COMPARISON OF DIFFERENT APPROACHES, MODEL S AND SAMPLE SIZES FOR THE ESTABLISHMENT OF LOCAL HEIGHT-DIAMETER RELATIONS

This study compares the predictability of 3 approaches, 4 models, and 10 different sample sizes to determine local relationships between tot al height and diameter at breast height in balsam fir stands less than 50 years old. The results show that a system of height-diameter curve s based on the mean diameter and mean height of the sampled trees (app roach 3) gives the most precise estimations in comparison with curves resulting from pooling all sampled trees in a single height-diameter m odel (approach 1) and with those resulting from the application of a h eight-diameter model for each of the combinations of sample plot - mea surement periods (approach 2). Depending on the sample size, the resid ual variance of the total height or the total volume is reduced 2 to 2 .5 times for the individual stems and 2 to 15 times for the mean stem, when using approach 3 instead of approach 1. Approach 3 is more preci se than approach 2 for sample sizes that vary between three and five s ampled trees per plot. However, this gain in precision becomes negligi ble when the sample size approaches 10 sampled trees per plot.