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ŠUMARSKI LIST 13/2011 str. 75     <-- 75 -->        PDF

H. Marjanović, M. Z. Ostrogović, G.Alberti, I. Balenović, E. Paladinić, K. Indir1,A. Peressotti, D. Vuletić: DINAMIKA Šumarski list – Posebni broj (2011), 59-73

SUMMARY: Net Ecosystem Productivity (NEP) and Net Ecosystem Carbon
Balance (NECB) of young Pedunculate oak (Quercus roburL.) stand were
investigated. Two independent methods for assessing NEP were used: a) micrometeorological
method of Eddy covariance (EC) and, b) combination of
biometric method for assessing Net Primary Productivity (NPP) and periodic
soil respiration (SR) measurements (named for reasons of brevity the combined
method). NEP from combined method was obtained as a difference of
NPP and heterotrophic respiration (Rh) which was estimated to have 50%
share in the measured total SR.

Maximal measured daily NEP from eddy covariance was 10,7 gC m-2
day-1in 2008., and 12,2 gC m-2day-1in 2009. The annual NEP ranged from
384 gC m-2yr-1in 2008 to584 gC m-2yr-1in 2009 indicating that the stands
around the EC tower were actively storing carbon during both years.

From biometric measurements of stem increment using dendrometer bands,
height increment and litter production we obtained an average NPP of the
stands in the footprint of 777 gC m-2yr-1in 2008 and 846 gC m-2yr-1in 2009.
Heterotrophic respiration (Rh) , estimated from SR measurements was 438 gC
m-2yr-1in 2008 and 441 gC m-2yr-1in 2009. By subtracting Rhfrom NPP, we
obtained NEP of 339 and 405 gC m-2yr-1in 2008 and 2009, respectively.

Comparison of results for NEP during vegetation season reveals that agreement
between the two methods was very good until July for both years. Later in
the summer and autumn, discrepancy occurs when stem growth ceases but trees
continue to actively store carbon. This leads to the underestimation of NEP from
combined method during that period, leading to the overall lower values of NEP
when compared with NEP values from eddy covariance. There could be several
reasons for the discrepancies namely, share of Rhin total SR could be less than
50 %, R:S could be higher than 0.257, or various combinations of both. Further
research is needed that would provide better estimates of share of Rhin SR, R:S
ratio and soil carbon content.

Key words:Eddy covariance method; soil respiration; carbon fluxes;
carbon sequestration