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Eddy Flux Tower and Sap Flow (HRM) Measurements

Abstract

The vertical distribution of sap flow was measured in a 54 year old stand of Picea abies in Europe. Data were compared against Eddy covariance and were also used to validate the gas exchange model, STANDFLUX.

Objective

Canopy exchange of water and carbon dioxide in a montane Norway spruce stand of Central Germany was analyzed with a three dimensional microclimate and gas exchange model STANDFLUX . The model describes canopy water vapor and carbon dioxide exchange based on rates calculated for individual trees and as affected by local gradients in photon flux density (PFD), atmospheric humidity, atmospheric carbon dioxide concentration, and air temperature . Direct, diffuse, and reflected PFD incident on foliage elements is calculated for a three dimensional matrix of points superimposed over the canopy . The model was used to calculate forest radiation absorption, net photosynthesis and transpiration of single trees, and gas exchange of the tree canopy . Model parameterization was derived for the Weidenbrunnen site, a 54 – year – old Picea abies stand . Parameterization included information on vertical and horizontal leaf area distribution, tree positions and tree sizes . Gas exchange was modeled using specific sets of physiological parameters for top, middle, and bottom of the canopy . Comparisons of the vertical distribution of modeled branch transpiration with water use estimates from xylem sapflow measurements in the canopy profile provided a test of the model .

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