The BOREAS Information System
Terrestrial Ecology (TE)


TE-12: Radiation and Gas Exchange of Canopy Elements in a Boreal Forest


P.I.(s): Elizabeth A. Walter-Shea -- University of Nebraska
Co-I(s): Tim J. Arkebauer - -University of Nebraska

Objectives: Coordinated research program emphasizing measurements of radiation and gas exchange characteristic of canopy elements and resulting interactions of radiation and gas exchange within canopy environments in a boreal forest ecosystem with the following components:

  1. Characterization of foliage element and substrate optical properties during critical periods. Leaf, needle, twig, substrate and shoot optical properties will be measured and conifer shoot geometry will be characterized. Models will be used to aid the in understanding of key variables influencing canopy element optical properties.
  2. Characterization of gas exchange of canopy elements during critical periods. Responses of CO2 exchange and stomatal conductance to environmental factors and diurnal courses of photosynthesis, respiration and stomatal conductance of canopy elements will be determined. Models will be used to describe the influence of relevant controlling variables on CO2 and water vapor fluxes.
  3. Integration of foliage optical properties and gas exchange characteristics. Models will be used to couple radiation and gas exchange of canopy elements under diffuse and total radiation conditions.


TE-12 Data Sets

  • Shoot Geometry
  • Leaf Optical Properties
  • Shoot Bidirectional Properties
  • Understory reflectance
  • Leaf water potential
  • Leaf gas exchange
  • Leaf Nitrogen
  • Canopy PAR transmittance
  • Leaf PAR properties

  • Get some TE-12 data using FTP (BOREAS Investigators only, password required). [FTP Help]


    TE-12 BOREAS Operations 1994


    Objectives:
    The goal of our coordinated research program is to gain an understanding of radiation and gas exchanges of canopy elements within a boreal forest and the coupling between radiation and gas exchange. The three objectives identified to achieve our goal are:

    1. Characterization of boreal forest canopy optical properties during critical periods of the year. Leaf, needle, twig, and substrate optical properties were measured at the BOREAS Southern Study Area (SSA) as well as in the laboratory using various combinations of spectroradiometer and integrating sphere. Conifer shoot geometry was also characterized. Models will be used to enhance the understanding of key variables influencing canopy element reflectances and transmittances.
    2. Characterization of gas exchange of boreal forest canopy elements during critical periods of the growing season. Responses of CO2 exchange and stomatal conductance of canopy elements to environmental factors and diurnal courses of photosynthesis, respiration and stomatal conductance of canopy elements will be determined. Models will be used to describe the influence of relevant controlling variables on CO2 and water vapor fluxes of boreal forest canopy elements.
    3. Integration of foliage optical properties and gas exchange characteristics. Models will be used to couple radiation and gas exchange of canopy elements under diffuse and total radiation conditions via absorbed photosynthetically active radiation.

    Group Data Type Equipment
    I Optical properties SE-590, integrating sphere,
    Leaf and conifer imaging system
    Twig -
    Substrate leaf and bark -
    Leaf and conifer shoot geometry Digital calipers, balance
    Shoot water potential Pressure chamber
    II Leaf and conifer shoot geometry &
    needle surface area
    Digital calipers, balance
    light response LI 6200 photosynthesis system, screens
    A/Ci LI 6200
    Ambient photosynthesis LI 6200
    respiration LI 6200, film developing bag
    III Substrate reflectance Exotech, calibrated reference, camera


    Places and Times of Measurements:


    Problems and Caveats:
    Calculations of needle transmittance in the visible portion of the spectrum occasionally yield negative numbers. The equation used in the calculation requires a measure of the non-intercepted fraction of the illumination beam (i.e., the fraction of light which passes between the mounted needle samples). The calculated transmittance is sensitive to any error in the fraction; our methods yield a fraction within 5% of the true value.
    Accurate determination of conifer needle surface area by the volume displacement method required image analysis of needle cross sections to quantify the ratio of the perimeter to the square root of the cross sectional area.


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    Last Updated: March 5, 1999