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Comparison of sampling techniques to estimate tree diversity and aboveground biomass in Sinharaja forest Sri Lanka
By lakmali | March 4, 2010
M.D.P. Kumarathunge, R.O. Thattil, S.P. Nissanka and P. Pathinayaka
The use of correct sampling techniques is of paramount importance since the precision of estimates greatly depends 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.
Tree sampling techniques, such as quadrat method, transect method, and point centered quarter method PCQ) were evaluated in this study. A total of 25, 15×15 m plots for quadrat method, eleven, 5×100 m strips for transect method and 120 sampling points for PCQ method were used for sampling. All stems greater than 5 cm diameter at breast height (DBH) were taken in to consideration and their species level and the tree height, DBH was recorded. Sampling techniques were compared for tree density, basal area, tree size distribution, aboveground biomass and diversity indices estimated by each technique. A simulation was done to estimate the minimum sampling area required to assess the number of tree species of the study area.
According to the results, PCQ method gave the highest precision for most of the parameters estimated. There were no significant variation between the parameters estimated by PCQ method and quadrat method for most of the situations. PCQ technique recorded the highest number of species per 100
individuals enumerated (18.12%). The negative exponential functions fitted for the species – area (quadrat method) and species point (PCQ method) relationships estimated that the minimum 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. But it was difficult to estimate the minimum sampling area required to estimate the above ground biomass in Sinharaja since there was no underlining 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 the site stratification and random placement of sampling points in the study area are performed. Considering the highest 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.
M.D.P. Kumarathunge, R.O. Thattil, S.P. Nissanka and P. Pathinayaka
Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Sri Lanka.
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