... E-mail: g.phoenix@sheffield.ac.uk ... One-sided projected leaf area of each species was measu... more ... E-mail: g.phoenix@sheffield.ac.uk ... One-sided projected leaf area of each species was measured using a Delta-T digital image analysis system 1.10 (Delta-T, Burwell, UK) to calculate leaf area index (LAI, m2 leaves per m )2 ground) for each species and overall. ...
The Arctic has already warmed significantly, and warming of 4-7 °C is expected over the next cent... more The Arctic has already warmed significantly, and warming of 4-7 °C is expected over the next century. However, linkages between climate, the carbon cycle, the energy balance, and hydrology mean that the response of arctic ecosystems to these changes remains poorly understood. The release by warming of considerable but poorly quantified carbon stores from high latitude soils could accelerate the
Soil organic matter content was highly variable on a range of scales, which complicates upscaling... more Soil organic matter content was highly variable on a range of scales, which complicates upscaling. Further, soil processes differed between dominant vegetation types. The 14 C content of CO 2 released from the soils of birch woodlands increased substantially in ...
Soil organic matter content was highly variable on a range of scales, which complicates upscaling... more Soil organic matter content was highly variable on a range of scales, which complicates upscaling. Further, soil processes differed between dominant vegetation types. The 14 C content of CO 2 released from the soils of birch woodlands increased substantially in ...
Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying... more Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying underlying frequencies in nonstationary and gap-infested time series, such as eddy-covariance-measured net ecosystem exchange of CO2 (NEE). We employed OWT to analyze the frequency characteristics of synchronously measured and modeled NEE at adjacent pine (PP) and hardwood (HW) ecosystems. Wavelet cospectral analysis showed that NEE at PP was more correlated to light and vapor pressure deficit at the daily time scale, and NEE at HW was more correlated to leaf area index (LAI) and temperature, especially soil temperature, at seasonal time scales. Models were required to disentangle the impacts of environmental drivers on the components of NEE, ecosystem carbon assimilation (Ac) and ecosystem respiration (RE). Sensitivity analyses revealed that using air temperature rather than soil temperature in RE models improved the modeled wavelet spectral frequency response on time scales longer tha...
Nocturnal evapotranspiration (ETN) is often assumed to be negligible in terrestrial ecosystems, r... more Nocturnal evapotranspiration (ETN) is often assumed to be negligible in terrestrial ecosystems, reflecting the common assumption that plant stomata close at night to prevent water loss from transpiration. However, recent evidence across a wide range of species and climate conditions suggests that significant transpiration occurs at night, frustrating efforts to estimate total annual evapotranspiration (ET) from conventional methods such as
The biosphere-atmosphere flux of carbon dioxide responds to climatic variability at time scales f... more The biosphere-atmosphere flux of carbon dioxide responds to climatic variability at time scales from seconds to years. Orthonormal wavelet transformation (OWT) can quantify the interaction between flux and climate at multiple frequencies while controlling for inherent data gaps in eddy covariance measurement records and expressing time series variance in few energetic wavelet coefficients, offering a low-dimensional view of the measured climate-flux interaction. Here, we discuss the variability of net ecosystem exchange (NEE), gross ecosystem productivity (GEP) and ecosystem respiration (RE), and their co-variability with dominant climatic drivers, using eddy covariance data from 250 sites and nearly 1000 site-years from the global FLUXNET database. Results demonstrate that the NEE and GEP wavelet spectra are similar amongst plant functional types (PFTs) at weekly and shorter time scales, but significant divergence appears among PFT at the biweekly and longer time scales, when NEE and GEP also dampen climatic variability, on average. The RE spectra rarely differ among PFT across scales; they have greater low frequency variability, on average, and are amplified with respect to climatic variability at monthly to interannual time scales. Both measurements and theory demonstrate that `multi-annual' spectral peaks in flux may emerge at low (4+ year) time scales. Biological responses to climate and other internal system dynamics, rather than climate itself, provides the likely explanation for the observed multi-annual variability.
We use long-term eddy covariance data from a novel field experiment in adjacent grass, pine, and ... more We use long-term eddy covariance data from a novel field experiment in adjacent grass, pine, and hardwood ecosystems to investigate the degree of coupling between carbon and water fluxes at time scales from hours to years. The experimental setup is a model of post-agricultural ecosystem succession in the SE U.S. and can thus give insight into carbon / water relationships
... E-mail: g.phoenix@sheffield.ac.uk ... One-sided projected leaf area of each species was measu... more ... E-mail: g.phoenix@sheffield.ac.uk ... One-sided projected leaf area of each species was measured using a Delta-T digital image analysis system 1.10 (Delta-T, Burwell, UK) to calculate leaf area index (LAI, m2 leaves per m )2 ground) for each species and overall. ...
The Arctic has already warmed significantly, and warming of 4-7 °C is expected over the next cent... more The Arctic has already warmed significantly, and warming of 4-7 °C is expected over the next century. However, linkages between climate, the carbon cycle, the energy balance, and hydrology mean that the response of arctic ecosystems to these changes remains poorly understood. The release by warming of considerable but poorly quantified carbon stores from high latitude soils could accelerate the
Soil organic matter content was highly variable on a range of scales, which complicates upscaling... more Soil organic matter content was highly variable on a range of scales, which complicates upscaling. Further, soil processes differed between dominant vegetation types. The 14 C content of CO 2 released from the soils of birch woodlands increased substantially in ...
Soil organic matter content was highly variable on a range of scales, which complicates upscaling... more Soil organic matter content was highly variable on a range of scales, which complicates upscaling. Further, soil processes differed between dominant vegetation types. The 14 C content of CO 2 released from the soils of birch woodlands increased substantially in ...
Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying... more Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying underlying frequencies in nonstationary and gap-infested time series, such as eddy-covariance-measured net ecosystem exchange of CO2 (NEE). We employed OWT to analyze the frequency characteristics of synchronously measured and modeled NEE at adjacent pine (PP) and hardwood (HW) ecosystems. Wavelet cospectral analysis showed that NEE at PP was more correlated to light and vapor pressure deficit at the daily time scale, and NEE at HW was more correlated to leaf area index (LAI) and temperature, especially soil temperature, at seasonal time scales. Models were required to disentangle the impacts of environmental drivers on the components of NEE, ecosystem carbon assimilation (Ac) and ecosystem respiration (RE). Sensitivity analyses revealed that using air temperature rather than soil temperature in RE models improved the modeled wavelet spectral frequency response on time scales longer tha...
Nocturnal evapotranspiration (ETN) is often assumed to be negligible in terrestrial ecosystems, r... more Nocturnal evapotranspiration (ETN) is often assumed to be negligible in terrestrial ecosystems, reflecting the common assumption that plant stomata close at night to prevent water loss from transpiration. However, recent evidence across a wide range of species and climate conditions suggests that significant transpiration occurs at night, frustrating efforts to estimate total annual evapotranspiration (ET) from conventional methods such as
The biosphere-atmosphere flux of carbon dioxide responds to climatic variability at time scales f... more The biosphere-atmosphere flux of carbon dioxide responds to climatic variability at time scales from seconds to years. Orthonormal wavelet transformation (OWT) can quantify the interaction between flux and climate at multiple frequencies while controlling for inherent data gaps in eddy covariance measurement records and expressing time series variance in few energetic wavelet coefficients, offering a low-dimensional view of the measured climate-flux interaction. Here, we discuss the variability of net ecosystem exchange (NEE), gross ecosystem productivity (GEP) and ecosystem respiration (RE), and their co-variability with dominant climatic drivers, using eddy covariance data from 250 sites and nearly 1000 site-years from the global FLUXNET database. Results demonstrate that the NEE and GEP wavelet spectra are similar amongst plant functional types (PFTs) at weekly and shorter time scales, but significant divergence appears among PFT at the biweekly and longer time scales, when NEE and GEP also dampen climatic variability, on average. The RE spectra rarely differ among PFT across scales; they have greater low frequency variability, on average, and are amplified with respect to climatic variability at monthly to interannual time scales. Both measurements and theory demonstrate that `multi-annual' spectral peaks in flux may emerge at low (4+ year) time scales. Biological responses to climate and other internal system dynamics, rather than climate itself, provides the likely explanation for the observed multi-annual variability.
We use long-term eddy covariance data from a novel field experiment in adjacent grass, pine, and ... more We use long-term eddy covariance data from a novel field experiment in adjacent grass, pine, and hardwood ecosystems to investigate the degree of coupling between carbon and water fluxes at time scales from hours to years. The experimental setup is a model of post-agricultural ecosystem succession in the SE U.S. and can thus give insight into carbon / water relationships
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