Comparação de quatro métodos de medição num bosque secundário tropical

Abstract

The principal objective of this research was to compare inventory techniques in a secondary tropical forest located at Turrialba, Costa Rica in the "Tropical Pre-montane Wet Forest" life zone according to the Holdridge classification system. Applying an unrestricted random sampling design and using the same center in each sample plot, four different inventory methods were used: a) complete plot inventory in wich all trees with a dbh 20 cm and above were measured in a fixed area plot of 10 x 50 m, b) prism method or point sampling, c) flexible method in wich the six closest trees to the center of the plot were measured, d) average dbh method in wich all trees that appeared to be of average size in the plot of 10 x 50 m were measured. In each method the following data were taken: time require to measure the plot including demarcation of the plot and identification of the trees to species, genus or family. The total volumes per plot or per point of sampling were calculated and parameters of variability established. Considering the variation in volume per hectare and cost espressed in time, the relative efficiency of each method of measurement was determined with the following results: a) the complete inventory of plots was given a relative efficiency of 100 per cent and used as standard of comparison, b) the flexible method resulted in relative efficiency of 114 37 per cent, c) the average dbh method in 153 50 per cent and d) the prism method in a relative efficiency of 225 30 per cent. The prism method was thus determined to be the most efficient in estimating total and commercial volumes.