Comprehensive description of the carbon cycle of an ancient temperate broadleaved woodland

Abstract

There exist very few comprehensive descriptions of the productivity and carbon cycling of forest ecosystems. Here we present a description of the components of annual Net Primary Productivity (NPP), Gross Primary Productivity (GPP), autotrophic and heterotrophic respiration, and ecosystem respiration (<i>R</i><sub>ECO</sub>) for a temperate mixed deciduous woodland at Wytham Woods in southern Britain, calculated using "bottom-up" biometric and chamber measurements (leaf and wood production and soil and stem respiration). These are compared with estimates of these parameters from eddy-covariance measurements made at the same site. NPP was estimated as 7.0±0.8 Mg C ha<sup>−1</sup> yr<sup>−1</sup>, and GPP as 20.3+1.0 Mg C ha<sup>−1</sup> yr<sup>−1</sup>, a value which closely matched to eddy covariance-derived GPP value of 21.1 Mg C ha<sup>−1</sup> yr<sup>−1</sup>. Annual <i>R</i><sub>ECO</sub> was calculated as 18.9±1.7 Mg C ha<sup>−1</sup> yr<sup>−1</sup>, close to the eddy covariance value of 19.8 Mg C ha<sup>−1</sup> yr<sup>−1</sup>; the seasonal cycle of biometric and eddy covariance <i>R</i><sub>ECO</sub> estimates also closely matched. The consistency between eddy covariance and biometric measurements substantially strengthens the confidence we attach to each as alternative indicators of site carbon dynamics, and permits an integrated perspective of the ecosystem carbon cycle. 37% of NPP was allocated below ground, and the ecosystem carbon use efficiency (CUE, = NPP/GPP) calculated to be 0.35±0.05, lower than reported for many temperate broadleaved sites

Carbon dioxide fluxes over an ancient broadleaved deciduous woodland in southern England

“…In our study, there is a marked difference between the night-time average hourly fluxes for secondary stage processing approaches. Although the resultant fluxes are higher than typical winter values for deciduous forest of ∼1 µmol CO 2 m −2 s −1 (Baldocchi and Valentini, 2004), the negative night-time CO 2 flux removal correction appears to most realistically represent winter night-time fluxes when compared to chamber measurements of combined autotrophic (predominantly stem and leaf) and heterotrophic (predominantly soil and litter) respiration (Fenn et al, 2011) in Fig. 4.…”

“…The flux tower (SP 457 089) is located on the north slope of a moderate a hill, with fetch estimated to vary with atmospheric stability from ∼250 m in very unstable (daytime convective) conditions to over 2 km in very stable (calm night) conditions. Approximately 90 % of fluxes are estimated to occur within 200 to 600 m of the tower, predominantly covering areas of disturbed ancient woodland to the southwest (with south-westerly prevailing winds), including the 1 ha plot of biometric data collection described in Fenn et al (2011). This area is characterised by canopy tree species pedunculate oak (Quercus robur), ash (Fraxinus excelsior) and sycamore (Acer pseudoplatanus).…”

“…2.1 and 2.2). Our flux-based estimates of GPP and R e (21.1 and 19.8 Mg C ha −1 yr −1 respectively) can be compared with estimates of GPP and R e (26.5 ± 6.8 and 24.8 ± 6.8 Mg C ha −1 yr −1 respectively; Fenn et al, 2011). The flux tower values are about 20 % lower than the biometric estimates, but within the uncertainty lower band of these estimates.…”

“…bgc-jena.mpg.de/bgc-mdi/html/eddyproc/index.html. For night-time values (where solar radiation < 20 W m −2 ), the Lloyd-Taylor regression model (Lloyd and Taylor, 1994) was used to estimate respiration rates from air temperature (in fact, the largest source of ecosystem respiration at this site is stem respiration (Fenn et al, 2011) and our implicit assumption is that stem near-surface temperature, which was not monitored, closely tracks air temperature). The estimated value of respiration was then assigned to the central time point of the averaging interval (30 or 60 min) and linearly interpolated between time periods.…”

Airborne S-Band SAR for Forest Biophysical Retrieval in Temperate Mixed Forests of the UK

“…The site has been continuously covered by trees [37] while recently managed with timber removal and plantation (e.g., beech, sycamore) where ash and sycamore species composition has been changed over time [38]. Since the last decade, it has become one of the most studied temperate deciduous woodland in the country related to Ash die-back disease [39], long-term monitoring plots for soil respiration [40], aboveground productivity, respiration and leaf production [41,42].…”