Bayreuther Institut für Terrestrische Ökosystemforschung
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Evapotranspiration and CO2 gas exchange of the understory in forest ecosystems


From 01/1995 to 12/1997

Principal Investigator: John Tenhunen
Staff: Hans-Joachim Scharfenberg, Michael Wedler, Reiner Zimmermann
Grant: 0339476 B Vorhersage und Erklärung des Verhaltens und der Belastbarkeit von Ökosystemen unter veränderten Umweltbedingungen

Within the Lehstenbach catchment, Fichtelgebirge, understory composition, light climate and patch structure of the ground cover under monospecific Norway spruce (Picea abies [L.] KARST.) stands was characterized. The understory vegetation was classified into seven patch types. Each patch type was dominated by one plant species. Based on 90 plots and 42 biomass harvests in the catchment, it was found that forest stand age is significantly correlated with patch type. The parameters ‘stand age’ and ‘overstory LAI’ combined predict 57% of the understory cover. Estimates of understory and tree canopy evapotranspiration were obtained for five stands which exhibited large differences of structure and development. Understory vegetation cover ranged between 83% at a open 140 year old spruce stand to 10% within a dense stand of 40 year old spruce. Despite large structural differences, stand total water loss from the well drained sites was very similar and average Stand evapotranspiration was estimated at 2.3 ± 0.32 mm d-1. The stand structure related differences in overstory transpiration were almost completely compensated by variations in the water use of the understory. Only one edaphically wet site showed high tree evapotranspiration in combination with high understory water use and resulted in a total water use of 3.2 mm d-1. During observation time in July the contribution of the understory vegetation to total stand water use varied from 14 to 42 % in the observed stands. The microclimate measurements indicate that influence of water vapor saturation deficit and radiation load increased with vegetation cover. Turbulence and wind speed beneath the tree canopy layers are only important in stands with an open canopy structure.
/final report 1998)

List of publications of this Project

Bernhofer, C; Blanford, JH; Siegwolf, R; Wedler, M: Applying Single and Two Layer Canopy Models to Derive Conductances of a Scots Pine Plantation from Micrometeorological Measurements, Theoretical and Applied Climatology, 53, 95-104 (1996)
Wedler, M; Geyer, R; Heindl, B; Hahn, S; Tenhunen, JD: Leaf-level gas exchange and scaling-up of forest understory carbon fixation fluxes with a "patch-scale" canopy model, Theoretical and Applied Climatology, 53, 145-156 (1996)
Köstner, B: Der Einfluß von Klimaänderungen auf Stoff- und Energieflüsse im Ökosystem, Dynamik als ökologischer Faktor. Laufener Seminarbeiträge, Akademie für Naturschutz und Landschaftspflege, 3/95, 93-100 (1995)
Heindl, B; Bott, H: Charakterisierung der Bodenvegetation im Einzugsgebiet Lehstenbach. in Bayreuther Institut für Terrestrische Ökosystemforschung (BITÖK): Bayreuther Forum Ökologie, Selbstverlag, 18, 49-63 (1995)
Tenhunen, JD; Wedler, M; Heindl, B; Köstner, B; Hahn, S: Contribution of understory evatranspiration to total water vapor flux at the Hartheim scots pine plantation in Am. Met. Soc. (ed.): 21. Conference on Agricultural and Forest Meteorology, San Diego, CA, 187-192 (1994)
Köstner, B; Biron, P; Siegwolf, R; Granier, A: Estimates of xylem sap flow and canopy conductance of scots pine trees utilizing constant heating and constant temperature difference methods in Am. Met. Soc. (ed.): 21. Conference on Agricultural and Forest Meteorology, San Diego, CA, 193-196 (1994)
Köstner, B; Schulze, ED; Kelliher, FM; Hollinger, DY; Byers, JN; Hunt, JE; McSeveny, ; Meserth, R; Weir, PL: Transpiration and canopy conductance in a pristine broadleaved forest of Nothofagus: an analysis of xylem sap flow and eddy correlation measurements, Oecologia, 91, 350-359 (1992) -- Details
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