U radu je procijenjena neto produktivnost ekosustava (NEP) i neto bilanca ugljika (NECB) u mladoj sastojini hrasta lužnjaka (Quercus roburL.) pomoću dvije neovisne metode i to: a) mikrometeorološke metode vrtložne kovarijance (EC) te, b) kombinirane metode koja je uključivala biometrijsku izmjeru šumske biomase i periodičko mjerenje respiracije tla (SR). Maksimalni NEP zabilježen vrtložnom kovarijancom iznosio je 10,7 gC m-2 dan-1u 2008.godine, odnosno 12,2 gC m-2dan-1u 2009. godini. Godišnje vrijednosti NEP kretale su se od 384 gC m-2god-1u 2008. do 584 gC m-2god-1u 2009. Godini,iz čega je razvidno da su sastojine u dohvatu mjerne stanice u obje godine bile neto spremnik ugljika.
Biometrijskom metodom praćenja prirasta i produkcije listinca i sitnog drvnog otpada dobivenaje neto primarna produktivnost (NPP)od 777 gC m-2 god-1u 2008.godine, odnosno 846 gC m-2god-1u 2009. godini. Udio heterotrofne respiracije (Rh) procijenjen je na 50% od izmjerene ukupne SR, pa je Rh procijenjena na 438 gC m-2god-1u 2008.godini, odnosno 441 gC m-2god-1u 2009. godini. Kombiniranom metodom NEP je dobivena kao razlika NPP i Rh, a iznosila je 339 i 405 gC m-2god-1u 2008.godini, odnosno 2009. godini. Usporedba dvaju metoda procjene NEP-a daje dobro slaganje do srpnja za obje promatrane godine. Do odstupanja dolazi u drugom dijelu ljeta i jeseni kada prestaje debljinski prirast, ali stabla očito i dalje aktivno spremaju ugljik. Kombinirana metoda daje manje vrijednosti NEP-a u odnosu na metodu vrtložne kovarijance, iz više razloga npr.: udio Rh je manji od 50 %, omjer podzemnog i nadzemnog dijela biomase; R:S je veći od 0,257,i sl. Potrebna su daljnja istraživanja koja bi empirički odredila udio Rhu SR, omjer R:S te istraživanja količine ugljika u sastavnicama tla.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
