Forest leaves rich in nitrogen do not help to cool the atmosphere

A paper by a research group including Professor Philip Lewis and Dr Mathias Disney (UCL Geography) in Proceedings of the National Academy of Sciences challenges claims that forest leaves rich in nitrogen aid the reflection of infrared radiation and therefore cool the atmosphere. On the contrary, the research, led by Professor Yuri Knyazikhin at Boston University, shows that the richer individual leaves are in nitrogen the worse they become at reflecting infrared radiation.

This effect is masked by the complex arrangements of trees, with different patterns of leaves within a forest making it appear that higher levels of leaf nitrogen are leading to increased infrared reflection. Instead, it is the structure of forest canopies (the spatial arrangement of the leaves) that determines their ability to reflect infrared light

Mat Disney explains: “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.

The 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 their current state and how they are responding to climate change.”

See:

• http://www.ucl.ac.uk/news/news-articles/1212/04122012-nitrogen-leaves
• Knyazikhin, Y. et al., Hyperspectral remote sensing of foliar nitrogen content, PNAS 2012, December 4, 2012, doi:10.1073/pnas.1210196109
• http://www.pnas.org/search?submit=yes&pubdate_year=2012&volume=&firstpage=&doi=&author1=Knyazikhin&author2=&title=&andorexacttitle=and&titleabstract=&andorexacttitleabs=and&fulltext=&andorexactfulltext=and&fmonth=&fyear=&tmonth=&tyear=&tocsectionid=all&format=standard&hits=10&sortspec=relevance&submit=yes&submit=Submi