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Do the energy fluxes and surface conductance of boreal coniferous forests in Europe scale with leaf area?

Launiainen, Samuli; Katul, Gabriel G.; Kolari, Pasi; Lindroth, Anders LU ; Lohila, Annalea; Aurela, Mika; Varlagin, Andrej; Grelle, Achim and Vesala, Timo (2016) In Global Change Biology 22(12). p.4096-4113
Abstract

Earth observing systems are now routinely used to infer leaf area index (LAI) given its significance in spatial aggregation of land surface fluxes. Whether LAI is an appropriate scaling parameter for daytime growing season energy budget, surface conductance (Gs), water- and light-use efficiency and surface–atmosphere coupling of European boreal coniferous forests was explored using eddy-covariance (EC) energy and CO2 fluxes. The observed scaling relations were then explained using a biophysical multilayer soil–vegetation–atmosphere transfer model as well as by a bulk Gs representation. The LAI variations significantly alter radiation regime, within-canopy microclimate, sink/source distributions of... (More)

Earth observing systems are now routinely used to infer leaf area index (LAI) given its significance in spatial aggregation of land surface fluxes. Whether LAI is an appropriate scaling parameter for daytime growing season energy budget, surface conductance (Gs), water- and light-use efficiency and surface–atmosphere coupling of European boreal coniferous forests was explored using eddy-covariance (EC) energy and CO2 fluxes. The observed scaling relations were then explained using a biophysical multilayer soil–vegetation–atmosphere transfer model as well as by a bulk Gs representation. The LAI variations significantly alter radiation regime, within-canopy microclimate, sink/source distributions of CO2, H2O and heat, and forest floor fluxes. The contribution of forest floor to ecosystem-scale energy exchange is shown to decrease asymptotically with increased LAI, as expected. Compared with other energy budget components, dry-canopy evapotranspiration (ET) was reasonably ‘conservative’ over the studied LAI range 0.5–7.0 m2 m−2. Both ET and Gs experienced a minimum in the LAI range 1–2 m2 m−2 caused by opposing nonproportional response of stomatally controlled transpiration and ‘free’ forest floor evaporation to changes in canopy density. The young forests had strongest coupling with the atmosphere while stomatal control of energy partitioning was strongest in relatively sparse (LAI ~2 m2 m−2) pine stands growing on mineral soils. The data analysis and model results suggest that LAI may be an effective scaling parameter for net radiation and its partitioning but only in sparse stands (LAI <3 m2 m−2). This finding emphasizes the significance of stand-replacing disturbances on the controls of surface energy exchange. In denser forests, any LAI dependency varies with physiological traits such as light-saturated water-use efficiency. The results suggest that incorporating species traits and site conditions are necessary when LAI is used in upscaling energy exchanges of boreal coniferous forests.

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author
organization
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type
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publication status
published
subject
keywords
boreal forest, ecosystem modeling, eddy-covariance, energy budget, evapotranspiration, latent and sensible heat flux, leaf area index, light-use efficiency, remote sensing, water-use efficiency
in
Global Change Biology
volume
22
issue
12
pages
18 pages
publisher
Wiley-Blackwell
external identifiers
  • scopus:84995560966
  • wos:000387813300022
ISSN
1354-1013
DOI
10.1111/gcb.13497
language
English
LU publication?
yes
id
b4399d3e-36fe-4e13-adb7-4dce289caa6f
date added to LUP
2016-12-02 13:26:31
date last changed
2017-10-29 04:54:49
@article{b4399d3e-36fe-4e13-adb7-4dce289caa6f,
  abstract     = {<p>Earth observing systems are now routinely used to infer leaf area index (LAI) given its significance in spatial aggregation of land surface fluxes. Whether LAI is an appropriate scaling parameter for daytime growing season energy budget, surface conductance (G<sub>s</sub>), water- and light-use efficiency and surface–atmosphere coupling of European boreal coniferous forests was explored using eddy-covariance (EC) energy and CO<sub>2</sub> fluxes. The observed scaling relations were then explained using a biophysical multilayer soil–vegetation–atmosphere transfer model as well as by a bulk G<sub>s</sub> representation. The LAI variations significantly alter radiation regime, within-canopy microclimate, sink/source distributions of CO<sub>2</sub>, H<sub>2</sub>O and heat, and forest floor fluxes. The contribution of forest floor to ecosystem-scale energy exchange is shown to decrease asymptotically with increased LAI, as expected. Compared with other energy budget components, dry-canopy evapotranspiration (ET) was reasonably ‘conservative’ over the studied LAI range 0.5–7.0 m<sup>2</sup> m<sup>−2</sup>. Both ET and G<sub>s</sub> experienced a minimum in the LAI range 1–2 m<sup>2</sup> m<sup>−2</sup> caused by opposing nonproportional response of stomatally controlled transpiration and ‘free’ forest floor evaporation to changes in canopy density. The young forests had strongest coupling with the atmosphere while stomatal control of energy partitioning was strongest in relatively sparse (LAI ~2 m<sup>2</sup> m<sup>−2</sup>) pine stands growing on mineral soils. The data analysis and model results suggest that LAI may be an effective scaling parameter for net radiation and its partitioning but only in sparse stands (LAI &lt;3 m<sup>2</sup> m<sup>−2</sup>). This finding emphasizes the significance of stand-replacing disturbances on the controls of surface energy exchange. In denser forests, any LAI dependency varies with physiological traits such as light-saturated water-use efficiency. The results suggest that incorporating species traits and site conditions are necessary when LAI is used in upscaling energy exchanges of boreal coniferous forests.</p>},
  author       = {Launiainen, Samuli and Katul, Gabriel G. and Kolari, Pasi and Lindroth, Anders and Lohila, Annalea and Aurela, Mika and Varlagin, Andrej and Grelle, Achim and Vesala, Timo},
  issn         = {1354-1013},
  keyword      = {boreal forest,ecosystem modeling,eddy-covariance,energy budget,evapotranspiration,latent and sensible heat flux,leaf area index,light-use efficiency,remote sensing,water-use efficiency},
  language     = {eng},
  month        = {12},
  number       = {12},
  pages        = {4096--4113},
  publisher    = {Wiley-Blackwell},
  series       = {Global Change Biology},
  title        = {Do the energy fluxes and surface conductance of boreal coniferous forests in Europe scale with leaf area?},
  url          = {http://dx.doi.org/10.1111/gcb.13497},
  volume       = {22},
  year         = {2016},
}