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:
- 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.
- 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.
- 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
Leaf Optical Properties
Shoot Bidirectional Properties
Leaf water potential
Leaf gas exchange
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
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:
- 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.
- 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.
- 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:
- Group I: FFC-T and FFC-W: SSA OBS and OJP. Jack pine and black spruce optical properties were measured on samples collected from the sites and sent to Lincoln, Nebraska for analysis. IFC-1: SSA OBS, YJP and OA; IFC-2 and IFC-3: SSA OBS, YJP and YA. Jack pine and black spruce optical properties and shoot geometry were characterized on samples collected in the field and taken to the SSA laboratory for analysis, two visits per IFC, sampling from the top and bottom parts of the canopy. Aspen samples were collected and analyzed in the field. Water potential was collected on surrounding samples in the field and in the laboratory at the time of analysis. Substrate element properties were measured once per IFC.
- Group II: May 29-Aug. 9 and Sept. 7-9: SSA YA and YJP with occasional measurements at OA, OBS and the Mixed site. Properties were measured at various times during this period. For canopy element gas exchange properties our primary emphasis was on aspen at SSA YA and jack pine at SSA YJP sites. Other species included were aspen at SSA OA, black spruce at SSA OBS and mixed sites and hazelnut and balsam poplar at SSA YA site.
- Group III: IFCs: SSA OJP and YJP. Measured once per IFC.
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
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