Diurnal and spatial variation of xylem dielectric constant in Norway Spruce (Picea abies [L.] Karst.) as related to microclimate, xylem sap flow, and xylem chemistry

Kyle C. McDonald, Reiner Zimmermann, John S. Kimball

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Abstract

Spatial and temporal variations in vegetation dielectric properties strongly influence the microwave backscatter characteristics of forested landscapes. This paper examines the relationship between xylem tissue dielectric constant, xylem sap flux density, and xylem sap chemical composition as measured in the stems of two Norway Spruce (Picea abies [L.] Karst.) trees in the Fichtelgebirge region of Northern Bavaria, Germany. Dielectric constant and xylem sap flux were monitored continuously from June through October 1995, at several heights along the tree trunks. At the end of the measurement series, each tree was harvested, and its xylem sap extracted and analyzed to determine the concentrations of amino acids and cations. Results show that the sap flux density was correlated with vapor pressure deficit (VPD) at all heights in the stem. In contrast, the xylem tissue dielectric constant is influenced by VPD but can exhibit a significant temporal lag relative to changes in VPD. This lag varies with position along the tree trunk. The temporal variability of the dielectric constant is compared with both trees at several positions along the tree trunks. Results of xylem sap chemical analysis are presented. We show that spatial and temporal variability in the xylem tissue dielectric constant is influenced not only by water content, but by variations in xylem sap chemistry as well. This has important implications for microwave remote sensing of forested landscapes, as useful information may be acquired regarding stand physiology and water relations and where variations in dielectric properties within individual trees and across geographic areas can be significant error sources for forest inventory mapping.

Original languageEnglish
Pages (from-to)2063-2082
Number of pages20
JournalIEEE Transactions on Geoscience and Remote Sensing
Volume40
Issue number9
DOIs
StatePublished - Sep 2002

Funding

Manuscript received August 1, 2001; revised June 15, 2002. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology under contract to the National Aeronautics and Space Administration, and with support from the University of Bayreuth, Germany. K. C. McDonald is with the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8001 USA (e-mail: kyle.mcdonald@jpl.nasa.gov). R. Zimmermann is with the Max Planck Institute for Biogeochemistry, D-07701 Jena, Germany (e-mail: reiner.zimmermann@bgc-jena.mpg.de). J. S. Kimball is with the School of Forestry/NTSG, The University of Montana, Polson, MT 59860-9659 USA (e-mail: johnk@ntsg.umt.edu). Digital Object Identifier 10.1109/TGRS.2002.803737

FundersFunder number
University of Bayreuth
National Aeronautics and Space Administration
California Institute of Technology

    Keywords

    • Dielectric constant
    • Vegetation
    • Xylem chemistry
    • Xylem sap flux
    • Xylem water status

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