Eight Years Of Forest-Floor Co2 Exchange In A Boreal Black Spruce Forest: Spatial Integration And Long-Term Temporal Trends

  • Sites: CA-Obs
  • Publication Type: JOUR
  • Authors: Gaumont-Guay, D.; Black, T.; Barr, A.; Griffis, T.; Jassal, R.; Krishnan, P.; Grant, N.; Nesic, Z.

  • Automated measurements of the net forestfloor
    CO2 exchange (NFFE) were made in a mature (130yearold)
    boreal black spruce forest over an 8year
    period (2002–2009) with the objectives of (1) quantifying
    the spatial and temporal (seasonal and interannual) patterns in NFFE, soil respiration (SR) and gross forestfloor
    photosynthesis (GFFP), and (2) better understanding the key climatic controls on each component
    at both time scales. Scalingup
    of the component fluxes to the stand level showed that the feather moss
    community accounted for more than 85% of NFFE and SR, and more than 70% of GFFP. The remainder was
    partitioned almost equally between the sphagnum and lichen communities for all components fluxes,
    while the exposed mineral soil in hollows accounted for less than 1% of NFFE and SR. Soil temperature (Ts)
    was the dominant climate variable determining seasonal trends in NFFE and SR. The shape of the exponential
    response was, however, strongly modulated by soil water content (SWC) in the surface organic
    horizon, with reduced apparent temperature sensitivity at low SWC. A lowering of the water table depth
    also had an effect on NFFE and SR, although very weak, with increased CO2 loss from the hollows likely due
    to improved soil aeration. Air temperature (Ta) was the dominant climate variable determining seasonal
    trends in GFFP, while plant water status seemed to have played a minor role. Although not statistically
    significant (p = 0.9907), annual totals of scaledup
    NFFE varied from 505 ± 121 to 601 ± 144 g C m−2 y−1
    over the 8year
    period. The lowest NFFE was observed in 2004, the coldest and wettest year on record,
    while the highest was observed in 2005, a warmer year with slightly aboveaverage
    precipitation. SR, by
    far the dominant component of the forestfloor
    CO2 exchange, closely followed the interannual
    in NFFE, while GFFP was lowest in 2004 and highest in 2003, also a cold year but with very low precipitation.
    Over the 8year
    period, winter NFFE contributed 7% to annual NFFE while GFFP during the growing
    season reduced losses due to SR by 18%.
    While strong correlations were observed between the component fluxes and temperature (Ts or Ta) and
    SWC at the seasonal time scale, the mean annual values of these climate variables were poor predictors of
    the interannual
    trends when considered individually. Combining multiplicatively Ts and SWC for NFFE
    and SR, and Ta and SWC for GFFP, significantly increased the predictive ability of the models. The difference
    in predictability of the two time scales poses some interesting challenges for interpreting and modeling
    the longterm
    temporal trends in NFEE and its components. The results obtained in this relatively longterm
    study suggest that the interannual
    variability in the component fluxes was not driven by the mean
    annual climate conditions, but rather the shorter time scale changes in climate conditions, i.e. changes
    that occurred within days, weeks and/or seasons. Moreover, it appeared that the timing of the climatic
    changes within each year was also critical, spring and summer conditions having a far greater impact
    than fall and winter conditions in this stand.

  • Journal: Agricultural And Forest Meteorology
  • Funding Agency: —
  • Citation Information:
  • Volume: 184
  • No:
  • Pages: 25-35
  • Publication Year: 2014/01
  • DOI: 10.1016/j.agrformet.2013.08.010