4. indirect methods

  • Measurement objective is maximum LAI of the vegetation period. Measurements are to be performed in the month of expected maximum LAI.
  • SAI measurements in winter after all leaves are fallen, so preferably short before budswelling/ budbreak

4.1. Plant canopy analyzer

4.1.1 Measurement design

  • Remote mode: below canopy readings plus above canopy readings in a clearing in maximum 1km distance

Below canopy readings:

  • Generally at least 16 grid points, but more grid points, if standard error of the mean is above 5% -additonal points in the middle of each square (points 17-25)
  • Measurement height of 2m, bubble level mounted from below (for practical reasons); above canopy readings may be in different height, when 4th ring is not partly covered.
  • Generally without viewcaps, except for sloping terrain and extremely small clearings
  • When with viewcaps, keep compass direction of above canopy readings for below canopy readings, make sure that compass readings are not influenced by iron devices.
  • Move the grid point to another location, if obstacles are visible in a distance of less than 2m to the lens.
  • Follow manual of instrument

Above canopy readings:

  • log every 15 seconds;
  • opening adapted to 4 rings (about 60°), diameter = 3.2 times tree height; alternatively, when no such opening, use viewcaps for clearing with diameter of 1.6 times tree height.
  • level sensor by watching the bubble level vertically from above (or below)

4.1.2. Measurement equipment

  • 2 sensors + 2 logging units
  • 50% viewcap on sloping terrain
  • 75% viewcap on small opening
  • Software FV2000 1.10
  • Hemispherical photographs or TRAC for clumping index
  • Compass (optional)

4.1.3. Data collection

  • Preferably before sunrise or directly after sunset; but: sensor must react to obstacle in 10cm height above it and: no direct illumination in upper canopy. It is too dark, when leaves cannot be distinguished by eye.
  • Alternatively on days with uniformly overcast sky conditions; then: no shade should be visible on the ground.
  • No rain, dust, fog, snow
  • Recommended: always measure in the same order of grid points

4.1.4. variables and units

  • Combined above and below canopy readings in file (analogous to photo)
  • Effective LAI after Miller (1967) [-]
  • Gap fraction [fraction]
  • Between shoot clumping index [-]
  • In-shoot clumping index as given value for each species in the manual!
  • SAI [-]
  • LAI true (corrected for clumping),[-]
  • Estimated leaf angle [° to horizontal]
  • Sky conditions [distinguish readings with sun behind horizon from measurements during the day; view cap y/n]

4.1.5. Quality assurance

  • Above canopy readings not above 1000 (units?)
  • Standard error of the mean not above 5%
  • What to do with LAIeffective above 6.0: Average values won’t be given then (reported as “-1”), but single measurement values are anyway given.