EVALUATION OF THE PLOTLESS SAMPLING METHOD TO ESTIMATE ABOVEGROUND BIOMASS AND OTHER STAND PARAMETERS IN TROPICAL RAIN FORESTS

Abstract

Use of sampling techniques is of paramount importance since the precision of estimates greatly depend on it. Different methods of sampling have to be investigated to find out the best sampling technique for a given situation. This study was conducted to determine the best sampling technique to estimate tree diversity and aboveground biomass in Sinharaja forest. Three sampling techniques, namely; Quadrat method, Transect method, and Point centered quarter method (PCQ) were evaluated in this study. Sampling techniques were compared for tree density, basal area, aboveground biomass and diversity indices estimated by each technique. According to the results, PCQ method gave the highest precision for most of the parameters estimated. The non-linear functions fitted for the species – area (Quadrat method) and species – point (PCQ method) relationships estimated that the minimum total sampling area required to assess the number of tree species (in an area of 50 ha) of Singharaja forest as 6000 m2 for Quadrat method and 160 sampling points for PCQ method. It was difficult to estimate the minimum sampling area required to estimate the above ground biomass in Sinharaja since there was no clear cut relationship between biomass and number of sampling units. The results of the study emphasized that the PCQ method is a precise sampling technique that can be used to estimate the tree density, tree diversity and above ground biomass in natural forests. The random distribution of individuals is not necessary for tree diversity and biomass estimation by PCQ method if site stratification and random placement of sampling points in the study area are performed. Considering the higher precision of estimates and the saving of time and cost, the PCQ method can be recommended as an effective sampling technique for tree diversity and biomass studies.