ESTIMATING FOLIAGE SURFACE-AREA INDEX IN 8-YEAR-OLD STANDS OF PINUS-ELLIOTTII VAR. ELLIOTTII X PINUS-CARIBAEA VAR. HONDURENSIS OF VARIABLE QUALITY

Comparisons were made between allometric and gap fraction estimates of foliage surface area index (foliage SAT) and spectral reflectance cha racteristics of 8-year-old stands of Pinus elliottii Engelm. var. elli ottii x Pinus caribaea var. hondurensis Parr. et Golf of variable qual ity. Allometric foliage SAIs, estimated using an empirically derived r elationship between basal (1.3 m) sapwood area and leaf surface area ( R-2 = 0.88, n = 11), ranged from 4.46 to 9.77. Gap fraction estimates (LI-COR LAI-2000 plant canopy analyser, PCA) of foliage SAI, when corr ected for the nonrandom distribution of foliage elements, correlated w ell (R-2 = 0.90) With direct estimates, being, on average, 11% lower. Relationships between foliage SAI (allometric) and spectral reflectanc e characteristics were tested. Strong, inverse nonlinear relationships between foliage SAI and thematic mapper (TM) bands 5 (1550-1750 nm, R -2 = 0.91) and 3 (630-690 nm, R-2 = 0.71), principal component (PC) 1 of bands 3, 4, and 5 (PC1, R-2 = 0.86), and the composite of bands 3, 4, and 5 (R-2 = 0.92) were observed. Positive linear correlations with the normalised difference vegetation index (NDVI, R-2 = 0.81) and the simple ratio of TM band 4 to band 3 (SR, R-2 = 0.78) were also observ ed. However, foliage SAT was poorly related (R-2 = 0.02) to TM band 4 (760-900 nm). Strong relationships observed between various spectral r eflectance characteristics and the more commonly measured forest struc tural parameters basal area and predominant height suggest that these remote sensing techniques are promising for use in early-aged inventor y systems.