Interannual Variability Of The Carbon Balance Of Three Different-Aged Douglas-Fir Stands In The Pacific Northwest

  • Sites: CA-Ca1, CA-Ca2, CA-Ca3
  • Krishnan, P., Black, T. A., Jassal, R. S., Chen, B., Nesic, Z. (2009/11/24) Interannual Variability Of The Carbon Balance Of Three Different-Aged Douglas-Fir Stands In The Pacific Northwest, Journal Of Geophysical Research, 114(G4), .
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  • The seasonal and interannual variability of gross ecosystem photosynthesis (Pg) and
    ecosystem respiration (Re), and their relationships to environmental variables and stand
    characteristics were used to explain the variation of eddy-covariance-measured net
    ecosystem productivity (FNEP) of three different-aged Douglas-fir stands located on the
    east coast of Vancouver Island in British Columbia, Canada. During the 9-year period,
    1998–2006, which included a strong El Nin˜o/La Nin˜a event, the near-end-of-rotation
    stand (DF49, 57 years old in 2006) was a moderate carbon (C) sink for CO2 with annual
    FNEP ranging from 267 to 410 g C m2 yr1 (mean ± SD, 357 ± 51 g C m2 yr1
    The pole/sapling stand (HDF88, 18 years old in 2006) was a weak C source (FNEP =
    64 ± 75 g C m2 yr1
    ), and the recently harvested stand (HDF00, 6 years old in 2006)
    was a large C source (FNEP = 515 ± 88 g C m2 yr1
    ) during 2002–2006. Irrespective
    of stand age, all sites responded quite similarly to changes in environmental variables
    during each year. Daily total values of Pg and Re were highest in July–August in all three
    stands, while daily FNEP peaked during April–June at DF49, May–June at HDF88,
    and June–July at HDF00. Reductions in root-zone soil water content decreased both Pg
    and Re especially during the dry period from May to September, and this effect was more
    pronounced in the younger stands. Evapotranspiration and dry-foliage surface
    conductance also decreased with decreasing root-zone soil water content whereas water
    use efficiency appeared to be conservative, especially at DF49. Increasing spring
    temperature had a positive effect on annual Pg and Re but caused a slight decrease in
    annual FNEP. During the summer to autumn transition period, increases in soil water
    content resulted in a greater increase in Re than Pg causing a reduction in FNEP. The
    interannual variation in the C balance was determined mainly by the interannual variation
    in Re for the near-end-of-rotation stand and Pg for the two younger stands. The results
    indicate that regardless of the stand age, interannual variability in the C balance was
    mainly determined by year-to-year variability in spring temperature and water availability
    in late summer.