H. Smolander et P. Stenberg, RESPONSE OF LAI-2000 ESTIMATES TO CHANGES IN PLANT-SURFACE AREA INDEXIN A SCOTS PINE STAND, Tree physiology, 16(3), 1996, pp. 345-349
We assessed the accuracy with which the LAI-2000 plant canopy analyzer
measured changes in leaf area index (LAI) and plant area index (PAI)
in a 25-year-old Scots pine (Pinus sylvestris L.) stand. Stand density
was 2100 stems ha(-1) and mean tree height was 8.7 m. Needle and bran
ch areas of the stand were reduced progressively to zero by the stepwi
se removal of branches on all trees growing in a circular plot with a
radius of 25 m. An LAI-2000 estimate was taken after each step reducti
on. The needle and branch surface areas removed at each step were esti
mated from direct measurements and were compared with the changes in t
he LAI-2000 estimates. Initially (before removal of branches), directl
y measured PAI was 5.2 (needles = 86%, branches = 8% and stems = 6%).
The LAI-2000 estimate of total surface area was 66% of direct PAI and
77% of direct LAI. There was a nonlinear relationship between the LAI-
2000 estimate and directly measured PAI, such that their ratio (equiva
lent to the clumping factor) increased from 0.66 to 1.05 with decreasi
ng PAI. At the last measurement, when only stems were left, the LAI-20
00 estimate agreed well with the direct measurement of PAI. The LAI-20
00 underestimated the direct measurement of LAI at the first three ste
ps when LAI was > 2 and the proportion of woody area was small (< 20%)
. However, because the LAI-2000 estimate included stem and branch area
s, it overestimated the direct measurement of LAI at the last three me
asurements when the proportion of woody area was large (< 20%).