Net Carbon Uptake Has Increased through Warming-Induced Changes in Temperate Forest Phenology 

Prof. Trevor F Keenan1, Andrew D Richardson2, Josh Gray3, Mark A Friedl4, Michael P Toomey5, Gil Bohrer6, David Y Hollinger7, J William Munger5, Hans Peter E Schmid8, Ian Sue Wing9 and Bai Yang10, (1)Lawrence Berkeley National Laboratory, Berkeley, United States, (2)Northern Arizona University, School of Informatics, Computing and Cyber Systems, Center for Ecosystem Science and Society, Flagstaff, AZ, United States, (3)Boston University, Boston, MA, United States, (4)Boston University, Earth and Environment, Boston, MA, United States, (5)Harvard Univ, Cambridge, MA, United States, (6)The Ohio State University, Department of Civil, Environmental and Geodetic Engineering, Columbus, United States, (7)University of New Hampshire Main Campus, Durham, NH, United States, (8)Karlsruhe Institute of Technology, IMK-IFU, KIT-Campus Alpin, Karlsruhe, Germany, (9)Boston University, Department of Earth & Environment, Boston, United States, (10)Oak Ridge National Laboratory, Oak Ridge, TN, United States
Abstract:
The timing of phenological events exerts a strong control over ecosystem function and leads to multiple feedbacks to the climate system. Phenology is inherently sensitive to temperature and recent warming is reported to have led to earlier spring, later autumn and increased vegetation activity. Such greening could be expected to enhance ecosystem carbon uptake, although reports also suggest decreased uptake for boreal forests. Here we assess changes in phenology of temperate forests over the eastern US during the past two decades, and quantify the resulting changes in forest carbon storage. We combine long-term ground observations of phenology, satellite indices, and ecosystem-scale carbon dioxide flux measurements, along with 18 terrestrial biosphere models. We observe a strong trend of earlier spring and later autumn. In contrast to previous suggestions we show that carbon uptake through photosynthesis increased considerably more than carbon release through respiration for both an earlier spring and later autumn. The terrestrial biosphere models tested misrepresent the temperature sensitivity of phenology, and thus the effect on carbon uptake. Our analysis of the temperature–phenology–carbon coupling suggests a current and possible future enhancement of forest carbon uptake due to changes in phenology. This constitutes a negative feedback to climate change, and is serving to slow the rate of warming. 
Back to: Biosphere-Atmosphere Greenhouse Gas Fluxes in Terrestrial Ecosystem II