Forest carbon balance under elevated CO2

Abstract

Free-air CO enrichment (FACE) technology was used to expose a loblolly pine (Pinus taeda L.) forest to elevated atmospheric CO (ambient + 200 µl l). After 4 years, basal area of pine trees was 9.2% larger in elevated than in ambient CO plots. During the first 3 years the growth rate of pine was stimulated by ~26%. In the fourth year this stimulation declined to 23%. The average net ecosystem production (NEP) in the ambient plots was 428 gC m year, indicating that the forest was a net sink for atmospheric CO. Elevated atmospheric CO stimulated NEP by 41%. This increase was primarily an increase in plant biomass increment (57%), and secondarily increased accumulation of carbon in the forest floor (35%) and fine root increment (8%). Net primary production (NPP) was stimulated by 27%, driven primarily by increases in the growth rate of the pines. Total heterotrophic respiration (R ) increased by 165%, but total autotrophic respiration (R) was unaffected. Gross primary production was increased by 18%. The largest uncertainties in the carbon budget remain in separating belowground heterotrophic (soil microbes) and autotrophic (root) respiration. If applied to temperate forests globally, the increase in NEP that we measured would fix less than 10% of the anthropogenic CO projected to be released into the atmosphere in the year 2050. This may represent an upper limit because rising global temperatures, land disturbance, and heterotrophic decomposition of woody tissues will ultimately cause an increased flux of carbon back to the atmosphere.

Modeling nighttime ecosystem respiration from measured CO2 concentration and air temperature profiles using inverse methods

“…However, Lai et al [2002a] argued that in a first-order analysis, the respiration of woody tissue is less important than the contribution from foliage because the total woody surface area is less than the total leaf surface area (at least for this pine site), and the woody parts have smaller tissuespecific respiration rates than the foliage [Hamilton et al, 2002]. With this simplification, Lai et al [2002a] estimated the carbon source vertical distribution S t; z ð Þ by assuming that the entire plant surface area was only foliage leading to:…”

Implications of differing input data sources and approaches upon forest carbon stock estimation

“…Forests exchange large quantities of CO 2 with the atmosphere and make an important contribution to the global biogeochemical cycling of carbon (C) (Hamilton et al 2002;Denman et al 2007). Various approaches have been developed to assess forest ecosystem C exchange, from the measurement of temporal changes in biomass (Clark et al 2001) and soil C (Lal et al 2001) to the measurement of C exchanges themselves using eddy covariance flux towers (Baldocchi 2003).…”

The use of remote sensing in light use efficiency based models of gross primary production: A review of current status and future requirements

“…Terrestrial ecosystems absorb approximately 60 Gt of carbon annually through the physiological process of photosynthesis (Janzen, 2004), also referred to as Gross Primary Production (GPP) (Hamilton et al, 2002). Simultaneously, autotrophic and heterotrophic organisms release about the same amount of carbon back into the atmosphere thereby closing the terrestrial carbon cycle.…”