The BOREAS Information System
Terrestrial Ecology (TE)

TE-11: Seasonal Variations of Net Photosynthesis and Transpiration at the Tree Level

P.I.(s): Bernard Saugier -- Universite Paris
Collaborator(s): Andre Granier, Eric Dufrene, Jean-Yves Pontailler, Anne Ruimy

Objectives: To monitor the net assimilation and transpiration rate of trees throughout the 1994 growing season, at the Prince Albert Old Jack Pine site (and short sapflow measurements in P.A. mixed-stand). For this we propose the following steps using several original methods:

  1. Installation of sapflow probes in the trunk of 6 representative trees in SSA-OJP at the end of FFC-T, monitoring of sapflow from May to September 1994 (Prince Albert Mixed Site will be equipped with sapflow probes during the IFC-2 campaign only).. The probes are laboratory made, constant heated needles.
  2. Measurements during IFC-2 of CO2 and H2O exchanges of 2 representative branches (SSA-OJP). Estimation of the water use efficiency (WUE: CO2 assimilation/transpiration). The gas-exchange is measured in home-made cuvettes operating in a closed system for 5 minutes every half-hour.
  3. Modelling of photosynthesis, transpiration and WUE of the branch. WUE varies with VPD and may vary through the season (needle age). This will be checked by measuring the delta 13C of growing shoot samples collected monthly (collaboration with TF-5).
  4. Use of 1., 2. and 3. to predict trees transpiration and carbon uptake during whole season.
Sap flow measurements will be compared with eddy correlation measurements of H2O and CO2 fluxes above the forest. Simple models of forest productivity will be tested using data form the site: a "top-down" model of the Monteith type and a mechanistic "bottom-up" model, both developed in the laboratory.
Forest inventories, geostatistic models and remote sensing data will be used to extend the plot measurement to the region.
  1. Diameter at breast height inventories will be used to extrapolate single trees transpiration measurements to the stand.
  2. Extensive LAI measurements (from other teams will be used for geostatic purposes.
  3. Continuous and discrete algorithms of radiative transfer will be tested to derive surface parameters (PAR interception and LAI) from remote sensing data, and from cover maps. to extrapolate to the whole BOREAS region.
Tentatively, we'll try to measure CO2/H2O exchange of the lichen layer at SSA-OJP using plastic enclosures, including a T/RH sensor, connected to a portable IRGA (collab. with TE-5).

TE-11 Data Sets

  • Leaf Photosynthesis
  • Sap flow
  • Lichen and Moss Photosynthesis

  • Get some TE-11 data using FTP (BOREAS Investigators only, password required). [FTP Help]

    TE-11 BOREAS Operations 1994

    To monitor transpiration and CO2 exchanges of a forest stand over the whole growing season

    Type of Data Collected:

    Equipment Used:

    Place of Measurement:
    SSA-OJP site in Nippawin (near TF5)

    Times of Measurement:
    Sapflow days: 121 to 258, 1994
    Branch bags: days 206 to 222, 1994
    Lichens: scattered data from July 24 to August 10, 1994

    Known Problems:
    Good functioning of sap flow sensors, with encouraging comparisons with micromet technique on a daily basis. For work on a half-hourly basis, sap flow lags about one hour to one hour and a half behind transpiration (likely variations in plant water storage). Branch bags gave also a good data set, but measured transpiration appears too small. We do not yet have a good scheme for deriving CO2 exchange of the stand from both (sap flow and branch bags) datasets.
    The data collected on lichens by Anne Ruimy have not been placed in BORIS but Anne made a small report that can be sent on request.

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    Last Updated: October 29, 1997