Bayreuther Institut für Terrestrische Ökosystemforschung
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Köstner, B; Alsheimer, M; Tenhunen, JD: Tree canopy transpiration at different sites of a spruce forest ecosystem, Verhandlungen der Gesellschaft für Ökologie, 26, 61-68 (1996)
Within the framework of a forest catchment study, six Picea abies stands differing in age, structure, exposition, and soil conditions were selected to examine forest canopy transpiration (Ec) and total canopy conductance (gt). Under non-limiting soil water conditions, maximum daily rates of Ec measured by xylem sap flow were lowest at the oldest, 140-year-old site (2.0 mm d-1) and highest at a boggy, unmanaged 40-year-old site (3.0 mm d-1). Sap flux density was highest at the old site (0.04-0.15 kg cm-2 sapwood area d-1) and the boggy site (0.07-0.13 kg cm-2 sapwood area d-1). Differences in Ec between sites were associated with a decreasing ratio of needle area to sapwood cross-sectional area, with decreasing stand age, and increasing stand density. Greatest transpirational water loss occurred on days with maximum vapor pressure deficit (Dmax) of 20 hPa. On sunny days maximum canopy conductance (gtmax) was associated with Dmax of 10 hPa and decreased strongly with further increases in Dmax. In preliminary analyses, differences in Ec between sites were best explained by variation in stand density rather than in stand age or leaf area index (LAI).
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