effect, making it appear as if higher levels of leaf nitrogen are leading to increased infrared reflection.

Dr Disney said: "It is impossible to understand how forests reflect infrared without taking into account the arrangement of different types of leaf clumps, such as shoots and crowns, which make up the canopy, as well as the internal structure of the leaves.

"This paper proposes a way to account for structure when measuring canopy infrared reflectance. We hope it will improve our ability to measure forest biochemistry from satellites, allowing us to better quantify forests' current state and how they are responding to climate change."

The new paper is published in the  Proceedings of the National Academy of Sciences.