While most recent investigation in satellite- based remotely sensed data has concentrated upon the biophysical characteristics of overstory vegetation for large area, little attention has been given to the reflectance contribution of their associated understory, versus overstory plantation reflectance to the recorded pixel value. In this research, shrubs and herbs were considered as consistent backgrounds which have an inverse effect, in contrast to plantation overstory, to the recorded pixel value in terms of their surfaceexposure to satellite sensors. Given the fact that planted tree crown closure is correlated with their height and diameter at breast height (DBH) in the early stages of the plantation, it is expected that a relationship exists between tree canopy closure, height, DBH and their associated reflectance values. The proposed concept was tested in a case study for a Jack Pine (pinus banksina) plantation using Landsat Thematic Mapper (T. M.). The crown width height, and DBH of planted trees were measured in an area of 30m X 30m, for every 2-year age interval from 1 to 21 years. Other understory natural regeneration within a 2m radius was recorded. Crown closure, mean height, and DBH of each plot (with shrub and herb understory of more than 60%) were plotted against their associated Digital Numbers (DN(s)) for 6 T. M. bands (1, 2, 3, 4, 5 and 7). The visible region of the spectrum (bands 1, 2 and 3) showed a narrow range of reflectance and was not suitable for this purpose. Band 4 revealed a greater range of DN(s) than bands 1, 2 and 3. A strong inverse linear relationship between DN(s) and their associated canopy closure, height, and DBH were found in band 5 as r2 = 0.863, 0.941, 0.873 respectively. Band 7 showed a stronger relationship with canopy closure (r2 = 0. 81) than did the other T. M. bands (except band 5). Overall, the results of this study have shown the importance of T. M. band 5 for estimating DBH and the height of plantations based on the contrast between reflectance of the overstory and understory.