Abstract
In 2017, the Birmingham Institute of Forest Research (BIFoR) began to conduct Free Air Carbon Dioxide Enrichment (FACE) within a mature broadleaf deciduous forest situated in the United Kingdom. BIFoR FACE employs large‐scale infrastructure, in the form of lattice towers, forming ‘arrays’ which encircle a forest plot of ~30 m diameter. BIFoR FACE consists of three treatment arrays to elevate local CO2 concentrations (e[CO2]) by +150 µmol/mol. In practice, acceptable operational enrichment (ambient [CO2] + e[CO2]) is ±20% of the set point 1‐min average target. There are a further three arrays that replicate the infrastructure and deliver ambient air as paired controls for the treatment arrays. For the first growing season with e[CO2] (April to November 2017), [CO2] measurements in treatment and control arrays show that the target concentration was successfully delivered, that is: +147 ± 21 µmol/mol (mean ± SD) or 98 ± 14% of set point enrichment target. e[CO2] treatment was accomplished for 97.7% of the scheduled operation time, with the remaining time lost due to engineering faults (0.6% of the time), CO2 supply issues (0.6%) or adverse weather conditions (1.1%). CO2 demand in the facility was driven predominantly by wind speed and the formation of the deciduous canopy. Deviations greater than 10% from the ambient baseline CO2 occurred <1% of the time in control arrays. Incidences of cross‐contamination >80 µmol/mol (i.e. >53% of the treatment increment) into control arrays accounted for <0.1% of the enrichment period. The median [CO2] values in reconstructed three‐dimensional [CO2] fields show enrichment somewhat lower than the target but still well above ambient. The data presented here provide confidence in the facility setup and can be used to guide future next‐generation forest FACE facilities built into tall and complex forest stands.
Highlights
The ‘greening’ of the terrestrial surface across planet Earth has been driven by changes to the dynamics of vegetation and their interac‐ tions, to a large extent, with increasing levels of carbon dioxide (CO2) in the atmosphere (Forzieri, Alkama, Miralles, & Cescatti, 2017; Zhu et al, 2016)
In 2017, the Birmingham Institute of Forest Research (BIFoR) began to conduct Free Air Carbon Dioxide Enrichment (FACE) within a mature broadleaf deciduous forest situated in the United Kingdom
For the first growing season with e[CO2] (April to November 2017), [CO2] measurements in treatment and control arrays show that the target concentration was successfully delivered, that is: +147 ± 21 μmol/mol or 98 ± 14% of set point enrichment target. e[CO2] treatment was ac‐ complished for 97.7% of the scheduled operation time, with the remaining time lost due to engineering faults (0.6% of the time), CO2 supply issues (0.6%) or adverse weather conditions (1.1%)
Summary
The ‘greening’ of the terrestrial surface across planet Earth has been driven by changes to the dynamics of vegetation and their interac‐ tions, to a large extent, with increasing levels of carbon dioxide (CO2) in the atmosphere (Forzieri, Alkama, Miralles, & Cescatti, 2017; Zhu et al, 2016). The uncertainty in the sensitivity of the land C sink to increasing atmospheric CO2 is due, in large part, to a lack of experimental data on mature forest ecosystems under future elevated [CO2] (e[CO2], Ellsworth et al, 2017; Norby et al, 2016). Our experimental knowledge of how such forest ecosystems re‐ spond to further increases in [CO2] is based on few ‘first‐generation’ Free Air CO2 Enrichment experiments (FACE), either on young, vig‐ orously growing forest plantations (Hendrey, Ellsworth, Lewin, & Nagy, 1999; Norby et al, 2006) or on small seedlings or saplings Oak Ridge National Laboratory FACE was perhaps most comparable, being a deciduous forest plantation with a high LAI of about 5.5, but the trees were younger and smaller, and the e[CO2] canopy volume was smaller and more uniform in each experimental patch (Norby et al, 2006). To what extent is CO2 consumption in this deciduous forest eco‐ system a function of PAR, wind speed and canopy phenology?
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