The carbon balance of a young Beech forest

Abstract

Summary1. We present measurements of CO 2 fluxes over 2 years above and within a young Beech stand in the east of France. This site is part of the Euroflux network set up to monitor fluxes over representative European forests. 2. The net ecosystem carbon (C) exchange was derived from continuous eddy flux measurements. Major components of the total flux (i.e. soil and above-ground biomass respiration and assimilation of leafy branches) were measured independently using chambers. The main C stocks (i.e. root, stem and branch biomass) were also quantified. 3. Daily minima of CO 2 flux were typically around -20 µ mol CO 2 m -2 s -1 during the period of full leaf expansion, while night-time ecosystem respiration varied between 5 and 15 µ mol CO 2 m -2 s -1. The seasonal pattern of net ecosystem assimilation was very close to that of net assimilation at the single branch scale. The seasonal variation of net ecosystem exchange was closely related to leaf expansion and soil water content during the dry year of 1996. 4. Measurements of ecosystem respiration (eddy flux) were corrected for CO 2 storage within the stand. This C flux showed a seasonal pattern, the maximum rates (4-7 g C m -2 day -1 ) occurring in spring and summer, and appeared to be correlated with soil temperature. Temporal variation of soil respiration showed the same pattern, and effects of both temperature and soil drying were found. Annual soil respiration was ≈ 70% of ecosystem respiration. Root respiration was 60% of the total below-ground respiration. 5. Annual net C exchange was -218 and -257 g C m -2 in 1996 and 1997, respectively, corresponding to net C uptake by the forest. These values are much lower than the annual biomass increment (stems and large roots) of the stand: 427 and 471 g C m -2 year -1 , respectively. The difference may be explained by a release of CO 2 from the decomposition of woody debris. 6. Ecosystem C loss by respiration was 800-1000 g C m -2 year -1 . Gross C gain was 1000-1300 g C m -2 year -1 . Ecosystem respiration therefore played a major role in the annual C balance of this forest.

Ten years of fluxes and stand growth in a young beech forest at Hesse, North-eastern France

“…Soil respiration is generally the largest TER component in forests and influences NEE to a large extent. From soil respiration measurements using chambers in 1996, 1997 (Epron et al, 1999a;Granier et al, 2000b(Ngao, 2005, Rs/TER was on average 0.64 at Hesse (0.58 to 0.69), i.e. close to the mean value of 0.69 found in 18 European forests by Janssens et al (2001).…”

“…fluxes and tree biomass), we calculated the annual net primary production (NPP) using two approaches: (i) NPP of the ecosystem (NPPec) was calculated from the above-canopy flux measurements: NPPec = -GPP -Raut, where Raut was the ecosystem autotrophic respiration. We assumed that Raut was equal to 72.2% of the total ecosystem respiration, a value obtained from a previous study in the same stand (Granier et al, 2000b); (ii) Biological NPP (NPPbio) was estimated from stand-scale biomass measurements: NPPbio = BI + P L + P R + P F + M, where: P L , P R and P F are the leaf, fine root and fruit production, respectively, and M is the woody mortality. We assumed (Granier et al, 2000b) that P R amounted to 43.5% of the annual leaf production.…”

“…We assumed that Raut was equal to 72.2% of the total ecosystem respiration, a value obtained from a previous study in the same stand (Granier et al, 2000b); (ii) Biological NPP (NPPbio) was estimated from stand-scale biomass measurements: NPPbio = BI + P L + P R + P F + M, where: P L , P R and P F are the leaf, fine root and fruit production, respectively, and M is the woody mortality. We assumed (Granier et al, 2000b) that P R amounted to 43.5% of the annual leaf production. Annual values of both NPP estimates are presented in Table IV.…”

“…Annual water vapour flux (E) was mainly explained by: (i) soil water deficit duration during the vegetation period, due to a strong stomatal control in beech by soil water content (Granier et al, 2000b) and (ii) LAI, that itself influenced the canopy conductance to water vapour. No significant correlation of annual E with other environmental variables was found, even if on a daily or hourly basis, water vapour flux was well correlated with net radiation, vapour pressure deficit and therefore to potential evapotranspiration (data not shown).…”

Deriving a light use efficiency model from eddy covariance flux data for predicting daily gross primary production across biomes

“…Because LAI data were scarce, comparison was only possible at a few sites. According to Granier et al (2000), the averaged LAI value at the Sarrebourg site was 4.9 AE 0.4 m 2 m À2 over the growing season of 1996-1997. Based on the BeerLambert law, the fPAR value of Sarrebourg would be 0.87.…”