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

Journal Article · Thu Oct 13 00:00:00 EDT 2016 · Global Change Biology

DOI:https://doi.org/10.1111/gcb.13497· OSTI ID:1400470

Launiainen, Samuli ^[1]; Katul, Gabriel G. ^[2]; Kolari, Pasi ^[3]; Lindroth, Anders ^[4]; Lohila, Annalea ^[5]; Aurela, Mika ^[5]; Varlagin, Andrej ^[6]; Grelle, Achim ^[7]; Vesala, Timo ^[8]

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1. Nature Resources Institute Finland Environmental Impacts of Production Jokiniemenkuja 1 Vantaa Finland
2. Nicholas School of the Environment Duke University PO Box 90328 Duke University Durham NC 27708‐0328 USA
3. Department of Physics University of Helsinki PO Box 64 00140 University of Helsinki Finland
4. Department of Earth and Ecosystem Sciences Lund University Sölvegatan 12 Lund 223 62 Sweden
5. Finnish Meteorological Institute P.O. Box 503 FI‐00101 Helsinki Finland
6. A.N. Severtsov Institute of Ecology and Evolution Russian Academy of Sciences Leninsky pr. 33 Moscow 119071 Russia
7. Department of Ecology Swedish University of Agricultural Sciences PO Box 7044 Uppsala 750 07 Sweden
8. Department of Physics University of Helsinki PO Box 64 00140 University of Helsinki Finland, Department of Forest Sciences University of Helsinki PO Box 27 00140 Helsinki Finland

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 ( G _s ), water‐ and light‐use efficiency and surface–atmosphere coupling of European boreal coniferous forests was explored using eddy‐covariance ( EC ) energy and CO ₂ fluxes. The observed scaling relations were then explained using a biophysical multilayer soil–vegetation–atmosphere transfer model as well as by a bulk G _s representation. The LAI variations significantly alter radiation regime, within‐canopy microclimate, sink/source distributions of CO ₂ , H ₂ 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 ² m ⁻² . Both ET and G _s experienced a minimum in the LAI range 1–2 m ² 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 m ² 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 m ² 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.

• Sponsoring Organization: USDOE
• OSTI ID: 1400470
• Journal Information: Global Change Biology, Journal Name: Global Change Biology Vol. 22 Journal Issue: 12; ISSN 1354-1013
• Publisher: Wiley-Blackwell
• Country of Publication: United Kingdom
• Language: English