TY - JOUR
T1 - Primary and secondary effects of climate variability on net ecosystem carbon exchange in an evergreen eucalyptus forest
AU - Van Gorsel, Eva
AU - Berni, J. A.J.
AU - Briggs, P.
AU - Cabello-Leblic, A.
AU - Chasmer, L.
AU - Cleugh, H. A.
AU - Hacker, J.
AU - Hantson, S.
AU - Haverd, V.
AU - Hughes, D.
AU - Hopkinson, C.
AU - Keith, H.
AU - Kljun, N.
AU - Leuning, R.
AU - Yebra, M.
AU - Zegelin, S.
N1 - Funding Information:
This work was supported in part by grants from the Australian Climate Change Science Program and its predecessors through the DCCEE. We would like to thank Michael Schaefer for internal review and to anonymous reviewers for their comments. We acknowledge C. Torrence and G. Compo for providing wavelet software ( http://atoc.colorado.edu/research/wavelets/ ) and D. Maraun for provision of the R package ‘SOWAS’. This work used eddy covariance data acquired by the FLUXNET community and in particular by the following networks: AmeriFlux (U.S. Department of Energy, Biological and Environmental Research, Terrestrial Carbon Program (DE-FG02-04ER63917 and DE-FG02-04ER63911)), AfriFlux, AsiaFlux, CarboAfrica, CarboEuropeIP, CarboItaly, CarboMont, ChinaFlux, Fluxnet-Canada (supported by CFCAS, NSERC, BIOCAP, Environment Canada, and NRCan), GreenGrass, KoFlux, LBA, NECC, OzFlux, TCOS-Siberia, USCCC. We acknowledge the financial support to the eddy covariance data harmonization provided by CarboEuropeIP, FAO-GTOS-TCO, iLEAPS, Max Planck Institute for Biogeochemistry, National Science Foundation, University of Tuscia, Université Laval, Environment Canada and US Department of Energy and the database development and technical support from Berkeley Water Center, Lawrence Berkeley National Laboratory, Microsoft Research eScience, Oak Ridge National Laboratory, University of California – Berkeley and the University of Virginia. The National Centre for Earth Observation of Natural Environment Research Council UK, NCEO/NERC, financially supported the lidar collection.
PY - 2013/12/15
Y1 - 2013/12/15
N2 - To understand the dynamics of ecosystem carbon cycling more than 10 years of eddy covariance data, measured over an evergreen, temperate, wet sclerophyll forest, were analysed and related to climate drivers on time scales ranging from hours to years. On hourly timescales we find that incoming shortwave radiation is the major meteorological driver of net ecosystem carbon exchange (NEE). Light use efficiency is higher under diffuse light conditions and carbon uptake is further modulated by the effects of variable and suboptimal temperatures (optimal temperature Topt=18°C) as well as by water demand (critical vapour pressure deficit VPDcrit=12hPa). Incoming shortwave radiation is also the major driver on daily time scales. Effects of increased light use efficiency under diffuse conditions, however, are overcompensated by the increased carbon uptake with larger amounts of total incoming shortwave radiation under clear sky conditions. On synoptic time scales a low ratio of actual to potential incoming shortwave radiation is also related to a reduced carbon uptake, or carbon release, and associated with precipitation events. Overcast conditions during an extended wet period (2010-2011) led to lower than average carbon uptake as did extended dry periods during 2003 and 2006. The drought in 2003 triggered an insect attack which turned the ecosystem into a net source of carbon for almost one year. The annual average normalised difference vegetation index (NDVI) is highly correlated with NEE at this site and multiple linear regression shows that NDVI, incoming solar radiation and air temperature explain most of the variance in NEE (r2=0.87, p<0.001). Replacing air temperature with average spring air temperatures further increases the correlation (r2=0.91, p<0.001). Results demonstrate that carbon uptake in this ecosystem is highly dynamic, that wavelet analysis is a suitable tool to analyse the coherence between the carbon exchange and drivers seamlessly, and that long time series are needed to capture the variability.
AB - To understand the dynamics of ecosystem carbon cycling more than 10 years of eddy covariance data, measured over an evergreen, temperate, wet sclerophyll forest, were analysed and related to climate drivers on time scales ranging from hours to years. On hourly timescales we find that incoming shortwave radiation is the major meteorological driver of net ecosystem carbon exchange (NEE). Light use efficiency is higher under diffuse light conditions and carbon uptake is further modulated by the effects of variable and suboptimal temperatures (optimal temperature Topt=18°C) as well as by water demand (critical vapour pressure deficit VPDcrit=12hPa). Incoming shortwave radiation is also the major driver on daily time scales. Effects of increased light use efficiency under diffuse conditions, however, are overcompensated by the increased carbon uptake with larger amounts of total incoming shortwave radiation under clear sky conditions. On synoptic time scales a low ratio of actual to potential incoming shortwave radiation is also related to a reduced carbon uptake, or carbon release, and associated with precipitation events. Overcast conditions during an extended wet period (2010-2011) led to lower than average carbon uptake as did extended dry periods during 2003 and 2006. The drought in 2003 triggered an insect attack which turned the ecosystem into a net source of carbon for almost one year. The annual average normalised difference vegetation index (NDVI) is highly correlated with NEE at this site and multiple linear regression shows that NDVI, incoming solar radiation and air temperature explain most of the variance in NEE (r2=0.87, p<0.001). Replacing air temperature with average spring air temperatures further increases the correlation (r2=0.91, p<0.001). Results demonstrate that carbon uptake in this ecosystem is highly dynamic, that wavelet analysis is a suitable tool to analyse the coherence between the carbon exchange and drivers seamlessly, and that long time series are needed to capture the variability.
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U2 - 10.1016/j.agrformet.2013.04.027
DO - 10.1016/j.agrformet.2013.04.027
M3 - Article
AN - SCOPUS:84885318226
SN - 0168-1923
VL - 182-183
SP - 248
EP - 256
JO - Agricultural and Forest Meteorology
JF - Agricultural and Forest Meteorology
ER -
