Selected breakpoints of net forest carbon uptake at four eddy-covariance
                        sites

Foken, Thomas; Babel, Wolfgang; Munger, J. William; Grönholm, Tiia; Vesala, Timo; Knohl, Alexander

doi:10.1080/16000889.2021.1915648

Cited by 14 publications

(7 citation statements)

References 61 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This sense of decadal “breakpoints” in long‐term NEE found at US‐Ha1 and also noted in our record of US‐PFa is further confirmed in Foken et al. ( 2021 ), which considered several long‐running (minimum 20 years) EC sites in Europe (FI‐Hyy, DE‐Hai, and De‐Bay) in addition to US‐Ha1. That manuscript noted that abrupt or step changes in annual fluxes were common and linked to potential “regime transitions” associated with step changes in drivers, pointing to the non‐smooth trends typical in climate change outside CO 2 , such as the reported regime shift in the 1980s related to cascading effects from episodic events like volcanic eruptions (Reid et al., 2016 ).…”

Section: Discussionsupporting

confidence: 92%

“…EC flux towers are a mature technology (Baldocchi, 2020 ). The growing number of long‐term records has challenged our estimation of trends, sensitivities, and models (Foken et al., 2021 ; Keenan et al., 2012 ). Insight from tower clusters sampling key gradients or representative ecosystems has helped resolve spatial variation in carbon cycle‐climate sensitivity (e.g., Biederman et al., 2017 ) or regional upscaling (e.g., J. Xiao et al., 2011 ).…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Drivers of Decadal Carbon Fluxes Across Temperate Ecosystems

et al. 2022

View full text Add to dashboard Cite

Long‐running eddy covariance flux towers provide insights into how the terrestrial carbon cycle operates over multiple timescales. Here, we evaluated variation in net ecosystem exchange (NEE) of carbon dioxide (CO2) across the Chequamegon Ecosystem‐Atmosphere Study AmeriFlux core site cluster in the upper Great Lakes region of the USA from 1997 to 2020. The tower network included two mature hardwood forests with differing management regimes (US‐WCr and US‐Syv), two fen wetlands with varying levels of canopy sheltering and vegetation (US‐Los and US‐ALQ), and a very tall (400 m) landscape‐level tower (US‐PFa). Together, they provided over 70 site‐years of observations. The 19‐tower Chequamegon Heterogenous Ecosystem Energy‐balance Study Enabled by a High‐density Extensive Array of Detectors 2019 campaign centered around US‐PFa provided additional information on the spatial variation of NEE. Decadal variability was present in all long‐term sites, but cross‐site coherence in interannual NEE in the earlier part of the record became weaker with time as non‐climatic factors such as local disturbances likely dominated flux time series. Average decadal NEE at the tall tower transitioned from carbon source to sink to near neutral over 24 years. Respiration had a greater effect than photosynthesis on driving variations in NEE at all sites. Declining snowfall offset potential increases in assimilation from warmer springs, as less‐insulated soils delayed start of spring green‐up. Higher CO2 increased maximum net assimilation parameters but not total gross primary productivity. Stand‐scale sites were larger net sinks than the landscape tower. Clustered, long‐term carbon flux observations provide value for understanding the diverse links between carbon and climate and the challenges of upscaling these responses across space.

show abstract

Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 99%

Drivers of Decadal Carbon Fluxes Across Temperate Ecosystems

et al. 2022

View full text Add to dashboard Cite

show abstract

“…The results here further showed that increasing canopy roughness and concomitant shrinking of flux footprint imposes additional challenges to estimate footprint‐weighted LAI and species composition trends at site level. The effects of such small‐scale heterogeneities, occurring often at scales beyond the resolution of current LAI products, should be further explored whenever interpreting long‐term trends from forest FluxNet sites (Foken et al, 2021). In the Nordic countries, emerging high‐resolution (sub 25 m) biomass and vegetation data products that combine data from national forest inventory plots and remote sensing (Kangas et al, 2018) can provide an interesting opportunity for such analyses, as well as for benchmarking the global LAI products (Härkönen et al, 2015; Zhu et al, 2013b).…”

Section: Discussionmentioning

confidence: 99%

Does growing atmospheric CO₂ explain increasing carbon sink in a boreal coniferous forest?

Launiainen

Katul

Haahti

et al. 2022

Global Change Biology

Self Cite

View full text Add to dashboard Cite

show abstract

“…For comparison reasons, the eddy covariance data with a sampling frequency of 10 Hz at a 36 m height and the FODS data of quartet array from the turbulence tower located approximately 70 m away from the main tower were used. See Foken et al (2021) for more details on the turbulence tower specification. The quartet fiber configuration at the turbulence tower is the same as the main tower extending from the ground to a 34 m height.…”

Section: Part 2: Shroud Experiments In a Forestmentioning

confidence: 99%

Toward quantifying turbulent vertical airflow and sensible heat flux in tall forest canopies using fiber-optic distributed temperature sensing

Abdoli

Lapo²,

Schneider³

et al. 2023

Atmos. Meas. Tech.

View full text Add to dashboard Cite

Abstract. The paper presents a set of fiber-optic distributed temperature sensing (FODS) experiments to expand the existing microstructure approach for horizontal turbulent wind direction by adding measurements of turbulent vertical component, as well as turbulent sensible heat flux. We address the observational challenge to isolate and quantify the weaker vertical turbulent motions from the much stronger mean advective horizontal flow signals. In the first part of this study, we test the ability of a cylindrical shroud to reduce the horizontal wind speed while keeping the vertical wind speed unaltered. A white shroud with a rigid support structure and 0.6 m diameter was identified as the most promising setup in which the correlation of flow properties between shrouded and reference systems is maximized. The optimum shroud setup reduces the horizontal wind standard deviation by 35 %, has a coefficient of determination of 0.972 for vertical wind standard deviations, and a RMSE of less than 0.018 ms−1 when compared to the reference. Spectral analysis showed a fixed ratio of spectral energy reduction in the low frequencies, e.g., <0.5 Hz, for temperature and wind components, momentum, and sensible heat flux. Unlike low frequencies, the ratios decrease exponentially in the high frequencies, which means the shroud dampens the high-frequency eddies with a timescale <6 s, considering both spectra and cospectra together. In the second part, the optimum shroud configuration was installed around a heated fiber-optic cable with attached microstructures in a forest to validate our findings. While this setup failed to isolate the magnitude and sign of the vertical wind perturbations from FODS in the shrouded portion, concurrent observations from an unshrouded part of the FODS sensor in the weak-wind subcanopy of the forest (12–17 m above ground level) yielded physically meaningful measurements of the vertical motions associated with coherent structures. These organized turbulent motions have distinct sweep and ejection phases. These strong flow signals allow for detecting the turbulent vertical airflow at least 60 % of the time and 71 % when conditional sampling was applied. Comparison of the vertical wind perturbations against those from sonic anemometry yielded correlation coefficients of 0.35 and 0.36, which increased to 0.53 and 0.62 for conditional sampling. This setup enabled computation of eddy covariance-based direct sensible heat flux estimates solely from FODS, which are reported here as a methodological and computational novelty. Comparing them against those from eddy covariance using sonic anemometry yielded an encouraging agreement in both magnitude and temporal variability for selected periods.

show abstract

Selected breakpoints of net forest carbon uptake at four eddy-covariance sites

Cited by 14 publications

References 61 publications

Drivers of Decadal Carbon Fluxes Across Temperate Ecosystems

Drivers of Decadal Carbon Fluxes Across Temperate Ecosystems

Does growing atmospheric CO₂ explain increasing carbon sink in a boreal coniferous forest?

Toward quantifying turbulent vertical airflow and sensible heat flux in tall forest canopies using fiber-optic distributed temperature sensing

Contact Info

Product

Resources

About

Selected breakpoints of net forest carbon uptake at four eddy-covariance sites

Cited by 14 publications

References 61 publications

Drivers of Decadal Carbon Fluxes Across Temperate Ecosystems

Drivers of Decadal Carbon Fluxes Across Temperate Ecosystems

Does growing atmospheric CO2 explain increasing carbon sink in a boreal coniferous forest?

Toward quantifying turbulent vertical airflow and sensible heat flux in tall forest canopies using fiber-optic distributed temperature sensing

Contact Info

Product

Resources

About

Does growing atmospheric CO₂ explain increasing carbon sink in a boreal coniferous forest?