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Seasonal controls on interannual variability in carbon dioxide exchange of a near-end-of rotation Douglas-fir stand in the Pacific Northwest, 1997–2006

Authors

  • BAOZHANG CHEN,

    1. Department of Forest Resources Management, Faculty of Forestry, University of British Columbia, Vancouver, BC, Canada V6T 1Z4,
    2. Biometeorology and Soil Physics Group, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
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  • T. ANDREW BLACK,

    1. Biometeorology and Soil Physics Group, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
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  • NICHOLAS C. COOPS,

    1. Department of Forest Resources Management, Faculty of Forestry, University of British Columbia, Vancouver, BC, Canada V6T 1Z4,
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  • PRAVEENA KRISHNAN,

    1. Biometeorology and Soil Physics Group, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
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  • RACHHPAL JASSAL,

    1. Biometeorology and Soil Physics Group, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
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  • CHRISTIAN BRÜMMER,

    1. Biometeorology and Soil Physics Group, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
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  • ZORAN NESIC

    1. Biometeorology and Soil Physics Group, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
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Baozhang Chen, Department of Forest Resources Management, Faculty of Forestry, University of British Columbia, Vancouver, BC, Canada V6T 1Z4, tel. +1 604 822 9138, fax +1 604 822 2184, e-mail: Baozhang.chen@ubc.ca

Abstract

This study analyzes 9 years of eddy-covariance (EC) data carried out in a Pacific Northwest Douglas-fir (Pseudotsuga menzesii) forest (58-year old in 2007) on the east coast of Vancouver Island, Canada, and characterizes the seasonal and interannual variability in net ecosystem productivity (NEP), gross primary productivity (GPP), and ecosystem respiration (Re) and primary climatic controls on these fluxes. The annual values (± SD) of NEP, GPP and Re were 357 ± 51, 2124 ± 125, and 1767 ± 146 g C m−2 yr−1, respectively, with ranges of 267–410, 1592–2338, and 1642–2071 g C m−2 yr−1, respectively. Spring to early summer (March–June) accounted for more than 80% of annual NEP while late spring to early autumn (May–August) was mainly responsible for its interannual variability (∼80%). The major drivers of interannual variability in annual carbon (C) fluxes were annual and spring mean air temperatures (Ta) and water deficiency during late summer and autumn (July–October) when this Douglas-fir forest growth was often water-limited. Photosynthetically active radiation (Q), and the combination of Q and soil water content (θ) explained 85% and 91% of the variance of monthly GPP, respectively; and 91% and 96% of the variance of monthly Re was explained by Ta and the combination of Ta and θ, respectively. Annual net C sequestration was high during optimally warm and normal precipitation years, but low in unusually warm or severely dry years. Excluding 1998 and 1999, the 2 years strongly affected by an El Niño/La Niña cycle, annual NEP significantly decreased with increasing annual mean Ta. Annual NEP will likely decrease whereas both annual GPP and Re will likely increase if the future climate at the site follows a trend similar to that of the past 40 years.

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