Theoretical and Applied Climatology

, Volume 53, Issue 1–3, pp 145–156 | Cite as

Leaf-level gas exchange and scaling-up of forest understory carbon fixation rates with a “patch-scale” canopy model

  • M. Wedler
  • R. Geyer
  • B. Heindl
  • S. Hahn
  • J. D. Tenhunen


During the Hartheim experiment (HartX) 1992, conducted in the Upper Rhine Valley, Germany, we estimated water vapor flux from the understory by several methods as reported in Wedler et al. (this issue). We also examined the photosynthetic gas exchange of the dominant understory speciesBrachypodium pinnatum, Carex alba, andCarex flacca at the leaf level with an CO2/H2O porometer. A mechanisticallybased leaf gas exchange model was parameterized for these understory species and validated via the measured diurnal courses of carbon dioxide exchange. Leaf CO2 gas exchange was scaled-up to patch- and then to stand-level utilizing the leaf gas exchange model as a component of the canopy light interception/energy balance model GAS-FLUX, and by further considering variation in vegetation “patch-type” distribution, patch-specific spatial structure, patch-type leaf area index, and microclimate beneath the tree canopy.

At patch-level,C. alba exhibited the lowest net CO2 uptake of ca. 75 mmol m−2 d−1 due to a low leaf-level photosynthetic capacity, whereas net CO2 fixation ofB. pinnatum- andC. flacca-patches was approx. 178 and 184 mmol m−2 d−1, respectively. Highest CO2 uptake was estimated for mixed patches whereB. pinnatum grew together with the sedge speciesC. alba orC. flacca. Scaling-up of leaf gas exchange to stand level resulted in an estimated average rate of total CO2 fixation by the graminoid understory patches of approximately 93 mmol m−2 d−1 during the HartX period. The conservative gas exchange behavior ofC. alba at Hartheim and its apparent success in space capture seems to affect overall functioning of this pine forest ecosystem by limiting understory CO2 uptake. The CO2 uptake by the understory is approximately 20% of stand total CO2 uptake. CO2 uptake fluxes mirror the relative differences in water loss from the understory and crown layer during the HartX period. Comparative measurements indicate that understory vegetation in spruce and pine forests is not greatly different from that of other low-statured natural ecosystems such as tundra or marshes under high light conditions, although CO2 capture by the understory at Hartheim is at the low extreme of the estimates, apparently due to the success ofC. alba.


Alba Water Vapor Flux Crown Layer Carbon Fixation Rate Pine Forest Ecosystem 
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Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • M. Wedler
    • 1
  • R. Geyer
    • 1
  • B. Heindl
    • 1
  • S. Hahn
    • 1
  • J. D. Tenhunen
    • 1
  1. 1.Bayreuther Institut für Terrestrische Ökosystemforschung (BITÖK), Lehrstuhl Pflanzenökologie IIUniversität BayreuthGermany

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