Primary and secondary effects of climate variability on net ecosystem carbon exchange in an evergreen Eucalyptus forest

Eva van Gorsel, J.A.J. Berni, P. Briggs, A. Cabello-Leblic, L. Chasmer, Helen Cleugh, Jorg Hacker, S. Hantson, V. Haverd, D. Hughes, C. Hopkinson, H. Keith, L. Kljun, Ray Leuning, M. Yebra, S. Zegelin

    Research output: Contribution to journalArticlepeer-review

    30 Citations (Scopus)

    Abstract

    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.

    Original languageEnglish
    Pages (from-to)248-256
    Number of pages9
    JournalAgricultural and Forest Meteorology
    Volume182-183
    DOIs
    Publication statusPublished - 15 Dec 2013

    Keywords

    • Carbon dioxide
    • Climate drivers
    • Coherence
    • Disturbance
    • Drought
    • Insects

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